Effect of local immunization of the mammary gland on phagocytosis and intracellular kill of Staphylococcus aureus by polymorphonuclear neutrophils.

Four cows in the latter part of their 2nd, 3rd, or 4th lactations were immunized by multiple intramammary infusions of heat-killed Staphylococcus aureus in 2 quarters. The direct bactericidal effects of milk whey from the immunized and control quarters, before and after immunization, and the ability of these whey to support phagocytosis and intracellular kill were determined by incubating live S aureus with polymorphonuclear neutrophils isolated from milk. Immunoglobulins (Ig) were determined by single radial immunodiffusion. One immunized and 1 control quarter in each cow were challenge exposed with live S aureus and the courses of the infections were determined for 2 weeks. There were significant cow differences in all Ig classes and in percentage of phagocytosis. Immunization resulted in a significant increase in IgA, IgG2, and IgM in the immunized quarters. Whey collected from immunized quarters supported phagocytosis of S aureus by isolated milk polymorphonuclear neutrophils significantly greater than did whey from control quarters. Extracellular live S aureus in the incubation medium was decreased by 59% in whey collected after immunization from immunized quarters. This decrease in extracellular S aureus was associated with a concomitant increase in total intracellular S aureus. However, intracellular live organisms showed no change. This lack of change indicated that the additional S aureus that were phagocytosed were killed. Direct bactericidal effects of whey were not observed. Intracellular live S aureus was not significantly correlated with any of the variables measured.