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

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-titeranti-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.