Affinity-purified bovine
immunoglobulin isotypes were bacteriolytic for Pasteurella haemolytica biotype A, serotype 1 (PHA-1). This bacteriolysis was specific and
complement-dependent. The
IgM and
IgG1 were the most active isotypes in the classic
complement cascade. These isotypes also induced bacteriolysis through the alternative
complement cascade. The comparative bacteriolytic activities of
IgG1 and
IgM were equal within each cascade; however, the bacteriolytic activities of
IgG1 and
IgM were lower in the alternative cascade than in the classical cascade. The
IgG2 was more bacteriolytic than
IgA in the classic and alternative
complement pathways. Bovine
immunoglobulins passively protected C57BL/6 mice from experimentally induced
pasteurellosis. There were no major differences in the protection among hyperimmune sera, purified
IgM, or purified
IgG. Mice were protected from PHA-1 by approximately 1.9 micrograms of
IgG and 1.2 or 0.1 micrograms of
IgM. Elimination of murine
complement with
cobra venom factor 3 reduced PHA-1 clearance in passively immunized C57BL/6 mice. The protective effect of
IgM mediated resistance was highly dependent on an intact
complement system. The intact
complement cascade was associated with enhanced clearance of PHA-1 from the liver. Although PHA-1 was susceptible to antibody
complement-mediated bacteriolysis in vitro, the dependence on an intact
complement cascade was not absolute in experimentally induced murine septicemic
pasteurellosis.