Suppression of interleukin-2 receptor expression on mouse CD4+ T cells by bovine kappa-caseinoglycopeptide

Bovine kappa-caseinoglycopeptide (residues 106-169, CGP) completely inhibited the PHA-induced proliferation of mouse splenocytes when CGP was added simultaneously with PHA. The inhibitory effect, however, was reduced to about one-half when CGP was added after 24 h of cultivating the splenocytes with PHA or when anti-IL-1ra antibody was added simultaneously with PHA and CGP. On the other hand, CGP bound to mouse CD4+ T cells but not to CD8+ T cells. CGP suppressed IL-2 receptor expression of the PHA-stimulated mouse CD4+ T cells.     

Regulation of IL-17, IFN-gamma and IL-10 in human CD8(+) T cells by cyclic AMP-dependent signal transduction pathway

In the present study, the expression of interleukin 17 (IL-17) by human CD8(+) T lymphocytes and its regulation following PKA activation was determined and compared with that of interferon gamma (IFN-gamma) and IL-10. IL-17 mRNA was highly expressed in human CD8(+) T lymphocytes at least at the same level than in CD4(+) T cells that were isolated from peripheral blood mononuclear cells (PBMC). Expression of IL-17 mRNA in CD8(+) T cell was induced by prior activation of PBMC for 18 h with Ca2+ ionophore and phorbol myristate acetate (PMA). Furthermore, our results clearly showed that CD8(+) T cells are sensitive to elevation of cAMP and PKA activation pathway. Data demonstrated a significant inhibition of IL-17 as well as of IFN-gamma mRNA expression in CD8(+) T cells isolated from activated PBMC cultured in the presence of either dibutyryl cAMP (db-cAMP) or PGE2. In contrast, IL-10 mRNA expression was strongly enhanced in the same experimental conditions. The differential expression of IL-10 and IFN-gamma production in CD8(+) T cells was also observed at the protein level as it was measured by a double immunofluorescence technique and flow cytometry analysis. Taken together, these results provide evidence that human CD8(+) T cells are also the source of massive expression of IL-17, and that PKA plays a prominent role in the switch of CD8(+) T cells to a Th2 like profile and an inhibition of IL-17 expression, thus suggesting that the activation of cAMP signal transduction pathway may have consequences for the relative role of CD8(+) T cells in the immune and inflammatory process.     

Ecologic studies of rodent reservoirs: their relevance for human health

To gain insight into the immunomodulatory effects of vitamin E (VE), immune cell population analyses were conducted using thymus and spleen from male broilers fed diets with various levels of VE supplementation (0, 17, 46, and 87 mg dl-alpha-tocopherol acetate/kg of feed). At 2 and 7 wk of age, the percentages of B cells, macrophages, and T cell subsets, delineated by the expression of CD4, CD8, and T cell receptor (TCR) isotype, in thymus and spleen were determined by flow cytometry. The percentages of thymic and splenic B cells and macrophages from 2- and 7-wk-old chickens, as well as the percentage of thymic T cells in 2-wk-old chickens, were unaffected by VE treatment. However, 7-wk-old broilers maintained on 87 mg VE/kg feed had a higher percentage of CD4+CD8- thymocytes, a higher CD4+CD8- to CD4-CD8+ thymocyte ratio, and a lower percentage of CD4+CD8+ thymocytes than chickens receiving no dietary VE supplementation. The VE-induced increase in the percentage of CD4+CD8- thymocytes was due to an increase in the TCR2+CD4+CD8- thymocyte subset, whereas the decrease in the percentage of CD4+CD8+ thymocytes involved all TCR defined T cell subsets. In the spleen, the percentage of CD4+CD8- T cells was lower in 2-wk-old chickens and higher in 7-wk-old chickens maintained on 87 mg/kg feed than in chickens receiving no dietary VE supplementation. The decrease in CD4+CD8- splenocytes at 2 wk of age was due to a decline in the percentage of TCR2+CD4+CD8- splenocytes, whereas the increase in CD4+CD8- splenocytes in 7-wk-old chicks was due to an increase in the percentages of all TCR defined CD4+CD8- T cell subsets. These data support an immunomodulatory effect of VE on CD4+CD8- T cells.     

