Reactive arthritis (ReA), a HLA-B27 associated arthropathy, develops in susceptible people after infection with certain bacteria. T cells have been implicated in the pathogenesis of the arthritis but which of the different subsets is involved is still debated. This study has further elucidated the role of the CD4+ and CD8+ T cells by examining the expression of various surface markers associated with activation.
Three colour flow cytometry was used to examine the phenotype of the T cells within the synovial fluid (SF) and peripheral blood (PB) of ReA patients.
ReA SF, compared with paired PB, contained a higher percentage of CD69+, CD25+, and HLA-DR+ CD3+ T cells. The majority of SF T cells also expressed the putative memory marker CD45RO. Within the T cell subsets, CD25 was expressed primarily on the CD4+ T cells; however more CD8+ T cells were HLA-DR+.
The results show that both CD4+ and CD8+ T cell populations demonstrate evidence of recent activation. Whether these cells are involved in inducing inflammation, regulating the inflammation, or have become active as a result of migration through the endothelium, remains to be determined by functional studies.