Mucosal adjuvant properties of the Shigella invasin complex.

The Shigella invasin complex (Invaplex) is an effective mucosal vaccine capable of protecting against Shigella challenge in animal models. The major antigenic constituents of Invaplex are the Ipa proteins and lipopolysaccharide. The cell-binding capacity of the Ipa proteins prompted the investigation into the adjuvanticity of Invaplex. Using ovalbumin (OVA) as a model antigen, intranasal immunization with OVA combined with Invaplex was found to enhance anti-OVA serum immunoglobulin G (IgG) and IgA responses and induce OVA-specific mucosal antibody responses at sites located both proximal and distal to the immunization site. The immune responses induced with OVA and Invaplex were comparable in both magnitude and duration to the immune responses induced after immunization with OVA and cholera toxin. The OVA-specific immune response was characterized by high levels of serum IgG1 and increased production of interleukin-4 (IL-4), IL-5, or IL-10 from lymphoid cells of immunized animals, suggesting a Th2 response. In addition to enhancing the immunogenicity of OVA, Invaplex-specific immune responses were also induced, indicating the potential for the development of a combination vaccine consisting of Invaplex and other immunogens. Preexisting Invaplex-specific immunity did not interfere with the capacity to enhance the immunogenicity of a second, unrelated vaccine antigen, suggesting that Invaplex could be used as a mucosal adjuvant in multiple vaccine regimens.