Effect of Radiotherapy on Natural Killer Activity in Childhood Acute Lymphoblastic Leukemia and Lymphoma

Natural killer (NK) activity was increased after 24 Gy prophylactic cranial irradiation in childhood acute lymphoblastic leukemia (ALL), although there was no change in the percentage and the number of CD16 (Leu 11)(+) cells. NK activity as well as the percentage and the number of CD16(+) cells was not decreased in malignant lymphoma children treated with high doses of cervical irradiation (20 Gy <). A single dose of 20 Gy irradiation to lymphocytes augmented NK activity 1.4-fold in vitro in healthy individuals. Radiosensitive concanavalin A-induced suppressor T cells did not play a role in the suppression of NK activity, indicating that the enhanced NK activity induced by irradiation was not due to irradiation-induced impairments of suppressor T cells. The supernatants from irradiated lymphocytes slightly enhanced NK activity. In conclusion, the augmentation of NK activity by irradiation seems to be due to its direct effect on NK cells, not via NK suppressor cells but perhaps humoral factors play some role in this respect.