Arginase release from red blood cells: possible link in transfusion induced immune suppression?

CD71+ RBCs: A potential immune mediator in transfusion

Donor - recipient sex - mismatched transfusion is associated with increased mortality. The mechanisms for this are not clear, but it may relate to transfusion-related immunomodulation. Recently, CD71⁺ erythroid cells (CECs), including reticulocytes (CD71⁺ RBCs) and erythroblasts, have been identified as potent immunoregulatory cells. The proportion of CD71⁺ RBCs in the peripheral blood is sufficient to play a potential immunomodulatory role. Differences in the quantity of CD71⁺ RBCs are dependent on blood donor sex. The total number of CD71⁺ RBCs in red cell concentrates is also affected by blood manufacturing methods, and storage duration. As a component of the total CECs, CD71⁺ RBCs can affect innate and adaptive immune cells. Phagocytosed CECs directly reduce TNF-α production from macrophages. CECs can also suppress the production of TNF-α production from antigen presenting cells. Moreover, CECs can suppress T cell proliferation thorough immune mediation and / or direct cell-to-cell interactions. Different in their biophysical features compared to mature RBCs, blood donor CD71⁺ RBCs may be preferential targets for the macrophages. This report summarizes the currently literature supporting an important role for CD71⁺ RBCs in adverse transfusion reactions including immune mediation and sepsis.

Allogeneic blood transfusion in 163 children with acute lymphocytic leukemia (a STROBE-compliant article)

Little research has been done about the effects of allogeneic blood transfusion (ABT) on the recurrence and prognosis in the cases with childhood acute lymphocytic leukemia (cALL). In order to provide a basis for clinical safe blood transfusion, the data of 163 cases with cALL were retrospectively analyzed to explore the issue.The data of 163 cases with cALL between 2006 and 2011 were retrospectively analyzed. According to the frequency of blood transfusion, the 163 cases were divided into 4 groups including non-transfusion group, 1 to 10-time transfusion group, 11 to 25-time transfusion group, and >25-time transfusion group. Survival rates were compared with Log-Rank test. Cox regression analysis was used in the effects of risk factors on recurrence and death.ABT was performed in 152 cases with cALL (93.25%). In low-risk and intermediate-and-high risk cALL, the survival rate significantly decreased in all transfusion groups compared with that in non-transfusion group (all P < .01). Cox regression analysis showed that >25-time transfusion was an independent prognosis index of recurrence (odds ratio [OR] = 3.015, 95% confidence interval [CI]: 1.368-6.646) and death (OR = 3.979, 95% CI: 1.930-8.207) in cALL.Frequency of ABT appears to affect the recurrence and death in cALL. We should be careful with blood transfusion and avoid unnecessary blood transfusion as far as possible in the cases with cALL.

Application of controlled hypotension combined with autotransfusion in spinal orthomorphia

Background:

Idiopathic scoliosis is a common spinal deformity in teenagers, which is managed mainly by orthomorphia. However, due to great trauma, long operative duration and large blood loss, a great amount of blood transfusion is needed during the surgery. Allogeneic blood transfusion should be reduced in order to release blood insufficient, decline blood transfusion expense, as well as avoid transfusion diseases.

Objective:

The objective of the following study is to investigate the value of controlled hypotension combined with autotransfusion in idiopathic scoliosis orthomorphia and in order to reduce surgical bleeding and reduction in blood transfusion.

Subjects and Methods:

Intra-operative controlled hypotension was performed during posterior orthomorphia surgery on all the 46 cases of idiopathic scoliosis, 17 cases in which were served as the control group, who underwent allogeneic blood transfusion without autotransfusion, whereas the other 29 cases were served as the experimental group, who underwent autotransfusion that including reinfusion of pre-operative deposited autologous blood and intra-operative salvaged autologous blood. The blood loss volume and transfusion status in two groups were observed.

Results and Conclusion:

Blood loss volume in the control group was 400-1000 (835.3 ± 167.5) mL and that in the experimental group was 350-1400 (812.1 ± 152.7) mL, there was no marked difference between the two groups (P > 0.05). The volume of allogeneic blood transfusion in the control group was 500-1800 (855.9 ± 321.1) mL, which was greater than that in the experimental group ((0-1300 (337.9 ± 258.3) mL) (P < 0.01). The results suggested that controlled hypotension reduces intraoperative bleeding and post-operative autotransfusion minimizes the need of allogeneic blood transfusion.

