Immunization onto bare skin with heat-labile enterotoxin of Escherichia coli enhances immune responses to coadministered protein and peptide antigensand protects mice against lethal toxin challenge

In this study, the potential of the bare skin as a non-invasive route for v accination was examined. Following application of heat-labile enterotoxin ( LT) of Escherichia toll onto bare skin of BALB/c mice, strong serum anti-LT antibody responses were observed, and mucosal immunoglobulin A (IgA) and I gG antibodies were measured in vagina washes. In addition, LT enhanced the serum and mucosal antibody and proliferative T-cell responses to the model protein antigen beta -galactosidase (beta -gal) when coadministered onto ba re skin, highlighting its potential to exert an adjuvant effect. When a pep tide representing a T-helper epitope (aa 307-319) from the haemagglutinin o f influenza virus was applied onto bare skin with LT or cholera toxin (CT), it primed effectively peptide- and virus-specific T cells, as measured in vitro by the interleukin-2 (IL-2) secretion assay. LT was shown to be as im munogenic as CT. Binding activity to GM1 gangliosides was essential for eff ective induction of anti-CT serum and mucosal antibody responses. Finally, mice immunized onto bare skin with LT were protected against intraperitonea l challenge with a lethal dose of the homologous toxin. These findings give further support to a growing body of evidence on the potential of skin as a non-invasive route for vaccine delivery. This immunization strategy might be advantageous for vaccination programmes in Third World countries, becau se administration by this route is simple, painless and economical.