Studies on the thymus from patients with multiple sclerosis and myasthenia gravis.

The thymus glands which were excised for therapy (myasthenia gravis; MG) or experimental therapy (multiple sclerosis; MS) were compared to thymic biopsies from patients undergoing cardiac surgery. There was no difference in the weight or total cells of MG and MS thymuses or of the cell density of control, of MG or MS glands. Only 1 of 25 MS thymuses was hyperplastic, as were 2 of 9 of the MG thymuses and none of the controls. Several differences were noted for thymic lymphocyte proliferation to mitogenes in MS patients and to antigens in MS and MG patients. Ms thymuses had a decreased stimulation index to antithymocyte globulin and to optimal concentrations of pokeweed mitogen. Myasthenia gravis thymuses showed a significantly increased stimulation of myelin basic protein. The % B and % T cell counts were normal for the MS patients. No differences were noted in the incidence of mixed lymphocyte reactions between thymocytes and peripheral lymphocytes in the three groups. Fresh thymic lymphocytes did not suppress concanavalin A stimulated lymphocyte proliferation. It is not known if the differences in lymphocyte proliferation between MS, MG, and control thymuses represent a primary or secondary change.