Monomeric bovine IgG2 is a potent stimulus for bovine neutrophils

Bovine plasma contains factors that can stimulate bovine neutrophils. Bovine plasma at 1:1,000,000–1:1,000 dilution induced a dose‐dependent superoxide production in bovine neutrophils. When bovine plasma was fractionated with a protein G column, only the IgG fraction contained induction activity. At similar concentrations purified IgG induced a much stronger response than that of plasma IgG. Purified monomeric bovine IgG induced a dose‐dependent increase in superoxide production. The maximum induction can be achieved at 100 μg/ml of bovine IgG. When subclasses of bovine IgG were examined, monomeric bovine IgG2 potently stimulated bovine polymorphonuclear leukocytes. In contrast, bovine IgG1 failed to induce a response at similar concentrations, and neither bovine IgG F(ab') 2 and Fc were effective. Both recombinant bovine granulocyte‐macrophage colony‐stimulating factor (r‐BoGM‐CSF) and recombinant bovine granulocyte colony‐stimulating factor (r‐BoG‐CSF) primed bovine neutrophils for superoxide production induced by bovine IgG. The above results suggest that: (1) bovine plasma contain factors that can activate bovine neutrophils; (2) bovine plasma IgG is the major component that is responsible for bovine neutrophil activation; (3) bovine plasma contains factors that can inhibit the effect of bovine IgG; (4) monomeric bovine IgG2, but not IgG1, can activate bovine neutrophils directly without Fc receptor cross‐linkage; (5) the integrity of bovine IgG is important in bovine polymorphonuclear leukocyte activation; and (6) bovine neutrophil activation induced by bovine IgG can be primed by r‐BoGM‐CSF or r‐BoG‐CSF. J. Leukoc. Biol. 58: 203–208; 1995.