Systemic immune responses induced by mucosal administration of lipopeptides without adjuvant.

We recently reported that parenteral injection of malaria palmitoyl-tailed peptides without adjuvant efficiently induces B, Th and CTL responses. We now show that intranasal (IN) or sub-lingual (SL) delivery of such lipopeptides induces strong systemic immune responses, as demonstrated by specific Th cell responses from the spleen as well as inguinal lymph nodes, and by the production ofhigh levels of serum antibodies. Overall, both types of responses were significantly higher than in parallel experiments in which the same lipopeptides were delivered by the subcutaneous (s.c.) route. Moreover, the mucosal route resulted in the preferential induction of IFN-gamma producing T cells and of IgG2a antibody production, as compared to the dominant IL-4 and IgG1 responses obtained by the s.c. route, thus bringing a distinct advantage in the field of many infectious diseases and allergy. Possibly related to this Th1 response, we found that dendritic cells, the principal immune-competent cells to encounter antigens within mucosal membranes, take up lipopeptide antigens more efficiently than macrophages. Mucosal immunization by lipidated peptides appears therefore as a novel, noninvasive vaccine approach that does not require the use of extraneous adjuvant and which, besides cost-effectiveness, has attractive practical and immunological features.