Identification of human thymic epithelial cells with antibodies to thymosin alpha 1 in myasthenia gravis.

Thymosin-alpha 1 (alpha 1) is a potent thymic polypeptide hormone. Using anti-alpha 1 antibodies, we applied indirect immunofluorescence to human normal thymus of different ages and to hyperplastic, thymomatous, and "involuted" thymus of myasthenia gravis (MG) patients. Alpha 1 was localized only in the epithelial cells, lying singly, grouped, in Hassell's corpuscles, and proliferated in thymomas. Whereas normal thymuses and fewer and weakly stained cells, MG thymuses had many strongly positive epithelial cells; this was more evident in thymomas. Germinal centers were unstained. "Involuted" MG thymuses had small islands of brightly stained cells lying among the fatty tissue. In cultured thymuses from three MG patients, epithelial cells but not fibroblasts were brightly stained for alpha 1. Our findings (a) demonstrate the location, and presumably the origin, of alpha 1 to be the thymic epithelial cell; (b) suggest the possibility that excess alpha 1, because of its known effect on T-lymphocyte maturation and transformation of precursors to helper T-cells, may act pathologically to facilitate and perpetuate the dysimmune mechanism in MG; (c) may partially explain the beneficial effect of thymectomy in MG patients of any age; and (d) indicate that epithelial cells may be autonomous for the production of alpha 1 as evidenced by their alpha 1 positivity in culture.