Chemotaxis, phagocytosis, and oxidative metabolism in bovine macrophages exposed to a novel interdigital phlegmon (foot rot) lesion isolate, Porphyromonas levii

Abstract

Objective.-To examine the host response toward Porphyromonas levii, by evaluating chemotaxis, phagocytosis, and oxidative burst of bovine macrophages in vitro. Sample Population.-Cultured bovine macrophages obtained from monocytes harvested from blood samples of 15 Holstein steers. Porphyromonas levii was isolated from the foot rot lesion of an acutely affected feedlot steer. Procedure.-Monocytes were cultured for macrophage differentiation over 7 days. Porphyromonas levii was cultured in strict anaerobic conditions for experimentation. Chemotaxis was evaluated by quantifying macrophage migration toward P levii in Boyden chambers. Phagocytosis was assessed by quantification of macrophages engulfing P levii following incubation with or without anti-P levii serum or purified IgG. Oxidative burst was measured by use of the nitroblue tetrazolium reduction assay. Results.-Chemotaxis toward P levii was not significantly different from control values at any of the tested bacterial concentrations. Phagocytosis of P levii was approximately 10% at a 10:1 bacterium to macrophage ratio and did not change significantly over time. When higher proportions of P levii were tested for phagocytosis, the 1,000:1 bacterium to macrophage ratio had a significant increase, compared with the 10:1 test group. Opsonization of P levii with high-titer anti-P levii serum or anti-P levii IgG produced a significant increase in macrophage phagocytosis. Oxidative production significantly increased compared with control in the 1,000:1 test group only. Conclusions and Clinical Relevance.-Porphyromonas levii may evade host detection by decreased chemotaxis, phagocytosis, and oxidative burst by macrophages. Acquired immunity may be beneficial for clearance of P levii in foot rot lesions in cattle.