Orally administered IL-6 induces elevated intestinal GM-CSF gene expression and splenic CFU-GM

Orally administered interleukin (IL)-6 has been shown to be of benefit in eliminating Campylobacter infection and in preventing sepsis following hemorrhage. In related experiments, it was seen that proliferating cells were found in the spleens of untreated mice given IL-6 by oral gavage. Injection of the DNA label, BrdU, showed that significant proliferation began at 4 h and peaked at 24 h in the splenic red pulp of animals given oral IL-6. Mice given saline showed no increase in splenic BrdU uptake. Histological analysis suggested a hematopoietic lineage for these cells. Clonogenic assays performed on spleen cells taken from mice given oral IL-6 revealed that increased granulocyte-macrophage colony forming units (GM-CFU) were present at 24 h post-IL-6 administration. No increase in GM colonies occurred in mice fed IL-3, granulocyte-colony stimulating factor (G-CSF) or granulocyte-macrophage (GM)-CSF. RT-PCR analysis of intestinal mRNA from treated mice revealed that GM-CSF mRNA was elevated at 4 h after oral IL-6 administration, but not in mice fed other cytokines. It is suggested that oral administration of IL-6 induces both proliferation and a brief elevation of GM-CFU in the hematopoietic spleens of mice. This increase appears to be the result of increased GM-CSF mRNA production in the intestines of mice fed IL-6.

Regulation of neonatal liver protein synthesis by insulin and amino acids in pigs

The high efficiency of protein deposition during the neonatal period is driven by high rates of protein synthesis, which are maximally stimulated after feeding. Infusion of amino acids, but not insulin, reproduces the feeding-induced stimulation of liver protein synthesis. To determine whether amino acid-stimulated liver protein synthesis is independent of insulin in neonates, and to examine the role of amino acids and insulin in the regulation of translation initiation in neonatal liver, we performed pancreatic glucose-amino acid clamps in overnight-fasted 7-day-old pigs. Pigs (n = 9-12/group) were infused with insulin at 0, 10, 22, and 110 ng.kg(-0.66).min(-1) to achieve 0, 2, 6, and 30 microU/ml insulin, respectively. At each insulin dose, amino acids were maintained at fasting or fed levels or, in conjunction with the highest insulin dose, allowed to fall to below fasting levels. Insulin had no effect on the fractional rate of protein synthesis in liver. Amino acids increased fractional protein synthesis rates in liver at each dose of insulin, including the 0 microU/ml dose. There was a dose-response effect of amino acids on liver protein synthesis. Amino acids and insulin increased protein S6 kinase and 4E-binding protein 1 (4E-BP1) phosphorylation; however, only amino acids decreased formation of the inactive 4E-BPI.eukaryotic initiation factor-4E (eIF4E) complex. The results suggest that amino acids regulate liver protein synthesis in the neonate by modulating the availability of eIF4E for 48S ribosomal complex formation and that this response does not require insulin.

Peripheral leptin administration alters hormone and metabolite levels in the young pig

The present study was conducted to determine if peripheral leptin administration can alter GH secretion or feed intake in young pigs. Six, 6 kg female pigs were fasted overnight and randomly chosen to receive porcine recombinant leptin or saline injections in a crossover design. Three leptin dosages were tested over a 10 day period, 100, 200 or 500 microg/kg body mass (L100, L200 or L500). Leptin was administered in 0.2% bovine serum albumin as a bolus injection into the carotid artery. Blood samples were obtained from the jugular vein over a 24 h period. Leptin delayed feeding in pigs treated with L200 and L500 (P<0.05), while reducing overall intake in pigs treated with L100 (P<0.05). L200 or L500 depressed blood glucose (P<0.05). Plasma insulin levels were elevated by feeding in control animals, while insulin levels were depressed in pigs treated with L200 or L500 (P<0.05). L200 elevated plasma growth hormone (P<0.05) with three peaks apparent at 5, 8, and 13 h post injection. The ability for a single injection of leptin to produce significant changes in hormone and metabolite levels suggests that this peptide has a role in regulation of peripheral metabolism.

Regulation of muscle protein synthesis in neonatal pigs during prolonged endotoxemia

In adults, protein synthesis in skeletal muscle is reduced by as much as 50% after a septic challenge, and is associated with repression of translation initiation. Neonates are highly anabolic and their muscle protein synthesis rates are elevated and uniquely sensitive to amino acid and insulin stimulation. In the present study, neonatal piglets were infused with Endotoxin (lipopolysaccharide, LPS) for 20 h at 0 (n = 6) and 13 microg/kg*h (n = 8). During the last 2 h, dextrose and an amino acid mixture were infused to attain fed plasma concentrations of amino acids, glucose, and insulin. Fractional protein synthesis rates and translational control mechanisms were examined. LPS reduced protein synthesis in glycolytic muscles by only 13% and had no significant effect in oxidative muscles. This depression was associated with reductions in the phosphorylation of 4E-BP1 (-31%) and S6 K1 (-78%), and a decrease in eIF4G binding to eIF4E (-62%), an event required for formation of the active mRNA binding complex. By comparison, LPS increased protein synthesis in the liver (+29%), spleen (+32%), and kidney (+27%), and in the liver, this increase was associated with augmented eIF4G to eIF4E binding (+88%). In muscle and liver, LPS did not alter eIF2B activity, an event that regulates initiator met-tRNA(i) binding to the 40S ribosomal complex. These findings suggest that during sustained endotoxemia, the high rate of neonatal muscle protein synthesis is largely maintained in the presence of substrate supply, despite profound changes in translation initiation factors that modulate the mRNA binding step in translation initiation.

Proteins and amino acids in enteral nutrition

PURPOSE OF REVIEW

This review reports recent findings on the effect of enterally fed protein and amino acids on metabolism, function, and clinical outcome, particularly during the neonatal period.

RECENT FINDINGS

Splanchnic tissues metabolize significant proportions of some enteral amino acids and this likely contributes to the higher requirement for these amino acids when they are provided enterally versus parenterally. Splanchnic tissues are particularly key in the provision of nutrition to preterm infants, who possess an exceedingly high protein anabolic drive, but limited tolerance to aggressive enteral feeding. The protein anabolic response to specific proteins is influenced by the rate of digestion and the pattern of feeding, as well as the amino acid composition of the proteins. The post-prandial rise in amino acids and insulin stimulates neonatal tissue protein synthesis by modulation of the nutrient and insulin signaling pathways that lead to translation initiation. A flurry of investigations into the metabolic response and clinical impact of individual amino acids suggests that leucine, glutamine, and arginine, in particular, have specific roles in regulating protein synthesis and immune function.

SUMMARY

Recent findings suggest that enteral nutrition support that provides an optimum combination of proteins and amino acids can have a beneficial impact on the clinical outcome of patients.

Amino acids do not alter the insulin-induced activation of the insulin signaling pathway in neonatal pigs

Feeding stimulates protein synthesis in skeletal muscle and liver of neonates and this response can be reproduced in muscle by the infusion of insulin or amino acids and in liver by the infusion of amino acids, but not insulin. Activation of insulin signaling components leading to translation initiation is associated with the feeding-induced stimulation of muscle protein synthesis in neonates. In this study, we examined the individual roles of insulin and amino acids in the activation of insulin signaling components leading to translation initiation, specifically, the insulin receptor (IR), insulin receptor substrate 1 (IRS-1), phosphatidylinositol 3-kinase (PI 3-kinase), protein kinase B (PKB) and ribosomal protein S6. Insulin secretion was blocked by somatostatin in food-deprived, 7-d-old pigs (n=8-12/group); insulin was infused to achieve plasma levels of approximately 0, 17, 52, and 255 pmol/L (approximately 0, 2, 6, 30 microU/mL), and amino acids were clamped at food-deprived or fed levels. In skeletal muscle, insulin increased the activation of IR, IRS-1, PI 3-kinase, PKB and S6 and stimulated protein synthesis. In liver, insulin increased the activation of IR, IRS-1, PI 3-kinase, PKB and S6, but had no effect on protein synthesis. Raising amino acids from the food-deprived to the fed level did not alter the insulin-induced activation of IR, IRS-1, PI 3-kinase and PKB but increased S6 phosphorylation and protein synthesis in skeletal muscle and liver. The results suggest that the stimulation of protein synthesis in muscle by insulin involves activation of insulin signaling components, and the stimulation of protein synthesis in muscle and liver by amino acids occurs by mechanisms independent of the early steps of this pathway. Furthermore, amino acids do not alter the insulin-stimulated activation of early steps in the insulin signaling pathway.

Endotoxin induces differential regulation of mTOR-dependent signaling in skeletal muscle and liver of neonatal pigs

In the present study, differential responses of regulatory proteins involved in translation initiation in skeletal muscle and liver during sepsis were studied in neonatal pigs treated with lipopolysaccharide (LPS). LPS did not alter eukaryotic initiation factor (eIF) 2B activity in either tissue. In contrast, binding of eIF4G to eIF4E to form the active mRNA-binding complex was repressed in muscle and enhanced in liver. Phosphorylation of eIF4E-binding protein, 4E-BP1, and ribosomal protein S6 kinase, S6K1, was reduced in muscle during sepsis but increased in liver. Finally, changes in 4E-BP1 and S6K1 phosphorylation were associated with altered phosphorylation of the protein kinase mammalian target of rapamycin (mTOR). Overall, the results suggest that translation initiation in both skeletal muscle and liver is altered during neonatal sepsis by modulation of the mRNA-binding step through changes in mTOR activation. Moreover, the LPS-induced changes in factors that regulate translation initiation are more profound than previously reported changes in global rates of protein synthesis in the neonate. This finding suggests that the initiator methionyl-tRNA-rather than the mRNA-binding step in translation initiation may play a more critical role in maintaining protein synthesis rates in the neonate during sepsis.

