Phenotypic and functional characterization of T cells from patients with myasthenia gravis.
 A study of cell surface phenotypes of PBL of myasthenia gravis (MG) patients showed that their T cells had a significantly higher percentage of 4B4+ T cells (the helper/inducer subset) than age- and sex-matched controls.
 The PBL of MG patients proliferated significantly higher than those of normal subjects (NS) in response to the purified alpha chain of the acetylcholine receptor (AChR).
 Anti-AChR antibody was present in sera of 88% of MG and none of the NS.
 The PBL B cells from MG only, when cultured with autologous T cells and stimulated with either pokeweed mitogen (69%), or AChR-alpha chain (38%), secreted antibody to AChR-alpha chain, whereas T and B cells alone secreted no antibody.
 T cells from PBL of MG patients were more readily cloned than T cells of NS, by limiting dilution, in the presence of recombinant IL-2 and in the absence of AChR-alpha chain.
 About 50% of T cell clones from MG patients, compared to none from NS, proliferated to AChR-alpha chain.
 This response was HLA-DR restricted.
 MG T cell clones did not display significant cytotoxic activity, as compared to control T cell clones.
 Our results indicate that in MG, 4B4+ regulatory T cells play their role in the pathogenesis of MG, not by cytotoxicity, but more likely by their ability to stimulate specific antibody production by B cells.