IL-2 receptor alpha-chain expression is independently regulated in primary and secondary lymphoid organs

The IL-2R is composed of three chains: IL-2R alpha, IL-2R beta, and IL-2R gamma. In mice, IL-2Ra is critical and determines IL-2 binding to the tripartite IL-2R complex. To extend our previous studies, which demonstrated that IL-2 regulates IL-2R alpha expression in vitro, we have analyzed expression in IL-2-deficient mice in vivo. As in control animals, CD4- CD8- thymocytes and bone marrow-derived B220+ pre-B cells were IL-2R alpha positive. In contrast, activated lymph node and splenic CD4 T cells (CD4+ CD69+) were found to be IL-2R alpha negative, whereas approximately 20% of the same cell populations from the MLR/lpr strain, which also accumulate large numbers of CD4-activated T cells in the presence of intact IL-2, retained expression. A similar pattern of IL-2R alpha expression was found among splenic CD8 cells from IL-2(-/-) and IL-2(+/-) animals. These findings demonstrate that in primary lymphoid organs, IL-2 is not directly involved in IL-2R alpha expression. However, at the level of mature lymphocytes, and more specifically CD4 T cells, IL-2 remains in vivo, as in vitro, the most critical cytokine controlling both IL-2R alpha expression and sensitivity to IL-2.     

The relation between arterial oxygen tension and cerebral blood flow during cardiopulmonary bypass

BACKGROUND: The precise mechanisms involved in islet xenograft rejection remain unknown. The purpose of the present study was to determine cellular mechanisms responsible for islet xenograft rejection in the liver to facilitate finding a procedure for prevention of immune rejection. METHODS: Hepatic mononuclear cells (MNC) as well as splenocytes, peripheral blood MNC, and thymocytes from streptozotocin-induced diabetic mice (BALB/c) rejecting the intrahepatic rat (Lewis) islet xenografts were isolated and examined by two-color FACS analysis. RESULTS: The characteristic finding of the hepatic MNC from the mice rejecting islet xenografts compared with mice receiving isografts was a significant increase in the yield as well as in the percentage of the cells expressing CD3+ interleukin-2 receptor (IL-2R) alpha- beta+, CD3+ CD8alpha+ beta+, and T cell receptor (TCR) alphabeta+ lymphocyte function-associated antigen-1+. The expression of CD3 and TCR alphabeta of these T cells was found to be of intermediate intensity (TCR(int) cells). The expansion of these TCR(int) cells occurred predominantly in the liver. There was no significant difference in the cells expressing CD3+ IL-2R alpha+, CD3+ CD4+, CD3+ TCRgammadelta+, CD3- IL-2Rbeta+ (natural killer cells), and B220+ (B cells). In vivo administration of anti-IL-2Rbeta monoclonal antibody directed to the expanded cells produced a prevention of rejection. CONCLUSIONS: These findings suggest that islet xenograft rejection in the liver from rat to mouse is an event for which the TCR(int) cells are responsible.     

Interleukin-7 modulates CD23 and HLA-DR expression on CD4+ T cells and promotes a Th-2 type citokine profile