Insulin/insulin-like growth factor-I hybrid receptor abundance decreases with development in suckling pigs

The activation of the insulin signaling pathway that leads to translation initiation is enhanced in skeletal muscle of neonates, and decreases with development in parallel with the developmental decline in muscle protein synthesis. Because the elevated expression of insulin receptor (IR)/insulin-like growth factor-I receptor (IGF-IR) hybrids has been associated with insulin resistance in some studies, we hypothesized that IR/IGF-IR hybrid abundance and binding affinity increase with development. To test this hypothesis, we determined the abundances and binding affinities of the IR, IGF-IR and hybrid receptor in skeletal muscle of 7- and 26-d-old pigs. We found that the abundances of IR, IGF-IR and hybrid receptor were higher in muscle of 7- than 26-d-old pigs. However, the relative proportions of hybrid receptor abundance compared with IR abundance and IGF-IR abundance were similar at both ages. The binding affinities of the IR, IGF-IR and hybrid receptor also were similar at both ages. Overall, the results suggest that insulin/IGF-I hybrid receptor abundance and binding affinity do not contribute to the developmental decline in the activation of the insulin signaling pathway.

Regulation of translation initiation by insulin and amino acids in skeletal muscle of neonatal pigs

Previous studies have shown that intravenous infusion of insulin and/or amino acids reproduces the feeding-induced stimulation of muscle protein synthesis in neonates and that insulin and amino acids act independently to produce this effect. The goal of the present study was to delineate the regulatory roles of insulin and amino acids on muscle protein synthesis in neonates by examining translational control mechanisms, specifically the eukaryotic translation initiation factors (eIFs), which enable coupling of initiator methionyl-tRNAi and mRNA to the 40S ribosomal subunit. Insulin secretion was blocked by somatostatin in fasted 7-day-old pigs (n = 8-12/group), insulin was infused to achieve plasma levels of approximately 0, 2, 6, and 30 microU/ml, and amino acids were clamped at fasting or fed levels or, at the high insulin dose, below fasting. Both insulin and amino acids increased the phosphorylation of ribosomal protein S6 kinase (S6K1) and the eIF4E-binding protein (4E-BP1), decreased the binding of 4E-BP1 to eIF4E, increased eIF4E binding to eIF4G, and increased fractional protein synthesis rates but did not affect eIF2B activity. In the absence of insulin, amino acids had no effect on these translation initiation factors but increased the protein synthesis rates. Raising insulin from below fasting to fasting levels generally did not alter translation initiation factor activity but raised protein synthesis rates. The phosphorylation of S6K1 and 4E-BP1 and the amount of 4E-BP1 bound to eIF4E and eIF4E bound to eIF4G were correlated with insulin level, amino acid level, and protein synthesis rate. Thus insulin and amino acids regulate muscle protein synthesis in skeletal muscle of neonates by modulating the availability of eIF4E for 48S ribosomal complex assembly, although other processes also must be involved.

Influence of Bacillus subtilis cell walls and EDTA on calcite dissolution rates and crystal surface features

This study investigates the influence of EDTA and the Gram-positive cell walls of Bacillus subtilis on the dissolution rates and development of morphological features on the calcite [1014] surface. The calcite dissolution rates are compared at equivalent saturation indicies (SI) and relative to its dissolution behavior in distilled water (DW). Results indicate that the presence of metabolically inactive B. subtilis does not affect the dissolution rates significantly. Apparent increases in dissolution rates in the presence of the dead bacterial cells can be accounted for by a decrease of the saturation state of the solution with respect to calcite resulting from bonding of dissolved Ca2+ by functional groups on the cell walls. In contrast, the addition of EDTA to the experimental solutions results in a distinct increase in dissolution rates relative to those measured in DW and the bacterial cell suspensions. These results are partly explained by the 6.5-8 orders of magnitude greater stability of the Ca-EDTA complex relative to the Ca-B. subtilis complexes as well as its free diffusion to and direct attack of the calcite surface. Atomic force microscopy images of the [1014] surface of calcite crystals exposed to our experimental solutions reveal the development of dissolution pits with different morphologies according to the nature and concentration of the ligand. Highly anisotropic dissolution pits develop in the early stages of the dissolution reaction at low B. subtilis concentrations (0.004 mM functional group sites) and in DW. In contrast, at high functional group concentrations (4.0 mM EDTA or equivalent B. subtilis functional group sites), dissolution pits are more isotropic. These results suggest that the mechanism of calcite dissolution is modified by the presence of high concentrations of organic ligands. Since all the pits that developed on the calcite surfaces display some degree of anisotropy and dissolution rates are strongly SI dependent, the rate-limiting step is most likely a surface reaction for all systems investigated in this study. Results of this study emphasize the importance of solution chemistry and speciation in determining calcite reaction rates and give a more accurate and thermodynamically sound representation of dead bacterial cell wall-mineral interactions. In studies of natural aquatic systems, the presence of organic ligands is most often ignored in speciation calculations. This study clearly demonstrates that this oversight may lead to an overestimation of the saturation state of the solutions with respect to calcite and thermodynamic inconsistencies.

Translational control of protein synthesis in muscle and liver of growth hormone-treated pigs

GH treatment increases protein deposition and the efficiency of dietary protein used for growth. To identify the mechanisms that regulate tissue protein synthesis in response to exogenous GH treatment, fully fed, growing swine were treated with GH for 7 d. Fasted and fed pigs were infused with [1-(13)C]leucine to determine protein synthesis rates, and translation initiation factor activity levels were measured in skeletal muscle and liver. Feeding increased protein synthesis and translational efficiency in both muscle and liver of control and GH-treated pigs, and this was associated with increased 4E-BP1 and S6 kinase 1 phosphorylation, decreased association of eukaryotic initiation factor (eIF) 4E with 4E-BP1, and increased association of eIF4E with eIF4G. GH increased muscle protein synthesis and translational efficiency in fed pigs. GH increased liver protein synthesis of fasted and fed pigs in association with increased ribosome number. In muscle, but not liver, GH increased eIF2B activity and 4E-BP1 phosphorylation in both the fasted and fed state and increased the association of eIF4E with eIF4G in the fed state. We conclude that GH increases muscle protein synthesis in the fed state, in part, via mechanisms that enhance the binding of mRNA and methionyl-tRNA to the 40S ribosomal subunit, whereas GH increases liver protein synthesis in the fasted and fed states by increasing ribosome number. The results further indicate that the GH-induced protein synthetic response is dependent upon nutritional state and is tissue specific.

Somatotropin-induced protein anabolism in hindquarters and portal-drained viscera of growing pigs

To differentiate the effect of somatotropin (ST) treatment on protein metabolism in the hindquarter (HQ) and portal-drained viscera (PDV), growing swine (n = 20) treated with ST (0 or 150 microg x kg(-1) x day(-1)) for 7 days were infused intravenously with NaH(13)CO(3) and [(2)H(5)]phenylalanine and enterally with [1-(13)C]phenylalanine while in the fed state. Arterial, portal venous, and vena cava whole blood samples, breath samples, and blood flow measurements were obtained for determination of tissue and whole body phenylalanine kinetics under steady-state conditions. In the fed state, ST treatment decreased whole body phenylalanine flux, oxidation, and protein degradation without altering protein synthesis, resulting in an improvement in whole body net protein balance. Blood flow to the HQ (+80%), but not to the PDV, was increased with ST treatment. In the HQ and PDV, ST increased phenylalanine uptake (+44 and +23%, respectively) and protein synthesis (+43 and +41%, respectively), with no effect on protein degradation. In ST-treated and control pigs, phenylalanine was oxidized in the PDV (34-43% of enteral and arterial sources) but not the HQ. In both treatment groups, dietary (40%) rather than arterial (10%) extraction of phenylalanine predominated in gut amino acid metabolism, whereas localized blood flow influenced HQ amino acid metabolism. The results indicate that ST increases protein anabolism in young, growing swine by increasing protein synthesis in the HQ and PDV, with no effect on protein degradation. Differing results between the whole body and the HQ and PDV suggest that the effect of ST treatment on protein metabolism is tissue specific.

Protein-tyrosine-phosphatase 1B activation is regulated developmentally in muscle of neonatal pigs

The high activity of the insulin-signaling pathway contributes to the enhanced feeding-induced stimulation of translation initiation in skeletal muscle of neonatal pigs. Protein-tyrosine-phosphatase 1B (PTP1B) is a negative regulator of the tyrosine phosphorylation of the insulin receptor (IR) and insulin receptor substrate 1 (IRS-1). The activity of PTP1B is determined mainly by its association with IR and Grb2. We examined the level of PTP1B activity, PTP1B protein abundance, PTP1B tyrosine phosphorylation, and the association of PTP1B with IR and Grb2 in skeletal muscle and liver of fasted and fed 7- and 26-day-old pigs. PTP1B activity in skeletal muscle was lower (P < 0.05) in 7- compared with 26-day-old pigs but in liver was similar in the two age groups. PTP1B abundances were similar in muscle but lower (P < 0.05) in liver of 7- compared with 26-day-old pigs. PTP1B tyrosine phosphorylation in muscle was lower (P < 0.05) in 7- than in 26-day-old pigs. The associations of PTP1B with IR and with Grb2 were lower (P < 0.05) at 7 than at 26 days of age in muscle, but there were no age effects in liver. Finally, in both age groups, fasting did not have any effect on these parameters. These results indicate that basal PTP1B activation is developmentally regulated in skeletal muscle of neonatal pigs, consistent with the developmental changes in the activation of the insulin-signaling pathway reported previously. Reduced PTP1B activation in neonatal muscle likely contributes to the enhanced insulin sensitivity of skeletal muscle in neonatal pigs.

