A rheumatoid arthritis B cell subset expresses a phenotype similar to that in chronic lymphocytic leukemia.

An abnormal subpopulation of B cells expressing the T1 antigen, which is normally restricted to T cells, was demonstrated in the peripheral blood of 16 patients with rheumatoid arthritis. This T1+ B cell population accounted for a mean of 19.6% (upper limit 48%) of the circulating B cells and did not correlate with clinical disease activity, rheumatoid factor, or drug treatment. The highest percentage of T1+ B cells found in the blood of 8 patients with connective tissue diseases, including systemic lupus erythematosus, was 5% of the B cells, and for normal controls, it was was 3% of the B cells. As previously reported, we confirmed that the T1+,Ig+ phenotype was a feature of leukemic cells in B-type chronic lymphocytic leukemia. The finding of increased numbers of T1+ B cells in patients with rheumatoid arthritis and those with B-type chronic lymphocytic leukemia raises the possibility that these cells play a role in a spectrum of diseases, including those involving autoimmunity and malignancy.