Subpopulations of lymphocytes in human thymomas.

Lymphocyte populations in six normal thymuses and ten thymomas were examined. The majority of lymphocytes from both thymus and thymoma differ from peripheral T lymphocytes in their capacity to form E-rosettes resistant to incubation at 37 degrees C. Low percentages of T lymphocytes bearing receptors for the Fc portion of IgG (TG) and IgM (TM) were found in normal thymus. In contrast, lymphocytes from five out of nine thymomas showed remarkable percentages of TM cells. Compared with normal thymocytes, lymphocytes from seven out of ten thymomas responded vigorously to mitogens. The possible origin and nature of thymoma lymphocytes are discussed.