Defining the source and effect of IL-23 in the lymph node during Experimental Autoimmune encephalomyelitis (EAE) induction

Multiple sclerosis (MS) is a chronic autoimmune, inflammatory, demyelinating, and neurodegenerative disease of the central nervous system (CNS). Experimental autoimmune encephalomyelitis (EAE) serves as the most widely used experimental model for MS. Interleukin-23 (IL-23), a heterodimeric cytokine consisting of a p40 subunit (shared with IL-12) and a unique p19 subunit, encoded by the Il23a gene. IL-23-deficient mice (Il-23a-/-) are resistant to EAE as the cytokine is pivotal during the priming phase of EAE in lymph nodes (LNs) and the development of encephalitogenic GM-CSF-producing Th17 cells. Here, we aim to define the specific cellular source of IL-23 in this process, which remains unclear. Using conditional IL-23 mutagenesis, we revealed that MOG35-55 / CFA challenged Cx3Cr1Cre: IL-23afl/fl mice develop, unlike their littermate controls, no EAE pathology. Consistent with IL-23 whole-body knockout mice, we observed a significant reduction in the generation of encephalitogenic GM-CSF-producing Th17 cells.

Our results establish that the critical IL-23 source is Cx3cr1+ cells or those expressing Cx3cr1 during the development. RT-PCR analysis of sorted LN cells of MOG-challenged animals revealed Il-23a expression in CD11b+ cells as an IL-23 source. Intriguingly, in particular, SiglecF+ neutrophils produced high levels of IL-23 in this system, followed by monocytes. Our data suggest that the resistance of Cx3cr1Cre: Il23afl/fl mice to EAE is due to impaired IL-23 production by neutrophils, resulting in reduced development of encephalitogenic GM-CSF-producing Th17 cells that drive immunopathology. We are currently trying to substantiate this conclusion using neutrophil-specific Il-23a mutagenesis and neutrophil ablation.