Effects of CD40 ligation on human keratinocyte accessory function

CD40/CD40 ligand interactions are known to play a key role in the development of immune reactions, especially by enhancing the costimulatory function of professional antigen-presenting cells (APC). Little is known, however, about the role this receptor plays on occasional APC, i.e. cells that are induced to express MHC class II molecules following an inflammatory process. In this study, we used CD40 ligand-transfected cells to analyze the effect of CD40 ligation on the phenotype, as well as accessory function, of human keratinocytes. We found that CD40 ligation enhanced ICAM-1 expression and did not upregulate HLA-DR, CD80 or CD86 expression on IFN-gamma-treated keratinocytes. CD40 triggering was not sufficient to generate primary allogeneic T-cell responses even in the presence of anti-CD28 monoclonal antibody (mAb). Moreover, CD40 ligation, in the presence or not of IFN-gamma, did not alter the accessory function of keratinocytes in PHA- or superantigen-induced T-cell activation. The lack of effect on the T-cell response was confirmed in blocking experiments using anti-CD40 mAbs. Collectively, these results suggest that CD40-CD40 ligand interactions on nonprofessional APC may amplify the inflammatory reaction without providing a mitogenic signal to the T cells.