The destruction of peripheral-blood lymphocytes by extracorporeal exposure to ultraviolet radiation

Venous blood from healthy adult human donors was circulated through a wholly extracorporeal circuit for periods up to 140 min without apparent damage to the lymphocytes. However, when the blood was exposed to short-wave ultraviolet radiation (UVC; lambda, 254 nm), separated mononuclear cells showed a depressed response to mitogen stimulation: the magnitude of this effect was related to the duration of exposure. This depression cannot be attributed to change in blood pH, partial pressures of oxygen and carbon dioxide, temperature of cell trauma. Plasma from irradiated blood was less satisfactory than non-irradiated plasma for the support of growth of phytohaemagglutinin-stimulated lymphocytes in culture, probably because of depletion of essential nutrients, and there was little evidence for the generation of growth-inhibitory humoral factors. The UVC-irradiated lymphocytes had normal ultrastructure when removed from the extracorporeal circuit, but underwent apoptosis and necrosis during the first day of tissue culture with or without mitogen stimulation.