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 bo vine plasma was fractionated with a protein G column, only the IgG fraction contained induction activity, At similar concentrations purified IgG induced a m uch stronger response than that of plasma IgG, Purified monomeric bovi ne IgG induced a dose dependent increase in superoxide production, The maximum induction can be achieved at 100 mu g/ml of bovine IgG, When subclasses of bovine IgG were examined, monomeric bovine IgG2 potently stimulated bovine polymorphonuclear leukocytes, In contrast, bovine I gG1 failed to induce a response at similar concentrations, and neither bovine Ige F(ab')(2) and Fc were effective. Both recombinant bovine g ranulocyte-macrophage colony-stimulating factor (r-BoGM-CSF) and recom binant bovine granulocyte colony-stimulating factor (r-BoG-CSF) primed bovine neutrophils for superoxide production induced by bo vine IgG, The above results suggest that: (1) bovine plasma contain factors that can activate bovine neutrophils; (2) bovine plasma IgG is the major c omponent that is responsible for bovine neutrophil activation; (3) bov ine plasma contains factors that can inhibit the effect of bovine IgG; (4) monomeric bovine IgG2, but not IgG1, can activate bovine neutroph ils directly without Fc receptor cross-linkage; (5) the integrity of b ovine IgG is important in bovine polymorphonuclear leukocyte activatio n; and (6) bovine neutrophil activation induced by bovine IgG can be p rimed by r-BoGM-CSF or r-BoG-CSF.