Effects of bovine viral diarrhea virus infection on bovine polymorphonuclear leukocyte function.

Four procedures were used to evaluate the function of polymorphonuclear leukocytes (PMN) isolated from the blood of cattle experimentally infected with bovine viral diarrhea (BVD) virus: (1) uptake of am emulsion of paraffin oil and Escherichia coli lipopolysaccharide, (2) nitroblue tetrazolium reduction, (3) chemiluminescence, and (4) iodination, or the conversion of iodide to a trichloroacetic acid-precipitable form. A marked impairment of iodination was consistently observed after infection with either a cytopathogenic or a noncytopathogenic strain of BVD virus. A corresponding decrease in paraffin oil uptake, nitroblue tetrazolium reduction, and chemiluminescence was not observed. Serum from BVD virus-infected animals did not depress iodination by normal control PMN in vitro. The iodination, procedure evaluates the activity of the myeloperoxidase, hydrogen peroxide, halide system. This system has potent bactericidal, fungicidal, and virucidal effects. The data indicate that oxidative metabolism by PMN from BVD virus-infected cattle is normal, but that the myeloperoxidase, hydrogen peroxide, halide antibacterial system is impaired. This could be explained by an inhibition of degranulation in PMN from infected cattle. The observed defect in iodination by PMN after BVD virus infection was compounded by a decrease in the number of circulating PMN. The impairment of PMN function may partially explain the increased susceptibility of cattle to secondary bacterial infection during infection with BVD virus.