Insulin and amino acids independently stimulate skeletal muscle protein synthesis in neonatal pigs

Infusion of physiological levels of insulin and/or amino acids reproduces the feeding-induced stimulation of muscle protein synthesis in neonates. To determine whether insulin and amino acids independently stimulate skeletal muscle protein synthesis in neonates, insulin secretion was blocked with somatostatin in fasted 7-day-old pigs (n = 8-12/group) while glucose and glucagon were maintained at fasting levels and insulin was infused to simulate either less than fasting, fasting, intermediate, or fed insulin levels. At each dose of insulin, amino acids were clamped at either the fasting or fed level; at the highest insulin dose, amino acids were also reduced to less than fasting levels. Skeletal muscle protein synthesis was measured using a flooding dose of l-[4-(3)H]phenylalanine. Hyperinsulinemia increased protein synthesis in skeletal muscle during hypoaminoacidemia and euaminoacidemia. Hyperaminoacidemia increased muscle protein synthesis during hypoinsulinemia and euinsulinemia. There was a dose-response effect of both insulin and amino acids on muscle protein synthesis. At each insulin dose, hyperaminoacidemia increased muscle protein synthesis. The effects of insulin and amino acids on muscle protein synthesis were largely additive until maximal rates of protein synthesis were achieved. Amino acids enhanced basal protein synthesis rates but did not enhance the sensitivity or responsiveness of muscle protein synthesis to insulin. The results suggest that insulin and amino acids independently stimulate protein synthesis in skeletal muscle of the neonate.

Endotoxemia reduces skeletal muscle protein synthesis in neonates

Protein synthesis in skeletal muscle is reduced by as much as 50% as early as 4 h after a septic challenge in adults. However, the effect of sepsis on muscle protein synthesis has not been determined in neonates, a highly anabolic population whose muscle protein synthesis rates are elevated and uniquely sensitive to insulin and amino acid stimulation. Neonatal piglets (n = 10/group) were infused for 8 h with endotoxin [lipopolysaccharide (LPS), 0 and 10 microg. kg(-1). h(-1)]. Plasma amino acid and glucose concentrations were kept at the fed level by infusion of dextrose and a balanced amino acid mixture. Fractional protein synthesis rates were determined by use of a flooding dose of [(3)H]phenylalanine. LPS infusion produced a septic-like state, as indicated by an early and sustained elevation in body temperature, heart rate, and plasma tumor necrosis factor-alpha, interleukin-1, cortisol, and lactate concentrations. Plasma levels of insulin increased, whereas glucose and amino acids decreased, suggesting the absence of insulin resistance. LPS significantly reduced protein synthesis in longissimus dorsi muscle by only 11% and in gastrocnemius by only 15%, but it had no significant effect in masseter and cardiac muscles. LPS increased protein synthesis in the liver (22%), spleen (28%), kidney (53%), jejunum (19%), diaphragm (21%), lung (50%), and skin (13%), but not in the stomach, pancreas, or brain. These findings suggest that, when substrate supply is maintained, skeletal muscle protein synthesis in neonates compared with adults is relatively resistant to the catabolic effects of sepsis.

Acute IGF-I infusion stimulates protein synthesis in skeletal muscle and other tissues of neonatal pigs

Studies have shown that protein synthesis in skeletal muscle of neonatal pigs is uniquely sensitive to a physiological rise in both insulin and amino acids. Protein synthesis in cardiac muscle, skin, and spleen is responsive to insulin but not amino acid stimulation, whereas in the liver, protein synthesis responds to amino acids but not insulin. To determine the response of protein synthesis to insulin-like growth factor I (IGF-I) in this model, overnight-fasted 7- and 26-day-old pigs were infused with IGF-I (0, 20, or 50 microg. kg(-1). h(-1)) to achieve levels within the physiological range, while amino acids and glucose were clamped at fasting levels. Because IGF-I infusion lowers circulating insulin levels, an additional group of high-dose IGF-I-infused pigs was also provided replacement insulin (10 ng. kg(-0.66). min(-1)). Tissue protein synthesis was measured using a flooding dose of L-[4-(3)H]phenylalanine. In 7-day-old pigs, low-dose IGF-I increased protein synthesis by 25-60% in various skeletal muscles as well as in cardiac muscle (+38%), skin (+24%), and spleen (+32%). The higher dose of IGF-I elicited no further increase in protein synthesis above that found with the low IGF-I dose. Insulin replacement did not alter the response of protein synthesis to IGF-I in any tissue. The IGF-I-induced increases in tissue protein synthesis decreased with development. IGF-I infusion, with or without insulin replacement, had no effect on protein synthesis in liver, jejunum, pancreas, or kidney. Thus the magnitude, tissue specificity, and developmental change in the response of protein synthesis to acute physiological increases in plasma IGF-I are similar to those previously observed for insulin. This study provides in vivo data indicating that circulating IGF-I and insulin act on the same signaling components to stimulate protein synthesis and that this response is highly sensitive to stimulation in skeletal muscle of the neonate.

Stimulation of protein synthesis by both insulin and amino acids is unique to skeletal muscle in neonatal pigs

In neonatal pigs, the feeding-induced stimulation of protein synthesis in skeletal muscle, but not liver, can be reproduced by insulin infusion when essential amino acids and glucose are maintained at fasting levels. In the present study, 7- and 26-day-old pigs were studied during 1) fasting, 2) hyperinsulinemic-euglycemic-euaminoacidemic clamps, 3) euinsulinemic-euglycemic-hyperaminoacidemic clamps, and 4) hyperinsulinemic-euglycemic-hyperaminoacidemic clamps. Amino acids were clamped using a new amino acid mixture enriched in nonessential amino acids. Tissue protein synthesis was measured using a flooding dose of L-[4-(3)H]phenylalanine. In 7-day-old pigs, insulin infusion alone increased protein synthesis in various skeletal muscles (from +35 to +64%), with equivalent contribution of myofibrillar and sarcoplasmic proteins, as well as cardiac muscle (+50%), skin (+34%), and spleen (+26%). Amino acid infusion alone increased protein synthesis in skeletal muscles (from +28 to +50%), also with equivalent contribution of myofibrillar and sarcoplasmic proteins, as well as liver (+27%), pancreas (+28%), and kidney (+10%). An elevation of both insulin and amino acids did not have an additive effect. Similar qualitative results were obtained in 26-day-old pigs, but the magnitude of the stimulation of protein synthesis by insulin and/or amino acids was lower. The results suggest that, in the neonate, the stimulation of protein synthesis by feeding is mediated by either amino acids or insulin in most tissues; however, the feeding-induced stimulation of protein synthesis in skeletal muscle is uniquely regulated by both insulin and amino acids.

Idiotype vaccination following ABMT can stimulate specific anti-idiotype immune responses in patients with B-cell lymphoma

Vaccination with the idiotype (Id) protein derived from B-cell malignancies can produce Id-specific immune responses that correlate with improved remission duration and survival rates in patients with follicular non-Hodgkin's lymphoma (NHL). A state of minimal or no residual disease correlates strongly with the laboratory detection of a cellular or humoral immune response. High-dose cytotoxic therapy (HDCT) with autologous stem cell support (autologous bone marrow transplantation [ABMT]) can provide profound cytoreduction of B-cell NHL, but the potential immune suppression associated with myeloablative therapy may compromise a patient's ability to mount a specific immune response. To determine whether patients with NHL could mount detectable immuneresponses following ABMT, Id vaccines were administered at 2 to 12 months following myeloablative therapy to a series of patients with relapsed or resistant B-cell NHL. Two different vaccination strategies produced robust immune responses against KLH in all patients, supporting the capacity of the reconstituted immune system following HDCT to react against a strong antigen. Combining the results from both vaccination strategies, 10 of 12 patients mounted Id-specific humoral or cellular responses. Vaccinations were consistently well tolerated. Of the 12 patients, 7 have experienced prolonged remissions with a follow-up from HDCT ranging from 3 to more than 11 years. Our experience serves to document the ability of the recovering immune system to react against both self and xenotypic antigens and supports the feasibility and safety of antigen-specific vaccination following myeloablative therapy in patients with B-cell NHL.

Developmental decline in components of signal transduction pathways regulating protein synthesis in pig muscle

Our previous studies showed that the feeding-induced stimulation of protein synthesis in skeletal muscle of neonatal pigs is accompanied by enhanced phosphorylation of the eukaryotic initiation factor (eIF)4E-binding protein (4E-BP1) and the ribosomal protein S6 kinase (S6K1). These effects of feeding are substantially reduced with development. The goal of the present investigation was to delineate the basis for the reduced responsiveness to feeding observed in the older animals. In these studies, the content and activity of protein kinases located upstream of S6K1 and 4E-BP1 in signal transduction pathways activated by amino acids, insulin, and insulin-like growth factor I were examined in 7- and 26-day-old pigs that were either fasted overnight or fed porcine milk after an overnight fast. Feeding stimulated phosphatidylinositol (PI) 3-kinase activity to the same extent in muscle of 7- and 26-day-old pigs, suggesting that PI 3-kinase is not limiting in muscle of older animals. In contrast, protein kinase B (PKB) activity was significantly less in muscle from 26- vs. 7-day-old pigs, regardless of nutritional status, suggesting that its activity is regulated by mechanisms distinct from PI 3-kinase. In part, the reduced PKB responsiveness can be attributed to a developmental decline in PKB content. Likewise, muscle content of the protein kinase termed mammalian target of rapamycin (mTOR) in 26-day-old pigs was <25% of that in 7-day-old animals. Finally, in agreement with our earlier work showing that S6K1 phosphorylation is reduced in older animals, S6K1 activity was stimulated to a lesser extent in 26- compared with 7-day-old pigs. Overall, the results suggest that the blunted protein synthetic response observed in 26- vs. 7-day-old neonatal pigs is due in part to decreased content and/or activity of signaling components downstream of PI 3-kinase, e.g., PKB, mTOR, and S6K1.

