Integrin and transcriptomic profiles identify a distinctive synovial CD8+ T cell subpopulation in spondyloarthritis

Current evidence suggests that immune events in the gut may impact joint inflammation in ankylosing spondylitis (AS) but the expression of gut-related trafficking molecules in the inflammed joint is poorly characterised. We aimed to (1) assess differential expression patterns of trafficking molecules between patients and controls, (2) generate joint-specific cellular signatures and (3) obtain transcriptomic profiles of noteworthy cell subpopulations.

Male subjects under 40 years of age fulfilling the mNY criteria were recruited. The following cells were surface stained using a 36-marker mass cytometry antibody panel: (1) peripheral blood mononuclear cells from AS patients, and healthy controls; (2) synovial fluid mononuclear cells from AS and rheumatoid arthritis (RA) patients. Additionally, RNA-seq was performed on CD8+ T cell subpopulations from the synovial fluid (SF).

Mature CD8+ T cells were enriched in AS SF, with a distinct pattern of integrin expression (β7, CD103, CD29 and CD49a). RNA-seq analysis of SF-derived CD103+CD49a+CD8+ T cells revealed elevated TNFAIP3, GZMB, PRF1 and IL-10.

We have identified a novel integrin-expressing mature CD8+ T cell population (CD49a+CD103+β7+CD29+) that appears to be more prevalent in AS SF than RA SF. These cells seem to possess dual cytotoxic and regulatory profiles which may play a role in AS pathogenesis.