DEFECTIVE POLYMORPHONUCLEAR NEUTROPHIL FUNCTION IN DAIRY-COWS SHOWINGENHANCED SUSCEPTIBILITY TO INTRAMAMMARY INFECTIONS

Polymorphonuclear-neutrophil (PMN) oxidative-burst activity, chemotact ic and chemokinetic migratory responses, and surface-adhesion protein expression in a mastitis-prone group of dairy cows were compared with corresponding variables in healthy cows. The cows had a well-documente d history of udder infection caused by major mastitis pathogens. Analy sis of PMN functions revealed a deficiency in the luminol-enhanced che miluminescence responses that seemed to be associated with the mobiliz ation of myeloperoxidase (MPO) in the PMN of the patient group, as com pared with the healthy controls. The migratory capacity of the PMN in response to a variety of chemotactic substances was enhanced in the pa tients. However, there were no significant differences between the two groups in the expression of surface-adhesion proteins (CD11a/CD18). I t is proposed that the migratory activity of PMN cells was enhanced in order to compensate for their depressed respiratory-burst activity. S tudies are under way to assess whether the defective mobilization of M PO in PMN of mastitis-prone cows is an acquired transient defect or a permanent hereditary defect.