EFFECTS OF ULTRAVIOLET-B EXPOSURE ON THE RESISTANCE TO LISTERIA-MONOCYTOGENES IN THE RAT

A rat infection model using the bacterial pathogen Listeria monocytoge nes was employed to analyze the immunosuppressive activity of UVB radi ation. Rats were exposed to suberythemal doses of UVB radiation for 5 or 7 consecutive days, using Kromayer or FS40 lamps respectively. Subs equently, the rats were infected subcutaneously or intravenously with Listeria. Exposure to UVB resulted in an increased number of bacteria in the spleen 4 days after infection. Listeria-specific lymphocyte pro liferation assays as well as delayed-type hypersensitivity reactions d emonstrated that T cell-mediated immunity to Listeria was impaired by UVB as measured 4 and 8 days after infection. In addition, UVB exposur e decreased phagocytotic activity of peripheral blood macrophages. Thi s study demonstrated that suberythemal doses of UVB radiation caused a delay in the clearance of Listeria bacteria from the spleen of the ra ts and that this was probably caused by impaired nonspecific phagocyto sis of Listeria by macrophages in addition to an impaired activity of Listeria-specific T cells.