Rheumatoid arthritis (RA) is a chronic, inflammatory, systemic autoimmune disease of the joints . CD4+ T cells are predominant in the synovial tissue with increased number of CD8 effector and memory T cells in synovial fluid and tissue of RA patients . CD8 functions as a dimer; including homodimer CD8αα and heterodimer CD8αβ . CD8αβ is a superior T-cell co-receptor that enhances functional avidity, CD8αα functions as a TCR corepressor to negatively regulate T cell activation . CD8αα T cells are found in human intestine and peripheral blood . CD8αα T cells increased markedly in the lesions of psoriasis where they played a pro-inflammatory role . The lower percentage of CD8αα+ mucosa associated-invariant T (MAIT) cells was found to be associated with MAIT cell dysfunction in gut immunity in necrotizing enterocolitis patients . T cells express the CD8β chain either at a high (CD8βhigh) or low density (CD8βlow ). There was a relative increase in CD8βlow cells in patients with SLE which were associated with an increased disease activity . Double positive (DP) T lymphocytes, include CD4CD8αβhigh and CD4CD8αα T cell subsets in the human blood . DP8α cells decreased in the blood and colonic mucosa of patients with inflammatory bowel disease compared with healthy individuals . CD4CD8αβhigh T cells are present at higher frequencies in some auto-immune diseases . Whether CD8αα or CD8αβ T cells contribute to the pathogenesis of RA, has not been clarified so far. investigators hypothesize that, an alteration in the frequency and distribution of these T cell subsets in RA patients might be associated with disease activity
To evaluate the changes in the frequencies of circulating CD4+ and CD4- T cells expressing CD8αα and CD8αβ in peripheral blood of RA patients in comparison with healthy controls. Also, to correlate circulating and synovial fluid levels of these cells with disease activity score (DAS28) and other indices of disease severity.