T-cell activation antigens and cytokine transcripts in osteoarthritis

Osteoarthritis (OA) often exhibits inflammatory infiltrates in synovial membranes (SM) but the importance of T cells In these infiltrates is not known. T-cell activation antigens were analyzed by immunohistochemistry and T-cell cytokine transcripts were measured by competitive PCR in SM from patients with OA and rheumatoid arthritis (RA). Lymphoid aggregates (>40 densely packed mononuclear cells) consisting primarily of CD3+ T cells were present In 65% of patients with OA. Mononuclear cells expressing the activation antigens CD69, CD25, CD38, CD43, CD45RO, and HLA-class II, were present in both patient groups albeit heavier in RA than OA. IL-2 transcripts were detected in 55.5% of OA specimens (vs 92.3% of RA: P=0.03), whereas IFN-y transcripts were detected in 50% and IL-10 transcripts in 88.9% of OA specimens (vs 76.9X and 92.3% of RA, respectively, NS). IL-4 and IL-5 were not detected in any patient. The levels of IFN-y were lower in OA compared to RA (p=0.01). SM that expressed IL-2 and IFN-y transcripts were more likely to have heavier infiltration of T cells and cells bearing activation markers than SM that did not express these cytokines (p<0.001). The detection of lymphoid aggregates and T cell activation markers and TH1 cytokine transcripts in OA chronic joint lesions suggests a cell-mediated immune response in a large proportion of OA.