Phenotypic and functional features of CD5+ B lymphocytes in rheumatoid arthritis

Using flow cytometry B lymphocytes expressing CD5 were increased in the blood of 15 out of 31 patients with rheumatoid arthritis (RA). In contrast to the monoclonal CD5+ B lymphocytes in patients with B-chronic lymphocytic leukaemia, CD5+ B cells from RA patients and neonatal cord blood are polyclonal as demonstrated by kappa/lambda expression. These B cells co-express mu and delta heavy chains and are CD19, CD20, CD21 positive. Purified CD5+ and CD5- B cells appeared of similar size and granularity as judged by light scatter values. Staphylococcus aureus C stimulated cord blood B cells showed loss of CD5 antigen following activation and production of similar amounts of IgM-rheumatoid factor (RF). EBV stimulation of purified RA B subsets lead to greater production of IgM-RF by CD5+ B cells than by CD5-B cells suggesting an enrichment of precursor cells in this fraction.