CD5+ B-CELLS IN THE THYMUS OF PATIENTS WITH MYASTHENIA-GRAVIS

CD5+ B and coexisting T cells in the thymus of control individuals and patients with myasthenia gravis (MG) were analyzed with monoclonal antibodies in conjunction with a two-color immunofluorescence test. Similar to findings in a mouse study, we found that, in 9 control subjects, CD5+ B cells (mean: 1.5%) were the predominant subset (approximately 80%) among thymic B cells (1.8% of thymocytes). In patients with MG (n=6), both the proportion of CD5+ B (3.2%) and total B cells (7.8%) in the thymus were significantly elevated (P=0.005). In this regard, the ratio of CD5+ B / total B cells in MG (45%) was somewhat lower than in control subjects. This raises the possibility that some CD5- B cells are a CD5-sister population of CD5+ B cells in MG, as has been shown in mouse studies. Coexisting thymic T cells in MG were somewhat different (e.g., in exhibiting a reduction in the double-positive CD4+ CD8+ population) from those in controls. The reason for this finding is discussed with reference to recent findings of medullary T cells in the thymus. The present results might be intimately related to the pathogenesis of MG.