ULTRAVIOLET B-EXPOSED MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II POSITIVE KERATINOCYTES AND ANTIGEN-PRESENTING CELLS DEMONSTRATE A DIFFERENTIAL CAPACITY TO ACTIVATE T-CELLS IN THE PRESENCE OF STAPHYLOCOCCAL SUPERANTIGENS

In this study we tested the capacity of ultraviolet B (UVB)-irradiated major histocompatibility complex (MHC) class II+ keratinocytes, monoc ytes and dendritic cells to activate T cells in the presence of Staphy lococcus enterotoxin B, We demonstrated that UVB irradiation of MHC cl ass II+ keratinocytes does not change their capacity to activate T cel ls in the presence of Staphylococcus enterotoxin B. In contrast, UVB i rradiation of antigen-presenting cells decreases their capacity to act ivate T cells. This differential capacity to activate T cells after UV B irradiation was not due to factors released from UVB-irradiated cell s, The interferon-gamma induced upregulation of HLA-DR and intercellul ar adhesion molecule-1 on keratinocytes does not seem to be the only e xplanation, since UVB irradiation decreased the accessory cell functio n of interferon-gamma pretreated monocytes. Differential requirements for and UVB regulation of costimulatory molecules map be involved, sin ce blocking of the B7/CD28 pathway affects the capacity of dendritic c ells but not keratinocytes to activate T cells in the presence of Stap hylococcus enterotoxin B, Thus, MHC class II+ keratinocytes in the pre sence of superantigens released from staphylococci may activate T cell s and maintain inflammation despite UVB treatment.