Cuticular proteins from the lobster, Homarus americanus

The interleukin-12 receptor (IL-12R)beta1 chain is an essential component of the functional IL-12R on both human T and natural killer cells. In this report it is shown that activation of human peripheral blood mononuclear cells (PBMC) with anti-CD3 monoclonal antibody (mAb) or phytohemagglutinin resulted in the up-regulation of IL-12Rbeta1 expression and IL-12 binding. Kinetic studies revealed that maximum expression of IL-12Rbeta1 and IL-12 binding occurred on days 3-4. Anti-CD3-induced expression of IL-12Rbeta1 chain and IL-12 binding by PBMC was augmented by anti-CD28 mAb, indicating that the potentiating effect of anti-CD28 on T cell responses to IL-12 could be mediated, at least in part, by the enhancement of IL-12R expression. Among 16 cytokines tested, IL-2, IL-7 and IL-15 markedly induced IL-12Rbeta1 expression and IL-12 binding on resting PBMC, whereas IL-1alpha and tumor necrosis factor-alpha had a minimal enhancing effect. In contrast, IL-3, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, interferon (IFN)-alpha, IFN-gamma, granulocyte/macrophage colony-stimulating factor and transforming growth factor (TGF)-beta2 had no detectable enhancing effect. Anti-CD3-induced expression of IL-12Rbeta1 and of low-affinity IL-12 binding sites was partially inhibited by TGF-beta2, IL-10 and IL-4; however, TGF-beta2 and IL-10 completely abolished anti-CD3-induced expression of high-affinity IL-12 binding sites. Consistent with the reduction of high affinity IL-12 binding sites, PBMC activated with anti-CD3 mAb in the presence of TGF-beta2 or IL-10 failed to produce IFN-gamma or to proliferate in response to IL-12. These results suggest that Th2 cell-derived cytokines can inhibit IL-12-induced biological functions by inhibiting IL-12R expression and that expression of a second subunit of the IL-12R (IL-12Rbeta2), required for the formation of high-affinity IL-12 binding sites, may be more highly regulated by TGF-beta2 and IL-10 than is expression of IL-12Rbeta1.     

Severe mycobacterial and Salmonella infections in interleukin-12 receptor-deficient patients

Interleukin-12 (IL-12) is a cytokine that promotes cell-mediated immunity to intracellular pathogens by inducing type 1 helper T cell (TH1) responses and interferon-gamma (IFN-gamma) production. IL-12 binds to high-affinity beta1/beta2 heterodimeric IL-12 receptor (IL-12R) complexes on T cell and natural killer cells. Three unrelated individuals with severe, idiopathic mycobacterial and Salmonella infections were found to lack IL-12Rbeta1 chain expression. Their cells were deficient in IL-12R signaling and IFN-gamma production, and their remaining T cell responses were independent of endogenous IL-12. IL-12Rbeta1 sequence analysis revealed genetic mutations that resulted in premature stop codons in the extracellular domain. The lack of IL-12Rbeta1 expression results in a human immunodeficiency and shows the essential role of IL-12 in resistance to infections due to intracellular bacteria.     

Prostaglandin E2 and dexamethasone inhibit IL-12 receptor expression and IL-12 responsiveness

Regulation of the factors governing IL-12R expression and IL-12 responsiveness has been shown to be important in the generation and stability of Th1- and Th2-type responses. In this regard, cytokines have been shown to have a prominent role in regulating IL-12R expression. In this study, the role that PGE2 and dexamethasone (DXM) have in regulating IL-12R expression was evaluated. Addition of PGE2 or DXM to human PBMCs stimulated with immobilized anti-CD3 plus IL-12 inhibited the production of IFN-gamma in a dose-responsive manner. Moreover, PBMCs stimulated with immobilized anti-CD3 in the presence of PGE2 or DXM for 3 days, washed extensively, and restimulated in the presence of IL-12 still did not produce IFN-gamma. This lack of IL-12 responsiveness from cells cultured in either PGE2 or DXM was correlated with diminished surface expression of IL-12Rbeta1, IL-12Rbeta2 mRNA expression, and IL-12 binding. Finally, the PGE2- and DXM-mediated inhibition of IL-12R expression was not affected significantly by addition of neutralizing Abs against either IL-4, IL-10, or TGF-beta. By contrast, addition of dibutyryl cAMP, 8-bromoadenosine 3:5 cAMP (8-Br-cAMP), or cholera toxin substantially reduced IL-12R expression, suggesting that PGE2 may be mediating its effects through enhancement of cAMP.     

