Effect of C5a and Tumor Necrosis Factor-α on Phagocytosis of Streptococcus agalactiae NT/X and IV/X by Bovine Neutrophils

Abstract

Neutrophils can be primed by inflammatory mediators to have enhanced functional activity, so that when they reach the site of an infection, these cells are no longer in a quiescent state as they are in the blood compartment but are ready to exert their phagocytic and bactericidal potential. Previous studies had shown (3, 4) that purified antibodies (Ab) to group B polysaccharide (GBP) or to X-protein are poorly efficient opsonins for mastitis-causing strains of Streptococcus agalactiae in the absence of a source of complement. The fact that Ab to X-protein alone were poorly efficient but promoted phagocytosis by bovine neutrophils in the setting of heat-treated (56°C, 30 min) immune serum (4), suggested that serum may contain components that activate neutrophils and allow them to ingest IgG-coated bacteria. Here we show that C5a^desArg and TNF-α, inflammatory mediators commonly encountered at inflammation sites, were able to enhance the in vitro phagocytosis of S. agalactiae opsonized with either normal bovine serum (NBS), anti-GBP or anti-X IgG.