Lymphocyte response to phytohaemagglutinin after in vitro irradiation

An investigation into the response of in vitro irradiated human lymphocytes to phytohaemagglutinin (PHA) has demonstrated a decrease in the transformation index to 95, 56 and 38% of control (non-irradiated) lymphocytes following incremental doses of 625, 1250 and 2500 rad respectively, but antigen-induced mitogenesis or that in mixed lymphocyte culture appeared to be severly inhibited even following low radiation doses. Peripheral blood lymphocytes from eight healthy adult donors were examined after separation on a Ficoll-Hypaque gradient. The response to stimulation with specific antigens (Candida Albicans) or with allogenic lymphocytes was evaluated by measuring the uptake of 3H-thymidine from seven-day-old cultures. The results clearly showed that an almost complete suppression in lymphocyte reactivity had occurred after a dose of 625 rad. Possible explanations are discussed. (U.K.)