Oral immune dysfunction is associated with the expansion of FOXP3+PD-1+Amphiregulin+ T cells during HIV infection

Residual systemic inflammation and mucosal immune dysfunction persist in people living with HIV, despite treatment with combined anti-retroviral therapy, but the underlying immune mechanisms are poorly understood. Here we report that the altered immune landscape of the oral mucosa of HIV-positive patients on therapy involves increased TLR and inflammasome signaling, localized CD4+ T cell hyperactivation, and, counterintuitively, enrichment of FOXP3+ T cells. HIV infection of oral tonsil cultures in vitro causes an increase in FOXP3+ T cells expressing PD-1, IFN-γ, Amphiregulin and IL-10. These cells persist even in the presence of anti-retroviral drugs, and further expand when stimulated by TLR2 ligands and IL-1β. Mechanistically, IL-1β upregulates PD-1 expression via AKT signaling, and PD-1 stabilizes FOXP3 and Amphiregulin through a mechanism involving asparaginyl endopeptidase, resulting in FOXP3+ cells that are incapable of suppressing CD4+ T cells in vitro. The FOXP3+ T cells that are abundant in HIV-positive patients are phenotypically similar to the in vitro cultured, HIV-responsive FOXP3+ T cells, and their presence strongly correlates with CD4+ T cell hyper-activation. This suggests that FOXP3+ T cell dysregulation might play a role in the mucosal immune dysfunction of HIV patients on therapy.

Mucosal T-cell immunoregulation varies in early and late inflammatory bowel disease

BACKGROUND AND AIMS

Crohn's disease is a life-long form of inflammatory bowel disease (IBD) mediated by mucosal immune abnormalities. Understanding of the pathogenesis is limited because it is based on data from adults with chronic Crohn's disease. We investigated mucosal T-cell immunoregulatory events in children with early Crohn's disease.

METHODS

Mucosal biopsies and T-cell clones were derived from children experiencing the first attack of Crohn's disease, children with long-standing Crohn's disease, infectious colitis, and children without gut inflammation.

RESULTS

As in acute infectious colitis, interleukin (IL) 12 induced T cells from early Crohn's disease to acquire a strongly polarised T helper (Th) type 1 response characterised by high IFN-gamma production and IL12Rbeta2 chain expression. Th1 polarisation was not induced in clones from late Crohn's disease. Mucosal levels of IL12p40 and IL12Rbeta2 messenger RNA were significantly higher in children with early than late Crohn's disease. These results demonstrate that susceptibility to IL12-mediated modulation is strongly dependent on the stage of Crohn's disease.

CONCLUSIONS

At the onset of Crohn's disease mucosal T cells appear to mount a typical Th1 response that resembles an acute infectious process, and is lost with progression to late Crohn's disease. This suggests that mucosal T-cell immunoregulation varies with the course of human IBD. Patients with the initial manifestations of IBD may represent an ideal population in which immunomodulation may have optimal therapeutic efficacy.

IL-4 instructs TH1 responses and resistance to Leishmania major in susceptible BALB/c mice

Immunity to infection with intracellular pathogens is regulated by interleukin 12 (IL-12), which mediates protective T helper type 1 (TH1) responses, or IL-4, which induces TH2 cells and susceptibility. Paradoxically, we show here that when present during the initial activation of dendritic cells (DCs) by infectious agents, IL-4 instructed DCs to produce IL-12 and promote TH1 development. This TH1 response established resistance to Leishmania major in susceptible BALB/c mice. When present later, during the period of T cell priming, IL-4 induced TH2 differentiation and progressive leishmaniasis in resistant mice. Because immune responses developed via the consecutive activation of DCs and then T cells, the contrasting effects of IL-4 on DC development and T cell differentiation led to immune responses that had opposing functional phenotypes.

Decreased Bax expression by mucosal T cells favours resistance to apoptosis in Crohn's disease

BACKGROUND

Activated T cells are more susceptible to apoptosis than resting T cells. As intestinal T cells normally exhibit a higher state of activation, increased apoptosis may be necessary to maintain immune homeostasis in the specialised microenvironment of the mucosa. On the other hand, in Crohn's disease (CD) mucosal T cells are resistant to apoptosis, suggesting abnormal regulation of cell death mechanisms.

AIMS

To investigate differences in expression of anti- and proapoptotic Bcl-2 family proteins, key regulators of apoptosis, between circulating and mucosal T cells, and possible alterations in CD.

PATIENTS AND METHODS

Lamina propria T cells (LPT) were isolated from 10 control, seven CD, and eight ulcerative colitis (UC) patients, and peripheral blood T cells (PBT) from healthy volunteers. Purified T cells were stained intracellularly for Bcl-2, Bcl-x(L), and Bax, and mean fluorescence intensity measured by flow cytometry.

RESULTS

Compared with PBT, the expression level of Bcl-2 and Bax, but not Bcl-x(L), was significantly greater in LPT, resulting in lower Bcl-x(L)/Bax ratios. In PBT, Bax expression was highly and significantly correlated with both Bcl-2 and Bcl-x(L), but correlation with Bcl-2 was absent in LPT. Bax expression in CD, but not UC, LPT was significantly lower than in control LPT, resulting in a significantly higher Bcl-x(L)/Bax ratio. The significant correlation of Bcl-x(L) to Bax was preserved in CD, but not UC, LPT.

CONCLUSIONS

Regulation of Bcl-2 family protein expression differs between circulating and mucosal T cells, probably underlying diverse survival potentials. In CD LPT, a low Bax expression and a high Bcl-x(L)/Bax ratio favour resistance to apoptosis and may contribute to the chronicity of inflammation.

Regulation of life and death in lamina propria T cells

T cells are essential to initiation, amplification, and regulation of an immune response. This response is terminated when T cells undergo apoptosis, a physiological process of cell death triggered by various mechanisms and regulated by signaling pathways leading to enzymatic degradation of chromatin. An effective immune response depends on the proper balance between proliferation and death of activated T cells. This is particularly important in the intestine, where mucosal T cells are subjected to the high antigenic pressure of lumenal antigens and apoptosis is required to induce tolerance and maintain a state of 'physiological' inflammation. Insufficient apoptosis may result in excessive T cell retention and chronic intestinal inflammation, as seen in conditions associated with defective apoptosis of lamina propria T cells.

Reversal of established delayed type hypersensitivity reactions following therapy with IL-4 or antigen-specific Th2 cells

Delayed-type hypersensitivity reactions (DTHR) are mediated by IFN-gamma-producing CD4+ (Th1) or CD8+ T cells (Tc1) and can be prevented by steering T cells toward an IL-4-producing Th2 or Tc2 phenotype. It is currently accepted that T cells can be directed toward a Th2 or Tc2 phenotype only during the initiation of an immune response. Once established, the cytokine pattern of immune reactions is believed to be stable. Therefore, inhibition of DTHR by the induction of Th2/Tc2 responses, termed immune deviation, is considered only as a prevention but not as a therapy of harmful DTHR. Here we demonstrate that therapeutic immune deviation can reverse established contact hypersensitivity (CHS), a Th1/Tc1-mediated DTHR. One or two weeks after induction of CHS, mice received either a single cycle of IL-4 therapy or adoptive transfer of antigen-specific Th2 cells. This treatment generated a novel state of immunity that provided long-lasting protection against tissue destruction and neutrophil recruitment during subsequent antigen exposures. Therapeutic immune deviation of established CHS was dependent on CD4+ T cells and the induction of endogenous IL-4 synthesis. Thus, a population of immunoregulatory Th2 cells persists during advanced inflammatory responses that can be used for therapeutic deviation of established DTHR.

