The malononitrilamide FK778 inhibits activation of NF-kappaB in human dendritic cells.

FK778, a derivative of the active leflunomide-metabolite, A77 1726, has been shown to be a powerful immunosuppressant in several transplantation models, particularly efficient in prevention of chronic allograft rejection. However, the cellular and molecular mechanisms underlying these effects of FK778 have not been investigated yet in detail. Because dendritic cells (DCs) are a crucial cell type in initiation of immune responses including chronic allograft rejection, we investigated whether FK778 affects this peculiar cell population. NF-kappaB is the essential transcription factor involved in DC activation and function. We found that lipopolysaccharide (LPS)-induced activation of NF-kappaB, as assessed using electromobility shift assay, is markedly inhibited by FK778 in human monocyte-derived DCs. Hence, FK778 could exert its immunosuppressive effects via inhibition of activation and thus function of the central antigen-presenting cell, ie, DC.