Immunosuppressive CD71+ erythroid cells compromise neonatal host defence against infection

Newborn infants are highly susceptible to infection. This defect in host defence has generally been ascribed to the immaturity of neonatal immune cells; however, the degree of hyporesponsiveness is highly variable and depends on the stimulation conditions. These discordant responses illustrate the need for a more unified explanation for why immunity is compromised in neonates. Here we show that physiologically enriched CD71(+) erythroid cells in neonatal mice and human cord blood have distinctive immunosuppressive properties. The production of innate immune protective cytokines by adult cells is diminished after transfer to neonatal mice or after co-culture with neonatal splenocytes. Neonatal CD71(+) cells express the enzyme arginase-2, and arginase activity is essential for the immunosuppressive properties of these cells because molecular inhibition of this enzyme or supplementation with L-arginine overrides immunosuppression. In addition, the ablation of CD71(+) cells in neonatal mice, or the decline in number of these cells as postnatal development progresses parallels the loss of suppression, and restored resistance to the perinatal pathogens Listeria monocytogenes and Escherichia coli. However, CD71(+) cell-mediated susceptibility to infection is counterbalanced by CD71(+) cell-mediated protection against aberrant immune cell activation in the intestine, where colonization with commensal microorganisms occurs swiftly after parturition. Conversely, circumventing such colonization by using antimicrobials or gnotobiotic germ-free mice overrides these protective benefits. Thus, CD71(+) cells quench the excessive inflammation induced by abrupt colonization with commensal microorganisms after parturition. This finding challenges the idea that the susceptibility of neonates to infection reflects immune-cell-intrinsic defects and instead highlights processes that are developmentally more essential and inadvertently mitigate innate immune protection. We anticipate that these results will spark renewed investigation into the need for immunosuppression in neonates, as well as improved strategies for augmenting host defence in this vulnerable population.

Update in critical care for the nephrologist: transfusion in nonhemorrhaging critically ill patients

A growing number of guidelines and recommendations advocate a restrictive transfusion strategy. Strong evidence exists that a hemoglobin threshold of less than 7 g/dL conserves resources and may improve outcomes in critically ill patients and that platelet counts greater than 10,000/μL are well tolerated. Patients with coronary artery disease can be safely managed with a restrictive transfusion strategy, utilizing a hemoglobin threshold of less than 7 or 8 g/dL; a threshold of less than 8 g/dL can be applied to patients with acute coronary syndromes. In the absence of coagulopathy with bleeding or high risk for bleeding, plasma transfusion should be withheld. Complications from transfusion are significant and previously under-recognized immunologic complications pose a more serious threat than infections. Erythropoietin and iron administration do not reduce transfusion needs in the critically ill. Interventions to reduce blood loss and educate clinicians are successful in reducing transfusion requirements.

Persistence of elevated plasma CXCL8 concentrations following red blood cell transfusion in a trauma cohort

Red blood cell (RBC) transfusion is associated with alterations in systemic concentrations of IL-8/CXCL8 functional homologs in a murine model. Whether RBC transfusion alters systemic neutrophil chemokine concentrations in individuals sustaining traumatic injury is not known. We conducted a retrospective, single-center study of severely injured trauma patients presenting within 12 h of injury with a base deficit greater than 6 and hypotension in the field. Plasma concentrations of 25 chemokines, cytokines, and growth factors were obtained from both transfused (n = 22) and nontransfused (n = 33) groups in the first 48 h following admission. The transfused group (mean RBC units, 2.7 [SD, 1.7]) tended to be older (49.9 [SD, 21.1] vs. 40.4 [SD, 19.9] years, P = 0.10), with a higher percentage of females (40.9% vs. 18.2%, P = 0.06) and a higher Injury Severity Score (27.1 [SD, 12.7] vs. 21.4 [SD, 10.2], P = 0.07). In univariate and multivariate analyses, transfusion was associated with increased hospital and intensive care unit length of stay but not ventilator-free days. Plasma CXCL8 concentrations were higher in the transfused (84 [SD, 88] pg/mL) than the nontransfused group (31 [SD, 21] pg/mL, P = 0.003). Using a linear prediction model to calculate bioanalyte concentrations standardized for age, sex, Injury Severity Score, and admission SBP, we observed that CXCL8 concentrations diverged within 12 h following injury, with the transfused group showing persistently elevated CXCL8 concentrations by contrast to the decay observed in the nontransfused group. Other bioanalytes showed no differences across time. Red blood cell transfusion is associated with persistently elevated neutrophil chemokine CXCL8 concentrations following traumatic injury.