A mucosal IgA-mediated excretory immune system in vivo

The capacity of mucosal IgA Abs to serve as an excretory immune system in vivo was investigated. Mice expressing a transgenic TCR were immunized intragastrically with the cognate Ag to elicit a vigorous mucosal IgA Ab response. Soon after i.v. challenge, Ag was detected within the epithelial cells of the small intestinal crypts and to a lesser degree within the epithelial cells higher up the villi, paralleling the gradient in expression of the polymeric Ig receptor and the transport of its ligand, oligomeric IgA. Uptake of Ag into the epithelial cells occurred only from the basolateral aspect and only when Ag complexed to IgA Ab could be present in the lamina propria. The results support the concept that local IgA Abs can excrete Ags from the body by transporting them directly through mucosal epithelial cells, using the same mechanism that transports free IgA into the mucosal secretions.

Hierarchical cleavage of focal adhesion kinase by caspases alters signal transduction during apoptosis of intestinal epithelial cells

BACKGROUND & AIMS

Purified intestinal epithelial cells die of detachment-induced apoptosis due to loss of cell anchorage during isolation. Anchorage-dependent cells form focal adhesions, sites of enhanced cell-matrix attachment that confer survival signals. Focal adhesion kinase (FAK), a component of the focal adhesion signaling complex, transduces these antiapoptotic signals. In this report, the molecular events leading to cleavage of FAK by caspases during apoptosis and its functional implications are defined.

METHODS

Cytosolic extracts of human intestinal epithelial cells undergoing detachment-induced apoptosis were analyzed by Western blotting, immunoprecipitation, and kinase assay.

RESULTS

FAK is cleaved by the ordered proteolytic activity of 2 different members of the caspase-3 family. The first cleavage is mediated by caspase-3, generating a 94/92-kilodalton-terminal fragment, which is processed by caspase-6 to an 84-kilodalton fragment. After apoptosis is initiated, the level of FAK phosphorylation is rapidly decreased, and the phosphorylation pattern of FAK-associated proteins is dramatically modified, showing significant yet divergent changes in signal transduction.

CONCLUSIONS

Cleavage of FAK during apoptosis of normal human cells is an example of the sequential, highly regulated, and coordinate action of caspases that not only dismantle a cell by proteolysis, but also alter the cell's signaling machinery.

Apoptosis: implications for inflammatory bowel disease

Cells of the intestinal mucosa live in a harsh environment and therefore rely heavily on the highly regulated process of cell death, apoptosis, to maintain tissue integrity. Imbalance in the intracellular events that modulate apoptosis may contribute to the pathogenesis of inflammatory bowel disease.

Selective resistance of mucosal T-cell activation to immunosuppression in Crohn's disease

BACKGROUND & AIMS

The inappropriately high state of T-cell activation found in Crohn's disease could be due to failure to respond to inhibitory signals. We tested the hypothesis that Crohn's disease mucosal T-cells are resistant to the immunosuppressive action of interleukin4.

PATIENTS

Patients with Crohn's disease, ulcerative colitis, and other malignant and non-malignant conditions undergoing bowel resection.

METHODS

The effect of interleukin-4 on lamina propria mononuclear cells from Crohn's disease, ulcerative colitis and control mucosa was assessed on various T-cell functions: interleukin-2-induced cytotoxicity, soluble interleukin-2 receptor and interleukin-2 production, and expression of mRNA for interleukin-2R and interferon-gamma.

RESULTS

Cytotoxicity of control and ulcerative colitis cells was markedly decreased by interleukin-4, whereas Crohn's disease cells failed to be inhibited. Addition of interleukin-4 to interleukin-2-stimulated cultures decreased soluble interleukin-2R production significantly less in Crohn's disease and ulcerative colitis than control cells. In the same cultures, residual levels of interleukin-2 were significantly increased in control and ulcerative colitis, but not Crohn's disease cultures. Finally, Crohn's disease cells were significantly more resistant to interleukin-4-mediated inhibition of spontaneous and interleukin-2-induced expression of interleukin-2Ralpha and interferon-gamma mRNA compared to control cells.

CONCLUSIONS

The effector function, receptor expression and cytokine production of Crohn's disease mucosal T-cells are resistant to interleukin4-mediated inhibition. Failure to respond to down-regulatory signals may contribute to persistent T-cell activation and chronicity of inflammation in Crohn's disease.

Immunology of inflammatory bowel disease

The immunology of inflammatory bowel disease continues to be an intense area of investigation for clues to the pathogenesis of Crohn disease and ulcerative colitis. As typical with complex diseases, inflammatory bowel disease research is continuously evolving. Without abandoning traditional areas of study, such as humoral and cellular immunity and cytokines, investigation is broadening to explore new molecules and biologic phenomena. Novel cytokines and cell adhesion molecules appear to be involved in inflammation, while the role of nitric oxide is being clarified. Leukocyte resistance to apoptosis appears to be a major contributing factor to Crohn disease. Epithelial cell-derived defensins and receptors are arising as key molecules mediating the interaction of innate and acquired mucosal immunity with the enteric flora, and explaining how the latter participates in gut inflammation. The results of these combined studies are opening novel therapeutic horizons whose implementation offers better forms of treatment.

The differentiated state of intestinal lamina propria CD4+ T cells results in altered cytokine production, activation threshold, and costimulatory requirements

Intestinal lamina propria (LP) CD4+ T cells are memory-like effector cells that proliferate at relatively low levels and require high levels of TCR signaling and costimulation for full activation in vitro. To study LP CD4+ T cell functional potential we used DO11.10 TCR transgenic (Tg) mice specific for the class II MHC-restricted OVA323-339 peptide and nontransgenic BALB/c mice. Activation of LP Tg+ T cells with Ag using mucosal explants induced high levels of IL-2, IL-4, and IFN-gamma. Culturing isolated LP cells with IL-12 enhanced IFN-gamma production and down-regulated IL-4 and IL-2, whereas addition of IL-4 maintained IL-4 production without inhibiting IFN-gamma production. Systemic administration of relatively high dose (HD; 100 nM) OVA323-339 peptide induced similar levels of bromodeoxyuridine (BrdU) incorporation by LP and splenic Tg+ T cells in vivo, whereas low dose (LD; 4.5 nM) peptide injections induced 4-fold greater levels of BrdU incorporation for LP compared with splenic Tg+ T cells. Coadministration of CTLA-4Ig reduced BrdU incorporation for splenic cells by 70% with HD and LD stimulation, but had little effect on LP responses to HD stimulation. Results of in vivo studies were confirmed in nontransgenic BALB/c mice using HD (200 microg) and LD (10 microg) anti-CD3 mAb+/- CTLA-4Ig. These results suggest that LP T cells are differentiated effector cells that respond at high levels when activated with relatively low levels of Ag- and B7-mediated costimulation in vivo. The reduced activation threshold of LP T cells may facilitate responses to low levels of Ag derived from mucosal pathogens.

