Comparison of phagocytosis and chemiluminescence by blood and mammary gland neutrophils from multiparous and nulliparous cows.

Neutrophils were isolated from the blood and mammary gland of 3 multiparous lactating cows and 3 nulliparous heifers. Neutrophil function was evaluated by phagocytosis and luminol-dependent chemiluminescence. Peroxidase activity was detected by use of transmission electron microscopy. Compared with that for blood neutrophils, percentage of phagocytosis was 9.6% lower for neutrophils isolated from the mammary gland of lactating cows, but this difference was not observed between neutrophils isolated from the mammary gland and from the blood heifers. Similarly, after subtraction of chemiluminescence values in the absence of zymosan, phagocytosing neutrophils from the mammary gland of lactating cows had lower chemiluminescence than did those from the blood of such cows. For heifers, however, chemiluminescent activity by phagocytosing neutrophils obtained from the mammary gland was similar to that of blood neutrophils. Chemiluminescent activity of resting neutrophils from the mammary gland of lactating cows pretreated with cytochalasin B was not inhibited, compared with that of nontreated resting neutrophils (controls). This was attributed to xanthine oxidase activity. Transmission electron microscopy of mammary gland neutrophils from lactating cows revealed peroxidase-positive material associated with milk-fat globule membranes and with phagosomes containing zymosan. Results indicated that ingestion of fat and casein by neutrophils isolated from milk caused a decrease in phagocytic and chemiluminescent activity. Also, luminol-dependent chemiluminescence was not a reliable measure of milk neutrophil function, because of interference by xanthine oxidase.