[Relationship between arginase activity and the storage time of packed red blood cells]

OBJECTIVES

Given the increasing evidence regarding a relationship between packed red blood cells storage time and post-transfusion complications, we decided to determine the relationship between the arginase enzyme levels, biochemical parameters and haemolysis, with the storage time of transfused packed red blood cells.

MATERIAL AND METHODS

We designed a prospective study that included 24 units of packed cells that had been consecutively transfused to patients of our hospital. After recording the storage time of each bag, 15 ml of blood was removed to determine arginase activity, biochemical parameters and haemolysis. A univariate analysis was performed on all the recorded parameters, and included those that were significant in the multiple regression model (P<.05).

RESULTS

The mean storage time was 18.6±6.1 days (range: 6-31 days), with a haematocrit of 59.8%±0.05%, a haemoglobin of 20.3±1.8 g/dl, a pH of 6.5±0.1, and an arginase activity of 140.1±124.0 mU/ml. A linear relationship was observed in the univariate analysis between the storage time and the pH (P=.001), the actual HCO(3) (P=.001), the haemolysis index (P=.035) and the SpO(2) (P=.01). Once adjusted for the confounding variables of the univariate model, a linear relationship was observed between the arginase activity and the storage time (P=.031).

CONCLUSIONS

Our study shows a directly proportional linear relationship between the storage time of packed red blood cells and their arginase activity. We suggest that these findings could be associated with the high incidence of complications after transfusion that may be directly proportional to their storage time.

Arginases and arginine deficiency syndromes

PURPOSE OF REVIEW

Many physiologic and pathophysiologic processes are modulated by arginine availability, which can be regulated by arginase. An understanding of the conditions that result in elevated arginase activity as well as the consequences of arginine deficiency is essential for design of effective nutritional support for disease. This review will emphasize recent findings regarding effects of plasma arginase and arginine deficiencies in disease.

RECENT FINDINGS

Elevations in plasma arginase, derived primarily from hemolysis of red blood cells or liver damage, that are associated with arginine deficiency have been identified in an increasing number of diseases and conditions. Arginine insufficiency not only can activate a stress kinase pathway that impairs function of T lymphocytes but it also can inhibit the mitogen-activated protein kinase signaling pathway required for macrophage production of cytokines in response to bacterial endotoxin/lipopolysaccharide.

SUMMARY

There are at least two broad categories of arginine deficiency syndromes, involving either T-cell dysfunction or endothelial dysfunction, depending on the disease context in which arginine deficiency occurs. There is limited information regarding the safety and efficacy of supplementation with arginine or its precursor citrulline in ameliorating arginine deficiency in specific diseases, indicating the need for further studies.

Is the number of blood products transfused associated with lower survival in children with acute lymphoblastic leukemia?

BACKGROUND

Blood transfusion during acute lymphoblastic leukemia (ALL) of childhood is scarcely documented. Children with ALL are immunosuppressed by both the disease and its therapy. Transfusion may contribute to the course of ALL through its transfusion-related immunomodulation (TRIM) effect.

PROCEDURE

Blood transfusion history and response to therapy for 108 children <16 years of age at the time of ALL diagnosis was documented. Clinical files, electronic records, and blood bank registries were scrutinized. Overall survival (OS) and event-free survival (EFS) in relation to blood product type and number of transfusions was determined. Hazard ratios (HR) for death and relapse were estimated through uni- and multivariate Cox regression analysis.

RESULTS

One hundred eight ALL patients were included. Median age was 6 years (range: 0-15 years). Ninety-seven patients (89.8%) were transfused. Median number of transfused products was seven (range: 0-345). After multivariate analysis, transfusion of >5 packed red blood cells (PRBC) remained a significant predictor for death (P = 0.003) and relapse (P = 0.011). For platelets, maximal significance was observed when >30 platelet concentrates (PC) were transfused (P < 0.001). When both, PRBC and PC were considered, maximal significance for predicting death was observed with transfusion of >30 blood products (P < 0.001).

CONCLUSIONS

The number of blood products transfused to children with ALL appears to be significantly associated with lower survival rates. This may reflect both the severity of the disease and the TRIM effect, which may decrease immune surveillance capacity and the probability of leukemic clone eradication.

