Lymphocyte subclasses and immunoglobulins in adults receiving radiation treatment in infancy for thymic enlargement.

One-hundred and fifty-three subjects who were irradiated in infancy for an alleged enlarged thymus and 51 controls were studied to quantify the phenotypically different subpopulations of peripheral blood lymphocytes and immunoglobulins. These subjects were selected from a larger cohort which has been followed prospectively since the early 1950s. Previous studies of this cohort have shown a radiation dose-related increased risk of thyroid carcinomas and adenomas in the irradiated group as well as a recent excess of various extrathyroid neoplasms. In this substudy, no significant differences in lymphocyte subpopulations or immunoglobulin levels were observed between the irradiated and control groups. These findings support a hypothesis that the radiation-related excess of neoplasms in this cohort may have resulted from direct cellular damage with subsequent mutations rather than impaired immune function.