title: Restricted deposition of C3 on M+ group A streptococci: correlation with resistance to phagocytosis.
abstract: In this report, the mechanism of resistance to phagocytosis by group A streptococci and the participation of M protein in this process were studied. A quantitative fluorometric immunoassay was used to determine the amount of the opsonic third component of complement, C3, fixed by group A streptococci in the presence and absence of M protein. In the absence of M protein, phagocytosis was found to be dependent on the amount of C3 fixed. However, when M protein was present, the streptococci still bound sufficient C3 to have promoted phagocytosis, yet none was observed. Further investigation using immunofluorescent microscopy demonstrated that the C3 fixed to M+ chains was confined to dense patches, interspaced by areas devoid of detectable C3. This uneven distribution of C3 was dependent on the presence of a trypsin-sensitive structure; most likely the M protein. The significance of this restricted C3 deposition with respect to resistance to phagocytosis by group A streptococci is discussed.
mesh_terms: D000818:Animals; D000918:Antibody Specificity; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000276:immunology / Q000378:metabolism*; D002352:Carrier Proteins; D003176:Complement C3 / Q000032:analysis / Q000378:metabolism*; D003168:Complement Fixation Tests; D003170:Complement Pathway, Alternative; D003171:Complement Pathway, Classical; D005455:Fluorescent Antibody Technique; D006801:Humans; D009895:Opsonin Proteins / Q000276:immunology; D010587:Phagocytosis; D011817:Rabbits; D013297:Streptococcus pyogenes / Q000276:immunology / Q000378:metabolism
chemical_list: D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D003176:Complement C3; D009895:Opsonin Proteins; C014689:streptococcal M protein