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Ellen J Lee, Brieanna Brown, Emily Vance, Maya Lewinsohn, Phyllis B Silver, Rachel R Caspi, Holly Lallman Rosenzweig; A role for the Syk-CARD9 pathway in the pathogenesis of autoimmune uveitis. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2502.
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© ARVO (1962-2015); The Authors (2016-present)
While the role of adaptive T cell responses in uveitis has been extensively studied, we know little of the innate signals that precede and contribute to autoreactive T cell activation and disease. We, therefore, investigated the C-type lectin receptors (CLRs) in the T cell-dependent uveitis model, experimental autoimmune uveitis (EAU).
EAU was induced in Card9 knockout (KO) mice and C57BL/6J congenic wild-type (WT) controls by immunization with interphotoreceptor retinoid-binding protein (IRBP). Pathway-focused gene expression changes were quantified by real-time PCR-based multiplex arrays at d10 post-immunization. At d21, uveitis was assessed by fundus imaging and histopathology. Flow cytometry was used to quantify cellular infiltrate of eyes and antigen-specific CD4+ T cell effector responses from IRBP-stimulated splenocytes. The Syk inhibitor, piceatannol (5mg/kg x 4 i.p. injections), versus vehicle control was evaluated in WT mice (n=6/treatment).
Multiplex array analysis of isolated neuroretina revealed early induction of genes involved in fungal and mycobacterial host defense responses, including Dectin-1, Dectin-2, and Mincle, which comprise a subgroup of CLRs that transduce signals through Syk and CARD9. Card9 expression was essential for induction of “fungal-associated” transcriptional response and contributed functionally to EAU, as CARD9 KO mice were resistant to EAU. Card9 deficiency significantly impaired EAU development, as assessed by clinical fundus and histopathologic grading (WT=2.5±0.34 vs. KO=0.28±0.11, p<0.001), as well as by reduced leukocyte infiltration into the vitreous (WT=159±41 vs. KO=4±2, p<0.0001). Flow cytometry of whole eyes revealed marked reduction of CD4+ T cells, neutrophils and monocyte-macrophages. Card9 expression was essential for induction of IRBP-specific T cell effector responses, as KO mice demonstrated greater than 2-fold reduction in frequency of both Th1 and Th17 cells. The resistance of CARD9 KO mice to EAU was reproduced in WT mice by pharmacologic inhibition of the upstream kinase Syk, further underscoring the importance of the Syk-CARD9 pathway in orchestration of EAU.
Our studies uncover a role for the Syk-CARD9 pathway in induction of uveitogenic T cell responses and autoimmune uveitis and implicate CLRs as important players in uveitis. These pathways could constitute new targets for treatment of ocular inflammatory disease.
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