Intrathymic lymphoid cell differentiation in myasthenia gravis: an immunophenotypic study.

Thymocytes express multiple different surface antigens according to their stage of maturation. We studied lymphocyte surface differentiation antigens using direct immunofluorescence technique in the thymus of 20 patients with myasthenia gravis (MG) and 10 controls undergoing cardiac surgery. Fluorescein isothiocyanate-conjugated monoclonal antibodies were used to stain thymic cell surface antigens. We found a decrease in the percent expression of CD1, CD5, and CD7 surface antigens and a significant increase of CD20+ cells in myasthenic thymus compared with the controls. The changes in the percent expression of CD3, CD4, and CD8 antigens were not significant. These data suggest both the decrease in the immunophenotypes corresponding to cortical thymocytes (probably reflecting the cortical atrophy of the MG thymus) and the increase of mature B Cells (CD20+), which may participate in an active immune response.