Somatotropin-induced amino acid conservation in pigs involves differential regulation of liver and gut urea cycle enzyme activity

Somatotropin (ST) treatment promotes animal growth and allows for the conservation of amino acids by increasing nitrogen retention and reducing ureagenesis and amino acid oxidation. To determine whether the improvement in amino acid conservation with ST treatment involves regulation of urea cycle enzyme activities in both liver and intestine, growing swine were treated with either ST (150 microg x kg(-1) x d(-1)) or saline for 7 d. Fully fed pigs (n = 20) were infused intravenously for 2 h with NaH(13)CO(3) followed by a 4-h intraduodenal infusion of [1-(13)C]phenylalanine. Arterial and portal venous blood and breath samples were obtained at baseline and steady-state conditions for measurement of amino acid and blood urea nitrogen (BUN) concentrations and whole-body phenylalanine oxidation. Urea cycle enzyme activities were determined in liver and jejunum. ST decreased BUN (-46%), arterial (-34%) and portal venous (-43%) amino acid concentrations and whole-body phenylalanine oxidation (-30%). The activities of carbamoylphosphate synthase-I (-45%), argininosuccinate synthase (-38%), argininosuccinate lyase (-23%), arginase (-27%), and glutaminase (-18%), but not of ornithine carbamoyltransferase, ornithine aminotransferase, or glutamate dehydrogenase were reduced in liver of ST-treated pigs. ST slightly increased intestinal activity of glutaminase (+9%) but did not affect that of any other enzymes. ST decreased hepatic, but increased jejunal, N-acetylglutamate (an essential allosteric activator of carbamoylphosphate synthase-I; -26% and +32%, respectively) and carbamoylphosphate (a substrate for ornithine carbamoyltransferase; -20% and +28%, respectively) content. These results demonstrate that the reduced amino acid catabolism with ST treatment in growing pigs involves a reduction in hepatic urea cycle enzyme activities. The effect of ST treatment on porcine urea cycle enzymes is tissue-specific and is associated with a reduction in substrate availability for hepatic ureagenesis.

Developmental changes in the feeding-induced activation of the insulin-signaling pathway in neonatal pigs

In neonatal animals, feeding stimulates skeletal muscle protein synthesis, a response that declines with development. Both the magnitude of the feeding response and its developmental decline can be reproduced by insulin infusion, suggesting that an altered responsiveness to insulin is a primary determinant of the developmental decline in the stimulation of protein synthesis by feeding. In this study, 7- and 26-day-old pigs were either fasted overnight or fed porcine milk after an overnight fast. We examined the abundance and degree of tyrosine phosphorylation of the insulin receptor (IR), insulin receptor substrate-1 (IRS-1), and IRS-2 in skeletal muscle and, for comparison, liver. We also evaluated the association of IRS-1 and IRS-2 with phosphatidylinositol 3-kinase (PI 3-kinase). The abundance of IR protein in muscle was twofold higher at 7 than at 26 days, but IRS-1 and IRS-2 abundances were similar in muscle of 7- and 26-day-old pigs. The feeding-induced phosphorylations were greater at 7 than at 26 days of age for IR (28- vs. 13-fold), IRS-1 (14- vs. 8-fold), and IRS-2 (21- vs. 12-fold) in muscle. The associations of IRS-1 and IRS-2 with PI 3-kinase were also increased by refeeding to a greater extent at 7 than at 26 days (9- vs. 5-fold and 6- vs. 4-fold, respectively). In liver, the abundance of IR, IRS-1, and IRS-2 was similar at 7 and 26 days of age. Feeding increased the activation of IR, IRS-1, IRS-2, and PI 3-kinase in liver only twofold, and these responses were unaffected by age. Thus our findings demonstrate that the feeding-induced activation of IR, IRS-1, IRS-2, and PI 3-kinase in skeletal muscle decreases with development. Further study is needed to ascertain whether the developmental decline in the feeding-induced activation of early insulin-signaling components contributes to the developmental decline in translation initiation in skeletal muscle.

Differential effects of insulin on peripheral and visceral tissue protein synthesis in neonatal pigs

We recently demonstrated in neonatal pigs that, with amino acids and glucose maintained at fasting levels, the stimulation of protein synthesis in longissimus dorsi muscle with feeding can be reproduced by a physiological rise in insulin alone. In the current report, we determine whether the response of protein synthesis to insulin in the neonatal pig is 1) present in muscles of different fiber types, 2) proportional in myofibrillar and sarcoplasmic proteins, 3) associated with increased translational efficiency and ribosome number, and 4) present in other peripheral tissues and in viscera. Hyperinsulinemic-euglycemic-amino acid clamps were performed in 7- and 26-day-old pigs infused with 0, 30, 100, or 1,000 ng. kg(-0.66). min(-1) of insulin to reproduce insulin levels present in fasted, fed, refed, and supraphysiological conditions, respectively. Tissue protein synthesis was measured using a flooding dose of L-[4-(3)H]phenylalanine. Insulin increased protein synthesis in gastrocnemius muscle and, to a lesser degree, masseter muscle. The degree of stimulation of protein synthesis by insulin was similar in myofibrillar and sarcoplasmic proteins. Insulin increased translational efficiency but had no effect on ribosome number in muscle. All of these insulin-induced changes in muscle protein synthesis decreased with age. Insulin also stimulated protein synthesis in cardiac muscle and skin but not in liver, intestine, spleen, pancreas, or kidney. The results support the hypothesis that insulin mediates the feeding-induced stimulation of myofibrillar and sarcoplasmic protein synthesis in muscles of different fiber types in the neonate by increasing the efficiency of translation. However, insulin does not appear to be involved in the feeding-induced stimulation of protein synthesis in visceral tissues. Thus different mechanisms regulate the growth of peripheral and visceral tissues in the neonate.

Of flux and flooding: the advantages and problems of different isotopic methods for quantifying protein turnover in vivo : II. Methods based on the incorporation of a tracer

The most common methods for measuring the incorporation of tracer amino acids into tissue protein are the constant tracer infusion and the flooding dose. The flooding dose is an attractive method for measuring tissue protein synthesis because of its convenience and precision. A primary assumption of the method, that the free amino acid precursor pools are equilibrated with the true precursor pool, aminoacyl-transfer RNA, has recently been validated. When short labelling periods are involved, the large dose of amino acid does not appear to alter protein synthesis. The constant tracer infusion is a satisfactory method from a theoretical point of view, but its use requires the measurement of the protein synthetic precursor pool. The best estimate of the aminoacyl-tRNA precursor pool for the constant infusion method appears to be the acid-soluble tissue pool in muscle and VLDL apolipoprotein B-100 in the liver. The experimental approach chosen for measuring tissue protein synthesis should be dictated by the question being addressed.

Developmental changes in the feeding-induced stimulation of translation initiation in muscle of neonatal pigs

The rapid gain in skeletal muscle mass in the neonate is associated with a marked elevation in skeletal muscle protein synthesis in response to feeding. The feeding-induced response decreases with development. To determine whether the response to feeding is regulated at the level of translation initiation, the expression, phosphorylation, and function of a number of eukaryotic initiation factors (eIF) were examined. Pigs at 7 and 26 days of age were either fasted overnight or fed porcine milk after an overnight fast. In muscle of 7-day-old pigs, the hyperphosphorylated form of the eIF4E repressor protein, 4E-binding protein 1 (4E-BP1), was undetectable in the fasting state but rose to 60% of total 4E-BP1 after feeding; eIF4E phosphorylation was unaffected by feeding status. The amount of eIF4E in the inactive 4E-BP1. eIF4E complex was reduced by 80%, and the amount of eIF4E in the active eIF4E. eIF4G complex was increased 14-fold in muscle of 7-day-old pigs after feeding. The amount of 70-kDa ribosomal protein S6 (p70(S6)) kinase in the hyperphosphorylated form rose 2.5-fold in muscle of 7-day-old pigs after feeding. Each of these feeding-induced responses was blunted in muscle of 26-day-old pigs. eIF2B activity in muscle was unaffected by feeding status but decreased with development. Feeding produced similar changes in eIF characteristics in liver and muscle; however, the developmental changes in liver were not as apparent as in skeletal muscle. Thus the results demonstrate that the developmental change in the acute stimulation of skeletal muscle protein synthesis by feeding is regulated by the availability of eIF4E for 48S ribosomal complex formation. The results further suggest that the overall developmental decline in skeletal muscle protein synthesis involves regulation by eIF2B.