Regulation of ICAM-1-mediated fibroblast-T cell reciprocal interaction: implications for modulation of gut inflammation

BACKGROUND & AIMS

Immune-nonimmune cell interactions modulate mucosal immunity. We investigated the expression of adhesion molecules by intestinal fibroblasts, the effect of immune cell-derived factor on fibroblast binding of T cells, and the consequences of interfering with adhesion molecule expression on fibroblast-T cell interaction.

METHODS

Expression of fibroblast intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 surface and messenger RNA (mRNA) was measured before and after exposure to immune cell-derived supernatants. Fibroblasts were treated with antibodies to ICAM-1 or VCAM-1, or ICAM-1 antisense oligonucleotide Isis 2302, before a T-cell adhesion assay.

RESULTS

Fibroblast activation by immune cell-derived cytokines enhanced ICAM-1 and VCAM-1 surface expression and mRNA as well as adhesiveness for T cells. Blockade with neutralizing antibodies showed that binding was almost exclusively dependent on ICAM-1. Isis 2302 specifically reduced fibroblast ICAM-1 mRNA and dose-dependently inhibited ICAM-1 surface expression and T-cell binding.

CONCLUSIONS

ICAM-1 is essential for intestinal fibroblast binding of T cells, a phenomenon that is efficiently and specifically disrupted by ICAM-1 antisense oligonucleotides. These observations emphasize the crucial regulatory role of fibroblasts in mucosal immunity and their potential as targets for therapeutic intervention in intestinal inflammation.

Resistance of Crohn's disease T cells to multiple apoptotic signals is associated with a Bcl-2/Bax mucosal imbalance

Crohn's disease (CD) is a condition characterized by excessive numbers of activated T cells in the mucosa. We investigated whether a defect in apoptosis could prolong T cell survival and contribute to their accumulation in the mucosa. Apoptotic, Bcl-2+, and Bax+ cells in tissue sections were detected by the TUNEL method and immunohistochemistry. T cell apoptosis was induced by IL-2 deprivation, Fas Ag ligation, and exposure to TNF-alpha and nitric oxide. TUNEL+ leukocytes were few in control, CD, and ulcerative colitis (UC) mucosa, with occasional CD68+ and myeloperoxidase+, but no CD45RO+, apoptotic cells. Compared with control and UC, CD T cells grew remarkably more in response to IL-2 and were significantly more resistant to IL-2 deprivation-induced apoptosis. CD T cells were also more resistant to Fas- and nitric oxide-mediated apoptosis, whereas TNF-alpha failed to induce cell death in all groups. Compared with control, CD mucosa contained similar numbers of Bcl-2+, but fewer Bax+, cells, while UC mucosa contained fewer Bcl-2+, but more Bax+, cells. Hence, the Bcl-2/Bax ratio was significantly higher in CD and lower in UC. These results indicate that CD may represent a disorder where the rate of T cell proliferation exceeds that of cell death. Insufficient T cell apoptosis may interfere with clonal deletion and maintenance of tolerance, and result in inappropriate T cell accumulation contributing to chronic inflammation.

New isolation technique to study apoptosis in human intestinal epithelial cells

Intestinal epithelial cells derive from stem cells at the base of the crypt and migrate along the crypt-lumen axis. Their life is terminated as they reach the luminal surface where they detach and are shed. Intestinal epithelial cells show evidence of apoptosis in the region of shedding, and cell death is thought to resemble a form of apoptosis called detachment-induced cell death, or anoikis. Human intestinal epithelial cells die rapidly in vitro due to loss of anchorage during isolation, making primary culture of these cells a goal that has not yet been reached. However, the molecular mechanisms underlying this process of anoikis are largely unknown. In this study, a novel protocol for the rapid, temperature-controlled isolation of highly purified human colonic epithelial cells from surgical specimens is described. Using this method, early molecular events of anoikis in nontransformed epithelial cells were studied. Intestinal epithelial cells were isolated at the beginning of the apoptotic cascade, before the activation of caspase 3 family members and cleavage of poly(ADP-ribose) polymerase and DNA fragmentation. Elucidating the molecular mechanisms of detachment-induced cell death may facilitate the establishment of long-term primary cultures of human intestinal epithelial cells and enhance our understanding of homeostasis in the intestinal epithelium.

Sequential and rapid activation of select caspases during apoptosis of normal intestinal epithelial cells

Detachment-induced cell death (DICD) is considered to be one of the means by which intestinal epithelial cells (IEC) die of apoptosis as they reach the lumen and are shed. Caspases, a family of cysteine proteases, play a central role in initiating, amplifying, and executing apoptosis; however, the pattern of caspase activation in response to distinct apoptotic stimuli remains unknown. We investigated the kinetics of caspase activation during DICD in freshly isolated human IEC. DNA fragmentation is observed 90 min after detachment and is preceded by the sequential activation of preformed members of the CPP32 family of caspases. Activation of caspase 6 and cleavage of the endogenous caspase substrate poly(ADP-ribose) polymerase (EC 2.4.2.30) are detected within 15 min of detachment, 30-45 min before caspase 3 activation. Caspase 1 and caspase 10 are present as proenzymes, yet they remain inactive in response to this trigger of apoptosis. Human IEC are primed to rapidly undergo detachment-induced apoptosis involving the selective and sequential activation of preformed caspases. This study may enhance our understanding of physiological events occurring as IEC are shed. Their rapid apoptotic response to detachment may facilitate the high turnover of cells and ensure homeostasis in the intestinal epithelium.

Biogeochemical assessment of natural attenuation of JP-4-contaminated ground water in the presence of fluorinated surfactants

The biogeochemistry of the natural attenuation of petroleum-contaminated ground water was investigated in a field study. The focus of the study was a fire training site located on Tyndall Air Force Base in Florida. The site has been used by the Air Force for approximately 11 years in fire fighting exercises. An on-site above-ground tank of JP-4 provided fuel for setting controlled fires for the exercises. Various amounts of water and aqueous film forming foams (AFFF) were applied to extinguish the fires. The sources of contamination included leaks from pipelines transporting the fuel, leaks from an oil/water separator and runoff and percolation from the fire fighting activities. Previous investigations had identified jet fuel contamination at the site, however, no active remediation efforts have been conducted to date. The goal of this study was to use biogeochemical monitoring data to delineate redox zones within the site and to identify evidence of natural attenuation of JP-4 contamination. In addition to identifying several hydrocarbon metabolites, fluorinated surfactants (AFFF) were detected down-gradient of the hydrocarbon plume.

Crohn's disease and ulcerative colitis mucosal T cells are stimulated by intestinal epithelial cells: implications for immunosuppressive therapy

BACKGROUND

Crohn's disease (CD) and ulcerative colitis (UC) are chronic inflammatory diseases, and their pathogenesis is attributed, in part, to alterations of the mucosal immune system. This study was designed to define the possible contribution of epithelial cells to the activation of lamina propria T lymphocytes (LPTs) in CD and UC.

