Inhibition of human lymphocyte proliferation by ultraviolet radiation: effects of ultraviolet B (290 to 320 nm) on T-lymphocytes, monocyte accessory function, and induction of suppressor mechanisms.

In vitro exposure of peripheral blood lymphocytes (PBLs) to doses of ultraviolet radiation (UVR) achievable during recreational sun exposure produces profound inhibition of lymphocyte blastogenesis. This study demonstrates that this inhibition is mediated by a direct dose-dependent effect on populations enriched for T-lymphocytes and is reversible after incubation of responder cells with phytohemagglutinin (PHA). In contrast, monocyte accessory function for both antigen- and mitogen-induced proliferation is relatively unaffected by in vitro exposure to UVR at doses up to 30 mJ/cm2. Exposure of PBL to UVR also results in the induction of a suppressor mechanism that inhibits the proliferation of unirradiated PBLs. In vitro exposure of human blood cells to UVR may provide a valuable tool for examining the cellular basis for the immunosuppressive effects of UVR.