As the pure antigen is not accompanied by any of the elements that activate the defensive triggers of the innate immune system that would be present in the native pathogen, this approach results in an antigen that is well tolerated, but MDV3100 purchase usually requires the addition of an adjuvant in order to achieve high immunogenicity and long-term protection. A peptide antigen approach represents an additional step to the protein antigen approach. Peptide antigens may prove beneficial in the context of diseases where the pathogen evolves and protective antigens are numerous. In this setting, mixtures of different peptides known to be targets for protective immunity can be

used more efficiently than producing many different full-protein antigens. It is possible to identify and directly synthesise by various methods specific peptides that elicit adaptive immune responses. The peptides selected for vaccine development must contain epitopes that induce sufficient priming of naïve T cells to attain effective cellular and humoral immunity. Innate ‘defensive triggers’ may be conserved molecular structures, such as repeating units of carbohydrate moieties, certain nucleic Selleck SCR7 acid sequences, or molecules that are

recognised by specialised pathogen receptors on innate immune cells and certain other cell types. The activation of immune defence mechanisms requires the presence of both antigen and defensive triggers to communicate the nature of the potential threat and to induce adequate immune responses. These elements may be missing in subunit and recombinant vaccine antigens and, for that reason, the addition of adjuvants and/or alternative ways of helping the antigens to stimulate the immune system are needed. Influenza vaccine technology encompasses most

of the current approaches to antigen selection, including the use Thiamet G of whole viruses (Figure 3.7). The natural immune response to influenza viruses involves both humoral and cell-mediated immunity and the type-1 interferon response that is important for viral clearance. The humoral immune response is normally of more importance after viral clearance, and antibody responses associated with the immunoglobulin (Ig) G and IgA isotypes are important for protection against reinfection or infection with a new strain. Antibody against the haemagglutinin (HA) protein (a glycoprotein responsible for binding the virus to host cells) is considered the primary immune mediator of protection as this can inhibit virus binding to the epithelium, and thus block the early stages of infection. Antibody to the neuraminidase (NA) protein has also been considered as it can prevent cell-to-cell spread of the virus within the host. The evaluation of haemagglutinin inhibitory (HI) antibody titres has been used from the very beginning to assess influenza vaccine immune-protective abilities.