Interleukin-11 reduces T-cell-dependent experimental liver injury in mice.

Recombinant human interleukin-11 (rhIL-11) is a multifunctional cytokine that can reduce inflammation through the downregulation of multiple pro-inflammatory mediators from activated macrophages. rhIL-11 also inhibits production of several immunostimulatory cytokines such as IL-12 and interferon gamma (IFN-gamma) and has shown biological activity in multiple animal models of inflammatory disease consistent with immunomodulatory effects on macrophages and T cells. To further elucidate the anti-inflammatory activity of rhIL-11 in vivo, the effect of rhIL-11 in a model of Concanavalin A (Con-A)-induced T-cell-mediated hepatotoxicity was examined. Administration of a single dose of rhIL-11 before Con-A administration reduced centrilobular liver necrosis and enhanced survival. A dose-dependent reduction in serum levels of liver enzymes, tumor necrosis factor alpha (TNF-alpha), and IFN-gamma corresponded with this amelioration of liver damage. No significant change in infiltrating lymphocyte populations in the liver was observed following rhIL-11 treatment. Taken together, these results indicate that rhIL-11 ameliorates T-cell-mediated hepatic injury and suggests its therapeutic potential to treat inflammatory liver disease.

The role of recombinant murine IL-12 and IFN-gamma in the pathogenesis of a murine systemic Candida albicans infection.

Studies on murine candidiasis suggest that resistance to disease is linked to a Th1 response and production of IFN-gamma, while failure to elicit protection is associated with a Th2 response and production of IL-4 and IL-10. Experimental infection of C57BL/6 mice, IL-12 treatment of these mice, or both infection and IL-12 treatment resulted in a characteristic Th1 cytokine mRNA profile as measured by quantitative competitive PCR. Specifically, little or no IL-4 transcripts were detected, while IFN-gamma message was elevated, particularly with IL-12 treatment. Despite its role in driving increased IFN-gamma expression and production, IL-12 treatment, paradoxically, promoted disease progression in our model. Therefore, we examined the effect of IFN-gamma neutralization on IL-12-induced susceptibility to infection. None of the systemically infected mice receiving IL-12 alone survived, while IL-12- and anti-IFN-gamma-treated mice had a 70% survival rate, similar to that after infection alone. These results suggested that IFN-gamma induced by IL-12 treatment contributed to lethality. However, in separate studies, IFN-gamma knockout mice were more susceptible to infection than their wild-type counterparts, suggesting that IFN-gamma is required for resistance. Nonetheless, infected IFN-gamma knockout mice treated with recombinant murine IL-12 exhibited enhanced resistance, suggesting that the toxicities observed with IL-12 are directly attributable to IFN-gamma and that an optimal immune response to Candida infections necessitates a finely tuned balance of IFN-gamma production. Thus, we propose that although IFN-gamma can drive resistance, the overproduction of IFN-gamma during candidiasis, mediated by IL-12 administration, leads to enhanced susceptibility.

IL-12, as an adjuvant, promotes a T helper 1 cell, but does not suppress a T helper 2 cell recall response.

IL-12 is a potent inducer of NK and cytolytic T cell activity, IFN-gamma production, and T cell proliferation, and is necessary for differentiation of naive T cells to the Th1 subset. We have previously shown that IL-12 promotes a primary Th1 response and suppresses a primary Th2 response in lymph nodes of mice primed with a model hapten-protein conjugate, 2,4,6-trinitrophenyl (TNP)-keyhole limpet hemocyanin (KLH). We have now extended these studies to determine the Th phenotype of the recall response following immunization with soluble Ag and IL-12. For these experiments, mice were primed with TNP-KLH with or without treatment with IL-12, allowed to progress beyond the primary immune response, and challenged by i.p. injection of TNP-KLH. The phenotype of the recall response was monitored by measuring ex vivo production of IFN-gamma and IL-4 in Ag-stimulated lymph node and spleen cell cultures. Titer and isotype of TNP-specific serum Abs were also evaluated. Mice primed with Ag+IL-12 developed a Th1 recall response, as detected by KLH-specific IFN-gamma production from cultured spleen cells and the presence of TNP-specific IgG2a Ab in serum. However, they also developed an Ag-specific Th2 recall response, as characterized by Ag-induced IL-4 production from spleen cells and the presence of high titers of anti-TNP IgG1 in the serum. Studies of the cytokine profile during the primary response revealed that IL-12 induced in spleen cells the capacity to express both IL-4 and IFN-gamma. CD4+ T cells are necessary for production of IL-4 in the spleens of IL-12-treated mice, and most likely account for the Th2 recall response detected in mice primed with Ag+IL-12. These results indicate that the Th1 phenotype induced by immunization with IL-12 and Ag is maintained so that a Th1 recall response is expressed upon subsequent challenge with Ag. However, immunization with IL-12 also supports the development of a Th2 recall response, indicating that the Th1-inducing effect of IL-12 in vivo is not accompanied by a long lasting suppression of Th2 development.

Immunoglobulin isotype modulation after administration of IL-12.

We have begun a series of experiments assessing the role of IL-12 in the humoral immune response. IL-12 is known to enhance cellular immunity causing a shift toward a Th1, as opposed to a Th2, response. IL-12 is also a potent stimulator of IFN-gamma production which, among other activities, modulates isotype expression particularly with respect to IgG2a. We have performed a series of experiments involving the concurrent dosing of mice with murine IL-12 and TNP-KLH followed by the monitoring of IgG1 and IgG2a anti-TNP responses and total IgG1 and IgG2a levels. Following administration of IL-12, specific anti-TNP titers showed an IgG2a increase while IgG1 responses were markedly lower than those exhibited by animals which did not receive IL-12. Total IgG1 levels in IL-12 treated mice remained at or near baseline while untreated mice demonstrated an increase in total IgG1 levels. In addition, lymph nodes from these mice were removed, stimulated with KLH and assayed for expression of murine IFN-gamma and IL-4. Murine IFN-gamma levels in supernatants obtained from IL-12 treated mice were elevated over those seen in untreated mice while IL-4 levels were suppressed.