Decreased expression of FcγRIII (CD16) by γδ T cells in patients withrheumatoid arthritis

Some gamma delta T cells express a receptor for the Fc portion of immunoglobulin G (Fc gamma RIII - CD16). The relevance of this Fc receptor to gamma delta T-cell function is at present unclear. Our previous studies have shown that gamma delta T cells express activation markers in patients with rheumatoid arthritis (RA). In this study we have examined the relative proportions of CD16(+) gamma delta T cells in the blood and synovial fluid of these patients compared with control blood. CD16(+) gamma delta T cells from RA patients were significantly reduced in synovial fluid compared with the circulation. That this was due to blocking of antibody binding to CD16 was unlikely as treatment of blood gamma delta T cells with RA synovial fluid (known to contain immune complexes) failed to alter expression of CD16. Treatment of blood gamma delta T cells with phytohaemagglutinin in vitro, resulted in a time-dependent decrease in expression of CD16, with a concomitant increase in expression of human leucocyte antigen-DR, at the single cell level. We conclude that expression of CD16 by gamma delta T cells is lost in the synovial compartment as the result of activation.