The innate immune receptor Nlrp12 participates in protection against experimental autoimmune uveitis

Abstract

Purpose : Pathogen recognition receptors (PRRs) are crucial for host defense against infection via their ability to detect an array of microbes. The Nod-like receptor (NLR) Nlpr12 (Monarch) has been shown to negatively regulate inflammation but under some circumstances can activate the inflammasome in response to specific pathogens. Here, we sought to determine whether Nlrp12 plays a role in ocular immune responses in the context of experimental autoimmune uveitis (EAU).

Methods : Expression of Nlrp12 in dissected ocular tissues of healthy mice was evaluated by quantitative real-time PCR. To investigate the contribution of Nlrp12 to ocular inflammation, uveitis induced by immunization with interphotoreceptor retinoid-binding protein (IRBP) peptide _1-20 was compared in mice deficient in Nlrp12 (KO) vs. wild-type (WT) mice. Disease was assessed by clinical fundus examination and by histology up to day 28. Flow cytometric analysis of uveitic eyes was used to determine how Nlrp12 affects cellular composition of the ocular infiltrate. Analysis was performed on CD45+ gated events (leukocytes) to determine cell numbers and frequencies.

Results : We observed relatively high constitutive expression of Nlrp12 within the retina and RPE/choroid complex that was comparable to levels in the spleen or cornea. The iris/ciliary body showed minimal Nlrp12 expression. KO mice developed more severe EAU (p<0.05 vs. WT mice; n=10 mice/group) manifesting as extensive retinal damage, vasculitis and photoreceptor ablation. WT and KO mice immunized with adjuvant alone did not show signs of disease (n=8 mice/group), supporting antigen-specific control of Nlrp12. Flow cytometry revealed increased numbers of CD45+ cells in KO vs. WT eyes that consisted predominantly of CD11b+ myeloid cells (~60% of CD45+ gated cells). Of these cells, macrophages (F4/80+/Gr1^low) and neutrophils (Gr1^high/F4/80-) were significantly more numerous in KO mice vs. WT (n=8 mice/genotype).

Conclusions : These studies identify Nlrp12 as an essential PRR in protection against eye-specific autoimmunity. This function may be due in part to its ability to control the magnitude of myeloid cellular responses. Understanding of Nlrp12 in uveitis may suggest new approaches for treatment by exploitation of host protective responses.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.