Location of variable and conserved epitopes among the multiple serotypes of streptococcal M protein.

Abstract

M protein is a fibrillar molecule composed of two alpha-helical protein chains in a coiled-coil conformation extending from the surface of group A streptococci (1, 2). This molecule is the major virulence factor for the organism by virtue of its ability to render the bacterium resistant to phagocytosis in the human host (3). Based on type-specific antigenic determinants on the M molecule, approximately 65 different serological M types are currently recognized in nature. In man, resistance to streptococcal infection appears to be the result of the presence of type-specific antibodies directed to the M molecule which will neutralize its antiphagocytic properties (3).Previous investigations, which revealed very limited immunological crossreactions between purified M proteins of different serotypes, were primarily confined to detergent-extracted (4) or pepsin-extracted (5) M protein fragments. These fragments comprise only the amino-terminal half of the M molecule (2, 6) and, thus, do not represent all of the determinants present on the native protein.Development of a vaccine to control streptococcal infections may depend upon the identification of a common M protein epitope with the ability to evoke crossprotective antibodies against multiple group A streptococcal serotypes. Since 56 different M serotyping strains show DNA homology with a probe consisting of the gene for the M6 molecule, a common region(s) may exist within the M proteins of different serotypes (7).In an attempt to identify the location of epitopes responsible for broad and limited crossreactivity among 56 of the currently known group A streptococcal M serotypes, we have used monoclonal antibodies generated against phage lysinextracted M6 protein, which comprises nearly the complete M molecule (8). Our results localize a common (evolutionarily conserved) crossreactive epitope near This work was supported by grants AI 11822 (V. Fischetti) and

Protective and heart-crossreactive epitopes located within the NH2 terminus of type 19 streptococcal M protein.

“…Previous studies have shown that the NH2-terminal amino acid sequence of several Mproteins is quite variable from one serotype to another (9-12, 22, 23), whereas the COOH-terminal sequences are highly conserved (22)(23)(24). The M protein-crossreactive and tissue-crossreactive epitopes of pep M5 are located toward the COOH terminus of the molecule (7,8).…”

“…The strips were incubated overnight with affinity-purified SM19(1-24)C immune serum diluted 1 :100 . Inhibition experiments were performed by adding 100 ltg/ml of pep M19 or 100 nm/ml of SM19(1-24)C, SM19(1-14)C, or SM19 (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)C to the antiserum before the addition of the nitrocellulose strips . After an overnight incubation the strips were extensively washed in 0 .05 M Tris/0 .15 M NaCI/0 .05% Tween-20, pH 7 .5 .…”

Mucosal Vaccine Made from Live, RecombinantLactococcus lactisProtects Mice against Pharyngeal Infection withStreptococcus pyogenes

“…Since type specificity resides at the amino termini of M proteins (25,26) and antibodies to the CRR were not opsonic, despite their ability to fix complement on whole bacterial cells (28), it was believed that antibodies to CRR could not provide protection through the opsonic mechanism. A more recent study has revealed that antibodies raised against CRR-derived peptides are capable of eliciting opsonic antibodies (41).…”

“…Over 120 serotypes have been identified (13,30), which makes it difficult to find conserved epitopes that could be used to elicit cross-serotype protection. The CRR of M protein is one such epitope (2,5,15,25). However, CRR-specific secretory IgA and not serum IgG is required for prevention of pharyngeal infection with S. pyogenes (2,3).…”

“…It facilitates colonization of mucosal surfaces and enables the organism to escape host immune surveillance (22,24,27,30). Fischetti and colleagues have identified a region of the M protein that is repeated within the protein and conserved among many, if not all, serotypes (C-repeat region [CRR]) (25,26). Importantly, CRR-specific secretory immunoglobulin A (IgA) but not systemic IgG protects animals against streptococcal pharyngeal infections at the mucosal point of entry, as judged by a reduction in pharyngeal infection following nasal challenge (2,3,5,15,16).…”