SAT0349 CTLA4-IG DECREASES TH17 CELL LEVELS BUT MAINTAINS ILC3S WITH AN INCREASE IN THE ILC3/ILC1 RATIO IN THE GUT OF SKG MICE AS A MODEL OF SPONDYLOARTHRITIS.

Abstract

Background:SKG mice have been known for their autoreactive Th17 cells resulting from the insufficient thymic negative selection due to a Zap70 mutation1,2). Under specific pathogen-free conditions, they acquire features of spondyloarthritis (SpA) by intraperitoneal injection of curdlan, a (1,3)-β-glucan3). Several reports have shown that Th17 cells also increase in human SpA4). However, CTLA4-Ig, which ameliorates rheumatoid arthritis by suppressing pathogenic cells such as effector T cells, was unable to show adequate efficacy as much as expected in SpA patients5). Around the same time, innate lymphocytes began to be focused on, in the pathogenesis of SpA, including innate lymphoid cells (ILCs), which abundantly reside in the gut6).Objectives:This study aimed to clarify the effects of CTLA4-Ig on the pathogenesis of SpA by using curdlan-treated SKG mice, focusing on type 3 immunity such as Th17 cells and ILC3s.Methods:Two- to three-month-old female SKG mice were injected intraperitoneally with 3mg of curdlan or PBS at the beginning and with 500 µg of CTLA4-Ig or PBS every other week (n=5 per group). The body weight and arthritis score were measured weekly for a month. Then, the changes in the proportion of T cells and ILCs in the spleen and Peyer’s patches (PPs) were analysed by flow cytometry (FCM). BALB/c mice, without treatment, were also examined by FCM as a control cohort. In addition, a next-generation analysis of their feces was performed on 16S ribosomal coding genes before curdlan and CTLA4-Ig treatment.Results:SKG mice contained not only more Th17 cells but also more ILC1s and ILC3s than BALB/c mice, in their guts (the PPs). The feces of SKG mice intrinsically showed a decrease in the number of bacterial species, suggesting a dysbiosis. Then, in curdlan-treated SKG mice, CTLA4-Ig administration decreased the proportion of both Th17 cells and ILC3s in the spleen, but did not decrease the proportion of ILC3s in the PPs. Moreover, the ILC3/ILC1 ratio in the PPs was from low to high in the order of SKG mice without treatment, SKG mice injected with curdlan, and SKG mice injected with both curdlan and CTLA4-Ig. The phenotype corresponding to SpA features, in curdlan-treated SKG mice, continued after repeated CTLA4-Ig administration.Conclusion:Curdlan provoked SpA features in SKG mice with an intrinsic dysbiosis. Additional CTLA4-Ig injection decreased the proportion of Th17 cells but maintained that of ILC3s with increased ILC3/ILC1 ratio in the gut. This result supports the hypothesis that in the SpA pathophysiology, a weakened acquired immunity in the gut might lead to ILC3 activation, via dysbiosis, and its continuous disease progression, suggesting that ILC3s are a promising therapeutic target in SpA.