METHODS

LPTs isolated from CD, UC, and control surgical specimens were cocultured with freshly isolated allogeneic or autologous epithelial cells or epithelial cell lines. Resulting T-cell proliferation was evaluated by tritiated thymidine incorporation on day 5.

RESULTS

When intestinal epithelial cells were used to stimulate mucosal T-cell proliferation, CD and UC LPTs were less responsive than control LPTs (p < 0.05 and p < 0.03, respectively). This difference between inflamed and control T cells was consistently observed by using a variety of different intestinal epithelial cell types.

CONCLUSIONS

CD and UC mucosal T cells are hyporesponsive to activation by intestinal epithelial cells when compared with control LPTs. Elucidating the mechanism underlying the differential activation of CD and UC LPTs may help to better understand the immunopathogenesis of these conditions.

A strict requirement of interleukin-4 for interleukin-4 induction in antigen-stimulated human memory T cells

The role of interleukin-4 (IL-4) in the induction of IL-4 in mouse T cells is well established, but conflicting results have been reported with anti-CD3-primed human T cells and T cell clones. Therefore, IL-4 regulation was investigated in short-term cultured human T cells primed in vitro with either a superantigen or a hapten, nickel sulfate (NiSO4), for 3 days and expanded with IL-2 for another 5 days. Under these conditions, antigen-specific IL-4 producing T cells were generated in 35/40 cultures. Priming for IL-4 production was abrogated in all cultures by anti-IL-4 antibody or soluble IL-4 receptor (sIL-4R). Primed T cells that were IL-4- when cultured with IL-2 only developed an IL-4 producing phenotype when primed and expanded in the presence of exogenous IL-4. T cells primed in the presence of either endogenous or exogenous IL-4 produced 10-200-fold more IL-4 than T cells primed in the presence of anti-IL-4 antibody or sIL-4R. While IL-4 induction was absolutely dependent on IL-4, neither endogenous nor exogenous IL-4 influenced IFN-gamma synthesis. Most importantly, IL-4 induced and sIL-4R abolished priming for IL-4 production even in NiSO4-specific memory T cells from sensitized individuals. Thus, IL-4 induction in antigen-specific human memory T cell populations absolutely required IL-4. The IL-4 pathway of memory T cells retained a remarkable plasticity in sensitized individuals.

Interleukin 4 in inflammatory bowel disease and mucosal immune reactivity

BACKGROUND & AIMS

Interleukin (IL) 4 has immunoregulatory and anti-inflammatory activities, but little is known about IL-4 in the human gut. We investigated production of IL-4 by isolated lamina propria mononuclear cells (LPMCs) from normal and inflamed intestine and its capacity to modulate local immune responses.

METHODS

IL-4 levels were measured by enzyme-linked immunosorbent assay in cultures of control and inflammatory bowel disease LPMCs, and the effect of IL-4 on LPMC proliferation and interaction with IL-2, IL-1 beta, lipopolysaccharide, bacterial antigens, superantigen, and antibodies to various T-cell receptors was investigated.

RESULTS

Various stimuli induced LPMCs to produce IL-4, but inflammatory bowel disease cells expressed IL-4 messenger RNA and secreted protein in significantly lower amounts than control cells. IL-4 failed to stimulate proliferation by fresh LPMCs, but a vigorous dose-dependent response was observed after preactivation by phytohemagglutinin, IL-2, or IL-4. When added to fresh LPMCs, IL-4 inhibited IL-2-induced proliferation. IL-4 amplified proliferation to IL-1 beta, lipopolysaccharide, peptidoglycan-polysaccharide complexes, staphylococcus enterotoxin A, and antibodies to the CD3 and CD28 receptors but not to tetanus toxoid.

CONCLUSIONS

Decreased production of IL-4 in inflammatory bowel disease may cause defective immunosuppressive and anti-inflammatory mechanisms and may contribute to disease pathogenesis. The ability of IL-4 to differentially modulate LPMC reactivity probably influences mucosal immune homeostasis.

Microbial biosorption of copper and lead from aqueous systems

Biosorption of metal ions from aqueous systems was evaluated using a culture of acidic soil isolates grown in a completely mixed, aerobic, semi-batch culture reactor. The laboratory scale system was used to test single and bimetallic solutions of copper and lead with sulfates, chlorides, or nitrates. To elucidate the key factors influencing biosorption and to characterize metal uptake by cellular and extra cellular components of the microbial system, a dialysis testing procedure was developed. A direct contact technique was used to determine the rate of metal sorption on cellular surfaces. The effectiveness of biosorption was influenced by pH, initial metal concentrations, and anionic composition. Respirometric tests were carried out to identify potential inhibitory effects of metal accumulation on microbial oxygen uptake rates.

High level expression and refolding of mouse interleukin 4 synthesized in Escherichia coli

Mouse Interleukin 4 is a 20-kDa glycoprotein, synthesized by activated T lymphocytes and mast cells, which regulates the growth and/or differentiation of a broad spectrum of target cells of the immune system, including B and T lymphocytes, macrophages, and hematopoietic progenitor cells. Using an inducible recA promoter and the g10-L ribosome-binding site, recombinant non-glycosylated interleukin 4 (IL-4) was expressed as 17% of total cellular protein in Escherichia coli inclusion bodies, as a reduced, inactive 14.5-kDa polypeptide. The protein was refolded and aggregates dissociated when three disulfide bonds were reformed by slowly decreasing the concentration of guanidine hydrochloride and cysteine. The oxidized monomer was purified to homogeneity by sequential ion-exchange and size exclusion chromatography. When compared with native IL-4, E. coli-derived IL-4 displayed an identical specific activity of 4-7 x 10(7) units/mg. This recombinant IL-4 contained a three-amino-acid NH2-terminal extension, which did not affect its biological activity. Purified biologically active protein consisted of three isoforms as shown by two-dimensional gel electrophoresis, with a pI greater than 9.0. These data suggest that neither glycosylation nor the NH2 terminus of mouse IL-4 play a critical role in contributing to its in vitro biological activity.

Asp f I CD4+ TH2-like T-cell lines in allergic bronchopulmonary aspergillosis

Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity lung disease caused by bronchial colonization with Aspergillus fumigatus (Af) characterized by elevated serum total and Af-specific IgE levels and eosinophilia. In order to examine T-cell reactivity to Af antigens, six T-cell lines were established from the peripheral blood of patients with ABPA to Asp f I, an 18 kd protein purified from Af extracts. The Asp f I-specific T-cell lines, analyzed by flow cytometry, were 100% CD3+ CD4+. Lymphoproliferative responses of the T-cell lines were specific for Asp f I stimulation, 28,999 cpm (stimulation index = 12.2), and showed no response to tetanus toxoid stimulation, 2178 cpm (stimulation index = 1.1) (p < 0.001). Furthermore, Asp f I-stimulated lymphoproliferation was inhibited in two experiments by monoclonal anti-interleukin (IL)-4 antibody in a dose-response fashion, 78% and 84% inhibition at 5% concentration of anti-IL-4. In contrast, anti-IL-2 antibody did not inhibit Asp f I-stimulated proliferation. Asp f I-stimulated T-cell lines synthesized predominantly IL-4 (mean, 21.5 ng/ml) after 48 hours of culture, and nondetectable quantities of interferon-gamma and IL-2. In summary, Asp f I-specific T-cell lines established from patients with ABPA were characterized as being CD4+ TH2-like in their cytokine synthesis pattern, and secreted IL-4 behaved in an autocrine fashion, stimulating proliferation.

