Humoral immune components of resistance to experimental septicemic and pneumonic pasteurellosis

Typescript (photocopy).The bactericidal properties of bovine immunoglobulin classes and subclasses against Pasteurella haemolytica biotype A, serotype 1 (PHA1) were defined through both classical and alternative complement pathways. The role of complement in clearance of viable organisms in a murine septicemic pasteurellosis model was studied. A unique hemolysin-in-gel assay to measure the level of complement-fixing, anti-PHA1 antibodies in bovine sera was described. Antigen-capture and indirect-sandwich enzyme-linked immunosorbent assays were described to assess the interisotype competition effects of competing isotypes in polyclonal bovine sera against PHA1 somatic antigens. The repeatability, specificity, and precision were reported. These new serologic assays were applied to field models of experimental bovine pneumonic pasteurellosis to measure the anti-PHA1 humoral immunoglobulin levels by isotypic and complement-fixing characteristics. Resistance to all forms of experimental pasteurellosis was associated with consistently higher levels of humoral, complement-fixing, anti-PHA1 antibodies, especially IgG1 and IgM. These immunoglobulins were found to be directed against capsular polysaccharides, lipopolysaccharide, and various membrane proteins of PHA1