Feeding stimulates protein synthesis in muscle and liver of neonatal pigs through an mTOR-dependent process

Protein synthesis is repressed in both skeletal muscle and liver after a short-term fast and is rapidly stimulated in response to feeding. Previous studies in rats and pigs have shown that the feeding-induced stimulation of protein synthesis is associated with activation of the 70-kDa ribosomal protein S6 kinase (S6K1) as well as enhanced binding of eukaryotic initiation factor eIF4E to eIF4G to form the active eIF4F complex. In cells in culture, hormones and nutrients regulate both of these events through a protein kinase termed the mammalian target of rapamycin (mTOR). In the present study, the involvement of mTOR in the feeding-induced stimulation of protein synthesis in skeletal muscle and liver was examined. Pigs at 7 days of age were fasted for 18 h, and then one-half of the animals were fed. In addition, one-half of the animals in each group were administered rapamycin (0.75 mg/kg) 2 h before feeding. The results reveal that treating 18-h fasted pigs with rapamycin, a specific inhibitor of mTOR, before feeding prevented the activation of S6K1 and the changes in eIF4F complex formation observed in skeletal muscle and liver after feeding. Rapamycin also ablated the feeding-induced stimulation of protein synthesis in liver. In contrast, in skeletal muscle, rapamycin attenuated, but did not prevent, the stimulation of protein synthesis in response to feeding. The results suggest that feeding stimulates hepatic protein synthesis through an mTOR-dependent process involving enhanced eIF4F complex formation and activation of S6K1. However, in skeletal muscle, these two processes may account for only part of the stimulation of protein synthesis, and thus additional steps may be involved in the response.

Nonnutritive factors in colostrum enhance myofibrillar protein synthesis in the newborn Pig

Colostrum is a complex source of nutrients, immune factors, and bioactive substances consumed by newborn mammals. In previous work, we observed that protein synthesis in the skeletal muscle of newborn piglets is enhanced when they are fed colostrum rather than a nutrient-matched formula devoid of growth factors. To elucidate the mechanisms responsible for this response, we contrasted the fractional rates of sarcoplasmic and myofibrillar protein synthesis of newborn piglets that received only water with those fed for 24 h with colostrum, a nutrient-matched formula, or mature sow's milk. Compared with water, feeding resulted in a 2.5- to 3-fold increase in total skeletal muscle protein synthesis, and this increase was 28% greater in the colostrum-fed than either the formula- or mature milk-fed piglets. Feeding also stimulated muscle ribosome and total polyadenylated RNA accretion. Ribosomal translational efficiency, however, was similar across all fed groups. The greater stimulation of protein synthesis in colostrum-fed pigs was restricted entirely to the myofibrillar protein compartment and was associated with higher ribosome and myosin heavy chain mRNA abundance. Taken together, these data suggest that nonnutritive factors in colostrum enhance ribosomal accretion and muscle-specific gene transcription that, in turn, stimulate specifically the synthesis of myofibrillar proteins in the skeletal musculature of the newborn.

Rituximab anti-CD20 monoclonal antibody therapy in non-Hodgkin's lymphoma: safety and efficacy of re-treatment

PURPOSE

This phase II trial investigated the safety and efficacy of re-treatment with rituximab, a chimeric anti-CD20 monoclonal antibody, in patients with low-grade or follicular non-Hodgkin's lymphoma who relapsed after a response to rituximab therapy.

PATIENTS AND METHODS

Fifty-eight patients were enrolled onto this study, and two were re-treated within the study. Patients received an intravenous infusion of 375 mg/m(2) of rituximab weekly for 4 weeks. All patients had at least two prior therapies and had received at least one prior course of rituximab, with a median interval of 14.5 months between rituximab courses.

RESULTS

Most adverse experiences (AEs) were transient grade 1 or 2 events occurring during the treatment period. Clinically significant myelosuppression was not observed; hematologic toxicity was generally mild and reversible. No patient developed human antichimeric antibodies after treatment. The type, frequency, and severity of AEs in this study were not apparently different from those reported in the phase III trial of rituximab. The overall response rate in 57 assessable patients was 40% (11% complete response and 30% partial responses). Median time to progression (TTP) in responders and median duration of response (DR) have not been reached, but Kaplan-Meier estimated medians are 17.8 months (range, 5.4+ to 26.6 months) and 16.3 months (range, 3.7+ to 25.1 months), respectively. These estimated medians are longer than the medians achieved in the patients' prior course of rituximab (TTP and DR of 12.4 and 9.8 months, respectively, P: >.1) and in a previously reported phase III trial (TTP in responders and DR of 13.2 and 11.6 months, respectively). Responses are ongoing in seven of 23 responders.

CONCLUSION

In this re-treatment population, safety and efficacy were not apparently different from those after initial rituximab exposure.

Somatotropin increases protein balance independent of insulin's effects on protein metabolism in growing pigs

Somatotropin (ST) administration enhances protein deposition and elicits profound metabolic responses, including hyperinsulinemia. To determine whether the anabolic effect of ST is due to hyperinsulinemia, pair-fed weight-matched growing swine were treated with porcine ST (150 microg x kg body wt(-1) x day(-1)) or diluent for 7 days (n = 6/group, approximately 20 kg). Then pancreatic glucose-amino acid clamps were performed after an overnight fast. The objective was to reproduce the insulin levels of 1) fasted control and ST pigs (basal insulin, 5 microU/ml), 2) fed control pigs (low insulin, 20 microU/ml), and 3) fed ST pigs (high insulin, 50 microU/ml). Amino acid and glucose disposal rates were determined from the infusion rates necessary to maintain preclamp blood levels of these substrates. Whole body nonoxidative leucine disposal (NOLD), leucine appearance (R(a)), and leucine oxidation were determined with primed, continuous infusions of [(13)C]leucine and [(14)C]bicarbonate. ST treatment was associated with higher NOLD and protein balance and lower leucine oxidation and amino acid and glucose disposals. Insulin lowered R(a) and increased leucine oxidation, protein balance, and amino acid and glucose disposals. These effects of insulin were suppressed by ST treatment; however, the protein balance remained higher in ST pigs. The results show that ST treatment inhibits insulin's effects on protein metabolism and indicate that the stimulation of protein deposition by ST treatment is not mediated by insulin. Comparison of the protein metabolic responses to ST treatment during the basal fasting period with those in the fully fed state from a previous study suggests that the mechanism by which ST treatment enhances protein deposition is influenced by feeding status.

Combination immunotherapy of relapsed or refractory low-grade or follicular non-Hodgkin's lymphoma with rituximab and interferon-alpha-2a

Rituximab and IFN have each demonstrated single-agent activity in patients with low-grade non-Hodgkin's lymphoma (NHL). A single-arm, multicenter, Phase II trial was conducted to assess the safety and efficacy of combination therapy with rituximab and IFN-alpha-2a in 38 patients with relapsed or refractory, low-grade or follicular, B-cell NHL. IFN-alpha-2a [2.5 or 5 million units (MIU)] was administered s.c., three times weekly for 12 weeks. Starting on the fifth week of treatment, rituximab was administered by i.v. infusion (375 mg/m2) weekly for 4 doses. All 38 patients received four complete infusions of rituximab and were evaluable for efficacy, although 11 patients (29%) did not-receive all 36 injections of IFN. The mean number of IFN-alpha-2a injections was 31 doses; the mean total units received were 141 MIU (maximum, 180 MIU). The study treatment was reasonably well tolerated with no unexpected toxicities stemming from the combination therapy. No grade 4 events were reported. Frequent adverse events during the treatment period included asthenia (35 of 38 patients), chills (31 of 38), fever (30 of 38), headache (28 of 38), nausea (23 of 38), and myalgia (22 of 38). The overall response rate was 45% (17 of 38 patients); 11% had a complete response, and 34% had a partial response. The Kaplan-Meier estimates for the median response duration and the median time to progression in responders are 22.3 and 25.2 months, respectively. Further follow-up is needed to determine whether this treatment combination leads to a significantly longer time to progression than single-agent treatment with rituximab.

Regulation of myofibrillar protein turnover during maturation in normal and undernourished rat pups

The study tested the hypothesis that a higher rate of myofibrillar than sarcoplasmic protein synthesis is responsible for the rapid postdifferentiation accumulation of myofibrils and that an inadequate nutrient intake will compromise primarily myofibrillar protein synthesis. Myofibrillar (total and individual) and sarcoplasmic protein synthesis, accretion, and degradation rates were measured in vivo in well-nourished (C) rat pups at 6, 15, and 28 days of age and compared at 6 and 15 days of age with pups undernourished (UN) from birth. In 6-day-old C pups, a higher myofibrillar than sarcoplasmic protein synthesis rate accounted for the greater deposition of myofibrillar than sarcoplasmic proteins. The fractional synthesis rates of both protein compartments decreased with age, but to a greater degree for myofibrillar proteins (-54 vs. -42%). These decreases in synthesis rates were partially offset by reductions in degradation rates, and from 15 days, myofibrillar and sarcoplasmic proteins were deposited in constant proportion to one another. Undernutrition reduced both myofibrillar and sarcoplasmic protein synthesis rates, and the effect was greater at 6 (-25%) than 15 days (-15%). Decreases in their respective degradation rates minimized the effect of undernutrition on sarcoplasmic protein accretion from 4 to 8 days and on myofibrillar proteins from 13 to 17 days. Although these adaptations in protein turnover reduced overall growth of muscle mass, they mitigated the effects of undernutrition on the normal maturational changes in myofibrillar protein concentration.

