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, monocytes and dendritic cells to activate T cells in the presence of Staphylococcus enterotoxin B. We demonstrated that UVB irradiation of MHC class II+ keratinocytes does not change their capacity to activate T cells in the presence of Staphylococcus enterotoxin B. In contrast, UVB irradiation of antigen-presenting cells decreases their capacity to activate T cells. This differential capacity to activate T cells after UVB irradiation was not due to factors released from UVB-irradiated cells. The interferon-gamma induced upregulation of HLA-DR and intercellular adhesion molecule-1 on keratinocytes does not seem to be the only explanation, since UVB irradiation decreased the accessory cell function of interferon-gamma pretreated monocytes. Differential requirements for and UVB regulation of costimulatory molecules may be involved, since blocking of the B7/CD28 pathway affects the capacity of dendritic cells but not keratinocytes to activate T cells in the presence of Staphylococcus enterotoxin B. Thus, MHC class II+ keratinocytes in the presence of superantigens released from staphylococci may activate T cells and maintain inflammation despite UVB treatment.