Differential regulation of the interleukin-12 receptor during the innate immune response to Leishmania major

Previous studies have shown the central role of interleukin 12 (IL-12) in the development of resistance to Leishmania major infection in C3H mice. We now show that during the innate immune response the lymph node cells of L. major-infected C3H mice upregulate the IL-12 receptor on CD4(+), CD8(+), and B220(+) cells. An increase in the ability of the lymph node cells to bind IL-12 correlates with 9.3- and 4.6-fold increases in the mRNA expression levels of the IL-12Rbeta1 and -beta2 subunits, respectively. In contrast, BALB/c mice, which are susceptible to L. major infection, have no increase in the ability of the lymph node cells to bind IL-12 and correspondingly smaller increases in the mRNA expression levels of the IL-12Rbeta1 and -beta2 subunits of 2- and 1.5-fold, respectively. Neutralizing IL-4 and the administration of exogenous IL-12 upregulate IL-12R expression in BALB/c mice, while the neutralization of IL-12 in C3H mice blocks increased IL-12 receptor expression. These experiments reveal an important role for the regulation of the IL-12 receptor during the innate immune response after infection of mice with a pathogen.     

IL-15 promotes IL-12 production by human monocytes via T cell-dependent contact and may contribute to IL-12-mediated IFN-gamma secretion by CD4+ T cells in the absence of TCR ligation

At inflammatory sites, the number of activated bystander T cells exceeds that of Ag-activated T cells. We investigated whether IL-15, a monocyte-derived cytokine that shares several biologic activities with IL-2, may contribute to bystander T cell activation in the absence of IL-2 and triggering Ag. The addition of IL-15 to cocultures of monocytes and T cells stimulates CD4+ but not CD8+ T cells to produce IFN-gamma. IFN-gamma production requires endogenous IL-12, the production of which in turn is dependent upon CD40/CD154 interactions between CD4+ T cells and monocytes. Indeed, non-TCR-activated CD4+ but not CD8+ T cells express significant levels of CD154. IL-15 may enhance IFN-gamma in this system by up-regulating CD40 expression on monocytes and IL-12Rbeta1 expression on CD4+ T cells. Conversely, using neutralizing anti-IL-15 mAb, we show that the ability of IL-12 to augment IFN-gamma secretion is partly mediated by endogenous IL-15. Finally, in the absence of monocytes, a synergistic effect between exogenous IL-12 and IL-15 is necessary to induce IFN-gamma production by purified CD4+ T cells, while IL-15 alone induces T cell proliferation. It is proposed that this codependence between IL-12 and IL-15 for the activation of inflammatory T cells may be involved in chronic inflammatory disorders that are dominated by a Th1 response. In such a response, a self-perpetuating cycle of inflammation is set forth, because IL-15-stimulated CD4+ T cells may activate monocytes to release IL-12 that synergizes with IL-15 to induce IL-12 response and IFN-gamma production.     

In vitro interleukin 12 activation of peripheral blood CD3(+)CD56(+) and CD3(+)CD56(-) gammadelta T cells from glioblastoma patients