Somatotropin increases protein balance by lowering body protein degradation in fed, growing pigs

Somatotropin (ST) administration enhances protein deposition in well-nourished, growing animals. To determine whether the anabolic effect is due to an increase in protein synthesis or a decrease in proteolysis, pair-fed, weight-matched ( approximately 20 kg) growing swine were treated with porcine ST (150 microg. kg(-1). day(-1), n = 6) or diluent (n = 6) for 7 days. Whole body leucine appearance (R(a)), nonoxidative leucine disposal (NOLD), urea production, and leucine oxidation, as well as tissue protein synthesis (K(s)), were determined in the fed steady state using primed continuous infusions of [(13)C]leucine, [(13)C]bicarbonate, and [(15)N(2)]urea. ST treatment increased the efficiency with which the diet was used for growth. ST treatment also increased plasma insulin-like growth factor I (+100%) and insulin (+125%) concentrations and decreased plasma urea nitrogen concentrations (-53%). ST-treated pigs had lower leucine R(a) (-33%), leucine oxidation (-63%), and urea production (-70%). However, ST treatment altered neither NOLD nor K(s) in the longissimus dorsi, semitendinosus, or gastrocnemius muscles, liver, or jejunum. The results suggest that in the fed state, ST treatment of growing swine increases protein deposition primarily through a suppression of protein degradation and amino acid catabolism rather than a stimulation of protein synthesis.

Protein nutrition of the neonate

The period of growth and development between birth and weaning is crucial for the long-term well-being of the organism. Protein deposition is very rapid, is achieved with a high nutritional efficiency, and is accompanied by marked differences in the growth rates of individual tissues and a series of maturational processes. These important aspects of development occur while the neonate is consuming a single and highly-specific food source, milk. Surprisingly, although there is a clear relationship between the nutrient density of milk and the growth rate of its recipient, this relationship does not apply to the overall amino acid composition of mixed milk proteins. Some amino acids, notably glycine and arginine, are supplied in milk in quantities that are much less than the needs of the neonate. The milk-fed neonate is therefore capable of carrying out a tightly-regulated transfer of N from amino acids in excess to those that are deficient. The rapid growth of the neonate is supported by a high rate of tissue protein synthesis. This process appears to be activated by the consumption of the first meals of colostrum. Recent research has identified that skeletal muscle and the brain are specifically responsive to an unidentified factor in colostrum. Following the initial anabolic response the rate of protein synthesis in some tissues, notably muscle, falls from birth to weaning. This decrease reflects a progressively smaller anabolic response to nutrient intake, which not only involves an overall fall in the capacity for protein synthesis, but also in responses to insulin and amino acids. The study of growth and protein metabolism, and their regulation in the neonate is not only important for pediatrics, but may provide important pointers to more general aspects of regulation that could be applied to the nutrition of the mature animal.

Myelopoietin, a chimeric agonist of human interleukin 3 and granulocyte colony-stimulating factor receptors, mobilizes CD34+ cells that rapidly engraft lethally x-irradiated nonhuman primates

Myelopoietin (MPO), a multifunctional agonist of interleukin 3 and granulocyte colony-stimulating factor (G-CSF) receptors, was evaluated for its ability to mobilize hematopoietic colony-forming cells (CFC) and CD34+ cells relative to control cytokines in normal nonhuman primates. Additionally, the engraftment potential of MPO-mobilized CD34+ cells was assessed in lethally irradiated rhesus monkeys. Normal rhesus monkeys were administered either MPO (200 microg/kg/day), daniplestim (a high-affinity interleukin 3 receptor agonist) (100 microg/kg/day), G-CSF (100 microg/kg/day), or daniplestim coadministered with G-CSF (100 microg/kg/day each), subcutaneously for 10 consecutive days. The mobilization kinetics were characterized by peripheral blood (PB) complete blood counts, hematopoietic CFC [granulocyte-macrophage CFC (GM-CFC), megakaryocyte CFC (MK-CFC)], and the immunophenotype (CD34+ cells) of PB nucleated cells prior to and on day 3 to days 7, 10, 12, and 14, and at intervals up to day 28 following initiation of cytokine administration. A single large-volume leukapheresis was conducted on day 5 in an additional cohort (n = 10) of MPO-mobilized animals. Eight of these animals were transplanted with two doses of CD34+ cells/kg. A maximum 10-fold increase in PB leukocytes (white blood cells) (from baseline 7.8-12.3 x 10(3)/microL to approximately 90 x 10(3)/microL) was observed over day 7 to day 10 in the MPO, G-CSF, or daniplestim+G-CSF cohorts, whereas daniplestim alone stimulated a less than onefold increase. A sustained, maximal rise in PB-derived GM-CFC/mL was observed over day 4 to day 10 for the MPO-treated cohort, whereas the daniplestim+G-CSF, G-CSF alone, and daniplestim alone treated cohorts were characterized by a mean peak value on days 7, 6, and 18, respectively. Mean peak values for PB-derived GM-CFC/mL were greater for MPO (5,427/mL) than for daniplestim+G-CSF (3,534/mL), G-CSF alone (3,437/mL), or daniplestim alone (155/mL) treated cohorts. Mean peak values for CD34+ cells/mL were noted within day 4 to day 5 of cytokine administration: MPO (255/microL, day 5), daniplestim+G-CSF (47/microL, day 5), G-CSF (182/microL, day 4), and daniplestim (96/microL, day 5). Analysis of the mobilization data as area under the curve indicated that for total CFCs, GM-CFC, MK-CFC, or CD34+ cells, the MPO-treated areas under the curve were greater than those for all other experimental cohorts. A single, large-volume (3.0 x blood volume) leukapheresis at day 5 of MPO administration (PB: CD34+ cell/microL = 438 +/- 140, CFC/mL = 5,170 +/- 140) resulted in collection of sufficient CD34+ cells (4.31 x 10(6)/kg +/- 1.08) and/or total CFCs (33.8 x 10(4)/kg +/- 8.34) for autologous transplantation of the lethally irradiated host. The immunoselected CD34+ cells were transfused into autologous recipients (n = 8) at cell doses of 2 x 10(6)/kg (n = 5), and 4 x 10(6)/kg (n = 3) on the day of apheresis. Successful engraftment occurred with each cell dose. The data demonstrated that MPO is an effective and efficient mobilizer of PB progenitor cells and CD34+ cells, such that a single leukapheresis procedure results in collection of sufficient stem cells for transplantation and long term engraftment of lethally irradiated hosts.

Susceptibility or resistance to Leishmania infection is dictated by the macrophages evolved under the influence of IL-3 or GM-CSF

Although enhanced monocytopoiesis is a hallmark of leishmaniasis, its significance in determining the course of the disease has not been addressed. While the number of granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting cells increases in the draining lymph nodes in a resistant mouse strain (C57BL/6) during disease, in a susceptible strain (BALB/c) the number of interleukin-3 (IL-3)-secreting cells increases. Treatment of BALB/c mice with anti-IL-3 antibody significantly reduces the disease score. Bone marrow macrophages derived under stimulation with IL-3 (IL-3-Mphi) or GM-CSF (GM-Mphi) differ functionally. GM-Mphi are significantly more responsive to IFN-gamma-induced augmentation and more refractory to IL-4-mediated suppression of anti-leishmanial activity than IL-3-Mphi. LPS-induced IL-12 and TNF-alpha secretion by both the susceptible and resistant strain-derived macrophage subsets are down-regulated. Despite down-regulation of IL-12 secretion, GM-Mphi favor expansion of IFN-gamma-secreting cells and IL-3-Mphi favor IL-6-dependent expansion of the IL-4-secreting Th subset. Adoptive transfer of leishmanial antigen-pulsed IL-3-Mphi and GM-Mphi prior to infection either aggravated or reduced the disease score, respectively, in BALB/c mice. Anti-IL-6 treatment reverted the Th subset profile not only in vitro but also in vivo, resulting in a reduced disease score in both infected BALB/c mice and IL-3-Mphi recipients. The disease score in IL-3-Mphi recipients is also reduced significantly after anti-IL-4 treatment.

Aminoacyl-tRNA and tissue free amino acid pools are equilibrated after a flooding dose of phenylalanine

The flooding dose method, which is used to measure tissue protein synthesis, assumes equilibration of the isotopic labeling between the aminoacyl-tRNA pool and the tissue and blood free amino acid pools. However, this has not been verified for a phenylalanine tracer in an in vivo study. We determined the specific radioactivity of [(3)H]phenylalanine in the aminoacyl-tRNA and the tissue and blood free amino acid pools of skeletal muscle and liver 30 min after administration of a flooding dose of phenylalanine along with [(3)H]phenylalanine. Studies were performed in neonatal pigs in the fasted and refed states and during hyperinsulinemic-euglycemic-amino acid clamps. The results showed that, 30 min after the administration of a flooding dose of phenylalanine, there was equilibration of the specific radioactivity of phenylalanine among the blood, tissue, and tRNA precursor pools. Equilibration of the specific radioactivity of the three precursor pools for protein synthesis occurred in both skeletal muscle and liver. Neither feeding nor insulin status affected the aminoacyl-tRNA specific radioactivity relative to the tissue free amino acid specific radioactivity. The results support the assumption that the tissue free amino acid pool specific radioactivity is a valid measure of the precursor pool specific radioactivity and thus can be used to calculate protein synthesis rates in skeletal muscle and liver when a flooding dose of phenylalanine is administered.

