An IgA monoclonal antibody directed against type III antigen on group B streptococci acts as an opsonin.
We have investigated the mechanisms by which a murine IgA mAb directed against the type III Ag (IgA anti-III mAb) of group B streptococci (GBS) protects neonatal rats from lethal infection with these organisms. Purified IgA anti-III mAb enhanced phagocytosis of type III GBS by rat peritoneal macrophages in vitro by fourfold compared with phagocytosis of buffer-treated GBS. In the absence of antibody, neonatal rat serum did not promote phagocytosis, but addition of neonatal rat serum to GBS opsonized with IgA anti-III led to a sevenfold increase in phagocytosis. Heat inactivation of C destroyed the ability of neonatal rat serum to enhance phagocytosis in the presence of IgA. C3 deposition was observed when GBS coated with IgA anti-III mAb were incubated in untreated neonatal rat serum or in serum treated with Mg/EGTA. This latter observation suggested that C3 deposition occurred through activation of the alternative pathway. The control IgA mAb MOPC 315 did not enhance GBS ingestion or C3 deposition on GBS. Depletion of C in vivo by using cobra venom factor abolished the protective effect of IgA anti-III mAb in the neonatal rat model. These data suggest that the ability of this IgA to activate C further enhances its opsonic activity and may be essential for its protective effect in vivo.
Bohnsack
J F
JF
Department of Pediatrics, University of Utah School of Medicine, Salt Lake City 84132.
Hawley
M M
MM
Pritchard
D G
DG
Egan
M L
ML
Shigeoka
A O
AO
Yang
K D
KD
Hill
H R
HR
D000818:Animals; D000907:Antibodies, Bacterial / Q000502:physiology*; D000911:Antibodies, Monoclonal / Q000502:physiology*; D000942:Antigens, Bacterial / Q000276:immunology*; D001666:Binding Sites, Antibody; D001769:Blood / Q000276:immunology; D003176:Complement C3 / Q000378:metabolism; D007070:Immunoglobulin A / Q000502:physiology*; D009895:Opsonin Proteins / Q000502:physiology*; D010587:Phagocytosis; D051381:Rats; D011919:Rats, Inbred Strains; D013292:Streptococcus agalactiae / Q000276:immunology* / Q000378:metabolism
D000907:Antibodies, Bacterial; D000911:Antibodies, Monoclonal; D000942:Antigens, Bacterial; D003176:Complement C3; D007070:Immunoglobulin A; D009895:Opsonin Proteins