The effect of ultraviolet radiation on early stages of activation of human lymphocytes: inhibition is independent of effects on DNA.

Low doses (30-84 ergs/mm2, 1 erg = 10(7) J) of ultraviolet radiation (UV) caused severe inhibition of the proliferation of human lymphocytes in vitro. Greatest inhibition was produced when resting cells were irradiated immediately prior to stimulation with concanavalin A (Con A); this was true whether activation was measured by the incorporation of labelled leucine, uridine, or thymidine. If UV was applied at 44 h after culture in presence of Con A, the incorporation of [3H]thymidine measured 4 h later was seen to be inhibited but transcription and translation were scarcely affected. UV, applied after the appearance of the Con A induced thymidine transport system, did not inhibit its function. The disaggregation of chromatin and increase in nuclear volume characteristic of, and essential to, the proliferative response of lymphocytes were completely inhibited if the cells were irradiated before mitogen was added to the cultures, but were unaffected if irradiation occurred after 16 h of culture in presence of Con A. Cells irradiated with 84 ergs/mm2 at the onset of culture with mitogen did not show the early increase of cation pump function which is a characteristic of stimulated lymphocytes, when this was measured by means of 86Rb uptake after 2-4 h culture. The mitogen-stimulated activation of cation pump function has previously been shown to be unaffected by concentrations of cycloheximide and actinomycin D which produce virtually complete inhibition of protein and RNA synthesis, respectively. The major inhibitory effect of UV treatment of lymphocytes at onset of culture with Con A is therefore not on DNA or on DNA synthesis, but on some component(s) of the early activation process, possibly at the cell periphery; inactivation of this component prevents cells from proceeding into later stages of the proliferative pathway.