Class II MHC antigen expression by human keratinocytes results from lympho-epidermal interactions and gamma-interferon production.

Human peripheral blood lymphocytes were co-cultured with either allogeneic, autologous or purified protein derivative of tuberculin (PPD) pulsed autologous epidermal cells. In these mixed skin cell-lymphocyte culture reactions (MSLR), lymphocytes are stimulated to proliferate by epidermal cells. The supernatants of MSLR were examined for their capacity to induce class II MHC antigen expression on separately cultured epidermal cells. It is shown that supernatants from allogeneic and PPD pulsed autologous MSLR contained the factor(s) which stimulated HLA-DR antigen synthesis and expression by 30-40% of cultured epidermal cells. Kinetic analysis revealed a production rate maximum between 72 and 96 h of lympho-epidermal co-cultures. The factor mediating the induction of HLA-DR antigen expression on epidermal cells is thought to be gamma-interferon, because it was sensitive to pH 2 as well as heat incubation. Furthermore, anti-gamma-interferon monoclonal antibody abolished its activity. It is proposed, that HLA-DR antigen expression by keratinocytes observed in vivo in different dermatological inflammatory disorders originates from lympho-epidermal interactions and local gamma-interferon production as documented here in experiments in vitro.