The expression of CD23 on PHA-activated human PBT (peripheral blood T) cells of healthy donors was investigated. It appears that CD23 is expressed solely on activated CD4+ T cells. Cytofluorotometric analysis revealed that 6% of PHA-activated CD4+ T cells expressed CD23, while unstimulated CD4+ T cells express no detectable CD23. The addition of IL-7 (1000 U/ml) to activated CD4+ T cells resulted in a marked augmentation of CD23 expression (29%). CD23 expression was blocked by M20 and M26 mAbs, but no reduction was detected by anti-IL-2R (CD25) mAb. This suggests that IL-7 has a specific regulatory effect on CD23 expression independent of IL-2. Northern Blot analysis showed a marked increase of CD23 mRNA detected in PHA-activated CD4+ T cells plus IL-7. IL-7 was also able to upregulate the expression of HLA-DR on activated CD4+ T cells. Optimal HLA-DR and CD23 induction by IL-7 occurred at 48 and 72 h of culture. The addition of CHX revealed that the induction of CD23 and HLA-DR by IL-7 required intact protein synthesis. Furthermore, PHA activated CD4+ T cells cultured in the presence of IL-7 are polarized to a Th-2 pattern of cytokine production.     

Differential capacities of CD4+, CD8+, and CD4-CD8- T cell subsets to express IL-18 receptor and produce IFN-gamma in response to IL-18

IL-12 and IL-18 have the capacity to stimulate IFN-gamma production by T cells. Using a T cell clone, we reported that IL-18 responsiveness is generated only after exposure to IL-12. Here, we investigated the induction of IL-18 responsiveness in resting CD8+, CD4+, and CD4-CD8- T cells. Resting T cells respond to neither IL-12 nor IL-18. After stimulation with anti-CD3 plus anti-CD28 mAbs, CD8+, CD4+, and CD4-CD8- T cells expressed IL-12R, but not IL-18R, and produced IFN-gamma in response to IL-12. Cultures of T cells with anti-CD3/anti-CD28 in the presence of rIL-12 induced IL-18R expression and IL-18-stimulated IFN-gamma production, which reached higher levels than that induced by IL-12 stimulation. However, there was a substantial difference in the expression of IL-18R and IL-18-stimulated IFN-gamma production among T cell subsets. CD4+ cells expressed marginal levels of IL-18R and produced small amounts of IFN-gamma, whereas CD8+ cells expressed higher levels of IL-18R and produced more IFN-gamma than CD4+ cells. Moreover, CD4-CD8- cells expressed levels of IL-18R comparable to those for CD8+ cells but produced IFN-gamma one order higher than did CD8+ cells. These results indicate that the induction of IL-18R and IL-18 responsiveness by IL-12 represents a mechanism underlying enhanced IFN-gamma production by resting T cells, but the operation of this mechanism differs depending on the T cell subset stimulated.     

Regulated expression of gp130 and IL-6 receptor alpha chain in T cell maturation and activation

The functional receptor for the inflammatory cytokine IL-6 is composed of the ligand binding IL-6 receptor alpha chain (IL-6R alpha) and the signal transducing chain gp130, which is a shared component of multiple cytokine receptors. We analyzed the surface expression of gp130 and IL-6R alpha in thymocytes and peripheral T cells. While all thymocytes expressed gp130 throughout thymic maturation, they gained expression of IL-6R alpha at the CD4 or CD8 single-positive stage. Approximately 10-30% of the CD4-CD8+ and 40-50% of the CD4+CD8- thymocytes expressed IL-6R alpha. Within the CD4+CD8- population, the IL-6R alpha- subpopulation was cortisone sensitive, appeared immature according to the cell surface markers expressed and failed to proliferate after TCR cross-linking. Peripheral T cells were predominantly gp130+ and IL-6R alpha+, but down-regulated gp130 and IL-6R alpha expression upon TCR engagement in vitro and in vivo. Peripheral gp130low/-IL-6R alphalow/- T cells expressed surface markers characteristic of memory T cells. We show that gp130 and IL-6R alpha are expressed in a regulated manner in T cells, depending on the developmental and functional stage.     

