The CD5+ B cells and myasthenia gravis.

A high frequency of CD5+ B lymphocytes in the peripheral blood of patients with myasthenia gravis (MG) has been reported recently. These results seem to indicate an attractive linkage between CD5+ B lymphocytes and autoantibodies against Acetylcholine receptor in MG. We examined the frequency of CD5+ B cells in 20 patients with MG and 21 normal healthy controls by two-color flow cytometry. However, there were no significant differences in the percentages of CD5+ B lymphocytes between the two groups. We also examined the frequency of CD5+ B lymphocytes in the resected thymus of patients. The frequency of CD5+ B lymphocytes in the thymus was low and similar pattern to that in the peripheral blood. We checked the antibody (Ab) production against the human acetylcholine receptor in either CD5+ B or CD5- B lymphocytes using B lymphoblastoid cell line generated from the lymphocytes of 11 patients with anti-AChR Abs in the sera. Abs against the AChR in the human were mostly produced by CD5- B, not CD5+ B lymphocytes. The anti-AChR Abs (IgG) production of CD5+ B cells and CD5- B cells (mean +/- SD) were 6.8 +/- 2.4 fmol/ml and 18.5 +/- 17.6 fmol/ml, respectively. These results suggest that in MG, the frequencies of the CD5+ B lymphocytes in PBL may be genetic background and that there may be no strong linages between AChR Ab production and CD5+ B lymphocytes.