Thymoma: an immunohistochemical study.

Four thymomas, two from patients with myasthenia gravis, were studied using a panel of monoclonal antibodies. Almost all the associated lymphocytes were T-cells with the common thymic lymphocyte phenotype, suggesting that the neoplastic epithelium can provide a microenvironment that retains or perhaps attracts immature T-cells. HLA-Dr antigens were expressed by some of the epithelial cells and many of the lymphoid cells in the perivascular space. The Leu-7 antigen was present on a subset of epithelial cells and had a highly variable expression in different thymomas. The percentage of lymphocytes bearing the OKT8-defined antigen appeared to be lower in patients with myasthenia gravis, while the expression of other markers did not appear to be consistently or significantly different. There did not appear to be marked differences in the lymphocyte subpopulations of thymomas with different morphology, and there was no evidence of differentiation of the thymomas into cortical and medullary areas.