Expression and function of CD5 and CD28 in patients with rheumatoid arthritis

To assess the role of CD5 and CD28 in the pathogenesis of the decreased cellular immune function in patients with rheumatoid arthritis (RA) we analysed the expression and function of these T-cell surface molecules. The expression of CD5 as well as of CD28 in synovial and peripheral blood T cells was similar to that of control T cells. Monoclonal antibodies (mAb) directed at CD28 and CD5 were able to provide an accessory signal to anti-CD3 activated T cells both from the synovial fluid and from the peripheral blood. However, the proliferation induced by anti-CD3 mAb in conjunction with anti-CD5 or anti-CD28 mAb was always higher in peripheral blood (PB) T cells compared to the paired synovial fluid T cells. After simultaneous ligation of CD5 and CD28, proliferation was induced in the PB T cells. However, when compared to control PB T cells, this proliferation was significantly lower in the RA patients. Purified normal memory (CD45RO+) T cells proliferated less strongly than naive (CD45RA+) T cells, but no difference was observed between rheumatoid and normal memory T-cell proliferative responses. However, enriched PB CD45RA+ T cells from rheumatoid patients proliferated less vigorously to CD5 and CD28 ligation when compared to normal enriched CD45RA+ T cells. Synovial fluid (SF) T cells, which are mainly of the memory cell type, did not proliferate after simultaneous ligation of CD5 and CD28. This refractory state of synovial T cells could not be explained by a difference in the surface expression of CD5 or CD28. Our data suggest that the cellular immune dysfunction in the PB from rheumatoid patients may be due to a decreased responsiveness of the naive T-cell subset to accessory signals provided by CD5 and CD28. In addition, SF T cells appear hyporesponsive to stimulating signals provided through CD5 and CD28.