title: Milk complement and the opsonophagocytosis and killing of Staphylococcus aureus mastitis isolates by bovine neutrophils.
abstract: Phagocytosis of bacteria by bovine polymorphonuclear neutrophils (PMN) has long been regarded as essential for host defense against mastitis infection. Complement-mediated opsonisation by complement component 3 (C3) binding is an important component of the innate immune system. We investigated the role of milk complement as an opsonin and its involvement in the phagocytosis and killing of Staphylococcus aureus isolates from cases of bovine mastitis by bovine blood PMN. We show that deposition of milk C3 component occurred on six different isolates of S. aureus and that the alternative pathway was the sole complement pathway operating in milk of uninflamed mammary gland. This deposition was shown to occur at the same location as the capsule, but not on capsular antigen. Milk complement enhanced the chemiluminescence response of PMN induced by S. aureus. Nevertheless, the association of S. aureus to cells and the overall killing of bacteria by bovine PMN were not affected by the presence of milk complement. Therefore, as all milk samples contained antibodies to capsular polysaccharide type 5 and to other surface antigens, it is likely that milk antibodies were responsible for these two phagocytic events. Results of this study suggest that the deposition of milk complement components on the surface of S. aureus does not contribute to the defence of the mammary gland against S. aureus.
authors.affiliation: Equipe Mammites, Laboratoire de Pathologie Infectieuse et Immunologie, INRA, 37380 Nouzilly, France.
authors.forename: Maria Belén
authors.initials: MB
authors.lastname: Barrio
authors.forename: Pascal
authors.initials: P
authors.lastname: Rainard
authors.forename: Bernard
authors.initials: B
authors.lastname: Poutrel
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000032:analysis / Q000097:blood / Q000276:immunology; D000942:Antigens, Bacterial / Q000276:immunology; D016667:Bacterial Capsules / Q000276:immunology; D001433:Bacteriolysis; D002417:Cattle; D003167:Complement Activation; D003176:Complement C3 / Q000276:immunology*; D003181:Complement C4 / Q000276:immunology*; D005260:Female; D007150:Immunohistochemistry; D008163:Luminescent Measurements; D008414:Mastitis, Bovine / Q000276:immunology* / Q000382:microbiology; D008892:Milk / Q000166:cytology / Q000276:immunology* / Q000382:microbiology; D009504:Neutrophils / Q000502:physiology*; D009895:Opsonin Proteins / Q000276:immunology*; D010587:Phagocytosis; D016897:Respiratory Burst; D013203:Staphylococcal Infections / Q000276:immunology / Q000382:microbiology / Q000662:veterinary*; D013211:Staphylococcus aureus / Q000276:immunology*
chemical_list: D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D003176:Complement C3; D003181:Complement C4; D009895:Opsonin Proteins; C054106:capsular polysaccharide, type 5, Staphylococcus aureus