Radioresistance of Phytohemagglutinin-Treated Normal and Leukemic Lymphocytes2

Abstract

The effects of phytohemagglutinin (PHA) and X rays on suspensions of lymphocytes from normal human blood incubated in small test tubes for 6 days at 37° C were studied. Viable cell counts of untreated control suspensions showed that 63 percent of the lymphocytes survived incubation. Incubation of purified suspensions of lymphocytes with PHA resulted in enlargement of many lymphocytes, formation of some lymphoblastoid cells, and a few mitotic divisions. Irradiation of blood cell suspensions killed many lymphocytes, so that only 10 percent survived 6 days after a dose of 75 r and 5 percent after 150 r. PHA-treated suspensions were irradiated with 75 to 2400 r. Many lymphocytes and transformed lymphocytes survived irradiation even with a dose of 1200 and 2400 r. It was concluded that addition of PHA protected lymphocytes against the cytotoxic effects of irradiation. Radio-protection of lymphocytes was observed whether the PHA was added at any time from 4 days before to 2 days after irradiation with 300 r. Blood lymphocytes from 3 of 6 patients with chronic lymphocytic leukemia showed little or no radioprotection with PHA. The morphologic reaction of lymphocytes from leukemic patients was usually less than that observed with normal lymphocytes. One of the 6 patients with chronic lymphocytic leukemia had blood lymphocytes resistant to X irradiation with 2400 r even without PHA.