Defective mitogenic responses in myasthenia gravis and multiple sclerosis

Using in vitro lymphocyte proliferation induced by the phytomitogen concanavalin A (ConA), we investigated immune function and regulation in patients with myasthenia gravis (MG) and multiple sclerosis (MS). Unfractionated peripheral blood mononuclear cells of normal individuals responded to a wide range of ConA concentrations; the T cell fraction responded to a lesser degree and only to high concentrations. These findings suggest the presence of two receptors for ConA, one of high affinity present on a non-T cell accessory cell and the other of low affinity present on T cells. Contrasting defects in the level of response of unfractionated lymphocytes and T cells were found in patients with MG and MS. The peak response of T cells in the MG patients was 22.6 ± 9.6 x 10³ cpm (mean ± SEM) compared with 54.6 ± 6.5 x 10³ for controls (p < 0.05), while the response of unfractionated lymphocytes did not differ from that in controls. For MS patients, the unfractionated lymphocyte response was diminished; 56.3 ± 2.8 x 10³ cpm versus 70.5 ± 4.5 x 10³ for controls (p < 0.05), while the T cell response was normal. These results indicate a defect in the direct T cell response in MG; in contrast, in MS the response requiring T cell-accessory cell interaction is abnormal.