To investigate the membrane expression of the 52 kDa Ro(SS-A) and La(SS-B) antigens in human keratinocytes under the influence of an important mediator of inflammation, TNF alpha. Keratinocytes, isolated from human skins obtained at circumcision and identified using monoclonal antibodies, were treated with tumour necrosis factor alpha (TNF alpha) and incubated with antibodies to 52 kDa Ro(SS-A) isolated and purified from patients with systemic lupus erythematosus or Sjögren's syndrome, with mouse monoclonal antibody to La(SS-B), and (as controls) with sera from normal healthy blood donors and a mouse monoclonal antibody to U1RNP 68 kDa. Membrane expression of the 52 kDa Ro(SS-A) and La(SS-B) antigens was detected using cyto enzyme linked immunosorbent assays (ELISAs), laser scanning microscopy, and indirect immunofluorescence. After the incubation with TNF alpha, cyto ELISA revealed a significantly increased membrane binding of 52 kDa Ro(SS-A) antibodies, with a maximum after two hours, followed by enhanced 52 kDa Ro(SS-A) expression during the subsequent 24 hours. The La(SS-B) antigen was expressed rapidly after TNF alpha treatment (within one hour), with a fast decrease to the preincubation value within three hours. Indirect immunofluorescence with fixed normal human keratinocytes confirmed increased 52 kDa Ro(SS-A) and La(SS-B) antigen expression after the incubation with TNF alpha. TNF alpha mediates 52 kDa Ro(SS-A) and La(SS-B) autoantigen surface expression on human keratinocytes, and may be an important factor both in antibody induction and in the initiation of immunopathogenic processes which occur after antibody binding in autoimmune dermatitis.