The adjuvant monophosphoryl lipid A increases the function of antigen-presenting cells

The induction of immune responses in vivo is typically performed with antig ens administered in external adjuvants, like alum, complete Freund's adjuva nt, LPS and, more recently, monophosphoryl lipid A (MPL), However, the role of the adjuvant is still poorly defined. The aim of this study was to test whether the MPL affects the function of antigen-presenting cells (APC) in vitro and In vivo. Antigen-pulsed APC [including macrophages, B cells and d endritic cells (DC)] were incubated or not with MPL, and their ability to s ensitize naive T cells was tested in vitro and In vivo. The data show that MPL enhances the ability of macrophages and B cells to sensitize naive T ce lls, and confers to them the capacity to induce the development of T(h)1 an d T(h)2. Administration of MPL i.v. In mice results in the redistribution o f fully mature DC in the T cell area of the spleen, These observations sugg est that MPL may induce an antigen-specific primary immune response by prov oking the migration and maturation of DC that are the physiological adjuvan t of the immune system.