IL-4 induction of IgE class switching by lipopolysaccharide-activated murine B cells occurs predominantly through sequential switching

Resting murine B cells activated with bacterial LPS co-express membrane (m)IgG1 and mIgE upon stimulation with IL-4. In this report, we combine both cellular and molecular approaches to elucidate the mechanism underlying this co-expression. We demonstrate that an anti-IgG1 antibody specifically and selectively inhibits IgE secretion (approximately 70%) by LPS + IL-4-stimulated B cells, which provides functional evidence for mIgG1 expression by precursors of IgE-secreting cells. The IgG1 and IgE secretory responses are separated temporally by approximately 16 h, with IgE production developing later than IgG1. A similar delay is observed in the appearance of mIgE+ cells suggesting that class switching to IgG1 precedes that to IgE. In the sort-purified, mIgG1+mIgE+ B cell population approximately 25% of cells expressed cytoplasmic (c) (secretory) IgG1 and approximately 15% expressed cIgE at the time of their isolation. However, only a small percent of the mIgG1+mIgE+ cells co-expressed cIgG1 and cIgE, further suggesting a temporal separation in IgG1 and IgE secretion within individual cells, but indicating that single cells can co-secrete these two Ig isotypes. Furthermore, the absolute level and rate of increase of IgG1 secretion by mIgG1+mIgE+ cells, upon their isolation and reculture, is lower than that for mIgG1+mIgE- cells suggesting a loss of CH gamma 1 expression in the former population. Analysis of total, unselected circular DNA excision products in LPS + IL-4-activated B cells demonstrates that most, if not all, of the DNA encoding the IgG1 constant heavy gene (CH gamma 1) (i.e., products of a class switch to IgE) have been rearranged. Collectively this data provides strong evidence at both the cellular and molecular level that the predominant mode of switching to IgE in response to in vitro stimulation by LPS + IL-4 is from IgM to IgG1 to IgE.

IL-4 induction of IgE class switching by lipopolysaccharide-activated murine B cells occurs predominantly through sequential switching

Resting murine B cells activated with bacterial LPS co-express membrane (m)IgG1 and mIgE upon stimulation with IL-4. In this report, we combine both cellular and molecular approaches to elucidate the mechanism underlying this co-expression. We demonstrate that an anti-IgG1 antibody specifically and selectively inhibits IgE secretion (approximately 70%) by LPS + IL-4-stimulated B cells, which provides functional evidence for mIgG1 expression by precursors of IgE-secreting cells. The IgG1 and IgE secretory responses are separated temporally by approximately 16 h, with IgE production developing later than IgG1. A similar delay is observed in the appearance of mIgE+ cells suggesting that class switching to IgG1 precedes that to IgE. In the sort-purified, mIgG1+mIgE+ B cell population approximately 25% of cells expressed cytoplasmic (c) (secretory) IgG1 and approximately 15% expressed cIgE at the time of their isolation. However, only a small percent of the mIgG1+mIgE+ cells co-expressed cIgG1 and cIgE, further suggesting a temporal separation in IgG1 and IgE secretion within individual cells, but indicating that single cells can co-secrete these two Ig isotypes. Furthermore, the absolute level and rate of increase of IgG1 secretion by mIgG1+mIgE+ cells, upon their isolation and reculture, is lower than that for mIgG1+mIgE- cells suggesting a loss of CH gamma 1 expression in the former population. Analysis of total, unselected circular DNA excision products in LPS + IL-4-activated B cells demonstrates that most, if not all, of the DNA encoding the IgG1 constant heavy gene (CH gamma 1) (i.e., products of a class switch to IgE) have been rearranged. Collectively this data provides strong evidence at both the cellular and molecular level that the predominant mode of switching to IgE in response to in vitro stimulation by LPS + IL-4 is from IgM to IgG1 to IgE.

A role for tumor necrosis factor-alpha and interferon-gamma in the regulation of interleukin-4-induced human thymocyte proliferation in vitro. Heightened sensitivity in the Down syndrome (trisomy 21) thymus

The influence of recombinant interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF) on IL-4-induced proliferation of postnatal human thymocytes from eight children with Down syndrome (DS, trisomy 21) and 18 control children was evaluated. DS thymuses were studied because they are characterized by cortical depletion and abnormal thymocyte differentiation. IL-4, without mitogen, induced a dose-dependent proliferation of both DS and control thymocytes. The proliferation was comparable to that induced by IL-2 and far greater than the proliferation mediated by IL-1 beta in the absence of mitogen. The level of IL-4 responsiveness correlated with the proportion of cells expressing the gamma, delta chains of the T cell receptor. Furthermore, thymocyte preparations greatly enriched for T cell receptor gamma, delta-bearing cells were found to vigorously proliferate when treated with IL-4. Both IFN-gamma and TNF inhibited IL-4-driven proliferation in a dose-dependent manner, but DS thymocytes were found to be significantly more sensitive to inhibition by both cytokines. Our studies suggest an important role for IL-4 in the proliferation of T cell receptor gamma, delta+ thymocytes and demonstrate regulatory functions for IFN-gamma and TNF in human thymocyte proliferation. The increased sensitivity of DS thymocytes to IFN-gamma and TNF may explain anatomical abnormalities in DS thymuses and suggests the involvement of genes encoded on human chromosome 21 in the responses to both IFN-gamma and TNF.

Mechanism of pokeweed mitogen inhibition of rhIL-4-induced human IgE synthesis

Pokeweed mitogen (PWM) suppressed rhIL-4-induced IgE synthesis in a concentration-dependent manner. When rhIL-4 was present from Day 0, PWM added to cultures on Day 0 or 3 inhibited MNC IgE synthesis but not when it was added on Day 6 or later. The concentration of interferon-gamma (IFN-gamma) in MNC culture supernatants varied directly with the quantity of PWM added. Conversely, rhIL-4-stimulated MNC culture IgE concentrations varied inversely with the dose of PWM added and the IFN-gamma concentrations induced. The addition of a rabbit polyclonal neutralizing anti-human IFN-gamma antibody to rhIL-4 plus PWM-stimulated cultures partially or completely reversed PWM-induced inhibition of rhIL-4-induced IgE synthesis. PWM failed to inhibit rhIL-4-induced IgE synthesis by isolated B cells cocultured with monocytes and T cells from a clone unable to produce IFN-gamma message or protein. These findings are consistent with the postulate that PWM inhibits rhIL-4-induced IgE synthesis by inducing the production of IFN-gamma.

