Inhibition of C3 deposition on Streptococcus equi subsp. equi by M protein: a mechanism for survival in equine blood.
The effect of the M protein of Streptococcus equi subsp. equi on complement deposition, complement degradation, and bacterial survival in equine whole blood was examined in vitro. Preincubation of bacteria with rabbit M protein-specific immunoglobulin G (IgG) inhibited the survival of the M+ strain in whole blood by 20-fold (P < 0.01). In addition, preincubation of bacteria with M protein-specific F(ab')2 fragments inhibited the survival of M+ cells in whole blood by 3.8-fold (P < 0.01). In the absence of specific antibody, an M+ strain (CF32) of S. equi subsp. equi survived 100-fold better in whole blood than an M- isolate (strain 19) (P < 0.01). Complement inactivation by cobra venom factor significantly enhanced the ability of the M- and M+ strains of S. equi subsp. equi to survive in whole blood, the latter in the presence or absence of M protein-specific IgG. The major opsonic forms of C3, C3b and iC3b, were present on both M- and M+ cells after opsonization in nonimmune plasma. However, colloidal gold staining indicated that the M- strain bound four times as much C3 as the M+ strain (P < 0.02) and that preincubation of the M+ strain with M protein-specific IgG or F(ab')2 fragments also enhanced the amount of C3 deposited by a factor of 4 (P < 0.02). Therefore, at least part of the M protein's ability to enhance bacterial survival in equine whole blood may be related to its ability to interfere with the deposition of equine complement on the bacterial surface.
Boschwitz
J S
JS
Department of Veterinary Microbiology, Immunology, and Parasitology, Cornell University, Ithaca, New York 14853.
Timoney
J F
JF
D000818:Animals; D000942:Antigens, Bacterial; D016470:Bacteremia / Q000209:etiology / Q000662:veterinary*; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000276:immunology*; D001770:Blood Bactericidal Activity; D002352:Carrier Proteins; D003176:Complement C3 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006734:Horse Diseases / Q000209:etiology*; D006736:Horses; D007074:Immunoglobulin G / Q000276:immunology; D011817:Rabbits; D013290:Streptococcal Infections / Q000209:etiology / Q000662:veterinary*; D013291:Streptococcus / Q000276:immunology*
D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D003176:Complement C3; D007074:Immunoglobulin G; C014689:streptococcal M protein