Bovine Humoral-phagocyte interaction in defense against Brucella abortus

Abstract

Bovine phagocytic polymorphonuclear leukocytes were collected from peripheral blood and separated into neutrophil (NEUT) and eosinophil (EOS) enriched suspensions by density gradient centrifugation. The cells were stimulated and characterized by measuring their oxygenation activity using a chemiluminescence (CL) assay. NEUT were found to be stimulated by bovine serum opsonified zymosan (BOZ), heat aggregated bovine IgG, only slightly stimulated by phorbol myristate acetate (PMA) and concanavalin A and not stimulated by an N-formylmethionyl peptide. EOS were found to bre greatly stimulated by PMA but not BOZ or heat aggregated IgG. The oxygenation activity of NEUT and EOS stimulated by BOZ and PMA were measured with titrations of the chemiluminigenic probe luminol and the K(,m) and V(,max) were calculated and compared. Brucella abortus were opsonified with titrations of positive and negative bovine IgG and tested as stimulators of NEUT oxygenation activity. Positive IgG opsonified B. abortus resulted in greater stimulation than negative IgG when integral counts for a 2 hr assay were compared. An in vitro B. abortus killing assay was conducted to compare the brucellacidal capacities of NEUT and EOS in the presence of serologically positive and negative heat inactivated serum, negative serum, and no serum. The brucellacidal capacities were similar for both cell types, ie greatly accelerated killing was found with negative serum compared to positive or negative heat inactivated serum. Viable and irradiated inactivated B. abortus were compared, as stimulators of NEUT CL measured oxygenation activity, and found to be essentially equivalent. Pregnant cows were experimentally inoculated with B. abortus and the serologic responses and opsonic capacity of cows susceptible or resistant to infection were compared. Susceptible cows developed and maintained higher levels of agglutinating and complement fixing antibodies, and serum opsonic capacity than resistant cows. Although the hemolytic complement values of susceptible cows were depressed following infection, no differences were demonstrated in serum opsonic complement levels when neutrophils were stimulated by zymosan opsonified with serum from susceptible or resistant cows. Greater serum opsonic capacity appeared to correlate with susceptibility and may contribute to infection by accelerating phagocytosis and sequesteration of a facultative organism to a protected intracellular environment.