Immunohistochemical study of thymic B cells in myasthenia gravis and ulcerative colitis.

Abstract

The phenotypes of B cells and dendritic cells in human thymus were examined immunohistochemically using various monoclonal antibodies. Normal thymus contained a few B lymphocytes recognized by CD19, CD20, CD22, L26 and LN-2, which were localized in the medulla. These B cells were negative for LN-1, L30 and CD11c (Leu M5). Activated B cells recognized by CD23 (B6) and L29 antibodies were not present in normal thymus. Dendritic cells stained by CD11c were weakly positive for L26 and CD20. There was no difference in the distribution of dendritic cells between normal thymus and thymus from the patients. In the thymus from patients with myasthenia gravis, numerous B cells were demonstrated in the medullary area and lymphoid follicles. Activated B cells were seen mainly in the germinal center of lymphoid follicles and were scarce in the medulla. Many B cells were also found in the medulla and lymphoid follicles of the thymus from patients with ulcerative colitis. However most of those B cells were not activated, even in the lymphoid follicles. These results suggest that thymic B cells may contribute to the induction of immune abnormalities in patients with myasthenia gravis and those with ulcerative colitis, however, the mechanisms by which thymic B cells participate in the pathogenesis of these two diseases would be different.