IL-2 reduces graft-versus-host disease and preserves a graft-versus-leukemia effect by selectively inhibiting CD4+ T cell activity

We have recently demonstrated, in a fully MHC-mismatched murine bone marrow transplantation model, that administration of a short course of high dose IL-2 markedly diminishes graft-vs-host disease (GVHD) without compromising alloengraftment or the graft-vs-leukemia (GVL) effect of allogeneic T cells. We have now evaluated the mechanism of the dissociation of GVL and GVHD observed in this model. We demonstrate that CD4+ T cells were required to produce severe, acute GVHD in the fully MHC-mismatched plus minor histocompatibility Ag-mismatched A/J-->B10 strain combination. The GVHD-producing activity of A/J CD4+ T cells administered without CD8+ T cells was inhibited by IL-2 treatment. In contrast, CD8+ T cells alone mediated the GVL effect observed in the EL4 leukemia/lymphoma model, and CD4+ cells did not contribute to this effect. This CD8-mediated GVL activity was not inhibited by IL-2 treatment. Because naive A/J CD8+ T cells administered without CD4+ T cells did not produce acute GVHD, we were unable to evaluate the effect of IL-2 in this model. However, when A/J donors were presensitized with B10 skin grafts, CD4-depleted A/J spleen cells were capable of causing acute GVHD in B10 recipients. This CD8-mediated GVHD was not inhibited by treatment with IL-2. However, IL-2 did partially inhibit the GVHD produced by nondepleted presensitized A/J spleen cells, probably due to selective inhibition of the function of presensitized A/J CD4+ T cells. The dissociation of GVHD and GVL against the EL4 leukemia/lymphoma in IL-2-treated mice can therefore be explained by selective inhibition by IL-2 of CD4 activity.     

Fc epsilon receptor-positive cells are a major source of antigen-induced interleukin-4 in spleens of mice infected with Schistosoma mansoni

When cultured in vitro with either mitogen or parasite antigens, spleen cells from mice infected with Schistosoma mansoni produce significantly higher levels of IL-4 than splenocytes from control animals. Previous studies suggested that this increase in IL-4 production occurs because of a selective expansion of T helper type 2 (Th2) cells in infected mice. However, these experiments employed unfractionated spleen populations rather than purified T lymphocytes. Here we demonstrate that T-depleted spleen cells from infected animals synthesize high levels of interleukin-4 (IL-4), but no IL-5 when stimulated with parasite antigen in vitro. Nevertheless, when purified by sorting, T cells and non-B, non-T (NBNT) populations produced similar amounts of IL-4 in response to parasite antigen. The IL-4 producing NBNT cells were found to belong to an Fc epsilon receptor (Fc epsilon R)-positive population which after sort purification produced high levels of IL-4 (between 1000 and 2000 U of per 5 x 10(3) cells). FACS analysis revealed that these Fc epsilon R+ cells make up 0.53% of splenic NBNT cells in control animals while in 8-9-week-infected animals they increase to 3.8% of that population. In contrast, in mice with 8-week unisexual worm infections these cells comprise only 1.71% of NBNT cells, indicating that eggs are a major stimulus of the response. The expansion of Fc epsilon R+ cells and their production of IL-4 could be an important factor regulating the selection and induction of different CD4+ subsets in schistosome-infected hosts.     

The monoclonal antibody CZ-1 identifies a mouse CD45-associated epitope expressed on interleukin-2-responsive cells

We have previously described a monoclonal antibody (mAb), CZ-1, which reacts with an epitope expressed on most peripheral basophils, natural killer cells, B cells, and CD8+ T cells, but not with most thymocytes or peripheral CD4+ T cells. Here we show that mAb CZ-1 defines a sialic acid-dependent epitope associated with a subpopulation of CD45 molecules. This conclusion is based on the ability to block binding of mAb CZ-1 by sialic acid, neuramin-lactose, neuraminidase, and mAb to CD45RB, and by expression of the epitope on transfected psi 2 cells expressing exon B of CD45. The results suggest that the CZ-1 epitope is a post-translational modification expressed on a subpopulation of the CD45 molecules also expressing the B exon. Expression of the CZ-1 epitope was required for freshly isolated lymphocytes to respond to interleukin-2 (IL-2). Depletion of CZ-1+ cells by C' or by cell sorting of thymocytes or splenocytes eliminated the IL-2 responsive cells. The subpopulations of thymocytes and CD4+ splenocytes responding to IL-2 were exclusively within the small CZ-1+ subpopulation. mAb CZ-1 was also used to subdivide CD45+ and CD45RB+ splenocytes into IL-2-responsive and -nonresponsive subpopulations. The CZ-1 epitope was also expressed on virtually all lymphokine-activated killer cell precursors. These data, thus, indicate that cells responsive to IL-2 express this sialated modification of CD45.     

