COMPARISON OF THE CHEMILUMINESCENCE RESPONSES OF BOVINE NEUTROPHILS TO DIFFERENTLY OPSONIZED ZYMOSAN PARTICLES

Stimulatory effects of 6 zymosan preparations on luminol-dependent che miluminescence (CL) responses of isolated bovine neutrophils were comp ared. Unopsonized zymosan particles and zymosan particles opsonized wi th bovine IgG1, IgG2, fresh serum, or serum from which zymosan-specifi c antibodies, but not complement, had been removed (C3-serum) induced strong CL responses, with nearly equal maximal peaks in the presence o f extracellular Ca2+ and Mg2+, whereas the response to fetal bovine se rum-opsonized zymosan particles was markedly low. Removal of extracell ular divalent cations almost completely blocked the CL reaction trigge red by unopsonized, IgG1-opsonized, C3-opsonized, and fetal bovine ser um-opsonized zymosan particles. By contrast, no change in the respirat ory burst activity induced by serum-opsonized zymosan and only partial reduction in the response to IgG2-opsonized zymosan were seen under t hese conditions. Further experiments were performed with 4 zymosan pre parations on neutrophils isolated from 2 calves with a genetic deficie ncy of CD11/CD18 membrane antigens. The unopsonized zymosan-induced CL reaction was absent in these cells. A reduced, but clear, response wa s observed with C3-opsonized zymosan. Unexpectedly, in the absence of extracellular Ca2+ and Mg2+, serum-opsonized zymosan failed to generat e the respiratory burst, whereas response to IgG2-opsonized zymosan wa s normal in the CD11/CD18-deficient neutrophils. These findings indica te that unopsonized zymosan may act in a divalent cation-dependent man ner at the receptor for C3bi in bovine neutrophils, as it has been sho wn to do in the human system. In addition, it seems that IgG2-Fc recep tors capable of signaling the respiratory burst in the absence of extr acellular Ca2+ and Mg2+ exist on bovine neutrophils.