Immunohistology of human thymomas.

We analyzed lymphocyte surface markers in seven thymomas. In six mixed thymomas, the staining patterns were similar for T11, OKT8, OKT6, OKT4, Coulter clone T4, and Leu 3a/3b. Staining patterns for Ia and keratin showed a dendritic pattern. Occasional S 100-positive interdigitating dendritic cells were identified. In three patients with associated myasthenia gravis, no significant differences in staining patterns were identified. A different pattern was seen in a patient with hypogammaglobulinemia, red blood cell aplasia, and a spindle cell thymoma: T11-, T8-, and T6-positive cells each comprised 70% to 80% of the tumor; but, cells of the helper/inducer phenotype differed when measured with OKT4 antibody (0%) vs Coulter clone T4 antibody (60%) and Leu 3a/3b (60%). This unusual phenotype, which was present on both tumor cells and peripheral T cells, appears related to the antigenic polymorphism of the T4 antigen and is believed to have no functional significance. Importantly, this discrepancy among commercial antibodies has significant implications in the general use of these reagents in clinical evaluations.