Interleukin (IL)-12 has recently been shown to be directly involved in the activation of natural killer and alphabeta T cells via an IL-2-independent pathway. We show here that another type of human cytotoxic cell, gammadelta T cells activated by solid-phase anti-CD3 antibody and expanded using IL-2, obtained, in this case, from the peripheral blood of glioblastoma patients, displays significant tumoricidal activity. In addition, its cytotoxic activity against K562 or Daudi cells or against autologous glioblastoma targets (but not lymphocytes) is significantly enhanced when costimulated with IL-2 and IL-12. To study this synergistic activation by the two interleukins of the patients' gammadelta T cells, we screened the cells for the presence of the IL-2 receptor (IL-2R) and IL-12 receptor (IL-12R) using both flow cytometric analysis and PCR. The patients' gammadelta T cells constitutively expressed the high-affinity IL-2R; when stimulated with IL-12 plus IL-2, the levels of IL-2Ralpha and IL-2Rbeta increased, whereas that of IL-2gamma did not. They also expressed marginal levels of low-affinity IL-12R both immediately after IL-2 expansion and after 24-h incubation, and significantly higher levels after 72-h incubation, consistent with the level of gammadelta T-cell activation. IL-12 alone induced little proliferation of patients' gammadelta T cells in a 24-h assay and none in a 72-h assay; however, it caused a marked inhibition of the IL-2-induced proliferative response in the 72-h assay. The synergistic action of IL-2 and IL-12 was completely abolished by combined pretreatment with anti-IL-2alpha, beta, and gamma mAbs. IL-12-mediated enhancement of gammadelta T cell cytotoxic activity was inhibited by anti-IL-2Rbeta mAb in a dose-dependent manner but not by anti-IL-2Ralpha or anti-IL-2Rgamma mAbs. Thus, the increased expression of the IL-2Rbeta is critical for the synergistic activation of gammadelta T cells by IL-12 plus IL-2; it is also probable that at least the low-affinity IL-12R contributes to the activation of gammadelta T cells mediated by either IL-12 alone or IL-12 plus IL-2. We have, therefore, demonstrated that IL-12 can stimulate the cytotoxic activity of gammadelta T cells from glioblastoma patients, acting via the IL-2Rbeta component of the IL-2R and low-affinity IL-12R. IL-12 activation of patients' gammadelta T cells could possibly be of potential use in the treatment of glioblastoma patients.     

IL-12 up-regulates IL-18 receptor expression on T cells, Th1 cells, and B cells: synergism with IL-18 for IFN-gamma production

IL-18 is a product of macrophages and with IL-12 strikingly induces IFN-gamma production from T, B, and NK cells. Furthermore, IL-18 and 1L-12 synergize for IFN-gamma production from Th1 cells, although this combination fails to affect Th2 cells. In this study, we show that IL-12 and IL-18 promptly and synergistically induce T and B cells to develop into IFN-gamma-producing cells without engaging their Ag receptors. We also studied the mechanism underlying differences in IL-18 responsiveness between Th1 and Th2 cells. Pretreatment of T or B cells with IL-12 rendered them responsive to IL-18, which induces cell proliferation and IFN-gamma production. These IL-12-stimulated cells had both high and low affinity IL-18R and an increased IL-18R mRNA expression. In particular, IL-12-stimulated T cells strongly and continuously expressed IL-18R mRNA. However, when T cells developed into Th1 cells after stimulation with anti-CD3 and IL-12, they lowered this IL-12-induced-IL-18R mRNA expression. Then, such T cells showed a dominant response to anti-CD3 by IFN-gamma production when they were subsequently stimulated with anti-CD3 and IL-18. In contrast, Th2 cells did not express IL-18R mRNA and failed to produce IFN-gamma in response to anti-CD3 and IL-18, although they produced a substantial amount of IFN-gamma in response to anti-CD3 and IL-12. However, when Th1 and Th2 cells were stimulated with anti-CD3, IL-12, and IL-18, only the Th1 cells markedly augmented IFN-gamma production in response to IL-18, suggesting that IL-18 responsiveness between Th1 and Th2 cells resulted from their differential expression of IL-18R.     

Decreased drug accumulation in a mitoxantrone-resistant gastric carcinoma cell line in the absence of P-glycoprotein

The developmental commitment to a T helper 1 (Th1)- or Th2-type response can significantly influence host immunity to pathogens. Extinction of the IL-12 signaling pathway during early Th2 development provides a mechanism that allows stable phenotype commitment. In this report we demonstrate that extinction of IL-12 signaling in early Th2 cells results from a selective loss of IL-12 receptor (IL-12R) beta 2 subunit expression. To determine the basis for this selective loss, we examined IL-12R beta 2 subunit expression during Th cell development in response to T cell treatment with different cytokines. IL-12R beta 2 is not expressed by naive resting CD4+ T cells, but is induced upon antigen activation through the T cell receptor. Importantly, IL-4 and IFN-gamma were found to significantly modify IL-12 receptor beta 2 expression after T cell activation. IL-4 inhibited IL-12R beta 2 expression leading to the loss of IL-12 signaling, providing an important point of regulation to promote commitment to the Th2 pathway. IFN-gamma treatment of early developing Th2 cells maintained IL-12R beta 2 expression and restored the ability of these cells to functionally respond to IL-12, but did not directly inhibit IL-4 or induce IFN-gamma production. Thus, IFN-gamma may prevent early Th cells from premature commitment to the Th2 pathway. Controlling the expression of the IL-12R beta 2 subunit could be an important therapeutic target for the redirection of ongoing Th cell responses.     

