Phagocytic activity of milk leukocytes during chronic staphylococcal mastitis

Receptors for IgG on milk leukocytes were detected by rosette formation using sensitized erythrocytes. The percentage (41) of milk leukocytes from uninfected glands forming sensitized erythrocyte rosettes was significantly greater than the percentage (13) of leukocytes from glands with chronic staphylococcal mastitis. A greater percentage of polymorphonuclear leukocytes than macrophages formed sensitized erythrocyte rosettes, regardless of the infection status of the gland from which they were obtained. Both IgG-receptor and nonimmunologic receptor-mediated phagocytosis were greater for milk leukocytes from uninfected glands than for milk leukocytes from chronically infected glands. Preincubation of normal milk leukocytes in whey prepared from mastitic milk resulted in a decrease in their capacity to form sensitized erythrocyte rosettes as well as a reduction in their phagocytic capacity. Immune complexes prepared in vitro also reduced the phagocytic capacity of normal milk leukocytes and inhibited their capacity to form sensitized erythrocyte rosettes. These data indicate a factor, possibly consisting of immune complexes, was present in secretions from glands chronically infected with staphylococci. This factor reduced the phagocytic capacity of milk leukocytes.