Ex vivo expansion of autologous bone marrow CD34(+) cells with porcine microvascular endothelial cells results in a graft capable of rescuing lethally irradiated baboons

Hematopoietic stem cell (HSC) self-renewal in vitro has been reported to result in a diminished proliferative capacity or acquisition of a homing defect that might compromise marrow repopulation. Our group has demonstrated that human HSC expanded ex vivo in the presence of porcine microvascular endothelial cells (PMVEC) retain the capacity to competitively repopulate human bone fragments implanted in severe combined immunodeficiency (SCID) mice. To further test the marrow repopulating capacity of expanded stem cells, our laboratory has established a myeloablative, fractionated total body irradiation conditioning protocol for autologous marrow transplantation in baboons. A control animal, which received no transplant, as well as two animals, which received a suboptimal number of marrow mononuclear cells, died 37, 43, and 59 days postirradiation, respectively. Immunomagnetically selected CD34(+) marrow cells from two baboons were placed in PMVEC coculture with exogenous human cytokines. After 10 days of expansion, the grafts represented a 14-fold to 22-fold increase in cell number, a 4-fold to 5-fold expansion of CD34(+) cells, a 3-fold to 4-fold increase of colony-forming unit-granulocyte-macrophage (CFU-GM), and a 12-fold to 17-fold increase of cobblestone area-forming cells (CAFC) over input. Both baboons became transfusion independent by day 23 posttransplant and achieved absolute neutrophil count (ANC) >500/microL by day 25 +/- 1 and platelets >20,000/microL by day 29 +/- 2. This hematopoietic recovery was delayed in comparison to two animals that received either a graft consisting of freshly isolated, unexpanded CD34(+) cells or 175 x 10(6)/kg unfractionated marrow mononuclear cells. Analysis of the proliferative status of cells in PMVEC expansion cultures demonstrated that by 10 days, 99.8% of CD34(+) cells present in the cultures had undergone cycling, and that the population of cells expressing a CD34(+) CD38(-) phenotype in the cultures was also the result of active cell division. These data indicate that isolated bone marrow CD34(+) cells may undergo cell division during ex vivo expansion in the presence of endothelial cells to provide a graft capable of rescuing a myeloablated autologous host.

Single-agent monoclonal antibody efficacy in bulky non-Hodgkin's lymphoma: results of a phase II trial of rituximab

PURPOSE

A phase II trial was performed to evaluate the safety and efficacy of rituximab, a chimeric anti-CD20 monoclonal antibody, in patients with bulky (> 10-cm lesion) relapsed or refractory low-grade or follicular non-Hodgkin's lymphoma (NHL).

PATIENTS AND METHODS

Thirty-one patients received intravenous infusions of rituximab 375 mg/m(2) weekly for four doses. All patients had at least one prior therapy (median, three; range, one to 13) and had progressive disease at study entry. Patients were a median of 4 years from diagnosis.

RESULTS

No patient had treatment discontinued because of an adverse event. No patient developed human antichimeric antibody. The overall response rate in 28 assessable patients was 43% with a median time to progression of 8.1 months (range, 4.5 to 18.6+ months) and median duration of response of 5.9 months (range, 2.8 to 12.1+ months). The average decrease in lesion size in patients who achieved a partial response was 76%, and patients with stable disease had a decrease in average lesion size of 26%. Median serum antibody concentration was higher in responders compared with nonresponders, and a negative correlation was shown between antibody concentration and tumor bulk at baseline.

CONCLUSION

Rituximab single-agent outpatient therapy is safe and shows significant clinical activity in patients with bulky relapsed or refractory low-grade or follicular B-cell NHL.

Therapy of B-cell lymphoma with anti-CD20 antibodies can result in the loss of CD20 antigen expression

Rituximab is a chimeric antibody with human gamma-1 and kappa constant regions and murine variable regions. It recognizes the CD20 antigen, a pan B-cell marker. Therapeutic trials in patients with B-cell non-Hodgkin's lymphoma (NHL) have shown significant efficacy with a primary response rate of 50%, and a secondary response rate of 44% after repeat treatments in prior responders. The selection for proliferating tumor cells that no longer express CD20 may compromise repeated treatment. We have identified a patient who developed a transformed NHL that lost CD20 protein expression after two courses of therapy with rituximab. In a pretreatment lymph node biopsy, 83% of B cells (as defined by CD19 and surface immunoglobulin) expressed surface CD20. A biopsy from the recurrent tumor after two courses of rituximab revealed a diffuse large cell NHL where 0% of B cells expressed CD20 with no evidence of bound rituximab. Cytoplasmic staining showed no CD20 protein. Sequencing of immunoglobulin heavy chain cDNA identified identical variable sequences in the initial and recurrent lymphomas, confirming the association between the two tumors. Literature and database review suggests that approximately 98% of diffuse large cell lymphomas express CD20, which suggests that these tumors rarely survive without CD20. This is the first identified case of loss of CD20 expression in a lymphoma that has relapsed after rituximab therapy, although several other cases have since been identified. Considering the significant number of patients treated with anti-CD20 antibodies, this may occur only rarely and is unlikely to preclude recurrent therapy with anti-CD20 antibodies in the majority of patients. However, because many patients have relapsed after anti-CD20 antibody therapy and have not been biopsied to identify clones with down-regulated CD20 antigen, we do not currently know the true frequency of this phenomenon. When possible, patients should undergo evaluation for CD20 expression before repeated courses of anti-CD20 therapy.

A comparative study of the cell cycle status and primitive cell adhesion molecule profile of human CD34+ cells cultured in stroma-free versus porcine microvascular endothelial cell cultures

Porcine microvascular endothelial cells (PMVECs) plus cytokines support a rapid proliferation and expansion of human CD34+CD38- cells that are capable of multilineage engraftment within the bone marrow of a secondary host. CD34+CD38- cells contain the self-renewing, long-term culture-initiating cells (LTC-IC) that are ideal targets for retroviral gene transfer experiments. Previous experiments attempting retroviral infection of CD34+CD38- cells have failed partly because these cells do not enter cell cycle in response to cytokine combinations. In this study, we determined the cell cycle status and the cell adhesion molecule profile on purified CD34+ cells and the CD34+CD38- subset before and after ex vivo expansion on PMVECs. Purified human CD34+ cells were cocultured with PMVECs for 7 days in the presence of optimal concentrations of granulocyte/macrophage-colony-stimulating factor (GM-CSF) + interleukin (IL)-3 + IL-6 + stem cell factor (SCF) + Flt-3 ligand. The total CD34+ population and the CD34+CD38- subset increased 8.4- and 67-fold, respectively, with absolute increases in the number of colony-forming unit-granulocyte macrophage (CFU-GM) (28.2-fold), CFU-Mix (8.7 fold), and burst-forming unit-erythroid (BFU-E) (4.0-fold) progenitor cells. After 7 days of coculture with PMVECs, 44% of the CD34+CD38+ subset were found to be in G1, and 51% were in G2/S/M phase of the cell cycle. More remarkably, 53% of the CD34+CD38- subset were in G1, and 17% were in G2/S/M phase after 7 days of PMVEC coculture. In contrast, only 22% of the CD34+CD38- subset remaining after 7 days of stroma-free culture were in G1, and 6% were in G2/S/M phase. Despite the high level of cellular activation and proliferation induced by PMVEC coculture, the surface expression of adhesion molecules CD11a (LFA-1), CD11b, CD15s (sialyl-Lewis x), CD43, and CD44 (HCAM) on the total CD34+ population was maintained, and the surface expression of CD49d (VLA-4), CD54 (ICAM), CD58, and CD62L (L selectin) increased after ex vivo expansion. In contrast, CD34+ cells expanded on stroma-free cultures showed lower and more variable expression of CD62L and CD15s. These findings demonstrate that the primitive CD34+CD38- subset of marrow progenitor cells can be induced to enter cell cycle and can be significantly expanded ex vivo on a hematopoietic supportive microenvironment (PMVECs) while preserving the expression of cell adhesion molecules that may be important in stem cell homing and engraftment.

Dexamethasone inhibits small intestinal growth via increased protein catabolism in neonatal pigs

Our objective was to determine how dexamethasone (Dex) affects gastrointestinal protein metabolism and growth in neonatal pigs. Two-day-old pigs were given daily subcutaneous injections of either Dex (1 mg/kg body wt, n = 7) or saline (control, n = 6) for 7 days. In vivo protein synthesis was measured after 7 days with a bolus of [3H]phenylalanine. Tissue protein contents were measured in an initial control group of 2-day-old pigs and in control and Dex pigs after 7 days to estimate protein accretion and degradation. In control pigs, the protein accretion in the ileum was nearly sixfold greater than in the jejunum during the 7-day period. Dex nominally altered stomach growth but completely blocked the accretion of protein and DNA in the jejunum and ileum, with reduced villus height in the ileum. Dex increased the fractional protein degradation rate in the ileum (28%) and decreased the absolute protein synthesis rate in the jejunum and ileum by 17 and 21%, respectively. Dex resulted in a 40% lower total intestinal lactase activity compared with controls via reductions in both specific activity and tissue mass, especially in the ileum. Dex significantly decreased the circulating concentrations of insulin-like growth factor (IGF) I and IGF-binding protein (IGFBP)-1, -2, and -3. However, the tissue abundance of the IGF-I receptor in the stomach and ileum was greater in Dex pigs than controls. Our results suggest that Dex significantly inhibits small intestinal growth via both increased degradation and decreased synthesis of protein. Furthermore, the inhibition of intestinal growth resulted in significantly decreased lactose digestive capacity.

Of flux and flooding: the advantages and problems of different isotopic methods for quantifying protein turnover in vivo: I. Methods based on the dilution of a tracer

The advantages and problems, both practical and theoretical, of isotope dilution approaches to the determination of whole-body and tissue protein turnover are discussed. It was concluded that: (1) measurements made on the basis of the labelling of plasma and breath are well suited to the measurement of body amino acid oxidation and balance, but because of the problem of inhomogeneity of the body amino acid pools, this approach generally underestimates protein turnover; (2) in investigations of nutritional effects on whole-body amino acid turnover, closer attention should be paid to first-pass splanchnic amino acid metabolism; (3) the trans-organ tracer balance method, particularly if combined with the measurement of tissue amino acid labelling, is a potentially useful approach to the simultaneous and dynamic measurement of both protein synthesis and degradation; (4) leucine may be the most generally useful label for tracer level studies of both whole-body and muscle protein synthesis, as recent studies have shown quite close isotopic equilibrium between muscle-free and tRNA-bound leucine pools.