Nitric oxide scavenging by red blood cell microparticles and cell-free hemoglobin as a mechanism for the red cell storage lesion

BACKGROUND

Intravascular red cell hemolysis impairs nitric oxide (NO)-redox homeostasis, producing endothelial dysfunction, platelet activation, and vasculopathy. Red blood cell storage under standard conditions results in reduced integrity of the erythrocyte membrane, with formation of exocytic microvesicles or microparticles and hemolysis, which we hypothesized could impair vascular function and contribute to the putative storage lesion of banked blood.

METHODS AND RESULTS

We now find that storage of human red blood cells under standard blood banking conditions results in the accumulation of cell-free and microparticle-encapsulated hemoglobin, which, despite 39 days of storage, remains in the reduced ferrous oxyhemoglobin redox state and stoichiometrically reacts with and scavenges the vasodilator NO. Using stopped-flow spectroscopy and laser-triggered NO release from a caged NO compound, we found that both free hemoglobin and microparticles react with NO about 1000 times faster than with intact erythrocytes. In complementary in vivo studies, we show that hemoglobin, even at concentrations below 10 μmol/L (in heme), produces potent vasoconstriction when infused into the rat circulation, whereas controlled infusions of methemoglobin and cyanomethemoglobin, which do not consume NO, have substantially reduced vasoconstrictor effects. Infusion of the plasma from stored human red blood cell units into the rat circulation produces significant vasoconstriction related to the magnitude of storage-related hemolysis.

CONCLUSIONS

The results of these studies suggest new mechanisms for endothelial injury and impaired vascular function associated with the most fundamental of storage lesions, hemolysis.

Storage lesion in banked blood due to hemolysis-dependent disruption of nitric oxide homeostasis

PURPOSE OF REVIEW

Whereas blood storage is associated with an increased risk of cardiovascular events and multiorgan failure, the fundamental mechanisms underlying the 'storage lesion' in blood remain uncertain. A major abnormality in aged blood is the reduced red cell life-span after infusion, which is associated with microparticle and free hemoglobin release, and age-related loss of enzymatic functionality. However, the degree of intravascular hemolysis and microparticle formation in humans post-transfusion due to both storage and physiological shear has not been well studied.

RECENT FINDINGS

Our laboratories have discovered that even low levels of intravascular hemolysis severely disrupt nitric oxide bioavailability at the endothelium, via accelerated nitric oxide dioxygenation reactions with free plasma hemoglobin. This process contributes to endothelial dysfunction, adhesion molecule expression, platelet and hemostatic activation, and reactive oxygen species generation. Recent studies also suggest that red cells possess nitric oxide-generating functionality via nitrite reduction and red cell endothelial nitric oxide synthase activity, potentially providing novel pathways to therapeutically alleviate the 'storage lesion'.

SUMMARY

The understanding of the pathological effects of red cell hemolysis on endothelial function suggests that nitric oxide dysregulation may underlie the red cell storage lesion, driven by increased nitric oxide catabolism and loss of nitric oxide-generating functionality.

Ex-vivo changes in amino acid concentrations from blood stored at room temperature or on ice: implications for arginine and taurine measurements

Background

Determination of the plasma concentrations of arginine and other amino acids is important for understanding pathophysiology, immunopathology and nutritional supplementation in human disease. Delays in processing of blood samples cause a change in amino acid concentrations, but this has not been precisely quantified. We aimed to describe the concentration time profile of twenty-two amino acids in blood from healthy volunteers, stored at room temperature or on ice.

Methods

Venous blood was taken from six healthy volunteers and stored at room temperature or in an ice slurry. Plasma was separated at six time points over 24 hours and amino acid levels were determined by high-performance liquid chromatography.

Results

Median plasma arginine concentrations decreased rapidly at room temperature, with a 6% decrease at 30 minutes, 25% decrease at 2 hours and 43% decrease at 24 hours. Plasma ornithine increased exponentially over the same period. Plasma arginine was stable in blood stored on ice, with a < 10% change over 24 hours. Plasma taurine increased by 100% over 24 hours, and this change was not prevented by ice. Most other amino acids increased over time at room temperature but not on ice.

Conclusion

Plasma arginine concentrations in stored blood fall rapidly at room temperature, but remain stable on ice for at least 24 hours. Blood samples taken for the determination of plasma amino acid concentrations either should be placed immediately on ice or processed within 30 minutes of collection.

