Perturbed Mucosal Immunity and Dysbiosis Accompany Clinical Disease in a Rat Model of Spondyloarthritis

Objective: The HLA–B27/β₂-microglobulin (β₂m)–transgenic (Tg) rat is a leading model of B27-associated spondyloarthritis (SpA), and the disease is dependent on the presence of intestinal bacteria. Previous studies have shown that adult HLA–B27/β₂m–Tg rats have an altered intestinal microbiota. This study sought to better define the age-dependent changes to both mucosal immune function and dysbiosis in this rat model of SpA. Methods: Intestinal contents were collected from wild-type and HLA–B27/β₂m–Tg rats postweaning (ages 3 and 6 weeks), at disease onset (age 10 weeks), and after the establishment of disease (ages ≥16 weeks). The microbial community structure was determined by 16S ribosomal RNA sequencing and quantitative reverse transcription–polymerase chain reaction (qRT-PCR). Mucosal and systemic Th1, Th17, and Treg cell responses were analyzed by flow cytometry, as was the frequency of IgA-coated intestinal bacteria. Intestinal expression of inflammatory cytokines and antimicrobial peptides (AMPs) was determined by qRT-PCR. Results: An inflammatory cytokine signature and elevated AMP expression during the postweaning period preceded the development of clinical bowel inflammation and dysbiosis in HLA–B27/β₂m–Tg rats. An early and sustained expansion of the Th17 cell pool was specifically observed in the cecal and colonic mucosa of HLA–B27/β₂m–Tg rats. Strongly elevated intestinal colonization of Akkermansia muciniphila and an increased frequency of IgA-coated fecal bacteria were significantly associated with expression of HLA–B27 and arthritis development. Conclusion: HLA–B27/β₂m expression in this rat model renders the host hyperresponsive to microbial antigens from infancy. Early activation of innate immunity and expansion of a mucosal Th17 signature are soon followed by dysbiosis in HLA–B27/β₂m–Tg animals. The pathologic processes of perturbed mucosal immunity and dysbiosis strongly merit further study in both prediseased and diseased populations of patients with SpA.