Bacterial immunogens and protective immunity in swine.

This review provides a limited discussion of antibody-mediated immune responses to bacterial pathogens which cause disease in swine. Serum antibody titers or responses have been used to correlate immunization or convalescence with protection from a given disease or infectious agent. Though much effort has been devoted to the elucidation of the host's antibody response to bacterial antigens, there are limited examples where an antibody response to a singular antigen has induced protection from disease. Antibody responses have been shown to be very effective in neutralizing bacterial exotoxins, e.g. Escherichia, Pasteurella, Actinobacillus, and inhibiting the ability of bacterial pathogens to colonize mucosal surfaces, e.g. Escherichia, Salmonella. The protective role of monospecific antibody responses to other bacterial components are less clear; however, antibody responses are generally polyclonal in nature and are an important component of the host immune response following the onset of disease. Anticapsular antibodies have been shown to enhance phagocytosis of numerous pathogens, e.g. Actinobacillus, Streptococcus, Pasteurella. Humoral immune responses directed against the lipopolysaccharide (LPS) of many Gram-negative organisms have been shown to enhance phagocytosis and the activation of complement, e.g. Salmonella. Anti-LPS antibodies have also aided in the identification of the serotypic diversity of Gram-negative organisms, e.g. Serpulina, Salmonella, Pasteurella. Antibody responses to the outer membrane proteins of Gram-negative organisms enhance phagocytosis, activation of complement, or inhibit bacterial adhesion to host cell. Adhesion of Gram-positive microorganisms, e.g. Staphylococcus, Streptococcus, Clostridium, to eukaryotic cells can be inhibited by antibody against the peptidoglycan and these peptidoglycan-specific antibodies may also facilitate opsonization of these organisms. Mycoplasma species have been shown to be metabolically inhibited by antibody directed against membrane proteins. In addition to the protective aspects of humoral immunity, the host's antibody response has been used as a diagnostic and epidemiological tool to identify or determine the prevalence of infectious agents.