Bovine polymorphonuclear neutrophil-mediated phagocytosis and an immunoglobulin G(2) protease produced by Porphyromonas levii

Acute interdigital phlegmon (AIP) is a commonly occurring anaerobic bacteri al infection in cattle. This study examined in vitro the interaction of bov ine polymorphonuclear granulocytic neutrophils (PMN) from blood with bacter ial species involved in AIP, Polymorphonuclear neutrophils were purified fr om whole bovine blood, exposed to one of the three putative etiologic agent s of AIP and comparatively assessed for phagocytosis using light microscopy , Fusobacterium necrophorum and Prevotella intermedia were effectively phag ocytosed by PMN, but Porphyromonas levii was phagocytosed significantly les s effectively by PMN, The effect of high titre anti-P. levii bovine serum o n antibody-mediated phagocytosis by PMN was also evaluated, High titre seru m increased the efficiency of phagocytosis of P. levii by bovine PMN, This was independent of heat labile complement factors. Antibodies specific for P. levii were assessed for protease activity capable of cleaving bovine imm unoglobulins (IgG, IgG(1), IgG(2), and IgM), Partially purified supernatant from broth cultures of P. levii were incubated with biotinylated immunoglo bulins (Igs), Samples were taken from times 0 to 72 h and examined using SD S-PAGE followed by Western blot analysis, Streptavidin-alkaline phosphatase and NBT-BCIP were used to visualize the Igs for heavy and light chains as well as lower molecular weight fragments of these glycoproteins, Porphyromo nas levii produced an immunoglobulin protease which readily cleaved bovine IgG into fragments, but did not act against IgM, Specifically, the enzyme m ay be a significant virulence factor as it may act to neutralize the antibo dies demonstrated necessary for effective PMN-mediated phagocytosis.