Independent determinants of early death in critically ill surgical patients

Abnormalities in cardiocirculatory, respiratory, or coagulatory parameters are frequent after major surgery, but so far, no study has investigated their predictive value for early intensive care unit (ICU) mortality. We aimed to describe and quantify the relation between these parameters that are routinely determined on ICU admission and early death after complex surgery. Individual patient data were available from a local ICU database. We performed a retrospective observational cohort study using prospectively collected data from March 1, 1993, through February 28, 2005. A cohort of 4,214 cases who were admitted to the ICU immediately after operation was analyzed. We studied age, sex, number of red blood cell units transfused on admission day, and admission values for heart rate, systolic blood pressure, hemoglobin concentration, partial thromboplastin time, prothrombin time, respiratory function (Pao2/Fio2 ratio), and body temperature for their association with 4-day mortality. Effects were adjusted for the underlying disease and for disease severity during the first 24 h after admission. We used generalized additive models to fit continuous variables individually before combining them into the final generalized model. We found an independent linear association between the number of transfused red blood cell units, partial thromboplastin time, and body temperature with acute outcome. A smoothed model described the independent interaction between admission blood pressure and early death. Only values of less than 80 mmHg were associated with an increased risk of 4-day mortality. According to these results, bleeding complications after ICU admission should be treated aggressively to prevent early death of the patient. However, normotensive conditions do not seem to be required to prevent early mortality. Whether rapid rewarming may improve outcome needs further rigorous study.

Elevated plasma arginase-1 does not affect plasma arginine in patients undergoing liver resection

Arginine is an important substrate in health and disease. It is a commonly held view that arginase-1 release from injured erythrocytes and hepatocytes leads to arginine breakdown; however, the true relationship between plasma arginase-1 concentration and activity has remained unaddressed. In the present study, blood was sampled from patients undergoing liver resection, a known cause of hepatocyte injury and arginase-1 release, to determine arginase-1, arginine and ornithine plasma levels. Arginase activity was assessed in vitro by measuring changes in arginine and ornithine plasma levels during incubation of plasma and whole-blood samples at 37 degrees C. Arginase-1 plasma levels increased 8-10-fold during liver resection, whereas arginine and ornithine levels remained unchanged. In accordance with these in vivo findings, arginine and ornithine levels remained unchanged in plasma incubated at 37 degrees C irrespective of the arginase-1 concentration. In contrast, arginine plasma levels in whole blood decreased significantly during incubation, with ornithine increasing stoichiometrically. These changes were irrespective of arginase-1 plasma levels and were explained by arginase activity present in intact erythrocytes. Next, plasma samples with 1000-fold normal arginase-1 concentrations were obtained from patients undergoing cadaveric liver transplantation. A significant decrease in arginine plasma levels occurred in vivo and in vitro. In contrast with commonly held views, moderately increased arginase-1 plasma levels do not affect plasma arginine. Very high plasma arginase-1 levels are required to induce potential clinically relevant effects.

Packed red blood cell-associated arginine depletion is mediated by arginase

BACKGROUND

Packed red blood cells (PRBCs) transfusion is associated with immune suppression, but these mechanisms are incompletely understood. PRBCs contain arginase, an enzyme that converts arginine to ornithine, and is known to limit arginine availability and suppress cellular immunity. We sought to determine whether PRBC arginase causes arginine depletion, potentially contributing to immunosuppression.

METHODS

A model of transfusion was designed by adding either centrifuged acellular supernatant from the PRBC unit (plasma) or total fluid from the unit (plasma+RBC [red blood cells]) to cell culture media. Through an institutional review board-approved protocol, PRBC units were isolated and processed by an accredited blood bank and stored at 4 degrees C. Leukoreduced PRBCs or supernatant aliquots were withdrawn every 5 days to 7 days for 42 days. Cell cultures were created with standard Roswell Park Memorial Institute media, controlling the arginine level at 80 micromol/L (approximating human serum), and adding 20% plasma or plasma+RBC. An irreversible arginase blocker (nor-N-omega-OH-L-arginine) was added to selected cultures. After 24 hours, culture arginase activity was measured by ornithine synthesis, and amino acid levels were measured using mass spectroscopy.