Interleukin-12 primes human CD4 and CD8 T cell clones for high production of both interferon-gamma and interleukin-10

Interleukin-12 (IL-12) induces differentiation of T helper 1 (Th1) cells, primarily through its ability to prime T cells for high interferon-gamma (IFN-gamma) production. We now report that the presence of IL-12 during the first several days of in vitro clonal expansion in limiting dilution cultures of polyclonally stimulated human peripheral blood CD4+ and CD8+ T cells also induces stable priming for high IL-10 production. This effect was demonstrated with T cells from both healthy donors and HIV+ patients. Priming for IL-4 production, which requires IL-4, was maximum in cultures containing both IL-12 and IL-4. IL-4 modestly inhibited the IL-12-induced priming for IFN-gamma, but almost completely suppressed the priming for IL-10 production. A proportion of the clones generated from memory CD45RO+ cells, but not those generated from naive CD45RO- CD4+ T cells, produced some combinations of IFN-gamma, IL-10, and IL-4 even in the absence of IL-12 and IL-4, suggesting in vivo cytokine priming; virtually all CD4+ clones generated from either CD45RO(-) or (+) cells, however, produced high levels of both IFN-gamma and IL-10 when IL-12 was present during expansion. These results indicate that each Th1-type (IFN-gamma) and Th2-type (IL-4 and IL-10) cytokine gene is independently regulated in human T cells and that the dichotomy between T cells with the cytokine production pattern of Th1 and Th2 cells is not due to a direct differentiation-inducing effect of immunoregulatory cytokines, but rather to secondary selective mechanisms. Particular combinations of cytokines induce a predominant generation of T cell clones with anomalous patterns of cytokine production (e.g., IFN-gamma and IL-4 or IFN-gamma and IL-10) that can also be found in a proportion of fresh peripheral blood T cells with "memory" phenotype or clones generated from them and that may identify novel Th subsets with immunoregulatory functions.     

Amelioration of collagen-induced arthritis and suppression of interferon-gamma, interleukin-12, and tumor necrosis factor alpha production by interferon-beta gene therapy

Human Vgamma9Vdelta2 T cells contribute to immunity against intracellular pathogens and recognize nonpeptidic antigens, such as the mycobacterial phosphoantigen TUBAg. HIV infection is associated with a polyclonal decrease of peripheral Vgamma9Vdelta2 T cells and we previously reported that the remaining cells show a proliferative anergy to stimulation with Mycobacterium tuberculosis in 60% of patients. Because of alterations in the Th1/Th2 cytokine balance reported in HIV infection, we analyzed, at the single-cell level, the influence of exogenous IL-4, IL-10, IL-12 and IL-15 on the response to mycobacterial phosphoantigens of gammadelta T cells from HIV-infected patients and healthy donors. We report that the strong gammadelta T cell response to TUBAg is characterized by the rapid and selective production of the Th1/proinflammatory cytokines IFN-gamma and TNF-alpha in responder HIV-infected donors. In addition, a positive regulation by IL-12 and IL-15 of the production of these cytokines by Vgamma9Vdelta2 T cells in response to nonpeptidic ligands was observed, whereas IL-4 and IL-10 had no effect. In contrast, Vgamma9Vdelta2 T cells from the anergic HIV-infected donors had lost the ability to produce Th1 cytokines and were not shifted towards a Th2 profile. Furthermore, neither IL-12 nor IL-15 could reverse this functional anergy. The consequences of these observations are discussed in the context of HIV pathogenesis.     

