INDUCTION OF PNEUMOCOCCAL POLYSACCHARIDE-SPECIFIC MUCOSAL IMMUNE-RESPONSES BY ORAL IMMUNIZATION

Liposome and cholera toxin (CT) are considered to be effective antigen delivery vehicles and adjuvants for mucosal vaccines. The effect of t hese antigen delivery systems on adjuvant responses to mucosally admin istered pneumococcal polysaccharide (Pnup) was investigated in this st udy. Both mucosal (e.g oral) and systemic (IP) immunization of mice wi th purified preparations of Pnup type 23F induced antigen-specific IgM responses in sera. Interestingly, oral immunization of as little as 1 0 mu g of Pnup type 23P was sufficient to induce systemic IgM response s, Pnup-specific IgM antibodies peaked by day 7 and no booster respons es were evident after a second dose on day 14. In order to examine whe ther IgG and IgA Pnup-specific immune responses are induced by mucosal immunization, the mucosal adjuvant CT was mixed with Pnup type 23 as an oral vaccine, Go-oral administration of CT and Pnup type 23F result ed in the induction of Pnup-specific faecal IgA antibodies. These resu lts were confirmed by defecting antigen-specific IgA-spot-forming cell s in mononuclear cell suspensions prepared from the intestine of immun ized mice. These findings suggest that oral immunization with Pnup in the presence of mucosal adjuvants, such as CT, could induce Pnup-speci fic IgA responses whereas Pnup alone did not. In an attempt to further enhance antigen-specific antibody responses, Pnup type 23F was encaps ulated in liposomes and used as mucosal vaccine. However, immunogenici ty of Pnup was not improved. Copyright (C) 1996 Elsevier Science Ltd.