Mucosal immune responses and protection against tetanus toxin after intranasal immunization with recombinant Lactobacillus plantarum

The use of live microorganisms as an antigen delivery system is an effectiv e means to elicit local immune responses and thus represents a promising st rategy for mucosal vaccination. In this respect, lactic acid bacteria repre sent an original and attractive approach, as they are safe organisms that a re used as food starters and probiotics. To determine whether an immune res ponse could be elicited by intranasal delivery of recombinant lactobacilli, a Lactobacillus plantarum strain of human origin (NCIMB8826) was selected as the expression host. Cytoplasmic production of the 47-kDa fragment C of tetanus toxin (TTFC) was achieved at different levels depending on the plas mid construct. All recombinant strains proved to be immunogenic by the intr anasal route in mice and able to elicit very high systemic immunoglobulin G IgG1, IgG2b, and IgG2a) responses which correlated to the antigen dose. No significant differences in enzyme-linked immunosorbent assay IgG titers we re observed when mice were immunized with live or mitomycin C-treated recom binant lactobacilli. Nevertheless, protection against the lethal effect of tetanus toxin was obtained only with the strains producing the highest dose of antigen and was greater following immunization with live bacteria, Sign ificant TTFC-specific mucosal IgA responses were measured in bronchoalveola r lavage fluids, and antigen-specific T-cell responses were detected in cer vical lymph nodes, both responses being higher in mice receiving a double d ose of bacteria (at a 24-h interval) at each administration. These results demonstrate that recombinant lactobacilli can induce specific humoral (prot ective) and mucosal antibodies and cellular immune response against protect ive antigens upon nasal administration.