Inhibition of human lymphocyte stimulation by visible light and phthalocyanine photosensitization: mitogen and...

Mitogenic stimulation of human peripheral blood lymphocytes is inhibited by phthalocyanine photosensitization using visible light. The mechanism of inhibition was studied using stimulating agents differing in their mode of action. Stimulation by the plant lectin phytohemagglutinin (PHA) was the least sensitive to inhibition by photosensitization, followed by the tumor promoter phorbol myristate acetate (PMA) and the calcium ionophore A23187. Mitogenic stimulation could also be inhibited by light only, but higher fluences were needed. The order of efficacy was blue greater than red greater than green light, and the response to A23187 was least affected, followed by an increased inhibition of the response to PHA and PMA stimulation. Possible targets and mechanisms for these effects are discussed.