Mononuclear cells from patients with the hyper-IgE syndrome produce little IgE when they are stimulated with recombinant human interleukin-4

To investigate whether B cells from patients with the hyper-IgE syndrome are more sensitive to the effects of interleukin-4 in vitro than B cells of normal or atopic individuals, we stimulated blood mononuclear cells (MNC) with varying doses of recombinant human interleukin 4 (rhIL-4) and measured supernatant IgE concentrations after 18 days of culture. Geometric mean spontaneous IgE synthesis after 18 days of culture without rhIL-4 was low (less than 3 ng/ml) and similar for MNCs from nine patients with the hyper-IgE syndrome, nine atopic and nine normal subjects. As found in our previous studies, MNCs from the nine atopic and the nine normal donors produced significant and similar quantities of IgE (geometric mean maximum IgE, 25.2 and 18.7 ng/ml, respectively) when MNCs were stimulated with rhIL-4. MNCs from both donor groups had similar sensitivity to the concentration of IL-4 eliciting the IgE response. In striking contrast, MNCs from the nine patients with the hyper-IgE syndrome failed to produce significant IgE over that produced spontaneously when MNCs were stimulated by a wide range of rhIL-4 concentrations. Coculture of B cell-enriched subpopulations from patients with the hyper-IgE syndrome with T cell-enriched subpopulations from nonatopic and atopic donors failed to restore responsiveness to rhIL-4. The addition of anti-CD40 monoclonal antibody to MNC cultures did result in enhancement of rhIL-4 IgE synthesis by MNCs from patients with the hyper-IgE syndrome, but the concentration of anti-CD40 required to elicit this enhancement was tenfold higher than for control MNCs.(ABSTRACT TRUNCATED AT 250 WORDS)

IgE class switching is critically dependent upon the nature of the B cell activator, in addition to the presence of IL-4

Cross-linkage of membrane IgD on resting murine B cells, by anti-IgD mAb conjugated to dextran (alpha delta-dex), induces high levels of proliferation, and in the presence of IL-2 or IL-5, Ig secretion in vitro. The structural and functional similarities between alpha delta-dex and TNP-Ficoll for B cell responses led us to propose that alpha delta-dex could provide a model system for studying B cell activation induced by T cell-independent, type II Ag. In this report, we study the effects of Ig class switch and differentiation factors on Ig isotype production by murine B cells activated by alpha delta-dex, and directly compare these to responses obtained after activation by LPS. We show that an IL-4-containing CD4+ T cell supernatant (Th2 SN) stimulates large increases in IgG1 and IgE production by LPS-activated B cells, but fails to stimulate detectable levels of IgE by alpha delta-dex-activated cells, despite inducing high levels of secreted IgM and IgG1. This is correlated with undetectable steady state levels of both germ-line and rearranged (productive) IgE-specific RNA in B cells stimulated with alpha delta-dex + Th2 SN. Alpha delta-dex is selective in its failure to costimulate IgE production in that IFN-gamma-containing T cell supernatant (Th1 SN) and transforming growth factor-beta-supplemented Th2 SN selectively stimulate a large IgG2a and IgA secretory response, respectively. Anti-IgD conjugated to Sepharose beads, in distinct contrast to dextran, costimulates a strong IgE response. These findings underscore the importance of the specific B cell activator, in addition to IL-4, in the regulation of IgE production.

IgE class switching is critically dependent upon the nature of the B cell activator, in addition to the presence of IL-4

Cross-linkage of membrane IgD on resting murine B cells, by anti-IgD mAb conjugated to dextran (alpha delta-dex), induces high levels of proliferation, and in the presence of IL-2 or IL-5, Ig secretion in vitro. The structural and functional similarities between alpha delta-dex and TNP-Ficoll for B cell responses led us to propose that alpha delta-dex could provide a model system for studying B cell activation induced by T cell-independent, type II Ag. In this report, we study the effects of Ig class switch and differentiation factors on Ig isotype production by murine B cells activated by alpha delta-dex, and directly compare these to responses obtained after activation by LPS. We show that an IL-4-containing CD4+ T cell supernatant (Th2 SN) stimulates large increases in IgG1 and IgE production by LPS-activated B cells, but fails to stimulate detectable levels of IgE by alpha delta-dex-activated cells, despite inducing high levels of secreted IgM and IgG1. This is correlated with undetectable steady state levels of both germ-line and rearranged (productive) IgE-specific RNA in B cells stimulated with alpha delta-dex + Th2 SN. Alpha delta-dex is selective in its failure to costimulate IgE production in that IFN-gamma-containing T cell supernatant (Th1 SN) and transforming growth factor-beta-supplemented Th2 SN selectively stimulate a large IgG2a and IgA secretory response, respectively. Anti-IgD conjugated to Sepharose beads, in distinct contrast to dextran, costimulates a strong IgE response. These findings underscore the importance of the specific B cell activator, in addition to IL-4, in the regulation of IgE production.

Kinetics of interleukin-4 induction and interferon-gamma inhibition of IgE secretion by Epstein-Barr virus-infected human peripheral blood B cells

Interleukin-4 (IL-4) acts directly on purified human peripheral blood B cells cultured in the presence of Epstein-Barr virus (EBV) to induce IgE secretion and to enhance the secretion of IgG and IgM. Interferon-gamma (IFN-gamma) inhibits IgE secretion in this system, without affecting the secretion of the other Ig isotypes. To identify the time period during which EBV-infected B cells can be induced by IL-4 to secrete IgE, we have studied the effects of delayed addition of IL-4, or the termination of IL-4 stimulation by wash out or by neutralization with anti-IL-4 antibodies, on the induction of an IgE response. To induce a maximal IgE response, IL-4 had to be added to cultures of B cells plus EBV no later than 2 days after the initiation of culture, and had to remain present through the tenth day of culture. These two time points correspond to the initiation of detectable DNA synthesis (Days 3 to 4) and the earliest detectable Ig secretion (Days 10 to 12) by EBV-stimulated B cells. No IgE response was induced if the period during which EBV-stimulated B cells were cultured with IL-4 was less than 4 days, or if IL-4 were added later than the tenth day of culture, regardless of how long the culture was continued beyond that time. In contrast, IL-4 considerably enhanced IgG and IgM secretion and B cell CD23 expression, even if it was added after the tenth day of culture. IFN-gamma strongly inhibited the IgE response of B cells cultured with IL-4 plus EBV if added within 6 days of the initiation of culture, but had little effect on the generation of IgM or IgG responses made by these cells, regardless of the time of addition. Neither IL-4 nor IFN-gamma affected ongoing IgE secretion by an established, IgE-secreting, EBV-transformed cell line. These observations suggest that: (i) IL-4 first becomes able to induce EBV-activated B cells to secrete IgE as these cells begin to synthesize DNA, must stimulate B cells for at least 4 days to induce IgE secretion, and loses its ability to induce IgE secretion as these cells differentiate into Ig-secreting cells; (ii) the ability of IFN-gamma to suppress an IgE response is limited to this same time period; and (iii) IL-4 enhancement of CD23 expression and IgM and IgG secretion are independent of IL-4 induction of an IgE response.

Disulfide assignments in recombinant mouse and human interleukin 4

The disulfide pairings of mouse and human interleukin 4 (IL-4) proteins have been determined. The purified proteins, synthesized by recombinant DNA technology, are fully active as judged by their ability to stimulate an appropriate biological response in a variety of functional assays. Peptide maps were produced by digesting the proteins with pepsin and separating the resulting fragments by reverse-phase HPLC using linear acetonitrile-TFA gradients. Cystine-containing peptides were identified by determining which reverse-phase peaks showed an altered elution pattern after reduction. These peptides were purified further and defined by composition and sequence analysis. Three sets of disulfide-linked peptides were consistently identified for each protein. For mouse IL-4, the first and fifth, second and fourth, and third and sixth cysteines are joined. The disulfide bonds in human IL-4 are between the first and sixth, second and fourth, and third and fifth cysteines. A large double-loop region within the central three-fifths of each protein is stabilized by these bonds. Sequence analysis of the peptides containing the third and fifth cysteines of human IL-4 also demonstrated that only one of the potential N-glycosylation sites is used by C127 mammary tumor cells. Complete alkylation of mouse IL-4 under mild conditions completely destroyed its biological activity in a hematopoietic precursor cell proliferation assay.