RESULTS

Culture arginase activity was increased by both plasma and plasma+RBC, but with plasma+RBC this did not reach statistical significance. Arginine levels were decreased and ornithine levels increased in cultures containing either supernatant or PRBC, as compared with control media. Addition of nor-N-omega-OH-l-arginine significantly decreased cell culture arginase activity, restored arginine levels, and diminished ornithine synthesis.

CONCLUSIONS

Arginase is present in PRBC units and causes arginine depletion. Depletion of arginine by PRBC arginase is a potential novel mechanism for immunosuppression.

Red blood cell arginase suppresses Jurkat (T cell) proliferation by depleting arginine

BACKGROUND

Transfusion of packed red blood cells (PRBC) suppresses immunity, but the mechanisms are incompletely understood. PRBCs contain arginase, an enzyme which converts arginine to ornithine and depletes arginine in vitro. Arginine depletion suppresses proliferation of Jurkat T cells in other models. We hypothesize that PRBC arginase-mediated arginine depletion will suppress proliferation of T cells.

METHODS

A transfusion model was designed adding PRBC to culture RPMI media with or without an irreversible arginase blocker (nor-NOHA), incubating for 6-48 hours and then removing the PRBCs. Amino acid concentrations in the media were measured using liquid chromatography mass spectrometry. T cells were then added to the pre-conditioned media, cultured for 24 hours, and proliferation was measured.

RESULTS

PRBC depleted arginine significantly and increased ornithine in media compared to baseline PRBC treated wells and significantly decreased T cell proliferation. These effects were enhanced with volume of PRBC exposure. Nor-NOHA inhibition of arginase restored T cell proliferation in PRBC treated cultures.

CONCLUSIONS

Jurkat T cell proliferation was impaired by PRBC in clinically relevant volumes. The mechanism influencing T cell impairment appears to result from arginine depletion by arginase. Arginine depletion by PRBC arginase may be a novel mechanism for immunosuppression after transfusion.

Red cell transfusion: an essential factor for patient prognosis in surgical critical illness?

In contrast to randomized studies, previous cohort studies identified red cell transfusion as an independent predictor of mortality in critically ill patients. However, these cohort studies did not adjust for disease severity during intensive care unit (ICU) stay. We performed a retrospective, observational cohort study using prospectively collected data from March 1, 1993, through February 28, 2005. A cohort of 3037 consecutive surgical cases requiring intensive care therapy for more than one day was analyzed. We used two different sets of potentially confounding covariables (admission variables only or in combination with variables reflecting number and extent of organ dysfunction during ICU stay). We found that the total number of red cell units which a case had received during ICU stay, and the maximum number of units given on a single day, were independently associated with an increase in ICU mortality when only admission variables were considered for the analysis. After controlling for the additional effect of variables reflecting organ dysfunction during ICU stay, we found that red cell transfusion was no longer an independent risk factor for death. However, there was a significant effect of red cell transfusion on ICU LOS in survivors irrespective of the covariable sets used. We conclude that red cell transfusion during ICU stay may be only a surrogate marker for disease severity and is not causally related to ICU mortality. Relevant side effects of red cell transfusion are presumably small and may be only recognizable in surviving cases.

Transfusion of the injured patient: proceed with caution

Transfusion of the injured patient with packed red blood cells (PRBCs) is a dynamic process requiring vigilance during the acute resuscitative and recovery phases postinjury. Although adverse events have been reported in 2% to 10% of injured patients, the advent of new detection techniques for viral pathogens has markedly decreased the risk of infectious transmission. However, transfusions are strongly associated with immunosuppression in the host, which may occur days after the initial injury and may lead to bacterial infections. Conversely, early transfusion of stored PRBCs, > 6 units in the first 12 h postinjury, contributes to an early state of hyperinflammation that is a strong, independent predictor of multiple organ failure (MOF) in those patients with intermediate injury severity scores. The roles of prestorage leukoreduction are also reviewed with respect to the promotion of both immunosuppression and hyperinflammation. We further summarize studies with hemoglobin substitutes, whose use may obviate many of the untoward events of transfusion and promise to lead to better outcomes for injured patients.

A simple method to optimize peripheral blood mononuclear cell preparation from cynomolgus monkeys and improve mixed lymphocyte reactions

INTRODUCTION

The standard Ficoll-Hypaque method used to isolate peripheral blood mononuclear cells (PBMC) gives very variable results when used with cynomolgus monkey blood. We have improved the method by using special cell processing tubes (CP-tubes), originally developed for clinical use.

