Most studies investigating the function of IL-23 have concluded that it promotes IL-17-secreting T cells. Although some reports have also characterized IL-23 as having redundant pro-inflammatory effects with IL-12, we have instead found that IL-23 antagonizes IL-12-induced secretion of IFN-c. When splenocytes or purified populations of T cells were cultured with IL-23, IFN-c secretion in response to IL-12 was dramatically reduced. The impact of IL-23 was most prominent in CD8 1 T cells, but was also observed in NK and CD81 T cells in IL-23p19-deficient mice as compared with WT mice. This increase in IFN-c production coincided with increased LM clearance at days 2 and 3 post-infection. Our data suggest that IL-23 may be a key factor in determining the responsiveness of lymphocytes to IL-12 and their subsequent secretion of IFN-c.Key words: CD8 1 T cells . Cytokines . Innate immunity . Listeria monocytogenes Introduction IL-23 is an IL-12 family cytokine which is composed of the IL-12p40 subunit and a novel cytokine subunit, p19. The heterodimeric structure of IL-23 binds to a receptor complex containing the IL-12Rb1 and a novel receptor termed IL-23R [1]. Similar to IL-12, IL-23 is secreted by activated macrophages and dendritic cells [2] in response to gram-positive and -negative bacterial, viral, and fungal infections, as well as multiple other stimuli [3][4][5][6][7][8][9][10][11]. The majority of the research investigating the actions of IL-23 has focused on its role in maintaining populations of IL-17-secreting cells as well as the possibility of directly inducing IL-17 and IL-22 secretion from a variety of cell types (for reviews see [2,12]). Initially, however, IL-23 was found to have some overlapping functions with IL-12. In a previous report, stimulation of human CD4 1 T cells with anti-CD3 and anti-CD28 resulted in IFN-g secretion, which could be significantly enhanced by IL-12 and slightly enhanced by . Contrary to this, using the murine system, several studies have suggested that IL-23 does not induce production of IFN-g in CD4 1 T cells [13,14]. In this article, we also provide evidence that murine CD4 1 and CD8 1T cells do not respond to IL-23 by secreting IFN-g. IL-23 has been shown to play a role in infectious diseases, autoimmunity and cancer. Mice deficient in IL-23 show increased susceptibility to Mycobacterium tuberculosis, Klebsiella pneumoniae, Citrobacter rodentium, Toxoplasma gondii, Salmonella enterica, and Cryptococcus neoformans [15][16][17][18][19][20][21][22][23]. Increased susceptibility to these infections was linked to the ability of IL-23 to regulate the production of IL-17 and IL-22, although during certain infections, IL-23 does not regulate both cytokines. Figure 1. IL-12, but not IL-23, induces the differentiation of IFN-g secreting T cells. Purified CD8 1 (A, B, D, and E) or CD4 1 (C and F) T cells from naïve WT B6 mice were cultured 6 days on plates coated with anti-CD3 and soluble anti-CD28 in IL-2-supplemented medium with 5 ng/mL IL-12, 10 ng/ mL IL-23, or no additional ...

Immune responses to pathogens occur within the context of current and previous infections. Cross protection refers to the phenomena where infection with a particular pathogen provides enhanced resistance to a subsequent unrelated pathogen in an antigen-independent manner. Proposed mechanisms of antigen-independent cross protection have involved the secretion of IFN-c, which activates macrophages, thus providing enhanced innate immunity against the secondary viral or bacterial pathogen. Here we provide evidence that a primary infection with the chronic respiratory pathogen, Mycoplasma pulmonis, provides a novel form of cross protection against a secondary infection with Listeria monocytogenes that is not mediated by IFN-c, but instead relies upon IL-17 and mobilization of neutrophils. Mice infected with M. pulmonis have enhanced clearance of L. monocytogenes from the spleen and liver, which is associated with increased numbers of Gr-1 1 CD11b 1 cells and higher levels of IL-17. This enhanced clearance of L. monocytogenes was absent in mice depleted of Gr-1 1 cells or in mice deficient in the IL-17 receptor. Additionally, both the IL-17 receptor and neutrophils were essential for optimal clearance of M. pulmonis. Thus, a natural component of the immune response directed against M. pulmonis was able to enhance clearance of L. monocytogenes.

Mutant huntingtin (HTT) protein is the cause of Huntington's disease (HD), an incurable neurological disorder. Almost all patients are heterozygous for mutant HTT and approaches that reduce levels of mutant HTT while leaving expression of wild-type HTT intact might be ideal options for therapeutic development. We have developed several allele-selective strategies for silencing HTT, including single-stranded silencing RNAs (ss-siRNAs). ss-siRNAs are oligonucleotides containing chemical modifications that permit action through the RNA interference (RNAi) pathway. Modified ss-siRNAs chosen to test the effects of varying oligomer length, lipid modification, the introduction of mismatched bases, and variation of chemical modification. We find that several modified ss-siRNA are potent and allele-selective inhibitors of HTT expression. An ss-siRNA with three mismatched bases relative to the CAG repeat was an allele-selective inhibitor of HTT expression in the HdhQ175 mouse model. Multiple allele-selective ss-siRNAs provide a wide platform of modifications to draw on for further optimization and therapeutic development. Our data provide insights into how ss-siRNAs can be modified to improve their properties and facilitate the discovery of the lead compounds necessary for further development.

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Most studies have concluded that interleukin‐23 (IL‐23) promotes IL‐17 secreting T cells. While some reports have also characterized IL‐23 as having redundant pro‐inflammatory effects with IL‐12, we have instead found that IL‐23 can regulate the innate immune response in a novel manner, by antagonizing IL‐12 induced secretion of interferon‐γ (IFN‐γ). Our recent data documents the rapid, innate production of IFN‐γ from memory CD8 T cells, as well as NK cells, stimulated with IL‐12 and IL‐18. When splenocytes are cultured with IL‐23, IFN‐γ secretion in response to IL‐12 is dramatically reduced, as measured by ELISA and intracellular cytokine staining. The impact of IL‐23 is most prominent in CD8 T cells, but can also be seen in NK, NK‐T, and CD4 T cells. We also show that IL‐23 can regulate the induction of IFN‐γ by endogenously produced IL‐12 from Listeria monocytogenes (LM) infected macrophages. In vivo, LM infection induces higher serum IFN‐γ levels and a greater percentage of IFN‐γ + CD8 T cells in IL‐23p19 deficient mice as compared to wild‐type mice. We are currently investigating the mechanism by which IL‐23 inhibits IFN‐γ secretion, and if IL‐23 can inhibit other effector functions. Our data suggest that IL‐23 may be a key player in determining the responsiveness of lymphocytes to IL‐12 and their subsequent secretion of IFN‐γ.