THE CYTOTOXIC EFFECT OF NEONATAL LUPUS-ERYTHEMATOSUS AND MATERNAL SERA ON KERATINOCYTE CULTURES IS COMPLEMENT-DEPENDENT AND CAN BE AUGMENTED BY ULTRAVIOLET-IRRADIATION

To elucidate the role of autoantibodies and ultraviolet (UV) exposure in the pathogenesis of the skin lesions in neonatal lupus erythematosu s (NLE), keratinocytes were cultured, as the target cells, from a pati ent with NLE and from a normal neonate, We demonstrated that the expre ssion of nuclear/cytoplasmic Ro/SSA and La/SSB molecules on to the sur face of NLE keratinocytes occurred to a much greater extent than that on normal keratinocytes. A dose of 200 mJ/cm(2) UVB irradiation on NLE keratinocytes induced a 2.5-3-fold increase in Ro/SSA and La/SSB expr ession compared to non-irradiated cells, Sera derived from both the NL E patient and from his mother exhibited a cytotoxic effect on NLE kera tinocytes, but not on control cells, in the presence of complement, Fu rthermore, the cytotoxicity of the sera was enhanced on UVB-irradiated NLE keratinocytes, whereas it had no cytotoxic effects on UVB-irradia ted control cells. This suggests that the abnormal expression of both Ro/SSA and La/SSB on the surface membrane of NLE keratinocytes induces the autoantibodies and complements to injure the cells. This compleme nt-mediated cytotoxic effect can be augmented by UV irradiation, a con cept not incompatible with the exacerbation of the skin eruption in su n-exposed skin sites.