Induction of type 2 cytokines by a staphylococcal enterotoxin superantigen

Persistent intramammary infections of dairy cows with Staphylococcus aureus may involve immunosuppression mediated by bacterial toxins such as enterotoxins and other super-antigens (SAgs). Previously we found that stimulation of bovine PBMC with staphylococcal enterotoxin C (SEC) induced a unique phenotype of activated CD8+ T cells expressing a newly identified activation molecule, ACT3. In the present study we found that SEC induced the expression of interleukin (IL)-4 and IL-10 mRNAs, two cytokines associated with type 2 responses. Elevated levels of IL-4 and IL-10, observed between day 0 and day 4 of culture, were associated with temporary inhibition of proliferative responses of T cells, evidenced by a decrease in numbers of CD4+ T cells and a small increase in numbers of CD8+ T cells. Vigorous proliferation of T cells occurred between days 4 and 7 of culture and with a bias towards CD8+ T cells. Acquisition of the ACT3+ phenotype by CD8+ T cells was preceded by induction of IL-4 mRNA. Thus, in the bovine system, SAgs may hinder protective responses by inducing type 2 cytokines, which interfere with immune clearance of many microbial pathogens. The results of the study are consistent with the hypothesis that SAgs are involved in immunosuppression, and suggest possible immunomodulatory mechanisms.     

Cutting edge: JAK3 activation and rescue of T cells from HIV gp120-induced unresponsiveness

In early HIV disease, immunodeficiency is characterized by the inability of CD4+ T cells to produce a critical cytokine, IL-2, and to express the receptor for IL-2 (IL-2R) in response to antigenic or mitogenic stimulation. The shared common gamma-chain (gamma(c)) of IL-2R and its associated Janus kinase, JAK3, are indispensable for normal T cell function. Here, we show that the inhibition of IL-2R expression and proliferation induced by ligation of CD4 by HIV envelope glycoprotein, gp120, is correlated with inhibition of expression and activation of JAK3. Stimulation through the gamma(c)-related cytokine receptors restores JAK3 expression and activation and rescues CD4-mediated T cell unresponsiveness. Collectively, these data argue that inhibition of JAK3 expression and activation may, in part, explain the T cell dysfunction seen in early HIV disease. In addition, rescue from gp120-mediated T cell unresponsiveness by activation of JAK3 suggests a novel therapeutic approach for enhancing immune function in HIV disease.     

Analysis of type 1 and type 2 T cells in synovial fluid and peripheral blood of patients with rheumatoid arthritis

OBJECTIVE: It has been reported that CD4+ helper T cells play an important role in the pathogenesis of rheumatoid arthritis (RA). We evaluated the presence of intracellular cytokines interleukin 4 (IL-4) and interferon-gamma (IFN-gamma) produced by CD4+ and CD8+ T cells in the synovial fluid and peripheral blood of patients with RA at the single cell level. METHODS: We used 3 color flow cytometric analysis. Synovial fluid mononuclear cells (SFMC) and peripheral blood mononuclear cells (PBMC) were stimulated with phorbol myristate acetate (PMA) and calcium ionophore. The stimulated SFMC and PBMC were triple stained with conjugated mononuclear antibodies (Mab) against cytokines and surface antigens after fixation and permeabilization with a saponine buffer solution. The cells were analyzed for intracellular cytokines (IFN-gamma, IL-4) and surface antigens (CD3, CD4, CD8) using a flow cytometer. RESULTS: The CD4/CD8 ratio was significantly lower in SFMC than in PBMC. The positive rates of IFN-gamma producing cells among CD4+ T cells were significantly higher than those of IL-4 producing cells in both the SFMC and the PBMC of patients with active RA. In the SF of these patients, we also found CD8+ T cells that produce IL-4 alone, or both IL-4 and IFN-gamma. CONCLUSION: In the SF of patients with RA, CD4+ type 1 T cells, which may infiltrate into the synovium and cause pathogenic immune responses in the tissue, are predominant. We believe this cell type also induces migration and activation of CD8+ type 2 T cells into the active site of inflammation, which appears to downregulate the activity of CD4+ type 1 T cells, modulating the excess immune response.     