METHODS

Blood samples were collected from cynomolgus monkeys and processed for PBMC preparation using either the classical Ficoll-Hypaque method or CP-tubes following various centrifugation protocols. The preparations were compared according to their cellular content as well as their response in the mixed lymphocyte reaction (MLR).

RESULTS

Good PBMC separation was achieved in >90% of samples by centrifugation of blood samples in CP-tubes for 40-45 min at 1650 x g and 20 degrees C. For the remaining samples, poor PBMC separation was probably due to low corpuscular hemoglobin concentrations (< 28 g/dl), but this could be rectified by using one to two additional centrifugations. The PBMC preparations thus obtained showed lower red blood cell (RBC) and polymorphonuclear (PMN) cell contamination, reacted well to mitogen and showed improved MLR stimulation indices vs. standard Ficoll-Hypaque-PBMC-derived preparations. The inhibitory effect of Cyclosporine-A (CsA) was within the low nanomolar range with both methods.

DISCUSSION

These results demonstrate that the use of CP-tubes is a practical way of improving PBMC separation and MLR responses with cynomolgus monkey blood.

Anemia, allogenic blood transfusion, and immunomodulation in the critically ill

Anemia and allogenic RBC transfusions are exceedingly common among critically ill patients. Multiple pathologic mechanisms contribute to the genesis of anemia in these patients. Emerging risks associated with allogenic RBC transfusions including the transmission of newer infectious agents and immune modulation predisposing the patient to infections requires reevaluation of current transfusion strategies. Recent data have suggested that a restrictive transfusion practice is associated with reduced morbidity and mortality during critical illness, with the possible exception of acute coronary syndromes. In this article, we review the immune-modulatory role of allogenic RBC transfusions in critically ill patients.

Nitric oxide and blood: a review

Nitric oxide (NO) was identified as a physiological mediator of vascular tone in 1987. NO produced by endothelial cells causes vasodilatation and also inhibits platelet aggregation and leucocyte adhesion. Red cells metabolize NO to nitrate but may possibly carry and release, or even produce, NO in hypoxic conditions. NO physiology may have important implications for transfusion medicine, ranging from adverse effects of haemoglobin substitutes to preservation of stored platelets and to detrimental effects of stored red cells.

KUPFFER CELL???DEPLETED RATS HAVE A DIMINISHED ACUTE-PHASE RESPONSE FOLLOWING MAJOR LIVER RESECTION

Partial hepatectomy (PH)-induced Kupffer cell (KC) activation results in a rapid release of cytokines inducing the acute-phase response (APR). This study was done to evaluate the role of Kupffer cells (KCs) in the course of the APR following PH and a consecutive endotoxin challenge. KC depletion was performed in rats by i.v. administration of 1 mL liposome-encapsulated dichloromethylene diphosohonate (Cl2MDP). Control rats received 1 mL NaCl 0.9%. Forty-eight hours later, PH was performed. At 24 h after PH, rats were randomized to receive either 1 mL NaCl 0.9% (saline) or 50 microg/kg LPS i.v. in 1 mL. Animals were sacrificed at 4 h after LPS or saline infusion. The APR was determined by measuring hepatic gene expression of alpha 2-macroglobulin, alpha 1-acid glycoprotein, and IL-6 and expression of hepatic albumin. The APR was significantly depressed in KC-depleted rats. Despite increased IL-6 mRNA synthesis in response to low-dose LPS, no enhancement of acute-phase protein synthesis (APP) was found in KC-depleted rats. Hepatic failure was most profound in KC-depleted rats, as indicated by elevated plasma levels of liver transaminases and ammonia. We conclude that after PH, KC function in the remnant liver is important for the acute-phase reaction and reduces endotoxin-induced hepatocyte damage.

Derangement of immune responses by myeloid suppressor cells

In tumor-bearing mice and cancer patients, tumor progression is often associated with altered hematopoiesis leading to the accumulation of myeloid cells. Extensive studies in preclinical models indicate that these cells share the CD11b and the Gr-1 markers, possess a mixed mature-immature myeloid phenotype, and are responsible for the induction of T-cell dysfunctions, both tumor-specific and nonspecific. Moreover, CD11b(+)Gr-1(+) myeloid cells are described under different unrelated situations associated with temporary impairment of the T-lymphocyte reactivity. This review examines recent findings on the nature, properties, and mechanisms of action of these myeloid suppressor cells (MSCs).