EFFECTS OF RECOMBINANT GM-CSF AND IGA OPSONIZATION ON NEUTROPHIL PHAGOCYTOSIS OF LATEX BEADS COATED WITH P6 OUTER-MEMBRANE PROTEIN FROM HAEMOPHILUS-INFLUENZAE

Background-IgA is the major antibody class in mucosal secretions, yet its biological functions remain poorly understood and its role as an o psonin for neutrophils has been the subject of controversy. It has bee n reported that treatment of neutrophils with granulocyte-macrophage c olony stimulating factor (GM-CSF) induces the cells to phagocytose par ticles opsonised with IgA. A study was performed to investigate the ef fects of GM-CSF and IgA opsonisation on the ability of human neutrophi ls to recognise and phagocytose latex beads coated with the P6 outer m embrane protein of Haemophilus influenzae. Methods-Human neutrophils w ith and without preincubation with 100 pmol/l GM-CSF, were incubated w ith non-opsonised P6-coated latex beads or beads opsonised with IgA pu rified from the blood of a bronchiectatic patient with high titres of IgA anti-P6. Phagocytosis was measured by counting internalised beads during microscopic examination. Results-The phagocytosis of IgA opsoni sed beads by untreated neutrophils (mean (SE) 2.1 (0.43) beads/cell) w as significantly greater than that of non-opsonised beads (mean (SE) 1 .3 (0.30) beads/cell). Treatment of neutrophils with GM-CSF resulted i n increased phagocytosis of non-opsonised beads (mean (SE) 2.1 (0.39) beads/cell) but opsonisation with IgA increased this further (mean (SE ) 3.4 (0.53) beads/cell). Conclusions-Human neutrophils recognise and phagocytose non-opsonised particles coated with bacterial antigen. Ant ibodies of the IgA isotype opsonise for neutrophil phagocytosis of par ticles coated with bacterial antigen but this behaviour is enhanced, i n an additive fashion, by treatment of the cells with GM-CSF. The resu lts suggest that IgA and GM-CSF are important cofactors for neutrophil recognition and elimination of bacterial pathogens.