Effect of whole Staphylococcus aureus and mode of immunization on bovine opsonizing antibodies to capsule

Exopolysaccharide capsule is a major virulence factor of Staphylococcus aureus because it inhibits neutrophil recognition of antibodies to highly antigenic S. aureus cell wall. To circumvent this inhibition, two modes of immunization were tested for ability to induce anticapsular opsonins. Cows were immunized at drying off and boosted on d 14 and 28 by injection of Smith diffuse S. aureus plus dextran sulfate in the area of the supramammary lymph node or intramammarily. In cows immunized in the area of the supramammary lymph node, IgG1 and IgG2 sera antibody titers to capsule increased and remained elevated to the end of the study, 120 d postcalving. The IgM titers increased during the dry period but declined to preimmunization levels at calving. Response of serum IgG1 and IgM to intramammary immunization was similar to that with supramammary lymph node immunization, but more delayed and lower in magnitude. Antibodies of all four isotypes, IgG1, IgG2, IgA, and IgM, increased in dry secretions following immunization via lymph node. In cows immunized in the lymph node, IgG1 antibodies remained elevated throughout the study, but IgG2 antibodies dropped to baseline 15 d postcalving. In cows immunized intramammarily, only IgA antibodies increased significantly in lacteal secretions and remained elevated throughout the study. Immunization of cows in the lymph node during the dry period enhanced the ability of dry secretions and colostrum to support phagocytosis.