Functional CD40 ligand is expressed on epidermal Langerhans cells

Epidermal Langerhans cells (LC) are bone-marrow-derived major histocompatib ility complex (MHC) class II antigen-expressing antigen-presenting cells (A PC) that comprise 1-3% of total epidermal cells (EC). LC express high level s of MHC class II antigen and augment costimulatory molecules such as B7-1, B7-2 during culture. In a previous report, using purified murine LC, we sh owed that freshly prepared LC (fLC) do not express CD40, whereas cLC expres s CD40, Tumor necrosis factor alpha (TNF-alpha) enhanced CD40 expression on LC during culture. We examined the expression of CD40L on LC and found tha t both fLC and cLC expressed mRNA for CD40L. FAGS analysis revealed that cL C cultured for 36 h expressed CD40L but fLC did not. When we examined the c ytoplasmic CD40L, however, both. flC and cLC expressed cytoplasmic CD40L. T NF-alpha, which upregulated CD40 expression on LC during culture, did not m odulate CD40L. Go-culture of purified LC with anti-CD40L markedly inhibited the up-regulation of B7-1 expression on LC and caused partial inhibition o f B7-2 expression during culture. These results indicate that CD40L is expr essed on cLC, and that CD40L on LC modulates the expression of costimulator y molecules such as B7-1 and B7-2 on LC.