Low dose TGF-beta attenuates IL-12 responsiveness in murine Th cells

Expression of IL-12Rs is one important checkpoint for Th1 development. BALB/c DO11.10 CD4+ T cells stimulated by Ag in neutral conditions lose expression of the IL-12R beta 2 subunit and become unresponsive to IL-12. In contrast, B10.D2 or F1 (BALB/c x B10.D2) DO11.10 CD4+ T cells maintain IL-12R beta 2 expression when stimulated similarly. Here we show that the loss of IL-12 responsiveness by BALB/c T cells involves the action of endogenous TGF-beta. BALB/c T cells stimulated in the presence of anti-TGF-beta specifically maintain IL-12 responsiveness, express IL-12R beta 2 mRNA, and can stimulate nitric oxide production in peritoneal exudate cells. Low concentrations of TGF-beta added exogenously during primary activation of B10.D2 or F1 T cells significantly inhibit their development of IL-12 responsiveness. These effects of anti-TGF-beta are dependent on endogenous IFN-gamma and are inhibited by exogenously added IL-4. Thus, at least one effect of TGF-beta on Th1/Th2 development may be the attenuation of IL-12R beta 2 expression.     

Tpm1, a locus controlling IL-12 responsiveness, acts by a cell-autonomous mechanism

Th phenotype development is controlled not only by cytokines but also by other parameters including genetic background. One site of genetic variation between murine strains that has direct impact on Th development is the expression of the IL-12 receptor. T cells from B10.D2 and BALB/c mice show distinct control of IL-12 receptor expression. When activated by Ag, B10.D2 T cells express functional IL-12 receptors and maintain IL-12 responsiveness. In contrast, under the same conditions, BALB/c T cells fail to express IL-12 receptors and become unresponsive to IL-12, precluding any Th1-inducing effects if subsequently exposed to IL-12. Previously, we identified a locus, which we termed T cell phenotype modifier 1 (Tpm1), on murine chromosome 11 that controls this differential maintenance of IL-12 responsiveness. In this study, we have produced a higher resolution map around Tpm1. We produced and analyzed a series of recombinants from a first-generation backcross that significantly narrows the genetic boundaries of Tpm1. This allowed us to exclude from consideration certain previous candidates for Tpm1, including IFN-regulatory factor-1. Also, cellular analysis of F1(B10.D2 x BALB/c) T cells demonstrates that Tpm1 exerts its effect on IL-12 receptor expression in a cell-autonomous manner, rather than through influencing the extracellular milieu. This result strongly implies that despite the proximity of our locus to the IL-13/IL-4 gene cluster, these cytokines are not candidates for Tpm1.     

Differential effects of CD28 engagement and IL-12 on T cell activation by altered peptide ligands

To futher our understanding of the mechanisms underlying the diverse effects of altered peptide ligands (APL) on T cell activation, we used a population of nonactivated spleen cells from mice that expressed a transgenic TCR specific for myelin basic protein Ac1-11 and peptide analogues that display either enhanced or decreased affinities for TCR/MHC to address the question whether APL-induced signaling through the TCR can regulate the capability of APC to activate T cells. We demonstrate that weak agonists APL are poor inducers of all aspects of the activation of both the responder T cells and the APC. Enhancement of the antigenic signal by augmenting the binding of the weak agonists to MHC reversed their defective activating capacity. Enhancement of costimulation by engagement of CD28 only resulted in augmentation of the capacity of the weak agonist APL to induce proliferation and IL-2/IL-3 production, but not CD40L or IL-12Rbeta2 chain expression on T cells, CD80/CD86 expression on APC, IL-12 secretion, or IFN-gamma production. Exogenous IL-12 promoted IFN-gamma production in the presence of the weak agonists. These studies demonstrate that there is a critical threshold of antigenic signal required for full activation of the T cell-APC interactions needed for the differentiation of Th1 cells. The provision of excess costimulation can overcome some of the defects in T cell activation by weak agonists, but is insufficient to induce a sufficient level of CD40L expression needed for engagement of CD40 on APC with subsequent IL-12 production and induction of IL-12Rbeta2 chain expression.     