Cytokine production by T helper cell subpopulations during prolonged in vitro stimulation

In man, CD4+ T cells can be divided into phenotypically distinguishable subsets with different function whereas CD4+ T cells with the opposite pheno-CD45RO and low levels of CD45RA antigen provide help for mitogen-induced immunoglobulin production whereas CD4+ cells with the opposite phenotype suppress immunoglobulin production. However, studies examining cytokine production by phenotypically defined CD4+ T cell subsets have led to different conclusions. Further, very few studies have examined cytokine production by freshly isolated CD4+ T cell subsets during extended culture periods. Thus, we examined the production of several cytokines (at various time points) by CD4+ T cell subsets that were isolated in several ways, and stimulated with PWM, Con A, and PHA in a well-defined serum-free culture system. We found that CD4+, CD45RA- (or CD45RO+) T cells consistently produced the most IL-2, IFN-gamma, and TNF-alpha after mitogen stimulation for 2 days. PWM induced the largest quantities of each cytokine, although a similar pattern of production was observed in response to Con A and PHA. We were unable to detect IL-4 production by mononuclear cells and CD4+ T cell subsets suggesting that, if it is produced at all, IL-4 is produced in extremely small quantities. When the culture period of initially CD45RO- T cells was extended beyond 2 days, the culture supernatant contained increased quantities of each cytokine and the cells in the culture had an increased number of cells expressing CD45RO antigen. Together, these data indicate that CD4, CD45RA- (or CD45RO+) T cells in peripheral blood are the major producers of IL-2, IFN-gamma, and TNF-alpha following short-term mitogen stimulation, and that phenotypically defined peripheral blood T cell subsets do not maintain a distinct pattern of cytokines during extended culture periods.

Recombinant human IL-4 induces IgE and IgG synthesis by normal and atopic donor mononuclear cells. Similar dose response, time course, requirement for T cells, and effect of pokeweed mitogen

Unfractionated human blood mononuclear cells (MNC) from normal and atopic donors cultured in enriched Iscove's modified Dulbecco's medium supplemented with 10% FCS responded similarly to stimulation with purified human rIL-4 (rhIL-4) with respect to the concentration required to induce IgE synthesis and the magnitude and kinetics of the IgE response. The IgE response of MNC was IL-4 dose-dependent, increasing linearly with IL-4 concentrations between 0.2 and 2.5 ng/ml and plateauing at concentrations of 5 ng/ml or more. rhIL-4-induced IgE synthesis was first detected at 9 days after stimulation and supernatant IgE concentrations reached a maximum on day 18. rhIL-4 stimulated IgE synthesis by MNC from all donors tested, with peak supernatant IgE concentrations ranging from 3 to 372 ng/ml. The nonatopic group (n = 15) geometric mean peak concentration was 24.0 ng/ml and that of the atopic group (n = 19) was 20.0 ng/ml (p = NS). rhIL-4 also stimulated IgG synthesis by MNC from some (but not all) donors in quantities comparable to those induced by PWM. Maximum supernatant IgG concentrations in responders were found 18 days after stimulation. When PWM was added to the IL-4-stimulated cultures, it completely inhibited rhIL-4-induced IgE and IgG synthesis. rhIL-4 also completely inhibited PWM-induced IgG synthesis. Stimulation of IgE synthesis by rhIL-4 required the presence of T cells. T cell clone supernatants did not support rhIL-4-induced IgE synthesis by B cells. T cells from atopic and nonatopic donors restored rhIL-4-stimulated IgE synthesis by B cells from either source to a similar extent.

Recombinant human IL-4 induces IgE and IgG synthesis by normal and atopic donor mononuclear cells. Similar dose response, time course, requirement for T cells, and effect of pokeweed mitogen

Unfractionated human blood mononuclear cells (MNC) from normal and atopic donors cultured in enriched Iscove's modified Dulbecco's medium supplemented with 10% FCS responded similarly to stimulation with purified human rIL-4 (rhIL-4) with respect to the concentration required to induce IgE synthesis and the magnitude and kinetics of the IgE response. The IgE response of MNC was IL-4 dose-dependent, increasing linearly with IL-4 concentrations between 0.2 and 2.5 ng/ml and plateauing at concentrations of 5 ng/ml or more. rhIL-4-induced IgE synthesis was first detected at 9 days after stimulation and supernatant IgE concentrations reached a maximum on day 18. rhIL-4 stimulated IgE synthesis by MNC from all donors tested, with peak supernatant IgE concentrations ranging from 3 to 372 ng/ml. The nonatopic group (n = 15) geometric mean peak concentration was 24.0 ng/ml and that of the atopic group (n = 19) was 20.0 ng/ml (p = NS). rhIL-4 also stimulated IgG synthesis by MNC from some (but not all) donors in quantities comparable to those induced by PWM. Maximum supernatant IgG concentrations in responders were found 18 days after stimulation. When PWM was added to the IL-4-stimulated cultures, it completely inhibited rhIL-4-induced IgE and IgG synthesis. rhIL-4 also completely inhibited PWM-induced IgG synthesis. Stimulation of IgE synthesis by rhIL-4 required the presence of T cells. T cell clone supernatants did not support rhIL-4-induced IgE synthesis by B cells. T cells from atopic and nonatopic donors restored rhIL-4-stimulated IgE synthesis by B cells from either source to a similar extent.

A cell culture system that enhances mononuclear cell IgE synthesis induced by recombinant human interleukin-4

A new culture system is described in which recombinant human interleukin-4 (rhIL-4) consistently induces the synthesis of large quantities of IgE by human blood mononuclear cells (MNC). Unfractionated MNC were cultured in complete Iscove's modified Dulbecco's medium (C-IMDM), composed of IMDM enriched with human transferrin, bovine insulin, bovine serum albumin, oleic acid, palmitic acid, linoleic acid, and fetal calf serum (FCS). Under these culture conditions, MNC from four donors synthesized mean quantities of IgE of 76 ng/ml at plateau after stimulation with rhIL-4 in concentrations ranging from 0.04 to 80 ng/ml (plateau rhIL-4 concentrations were 5 ng/ml or greater). In contrast, rhIL-4 failed to induce significant IgE synthesis at any of those doses of rhIL-4 in parallel MNC cultures performed in RPMI 1640 supplemented with FCS (RPMI 1640). Additional optimal conditions for the induction of IgE synthesis in this system were a MNC concentration of 1-2 X 10(6)/ml and a culture time of 18 days. Variability was noted in the amount of IgE produced by different donors (CV 0.22) and by the same donor when tested on different occasions (mean CV 0.21), but no donor's MNC failed to produce significant IgE in response to rhIL-4 when cultured in C-IMDM. The geometric mean IgE production induced by optimal IL-4 concentrations for the entire group of 16 subjects was 36.8 ng/ml IgE, with the lowest day 18 mean IgE concentration for any donor being 10.6 ng/ml and the highest 372.2 ng/ml. The enhanced rhIL-4-induced IgE synthesis supported by C-IMDM was due to the combined effects of the added enrichment factors and not to differences in the viabilities of MNC cultured in C-IMDM and RPMI 1640. This culture system will alleviate the problems of inconsistent and low quantities of IgE induced by IL-4 that confound most current culture systems used to examine rhIL-4-induced IgE synthesis. It will, thereby, facilitate further investigation of the regulation of human IgE synthesis.