Detection of a high frequency of virus-specific CD4+ T cells during acute infection with lymphocytic choriomeningitis virus

Lymphocytic choriomeningitis virus (LCMV), like many viruses, induces a profound activation and expansion of CD8+ T cells. In contrast, CD4+ T cells do not increase in total number during the acute infection. We show here that mice infected with LCMV have a low but detectable frequency (<1/300) of CD4+ T cells, as detected by IL-2 production in limiting dilution assays, to each of two class II peptides during the peak of the acute LCMV response and into long-term memory. However, during the peak of the acute CD4+ T cell response, >20% of the CD4+ T cells secreted IFN-gamma after stimulation with PMA and ionomycin, and >10% of the CD4+ T cells secreted IFN-gamma after stimulation with the LCMV peptides. Thus, these new sensitive assays reveal a heretofore unappreciated, yet profound Ag-specific CD4+ T cell response during viral infections.     

Hepatocytes induce functional activation of naive CD8+ T lymphocytes but fail to promote survival

Intraperitoneal peptide injection of TCR-transgenic mice or expression of antigen in hepatocytes leads to an accumulation in the liver of specific apoptotic CD8+ T cells expressing activation markers. To determine whether liver cells are capable of directly activating naive CD8+ T cells, we have studied the ability of purified hepatocytes to activate TCR-transgenic CD8+ T cells in vitro. We show that hepatocytes which do not express CD80 and CD86 co-stimulatory molecules are able to induce activation and effective proliferation of specific naive CD8+ T cells in the absence of exogenously added cytokines, a property only shared by professional antigen-presenting cells (APC). Specific T cell proliferation induced by hepatocytes was comparable in magnitude to that seen in response to dendritic cells and was independent of CD4+ T cell help or bystander professional APC co-stimulation. During the first 3 days, the same number of divisions was observed in co-cultures of CD8+ T cells with either hepatocytes or splenocytes. Both APC populations induced expression of early T cell activation markers and specific cytotoxic T lymphocyte (CTL) activity. However, in contrast to T cells activated by splenocytes, T cells activated by hepatocytes lost their cytolytic function after 3 days of co-culture. This correlated with death of activated T cells, suggesting that despite efficient activation, proliferation and transient CTL function, T cells activated by hepatocytes did not survive. Death could be prevented by adding antigen-expressing splenocytes or exogenous IL-2 to the co-culture, indicating that hepatocytes are not involved in direct killing of CD8+ T cells but rather fail to promote survival. Dying cells acquired a CD8(low) TCR(low) B220+ phenotype similar to the one described for apoptotic intrahepatic T cells, suggesting an alternative model to account for the origin of these cells in the liver. The importance of these findings for the understanding of peripheral tolerance and the ability of liver grafts to be accepted is discussed.     

