Double labelled T suppressor lymphocytes in the thymus of a patient with myasthenia gravis: morphological and immunological characteristics.

Double labelled lymphocytes were prevalent in the thymus of a 32-year-old woman with myasthenia gravis. The simultaneous presence of both E and C3b surface receptors was demonstrated. Focal paranuclear acid phosphatase activity of the cells supported their T cell origin. Histological analysis revealed a hyperplastic thymus with germinal centres in one lobe and an unusual transition to "thymoma-like" diffuse sheets of thymocytes and large thymic epithelial cells in the other lobe. Immunological studies of isolated cells from the "thymoma-like" region revealed a high percentage of E rosettes (96%), EAC rosettes (87%) and IgG-EA rosettes (60%). The large number of "active" rosettes (94%) indicated high avidity of receptors for sheep red blood cells. The postoperative accumulation of acid phosphatase positive T cells with C3b surface receptors in the peripheral blood was striking. These characteristics suggest that this cell population represents an activated T subset (TG) with a certain degree of immaturity similar to a particular stage of foetal T cell development (prothymocytes).