ULTRAVIOLET-RADIATION REDUCES PHAGOCYTOSIS AND INTRACELLULAR KILLING OF MYCOBACTERIA AND INHIBITS NITRIC-OXIDE PRODUCTION BY MACROPHAGES INMICE

Exposure of mice to a single or multiple low doses of ultraviolet radi ation (UVR) decreases the induction of the delayed-type hypersensitivi ty (DTH) response to Mycobacterium bovis BCC and Mycobacterium lepraem urium (MLM) and impairs the clearance of bacteria from the lymphoid or gans, This study is an attempt to address the mechanism by which UV ra diation impairs the clearance of bacteria from the lymphoid organs by determining whether alterations in macrophage function such as ingesti on and intracellular killing of mycobacteria or production of reactive nitrogen intermediates might be responsible for these effects. BALB/c or C3H/HeN mice were exposed to a single dose of UVB (280-320 nm) rad iation ranging from 0.35 to 45 kJ/m(2), and at regular intervals after irradiation, the peritoneal and splenic macrophages were collected, c ultured, and infected with live BCG or MLM, Phagocytosis was assessed at 6 h by counting the number of acid-fast bacteria per macrophage aft er Ziehl-Neelsen staining, The rate of intracellular killing was asses sed by lysing the macrophages at 6, 12, 24, and 48 h after BCG infecti on, plating the suspension on 7H11 agar, and counting the number of co lony-forming units 21 days later, Similarly, the nitric oxide producti on, as measured by nitrite, by macrophages obtained from UVB-irradiate d and nonirradiated mice in response to BCG was assessed, There was a significant reduction in the uptake of organisms by both peritoneal an d splenic macrophages collected from UV-irradiated mice, The intracell ular killing of organisms was also significantly reduced, as was the p roduction of nitric oxide by peritoneal macrophages infected with BCG in vitro. These results indicate that UVR affects macrophage functions and are consistent with our hypothesis that impaired clearance of bac teria in vivo results from an alteration in macrophage function.