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.
Department of Veterinary Microbiology, Immunology, and Parasitology, Cornell University, Ithaca, New York 14853.
J S
JS
Boschwitz
J F
JF
Timoney
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