Immunochemical localization and amino acid sequences of crossreactive epitopes within the group A streptococcal M6 protein.

Abstract

M protein is a fibrous, predominantly a-helical, coiled-coil molecule extending from the cell surface of group A streptococci (1, 2). Through its ability to allow this organism to escape phagocytosis by the host's defenses, M protein acts as the primary virulence factor for these streptococci . Protection from streptococcal infection is due primarily to opsonization by type-specific antibodies directed against the M protein (3).Previously, serological crossreactions among purified M proteins of various serotypes proved limited (4, 5), with restricted crossprotection in phagocytic assays (5). These studies were confined, however, to fragments of the M protein that represent approximately the amino terminal half of the native molecule, distal to the streptococcal cell surface (6). Similar limited crossreactivity was seen (7-9) with peptides synthesized on the basis of amino acid sequence determinations within these amino terminal fragments. Opsonic antibodies in these studies, however, were type-specific. Recently, a study (10) using mAbs directed against the entire M6 protein suggested that the amino terminal region of the M protein molecule was variable with respect to antigenic epitopes shared among M serotypes. Conversely, more extensive crossreactions may be reserved for regions more proximal to the cell surface (i. e., the carboxy terminal half of the molecule). The mAb directed toward the amino terminal half of the M6 protein (10A11) crossreacted with 5 different M serotyping strains, whereas the mAb directed toward the carboxy terminal half (10136) did so with 20 of these serotyping strains. Through the use of DNA probes, the location of the conserved epitope was found (2) to be located more centrally in the native molecule, and just carboxy terminal to the pepsin cleavage site, which divides the molecule approximately in half. As a further definition of the antigenic structure of the M molecule, Manjula et al. (11) identified regions within the amino terminal half of the M5 and M6 proteins that crossreact, and they defined a hypervariable antigenic domain located in the amino terminal quarter of these proteins . In a more recent study using DNA probes of the M6 gene to identify constant and variable regions of M proteins in other serotypes, it was found that the carboxy terminal region of the M protein was conserved among strains of several different 1226 J. Exp. MED. C The Rockefeller University

T Cell Mimicry and Epitope Specificity of Cross-Reactive T Cell Clones from Rheumatic Heart Disease

“…The recognition of the C repeat region by a large number of T cell lines is in accordance with the fact that all M protein serotypes share a large region of homology in the C repeat region of the molecule (34,47,48). M protein serotypes M5 and M6 share homology within the B repeat region (49,50), which is the basis for the sharing of epitopes in the B repeat region of M5 and M6 proteins. Consequently, M6-proteinspecific T cell clones proliferated to B repeat peptides of M5 protein.…”

Generation and Surface Localization of Intact M Protein inStreptococcus pyogenesAre Dependent onsagA

“…Although normal clumping was observed for JRS4, no clumping was seen for JRS145 or JRS470, suggesting that, like the M Ϫ strain, the sagA mutant strain lacks surface M protein. This was confirmed by spotting whole cells onto nitrocellulose membranes and developing the membranes with MAb 10A11, which recognizes an epitope in the B repeat region of the M6 protein (24), and with DIG-labeled fibrinogen, which binds M protein (53,54) (Fig. 2).…”

“…4A). Whole-cell protein extracts from both wild-type and mutant strains were separated by SDS-PAGE and probed first with MAb 10A11, which recognizes an epitope in the B repeat region of the M6 molecule (24). The multiple banding pattern characteristic of full-length M6 protein (between Ϸ50 and Ϸ66 kDa) was observed in the wholecell extracts of wild-type strain JRS4 (Fig.…”

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).…”

“…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).…”