Cyclosporin A inhibits the decrease of CD4/CD8 expression induced by protein kinase C activation

Cyclosporin A (CsA) is a powerful immunosuppressive drug widely used in transplantation medicine. A major effect of CsA is inhibition of the differentiation of immature double-positive (DP) CD4+ CD8+ thymocytes into mature single-positive (SP) CD4+ CD8- or CD4- CD8+ thymocytes. The mechanisms underlying the changes in CD4/CD8 expression during normal differentiation of thymocytes and the way CsA interferes with this differentiation process are still unknown. Here we show that protein kinase C (PKC) activation by phorbol 12-myristate 13-acetate (PMA) causes a decrease of both CD4 and CD8 expression at the cell surface level and at the mRNA level in a CD4+ CD8+ T cell line and in freshly isolated thymocytes. A PKC inhibitor, staurosporin, interferes with the differentiation from DP to SP in fetal thymus organ culture system. These data suggest that the alternation of CD4/CD8 expression from DP to SP is dependent on PKC activation. CsA blocks this decrease of CD4/CD8 expression by PMA in vitro. Moreover, this PMA effect is also blocked by treatment with cycloheximide. These results suggest that the reduction of CD4/CD8 expression requires de novo synthesis of a protein(s) induced in response to a signal conveyed by activated PKC. CsA may block the transition from DP to SP by inhibition of CD4/CD8 down-regulation induced by PKC activation.     

Streptococcal preparation OK-432 is a potent inducer of IL-12 and a T helper cell 1 dominant state

Streptococcal preparation OK-432 is a bacterial immunopotentiator extensively used in Japan for adjuvant cancer therapy. Using a C57BL/6 mouse model, OK-432 was found to induce multiple cytokines including the Th1 polarizing cytokine IL-12. Expression of IL-12 protein by murine splenocytes was restricted to macrophages and B cells and led to high levels of IFN-gamma production from both CD4+ and CD8+ T cells. Of the Th2 cytokines IL-4 and IL-10, only IL-10 protein was detected and originated primarily from the adherent cell population. Its expression was delayed relative to IL-12. A similar pattern of cytokine induction was observed from human PBMCs. OK-432-driven IFN-gamma production was inhibited by anti-IL-12 Ab, anti-IL-2 Ab, anti-TNF-alpha Ab, and anti-IL-2R alpha Ab, suggesting that IFN-gamma production from Th1 cells is induced by the cooperation action of these cytokines through the IL-2R alpha pathway. When compared with another widely used immunopotentiator bacillus Calmette-Guérin (BCG), OK-432 was a stronger IL-12 and IFN-gamma inducer. Furthermore, the mechanism of IFN-gamma induction by OK-432 differed from BCG in that coincident granulocyte-macrophage CSF and IL-1 expression played little to no role. These results suggest that OK-432 is a potent multicytokine inducer, specifically a strong inducer of IL-12, and that OK-432 may exert its antitumor effect by promoting a Th1-dominant state.     

The IL-4 rapidly produced in BALB/c mice after infection with Leishmania major down-regulates IL-12 receptor beta 2-chain expression on CD4+ T cells resulting in a state of unresponsiveness to IL-12

Within 1 day of infection with Leishmania major, susceptible BALB/c mice produce a burst of IL-4 in their draining lymph nodes, resulting in a state of unresponsiveness to IL-12 in parasite-specific CD4+ T cells within 48 h. In this report we examined the molecular mechanism underlying this IL-12 unresponsiveness. Extinction of IL-12 signaling in BALB/c mice is due to a rapid down-regulation of IL-12R beta2-chain mRNA expression in CD4+ T cells. In contrast, IL-12R beta2-chain mRNA expression was maintained on CD4+ T cells from resistant C57BL/6 mice. The down-regulation of the IL-12R beta2-chain mRNA expression in BALB/c CD4+ T cells is a consequence of the early IL-4 production. In this murine model of infection, a strict correlation is shown in vivo between expression of the IL-12R beta2-chain in CD4+ T cells and the development of a Th1 response and down-regulation of the mRNA beta2-chain expression and the maturation of a Th2 response. Treatment of BALB/c mice with IFN-gamma, even when IL-4 has been produced for 48 h, resulted in maintenance of IL-12R beta2-chain mRNA expression and IL-12 responsiveness. The data presented here support the hypothesis that the genetically determined susceptibility of BALB/c mice to infection with L. major is primarily based on an up-regulation of IL-4 production, which secondarily induces extinction of IL-12 signaling.