Expression of the IL-12 receptor beta 1 and beta 2 subunits in human tuberculosis

To determine whether the Th1 response in tuberculosis correlated with IL-12R expression, we measured expression of the IL-12R beta 1 and IL-12R beta 2 subunits, as well as IL-12R beta 2 mRNA expression in tuberculosis patients and healthy tuberculin reactors. In tuberculosis patients, IFN-gamma production by Mycobacterium tuberculosis-stimulated PBMC was reduced, the percentages of T cells expressing IL-12R beta 1 and IL-12R beta 2 were significantly decreased, and IL-12R beta 2 mRNA expression was also markedly reduced. In contrast, in pleural fluid and lymph nodes at the site of disease in tuberculosis patients, in which IFN-gamma production is enhanced, IL-12R beta 2 mRNA expression was also increased. In M. tuberculosis-stimulated peripheral blood T cells from tuberculosis patients, anti-IL-10 and anti-TGF-beta enhanced IL-12R beta 1 and IL-12R beta 2 expression, and IFN-gamma production. In M. tuberculosis-stimulated peripheral blood T cells from healthy tuberculin reactors, recombinant IL-10 and TGF-beta reduced IL-12R beta 1 and IL-12R beta 2 expression, as well as IFN-gamma production. In combination with prior studies showing increased production of TGF-beta by blood monocytes from tuberculosis patients, this suggests that increased TGF-beta production is the underlying abnormality that reduces IL-12R beta 1 and IL-12R beta 2 expression in tuberculosis. Our findings provide evidence that IL-12R expression correlates well with IFN-gamma production in human tuberculosis, and that expression of IL-12R beta 1 and IL-12R beta 2 may play a central role in mediating a protective Th1 response.     

Human eosinophils produce biologically active IL-12: implications for control of T cell responses

The present study assessed the capacity of eosinophils (EOS) to synthesize the cytokine IL-12. Blood-derived, highly purified human EOS from six atopic patients and two nonatopic individuals were treated in culture with IL-4, IL-5, granulocyte-macrophage CSF, IFN-gamma, TNF-alpha, IL-1alpha, RANTES, and complement 5a, respectively. The expression of both IL-12 protein and mRNAs for the p35 and p40 IL-12 subunits was strongly induced in all donors by the Th2-like cytokines IL-4 and granulocyte-macrophage CSF and was also moderately induced by TNF-alpha and IL-1alpha. IL-5 treatment resulted in IL-12 synthesis in four atopic donors and one nonatopic donor, whereas IFN-gamma induced IL-12 synthesis in only two atopic donors. In contrast, RANTES exclusively induced mRNA for the p40 subunit without detectable protein release, and complement 5a had no effect on IL-12 mRNA or protein expression. EOS-derived IL-12 was biologically active, because supernatants derived from IL-4-treated EOS superinduced the Con A-induced expression of IFN-gamma by a human Th1-like T cell line. This activity was neutralized by anti-IL-12 Abs. In conclusion, EOS secrete biologically active IL-12 after treatment with selected cytokines, which mainly represent the Th2-like type. Consequently, EOS may promote a switch from Th2-like to Th1-like immune responses in atopic and parasitic diseases.     

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.     

Reduced IL-12 production by monocytes upon ultraviolet-B irradiation selectively limits activation of T helper-1 cells

The capacity of APC to stimulate the proliferation of human peripheral blood T cells decreases upon ultraviolet-B (UVB) irradiation. The aim of this study was to investigate whether all T cell subsets are equally sensitive to this reduced APC function. Established human Th1, Th2, and Th0 clones were stimulated with monocytes in a soluble CD3 mAb-mediated assay that is dependent on the presence of APC. Monocytes were exposed to low nonlethal doses of UVB radiation before coculture with T cells. UVB irradiation inhibited the capacity of monocytes to stimulate the proliferation and IFN-gamma production of Th1 cells in a dose-related fashion. In contrast, UVB-treated monocytes induced normal proliferation and IL-4 production in Th2 cells. Stimulation of Th0 cell proliferation by UVB-irradiated monocytes was normal, but a preferential suppression of IFN-gamma production was observed, thus leading to a more Th2-like cytokine response. The loss of Th1 proliferation upon stimulation with UVB-irradiated monocytes could be overcome by rIL-2; however, IFN-gamma production remained suppressed. IFN-gamma production could be completely restored by rIL-12, whereas the addition of IL-1 beta, TNF-alpha, or indomethacin had no such effect, nor did the addition of mAb to CD28, added to compensate for the reduced B7 expression of UVB-irradiated monocytes. Monocytes exposed to UVB radiation exhibited reduced expression of mRNA for the IL-1 2 subunits p35 and p40 and suppressed production of the IL-12 p70 protein. Our results thus indicate that UVB irradiation of APC selectively impairs Th1-like responses, a phenomenon caused by the UVB-induced suppression of monocyte IL-12 production.