INCREASED SURFACE EXPRESSION OF CD11B RECEPTORS ON POLYMORPHONUCLEAR LEUKOCYTES IS NOT SUFFICIENT TO SUSTAIN PHAGOCYTOSIS DURING ESCHERICHIA-COLI MASTITIS IN EARLY POSTPARTUM DAIRY-COWS

Phagocytosis, CD11a and CD11b adhesion receptor expression, O-2(-) pro duction and maturity of circulating polymorphonuclear leukocytes (PMN) were studied during acute coliform mastitis in early postpartum dairy cows to obtain a better insight in the role of neutrophils in the pat hology of this disease. The mammary gland of twelve newly calved high- yielding dairy cows was experimentally infected with Escherichia coil. Variability in clinical signs of mastitis and inhibition of milk prod uction among cows was very high. There was a significant negative corr elation between the number of circulating neutrophils immediately befo re infection and severity of mastitis represented by the decrease in m ilk production of non-infected quarters two days after infection, Pre- infection phagocytosis of E. coli, CD11a and CD11b receptor expression , phorbol myristate acetate (PMA)-induced O-2(-) production and maturi ty of neutrophils on a per cell basis were not related to severity of mastitis. However, significant correlations between severity of mastit is and the total number of phagocytic PMN and mature PMN in blood imme diately before infection were found. PMN characteristics responded dif ferently to mastitis depending on the severity of the disease. Neutrop hil functions from cows classified as severe (S) and moderate (M) resp onders to infection of the mammary gland were compared. Surface expres sion of CD11a receptors on PMN was decreased in all cows 24 h after in fection, and this decrease was long-continued in S responders. A bipha sic upregulation of the number of CD11b receptors on PMN was observed with a more pronounced response in S cows. PMN phagocytosis was decrea sed 12 h after infection in S cows and 18 h after infection in S and M cows and was normalized 24 h post-infection. The decrease of phagocyt osis coincided with the first peak of CD11b receptor expression. Phorb ol myristate acetate (PMA)-induced production of O-2(-) by PMN was dec reased for three days after infection in S responders compared to only one day in M responders and was followed by an upregulation. These da ta demonstrate a complexity in alterations of PMN functions during mas titis and suggest the involvement of differences in systemic factors d ependent on severity of mastitis. (C) 1997 Elsevier Science B.V.