Increased susceptibility to in vitro ultraviolet B radiation in fibroblasts and lymphocytes cultured from systemic lupus erythematosus patients

Sunlight is known to induce exacerbations of systemic lupus erythematosus (SLE) but its mechanism remains unclear. We have previously reported that ultraviolet A (UVA) exposure induces an increase in total DNA synthesis (DS) in vitro but a decrease in unscheduled DNA repair synthesis (UDRS) of splenocytes of murine SLE strains. In order to investigate whether similar observations are characteristic of human SLE, peripheral blood lymphocytes (PBL) and dermal fibroblast (DF) cultures of 20 patients and 15 matched controls were exposed in vitro to UVA or UVB at different doses. Thirteen (65%) SLE DF cultures exposed to UVB light (12–24 J/m 2) showed an increase in DS compared to paired unirradiated cultures. In contrast, UVB-irradiated DF from normal individuals had no significant increase in DS following UVB irradiation. When SLE DF were exposed to higher doses of UVB (48–96 J/m 2), 90% of cultures showed a decrease in DS compared to only 20% in the control group. All of the SLE DF cultures showed a decrease of their unscheduled DNA repair capacity following UVB (24–48 J/m 2) irradiation whereas no UDRS was apparent in 74% of controls under the same conditions. Similar findings regarding UDRS were observed in SLE PBL cultures and were also confirmed by autoradiography. UVA exposure (0–3840 J/m 2) had no effect on DS nor on UDRS in DF of PBL cultured from SLE and controls. The relevance of these in vitro findings to the in vivo pathogenesis of the disease is discussed.