Bovine S protein (vitronectin) increases phagocytosis of Streptococcus dysgalactiae

the effects of bovine s protein (vitronectin) on phagocytosis of streptococcus dysgalactiae strains isolated from cattle with mastitis were investigated. phagocytized streptococci were determined by a fluorometric microassay using glass adherent polymorphonuclear neutrophils (pmn). preincubation of s. dysgalactiae with bovine s protein significantly increased their phagocytosis by pmn. bovine s protein had no effect on phagocytic killing of non-s protein binding s. pyogenes cultures. enzymatic digestion of the bovine s protein binding sites on s. dysgalactiae with pronase resulted in a significative reduction of the effects of s protein on phagocytosis. it could thus be concluded that in addition to its role as a promoter of cellular adhesion and complement inhibitor, bovine s protein may also influence the phagocytosis of s. dysgalactiae during inflammatory processes.