The interleukin (IL)-12 family of cytokines plays a key role in the orchestration of cellular immune responses, bridging innate and adaptive immunity. The founding member, IL-12, was discovered in the late 1980s as the first heterodimeric cytokine, composed of a 40 kDa (p40) and 35 kDa (p35) subunit. Years of basic and clinical research on this prototypical T helper type (Th)1 cytokine revealed its importance in immunity to intracellular non-viral infections, as well as in cancer and autoimmune diseases. Since the discovery of IL-23 as another cytokine composed of the p40 subunit of IL-12 in the year 2000, IL-23, rather than IL-12, could be shown to be the key player in rodent models of autoimmune diseases such as multiple sclerosis and rheumatoid arthritis. With accumulating evidence revealing IL-23 as the crucial regulator of a non-classical pathway of cellular immunity which is hallmarked by IL-17 producing T cells it is intriguing to gain understanding of the importance of such findings in immunity to infections. The present work describes a series of in vivo studies investigating the role of endogenous as well as exogenous IL-23 in a murine model of chronic fungal infection, cryptococcosis. To address the role of endogenous IL-23, wild-type (WT), IL-12- (IL-12p35-/-), IL-23- (IL-23p19-/-) deficient, as well as IL-12- and IL-23- double deficient (p40-deficient) mice on a C57BL/6 background were infected with Cryptococcus neoformans (C. neoformans). Following infection, p40-deficient mice demonstrated higher mortality than IL-12p35-/- mice. Reconstitution of p40-deficient mice with recombinant murine IL-23 prolonged their survival to levels similar to IL-12p35-/- mice. IL-23p19-/- mice showed a moderately reduced survival time and delayed fungal clearance in the liver. While interferon (IFN)-γ production was similar in WT and IL-23p19-/- mice, production of IL-17 was strongly impaired in the latter. IL-23p19-/- mice produced fewer hepatic granulomata relative to organ burden and showed defective recruitment of mononuclear cells to the brain. Moreover, activation of microglia cells and expression of IL-1β, IL-6, and MCP-1 in the brain was impaired. SUMMARY - 80 - The second part of the present work explores the mechanisms underlying the IL-23 effects by characterizing the role of exogenous IL-23. C. neoformans-infected C57BL/6 WT mice treated with recombinant murine IL-23 showed significantly prolonged survival time as compared to mock-treated control mice. However, complete survival throughout the observation period (100 days) was only achieved following IL-12 treatment. At day 21 post infection (p.i.) the IL-23-treated mice as well as the IL-12 group had a significantly lower fungal burden in the brain than the control mice. However, while IL-12 treatment was associated with elevated serum levels of the proinflammatory mediators IFN-γ, tumor necrosis factor (TNF)-α and nitric oxide, IL-23-treated animals, although more resistant, developed a Th2 response similar to the control group as measured by serum IgE levels. Further experiments to assess the mechanism of action were based on the finding of reduced fungal burden at the site of infection, the peritoneal cavity, at day 8 p.i. following IL-23 treatment. This microbicidal effect was also seen in p40-deficient as well as in T and B cell deficient (RAG-deficient) mice. Administration of IL-23 led to enhanced recruitment of inflammatory cells, not only of T cells but also cells of the innate immune system such as DCs, natural killer cells and granulocytes to the infected site. Although numbers of macrophages were not altered following IL-23 treatment, co-stimulatory molecules were markedly up-regulated on such cells. The chemokine/cytokine pattern induced by IL-23 treatment was hallmarked by proinflammatory mediators such as MCP-1, IL-1β, IL-6, TNF-α and IL-17, but also the Th2 associated cytokine IL-5. From these results it can be concluded that a non-classical immune pathway induced by IL-23 complements the more dominant role of IL-12 in protection against C. neoformans. This novel immune response is characterized by an enhancement of the inflammatory cell response and the production of a proinflammatory cytokine pattern hallmarked by IL-1β, IL-6, TNF-α and IL-17.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa.de:swb:15-20070223-073730-7 |
| Date | 23 February 2007 |
| Creators | Kleinschek, Melanie |
| Contributors | Universität Leipzig, |
| Publisher | Universitätsbibliothek Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis |
| Format | application/pdf |
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