The frequency of CD5+ B lymphocytes in the peripheral blood of patients with myasthenia gravis.

A subset of human B lymphocytes expresses Leu-1 (CD5), a pan-T cell marker, which is the equivalent of the murine Lyt-1 molecule. CD5+ B cells produce autoantibodies in vitro; therefore, they may play a role in the pathogenesis of autoimmune disorders. In myasthenia gravis (MG), autoantibodies are directed against the nicotinic acetylcholine receptor (AChR) at the neuromuscular junction. We examined the peripheral blood leukocytes of MG patients (n = 21) and controls (n = 15) for the presence of Leu-1+ B lymphocytes. A fraction of B-1 (CD20)+ cells expressed Leu-1 at a low density. There was a statistically significant difference in the frequency of Leu-1+ B cells between patients and controls. We observed 2 frequency ranges of Leu-1+ B cells (0 to 30% and above 30%), which were not related to the total percentage of B-1+ cells in the blood. Fifty-seven percent of MG patients had a high frequency of Leu-1+ B cells compared with 13% of controls.