EFFECTS OF RECOMBINANT GM-CSF AND IGA OPSONIZATION ON NEUTROPHIL PHAGOCYTOSIS OF LATEX BEADS COATED WITH P6 OUTER-MEMBRANE PROTEIN FROM HAEMOPHILUS-INFLUENZAE
D. Burnett et al., EFFECTS OF RECOMBINANT GM-CSF AND IGA OPSONIZATION ON NEUTROPHIL PHAGOCYTOSIS OF LATEX BEADS COATED WITH P6 OUTER-MEMBRANE PROTEIN FROM HAEMOPHILUS-INFLUENZAE, Thorax, 48(6), 1993, pp. 638-642
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.