IgE secretion by Epstein-Barr virus-infected purified human B lymphocytes is stimulated by interleukin 4 and suppressed by interferon gamma

The cytokine interleukin 4 (IL-4) has been shown to induce lipopolysaccharide-activated murine B cells to differentiate into IgE-secreting cells and to stimulate IgE secretion by cultured human peripheral blood lymphoid cells. It is unclear, however, whether this effect of IL-4 on human peripheral blood lymphoid cells is a direct effect on the B cell because IL-4 can stimulate T cells and monocytes as well as B cells and does not induce purified human B cells to secrete immunoglobulin. To investigate this issue we studied the ability of IL-4 to induce IgE secretion by purified human B cells (93-96% CD20+, less than 1% CD3+) that were cultured with Epstein-Barr virus (EBV). Although B cells cultured with IL-4 alone did not secrete Ig and B cells cultured with EBV alone secreted IgM, IgG, and IgA but less than 150 pg of IgE per ml, the combination of EBV and IL-4 induced an IgE response that ranged from 11.4 to 40.3 ng/ml of culture supernatant after 26 days of culture. While IL-4 also enhanced IgM, IgG, and IgA secretion, as well as proliferation by EBV-infected B cells, these effects were less pronounced, occurred earlier during culture, and required a lower concentration of IL-4 than did the stimulation of IgE secretion. Furthermore, interferon gamma at 10 units per ml was found to inhibit IL-4/EBV-induced IgE secretion without inhibiting the other stimulatory effects of IL-4. We conclude that (i) IL-4 and interferon gamma can act directly on polyclonally activated human B cells to respectively stimulate and suppress IgE secretion and (ii) IL-4, in addition to its specific effect on IgE secretion, has a general stimulatory effect on the growth and differentiation of EBV-infected human B cells.

Superinduction of low affinity IgE receptors on murine B lymphocytes by lipopolysaccharide and IL-4

Recent work in both the human and murine systems has demonstrated that IL-4 is capable of specifically inducing the synthesis of the low affinity receptor for IgE (Fc epsilon RII). In addition, in conjunction with LPS, IL-4 will induce IgG1 and IgE synthesis. To analyze the correlation between Fc epsilon RII induction and IgE secretion, Fc epsilon RII and IgE levels were measured by RIA on murine splenic B cells stimulated with LPS and IL-4 over 7 days of culture. Treatment with LPS and IL-4 gave a 20- to 50-fold (day 3) "superinduction" of Fc epsilon RII levels compared with a 3- to 5-fold induction with IL-4 alone; removal of IL-4 resulted in a rapid decline in Fc epsilon RII levels. The cells expressing high Fc epsilon RII levels were determined to be blasts. Superinduction of Fc epsilon RII occurs at 10 U/ml IL-4 and remains relatively constant in the range of 10 to 1000 U/ml. In contrast, with increasing IL-4, IgE levels increase, reaching microgram levels at day 7 with 300 U/ml IL-4. Triggering the cells with anti-Ig, as expected, gave no Ig secretion, and in addition, Fc epsilon RII superinduction by IL-4 and anti-Ig was not seen. PMA is known to block Ig secretion induced by LPS. Concentrations of PMA that totally abrogated IgE secretion had no effect on Fc epsilon RII superinduction, indicating that the latter phenomena can be separated from IL-4-induced Ig secretion. Superinduction also results in higher levels of Fc epsilon RII fragment release into the media. Thus, attempts were made to influence IgE secretion by adding additional purified Fc epsilon RII fragment to the culture. The purified fragment did not have a significant influence on IgE levels in this system.

Molecular genetic characterization of the mRNA coding for an inducible suppressor factor specific for L-glutamic acid60-L-alanine30-L-tyrosine10

The suppressor T-cell hybridoma 1556A2.1 can be induced by the monoclonal L-glutamic acid60-L-alanine30-L-tyrosine10 (GAT)-specific suppressor inducer 372B3.5 and soluble GAT to synthesize a disulfide-linked heterodimeric protein (GAT-TsF2), which directly suppresses a primary in vitro immune response to GAT. Induction and synthesis of the GAT-TsF2 protein is correlated with the appearance of specific mRNA, as detected by translation in vitro in a wheat germ cell-free extract of RNA isolated at various times after induction. The mRNA coding for the polypeptide chain that bears a serologically defined I-J determinant (I-J+ chain) appeared 8 hr after induction, whereas the mRNA coding for the antigen-binding chain (AB+ chain) was not detected until 16 hr after induction. The mRNAs coding for the individual chains sedimented as different species, suggesting that the two-chain factor is the product of two genes. The AB+ chain of the 1556A2.1 GAT-TsF2 was synthesized on membrane-bound polysomes, whereas the I-J+ chain was translated on free polysomes. The AB+ chain was synthesized from two independent mRNA species sedimenting at 10 S and 28 S, whereas a single 16S mRNA encoded the I-J+ chain. The in vitro translated I-J+ chain was bound by a monoclonal antibody against the I-J+ determinant of only the appropriate H-2 haplotype. These results suggest that posttranslational modification, including glycosylation, is not required for biological activity or for expression of the I-J epitope on the GAT-TsF2 molecule.

Abundant nuclear ribonucleoprotein form of CAD RNA

Transcripts of the CAD gene in Syrian hamster cells are as abundant in the nucleus as in the cytoplasm. This was shown by in situ hybridization of whole cells and by solution and blot hybridization of subcellular fractions. Similar results were obtained both for wild-type cells and for a mutant containing amplified CAD genes in which the level of CAD RNA is 150-fold greater. CAD nuclear RNA is indistinguishable from mature mRNA by gel electrophoresis and blot hybridization. Discrete higher-molecular-weight precursors are undetectable, although the persistence of a short length of intervening sequence in the otherwise fully processed RNA is not excluded. CAD RNA is released from nuclei by sonication in physiological conditions in a ribonucleoprotein form that sediments as a broad peak at about 200S in a sucrose gradient. CAD sequences extracted from nuclei by treatment with EDTA and RNase are found in the 30S particles previously described.

Recombination and postreplication repair

The available data concerning postreplication repair are summarized. In Escherichia coli, recombination is implicated in this repair because the recA+ gene is necessary and because strand exchanges occur that extend over long regions. Other experiments involving phage-induced resistance also point to an interrelation between recombination and repair. In this phenomenon, gene products of lambda bacteriophage are introduced into bacteria, resulting in an increased resistance of the cells when they are subsequently exposed to X rays.