Opsonin-independent phagocytosis of group B streptococci: role of complement receptor type three.
The role of complement receptor type 3 (CR3) in nonopsonic recognition of group B streptococci (GBS) by macrophages was investigated. Monoclonal anti-CR3 (anti-Mac-1) inhibited phagocytosis of GBS strains by as much as 50% in serum-free cultures of both mouse peritoneal macrophages and the macrophage cell line PU5-1.8. GBS uptake was unaffected by the presence of anti-C3 or salicylhydroxamate, an inhibitor of the covalent binding reaction of C3. Soluble antibodies to LFA-1 or to the common beta-chain (CD18) of the LFA-1/CR3/p150,95 family of cell adhesion molecules did not inhibit GBS uptake. Down-modulation of surface Mac-1 on macrophages following adherence to anti-Mac-1- or anti-CD18-coated surfaces also inhibited uptake of GBS. Further evidence for GBS interaction with CR3 was demonstrated by reduction of EC3bi rosette formation in macrophages adherent to GBS-coated plates. These studies suggest that GBS can interact with macrophage CR3, promoting phagocytosis in a C3-independent fashion. In the absence of specific immunity in neonates, this recognition mechanism may be a significant virulence determinant for GBS which poorly activate the alternate complement pathway.
Antal
J M
JM
Department of Zoological & Biomedical Sciences, Ohio University, Athens 45701-2979.
Cunningham
J V
JV
Goodrum
K J
KJ
D000818:Animals; D002460:Cell Line; D003176:Complement C3 / Q000502:physiology; D016169:Lymphocyte Function-Associated Antigen-1 / Q000502:physiology; D016177:Macrophage-1 Antigen / Q000502:physiology*; D008264:Macrophages / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D009895:Opsonin Proteins / Q000502:physiology*; D010587:Phagocytosis; D013292:Streptococcus agalactiae / Q000276:immunology* / Q000472:pathogenicity; D014774:Virulence
D003176:Complement C3; D016169:Lymphocyte Function-Associated Antigen-1; D016177:Macrophage-1 Antigen; D009895:Opsonin Proteins