Early and late effects of irradiation for seminoma testis on the number of blood lymphocytes and their B and T subpopulations.

High voltage irradiation of the iliac and paraaortic lymph nodes for seminoma testis induces a grave, acute blood lymphocytopenia. A major part of this effect is probably caused by irradiation of the blood. Indications are presented that B lymphocytes are more gravely affected than T lymphocytes. It is possible that the treatment leaves a relatively radioresistant subpopulation of lymphocytes, mostly consisting of T lymphocytes. The total number of blood lymphocytes is normalized five to ten years after treatment. Six months after treatment the percentage of B lymphocytes is clearly higher than normal, remaining so for the first three years. The percentage of T lymphocytes is unchanged both during therapy and at all intervals thereafter. The results therefore indicate that the number of B lymphocytes is more rapidly normalized after radiotherapy than that of T lymphocytes, and that the post-irradiation lymphocytopenia is mainly a T lymphocytopenia. However, this shift in B/T lymphocyte ratio is not permanent, being completely or nearly normalized after ten years. This pattern of regeneration seems to be essentially the same in patients who have received additional treatment to the mediastinum, probably meaning that the thymus has only a marginal influence on the regeneration of T lymphocytes in the adult organism. It is possible that the rapid recovery of B lymphocytes relates to the ability of the bone marrow to extend into non-irradiated parts of the skeleton after radiation destruction.