Commensal microbiota as possible pathobiont in autoinflammatory disease

Abstract

Purpose : Our previous findings in mice demonstrated that ocular surface microbiome contributes to maintenance of local immune homeostasis in healthy individuals through IL-17 that is produced by γδ T cells. Cryopyrin Associated Periodic Syndrome (CAPS) is a systemic inflammation due to overactive NLRP3 inflammasome, causing excess of IL-1β, and downstream, of IL-17. Patients also suffer from severe conjunctivitis. We investigated whether beneficial ocular surface commensal flora can cause pathology in individuals with a dysregulated immune response.

Methods : Eyes of Balb/C and C57BL/6J mice bearing a mutated NLRP3 gene cloned from a CAPS patient were colonized with the commensal Corynebacterium mastitidis (C. mast). Ocular inflammation was assessed as conjunctivitis and immune cell infiltration. In addition, we analyzed ocular surface cells collected from CAPS patients by impression cytology and stimulated their PBMCs with C. mast in vitro. Conjunctival immune cells and PBMCs were characterized by flow cytometry and single cell transcriptomics using a droplet-based platform.

Results : γδ T cells were the major producers of IL-17 at the ocular surface with some contribution by αβ T cells and ILCs. C. mast colonization of previously negative CAPS mice increased conjunctival neutrophilia, and in some cases progressed to overt conjunctivitis. Expression of Il17a, cd69, ccr2 and s100a8 was upregulated in γδ T cells of C. mast colonized CAPS mice, suggesting activation and enhanced chemotactic ability. Notably, C. mast upregulated IL-17 production and expression of RORC, BATF and STAT3 in PBMCs from some CAPS patients compared to controls (C. mast status of subjects unknown). However, analysis of patient immune cells identified expression of genes consistent with IL-17 production in αβ T cells more than in γδ T cells. In addition, C. mast strongly upregulated interferon-related genes (IRF1, STAT1) in immune cells of CAPS patients.

Conclusions : Our results suggest that commensals can elicit an exaggerated response in immune cells of humans and mice with NLRP3-related autoinflammatory disease. While mice appear to use γδ T cells to respond to the commensal C. mast with IL-17 production, in patients this role may be taken on by other cells, or other commensals may be the stimulus. If indeed the conjunctivitis in CAPS patients reflects a response to their own commensals, adjunct antimicrobial therapy may be considered.

This is a 2020 ARVO Annual Meeting abstract.