Response of skeletal muscle protein synthesis to insulin in suckling pigs decreases with development

The elevated rate of muscle protein deposition in the neonate is largely due to an enhanced stimulation of skeletal muscle protein synthesis by feeding. To examine the role of insulin in this response, hyperinsulinemic-euglycemic-amino acid clamps were performed in 7- and 26-day-old pigs. Pigs were infused with 0, 30, 100, or 1,000 ng . kg-0.66 . min-1 of insulin to mimic the plasma insulin levels observed under fasted, fed, refed, and supraphysiological conditions, respectively. Whole body amino acid disposal was determined from the rate of infusion of an amino acid mixture necessary to maintain plasma essential amino acid concentrations near their basal fasting levels. A flooding dose of L-[4-3H]phenylalanine was used to measure skeletal muscle protein synthesis. Whole body amino acid disposal increased progressively as the insulin infusion rate increased, and this response was greater in 7- than in 26-day-old pigs. Skeletal muscle protein synthesis was stimulated by insulin, and this response was maximal at a low insulin infusion rate (30 ng . kg-0.66 . min-1). The stimulation of muscle protein synthesis by insulin was also greater in 7- than in 26- day-old pigs. These data suggest that muscle protein synthesis is more sensitive to insulin than whole body amino acid disposal. The results further suggest that insulin is a central regulatory factor in the elevated rate of muscle protein deposition and the increased response of skeletal muscle protein synthesis to feeding in the neonate.

Bone marrow repopulation by human marrow stem cells after long-term expansion culture on a porcine endothelial cell line

In vitro exposure of murine hematopoietic stem cells (HSCs) to cell cycle-inducing cytokines has been shown to result in a defect in the ability of these cells to engraft. We used a porcine microvascular endothelial cell (PMVEC) line in conjunction with exogenous interleukin (IL)-3, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), and stem cell factor (SCF) to expand human HSCs that express the CD34 and Thy-1 antigens but lack lineage-associated markers (CD34+Thy-1+Lin- cells). Ex vivo expansion of hematopoietic cells was evaluated in comparison to stromal cell-free, cytokine-supplemented cultures. Cells expressing the CD34+Thy-1+Lin- phenotype were detectable in both culture systems for up to 3 weeks. These cells were reisolated from the cultures and their ability to engraft human fetal bones implanted into SCID mice (SCID-hu bone) was tested. HSCs expanded in PMVEC coculture were consistently capable of competitive marrow repopulation with multilineage (CD19+ B lymphoid, CD33+ myeloid, and CD34+ cells) progeny present 8 weeks postengraftment. In contrast, grafts composed of cells expanded in stroma-free cultures did not lead to multilineage SCID-hu bone repopulation. Proliferation analysis revealed that by 1 week of culture more than 80% of the cells in the PMVEC cocultures expressing the primitive CD34+CD38- phenotype had undergone cell division. Fewer than 1% of the cells that proliferated in the absence of stromal cells remained CD34+CD38-. These data suggest that the proliferation of HSCs in the presence of IL-3, IL-6, GM-CSF, and SCF without stromal cell support may result in impairment of engraftment capacity, which may be overcome by coculture with PMVECs.

Anti-idiotype antibodies can induce long-term complete remissions in non-Hodgkin's lymphoma without eradicating the malignant clone

The immunoglobulin on the surface of B-cell lymphomas can be a tumor-specific target for monoclonal antibody therapy. Between 1981 and 1993, 45 individuals with low grade B-cell lymphoma were treated with 52 courses of custom-made anti-idiotype antibodies. The antibodies were used either alone or in combination with alpha-interferon, chlorambucil, or interleukin-2 (IL-2). The majority of these patients responded to treatment, with a 66% overall and 18% complete response rate. Six patients (13%) experienced prolonged complete remissions, five of which are ongoing from 4 to 10 years after therapy and are the subject of this report. We asked whether residual lymphoma could be found in these patients with prolonged remissions. We performed enzyme-linked immunosorbent assay (ELISA) assays for idiotype protein or anti-idiotype antibodies in serum. Blood and bone marrow samples were examined by flow cytometry for idiotype positive cells, and by polymerase chain reaction (PCR) for clonal gene rearrangements of immunoglobulin CDR3 sequences or t(14;18) translocations. Using these sensitive and specific tests it was possible to detect very low levels of residual lymphoma in five of these patients who had been in clinical remission for 3 to 8 years before this evaluation. These five have continued without recurrence for up to 3 years since. Thus, we have found a pattern of residual inactive disease in patients treated with anti-idiotype antibodies. The biology of follicular lymphoma evidently includes the potential for tumor dormancy after therapies with varied mechanisms of action, resulting in clinical inactivity for many years. Thus, long-term control of the disease is possible at a clinical level despite persistence of the malignant clone.

Amino acid metabolism and the energetics of growth

The nonessential amino acids are involved in a large number of functions that are not directly associated with protein synthesis. Recent studies using a combination of transorgan balance and stable isotopic tracers have demonstrated that a substantial portion of the extra-splanchnic flux of glutamate, glutamine, glycine and cysteine derives from tissue synthesis. A key amino acid in this respect is glutamic acid. Little glutamic acid of dietary origin escapes metabolism in the small intestinal mucosa. Furthermore, because glutamic acid is the only amino acid that can be synthesized by mammals by reductive amination of a ketoacid, it is the ultimate nitrogen donor for the synthesis of other nonessential amino acids. Because the synthesis of glutamic acid and its product glutamine involve the expenditure of adenosine triphosphate (ATP), it seems possible that nonessential amino acid synthesis might have a significant bearing on the energetics of protein synthesis and, hence, of protein deposition. This paper discusses the topic of the energy cost of protein deposition, considers the metabolic physiology of amino acid oxidation and nonessential amino acid synthesis, and attempts to combine the information to speculate on the overall impact of amino acid metabolism on the energy exchanges of animals.

Advances in the management of Hodgkin's and non-Hodgkin's lymphoma

Recent developments in the management of lymphoma continue to refine our approach to the disease. There is increasing acceptance of the International Lymphoma Study Group classification for non-Hodgkin's lymphoma. Identification of a new viral agent associated with certain subtypes of lymphoma and new immunologic therapies change our perspective on the disease. New data on treatment results further elucidate the role of radiotherapy and high-dose therapy in Hodgkin's disease and the non-Hodgkin's lymphomas.

Phorbol esters induce differentiation of human CD34+ hemopoietic progenitors to dendritic cells: evidence for protein kinase C-mediated signaling

The intracellular signals that mediate the differentiation of pluripotent hemopoietic progenitors to dendritic cells (DC) are largely undefined. We have found that the phorbol ester PMA by itself induced 47% +/- 8.7% of input human CD34+ hemopoietic progenitors to differentiate into cells with morphology and surface Ag phenotype characteristic of DC by day 7 of culture. Functionally, PMA-generated DC processed and presented whole soluble Ag and also induced resting T cell proliferation and Ag-specific CTL effector function. Unlike cytokine-driven DC differentiation, PMA suppressed proliferation and induced cell death (in part via apoptosis) in cells that did not differentiate to DC. The effects of PMA were blocked by inhibitors of protein kinase C activation, suggesting a central role for this signaling molecule. PMA-mediated signaling also induced expression of the RelB transcription factor, an NF-kappaB family member implicated in DC differentiation. These findings suggest that phorbol esters activate protein kinase C, which then initiates the terminal component of an intracellular signaling pathway(s) involved in the DC differentiation of CD34+ hemopoietic progenitors.

Inhibition of human mast cell growth and differentiation by interferon gamma-1b

In an effort to identify cytokines that inhibit human mast cell growth, we cultured HMC-1 cells and recombinant human stem cell factor (rhSCF)-dependent human bone marrow-derived mast cells (HBMCs) in the presence of interferon gamma (IFNgamma)-1b and interferon alpha (IFNalpha)-2b. HMC-1 cell numbers decreased in the presence of 1000 U/mL IFNgamma-1b but were unaffected by 1000 U/mL of IFNalpha-2b. HBMCs were then cultured for 0 to 7 days with 100 ng/mL rhSCF and 10 ng/mL recombinant human IL-3 (rhIL-3), followed by culture in rhSCF and administration of either 1000 U/mL IFNalpha-2b or 1000 U/mL IFNgamma-1b. HBMCs appearing in cultures with rhSCF alone or in combination with IFNalpha-2b were virtually identical in number through 8 weeks of culture. In cultures supplemented with IFNgamma-1b, HBMCs significantly decreased in number and incidence of granular metachromasia by 4 to 5 weeks (p<0.001). Similar results were obtained when human marrow was cultured from day 0 with rhSCF and IFNgamma-1b. Mature rhSCF-dependent HBMCs were also cultured at 5 weeks with rhSCF alone or in combination with IFNgamma-1b. Compared with cells cultured in rhSCF, mature 5-week HBMC cultures treated with rhSCF plus IFNgamma-1b revealed a decrease in mast cells, and those mast cells that remained had fewer toluidine blue- and tryptase-positive granules after 5 to 8 weeks. FACS analysis of rhSCF plus IFNgamma-1b-treated mature HBMCs revealed increased c-kit and Fc(epsilon)RI expression. Mast cell releasibility was not increased. IFNgamma-lb was thus able to suppress mast cell growth from CD34+ cells, suggesting that this agent should be considered as a candidate cytokine for the treatment of disorders of mast cell proliferation.