Functional expression of CD40 antigen on human epidermal Langerhans cells.

It is now well established that interactions of CD40 on the B cells, along with its ligand (CD40-L) on the T cells, regulate B cell proliferation and differentiation. However, the functional significance of CD40 expression on cells known for most efficient Ag-presenting function, i.e., dendritic cells, is not so clear. In this study, we demonstrate that CD40 is expressed on human dendritic Langerhans cells (LC) freshly isolated from epidermis. Using CD40-L transfected cells, CD40 triggering was found to enhance LC viability when cultured and to result in phenotypic alterations. Thus, a 2-day CD40 activation induced up-regulation of CD54 and CD86 at the LC surface, while it did not significantly affect the levels of HLA-DR, CD1a, CD58, and CD80 expression. These phenotypic changes correlate with enhanced LC allostimulatory property, as shown by the use of paraformaldehyde-fixed LC. Furthermore, mAbs against CD40, as well as CD40-L, strongly inhibit the primary T cell response to allogeneic LC. Collectively, these data support a role for CD40/CD40-L pair in the development of normal T cell functions.