Relations between absolute number of CD4 + CD29+ memory cells and levels of interleukin-6, rheumatoid factors, and acute phase proteins in rheumatoid synovial fluid.
Synovial fluid samples from 21 rheumatoid arthritis patients were analyzed for lymphocyte subsets using flow cytometry and antibodies to the lymphocyte surface antigens CD3, CD4, CD8, CD16, CD19, CD29, and CD45RA. Synovial fluid levels of interleukin-6, rheumatoid factors and acute phase proteins were also measured. Depletion of CD45RA+ cells and predominance of CD29+ cells were found. Interleukin-6 levels were markedly elevated (1155 pg/ml; range, 24-3875 pg/ml), as were levels of IgM, IgG and IgA rheumatoid factors and of acute phase proteins. CD4 + CD29+ counts were significantly correlated with interleukin-6 levels. Interleukin-6 levels were significantly correlated with levels of all three rheumatoid factor classes but not with levels of acute phase proteins. Significant correlations were also found between CD19+ B counts and levels of all three rheumatoid factor classes. These data suggest that synovial fluid CD4 + CD29+ cells may be involved in the immune dysregulation characteristic of rheumatoid arthritis. The correlation between CD4 + CD29+ counts and interleukin-6 levels is consistent with the recent hypothesis that, together with monocytes, CD4 + CD29+ cells are an important source of the elevated levels of interleukin-6 seen in rheumatoid synovial fluid.