Epitopes of streptococcal M proteins that evoke antibodies that cross-react with human brain

There is evidence suggesting that Sydenham's chorea, which is a major manifestation of acute rheumatic fever, may be mediated by streptococcal antibodies that cross-react with the brain. Our studies were undertaken to determine whether streptococcal M protein, the major virulence factor of group A streptococci, evoked antibodies that cross-react with human brain. Rabbits were immunized with pepsin-extracted M protein from rheumatogenic type 6 streptococci. Immune sera were screened for the presence of antibodies that cross-reacted with human brain by indirect immunofluorescence tests and immunoblot analyses. Type 6 M protein evoked antibodies that cross-reacted with several brain proteins and antibody binding to these proteins was completely inhibited by type 6 M protein and partially inhibited by types 5 and 19 M proteins, suggesting that these heterologous M proteins contain conserved brain-cross-reactive epitopes. Using synthetic peptides from several serotypes of M proteins, the conserved brain-cross-reactive epitopes were localized to a decapeptide contained within the covalent structure of the B repeat region of type 6 M protein. These peptides also inhibited brain-cross-reactive antibodies in the serum of a patient with active Sydenham's chorea. Our data indicate that streptococcal M proteins contain brain-cross-reactive epitopes that could potentially be involved in the pathogenesis of Sydenham's chorea.

Recombinant tetravalent group A streptococcal M protein vaccine

Previous studies have shown that the amino-terminal regions of group A streptococcal M proteins contain primarily protective (opsonic) epitopes and not tissue-cross-reactive epitopes. Limited primary structures from multiple serotypes of M protein containing only protective epitopes could potentially be linked together to form a broadly protective vaccine. The present studies were undertaken to determine the protective immunogenicity of a recombinant, multivalent hybrid molecule containing amino-terminal subunits of types 24, 5, 6, and 19 M proteins. Polymerase chain reaction primers were designed to amplify emm gene fragments ranging from 35 to 113 codons. The PCR products were ligated in tandem and inserted into pKK223-3. The tetravalent M protein that was purified from extracts of Escherichia coli migrated as a single band on SDS-PAGE with an apparent m.w. of 31 kDa. In immunoblot analyses, the hybrid protein reacted with serotype-specific antisera indicating that it contained all four M protein subunits. Rabbits immunized with the purified tetravalent M protein developed significant antibody levels against all four serotypes of native M proteins represented in the hybrid protein. None of the antisera cross-reacted with human tissues. The immune sera also opsonized all four serotypes of group A streptococci. Our data show that a hybrid protein containing subunits from multiple M proteins can evoke broadly protective immune responses without tissue-cross-reactive antibodies.

Recombinant tetravalent group A streptococcal M protein vaccine

Previous studies have shown that the amino-terminal regions of group A streptococcal M proteins contain primarily protective (opsonic) epitopes and not tissue-cross-reactive epitopes. Limited primary structures from multiple serotypes of M protein containing only protective epitopes could potentially be linked together to form a broadly protective vaccine. The present studies were undertaken to determine the protective immunogenicity of a recombinant, multivalent hybrid molecule containing amino-terminal subunits of types 24, 5, 6, and 19 M proteins. Polymerase chain reaction primers were designed to amplify emm gene fragments ranging from 35 to 113 codons. The PCR products were ligated in tandem and inserted into pKK223-3. The tetravalent M protein that was purified from extracts of Escherichia coli migrated as a single band on SDS-PAGE with an apparent m.w. of 31 kDa. In immunoblot analyses, the hybrid protein reacted with serotype-specific antisera indicating that it contained all four M protein subunits. Rabbits immunized with the purified tetravalent M protein developed significant antibody levels against all four serotypes of native M proteins represented in the hybrid protein. None of the antisera cross-reacted with human tissues. The immune sera also opsonized all four serotypes of group A streptococci. Our data show that a hybrid protein containing subunits from multiple M proteins can evoke broadly protective immune responses without tissue-cross-reactive antibodies.

A 28-kilodalton fibronectin-binding protein of group A streptococci

Lipoteichoic acid (LTA) has been implicated as a major adhesin of group A streptococci that interacts with fibronectin (Fn). It has been suggested that protein adhesins may also be involved in the binding of Fn to streptococci. We searched for such a protein by transblotting membrane preparations from M types 5, 19, and 24 group A streptococci to nitrocellulose and reacting the blot with 125I-Fn. The Fn reacted with a 28-kDa polypeptide from all three serotypes of streptococci. Using affinity-purified antibodies to the 28-kDa protein in immunoblots of membrane preparations from various streptococci, we demonstrated that the 28-kDa protein is present in all 17 strains tested. Affinity-purified antibodies to the 28-kDa protein also reacted in varying degrees with intact streptococci, demonstrating that the antigen is exposed on the surface of intact organisms. Our results suggest that, in addition to LTA, group A streptococci contain a common Fn-binding moiety that is expressed as a major component of membrane preparations and that is accessible on the surface of streptococci for interactions with Fn.

Streptococcal C5a peptidase is a highly specific endopeptidase

Compositional analysis of streptococcal C5a peptidase (SCPA) cleavage products from a synthetic peptide corresponding to the 20 C-terminal residues of C5a demonstrated that the target cleavage site is His-Lys rather than Lys-Asp, as previously suggested. A C5a peptide analog with Lys replaced by Gln was also subject to cleavage by SCPA. This confirmed that His-Lys rather than Lys-Asp is the scissile bond. Cleavage at histidine is unusual but is the same as that suggested for a peptidase produced by group B streptococci. Native C5 protein was also resistant to SCPA, suggesting that the His-Lys bond is inaccessible prior to proteolytic cleavage by C5 convertase. These experiments showed that the streptococcal C5a peptidase is highly specific for C5a and suggest that its function is not merely to process protein for metabolic consumption but to act primarily to eliminate this chemotactic signal from inflammatory foci.

Lipoteichoic acid and M protein: dual adhesins of group A streptococci

The roles of lipoteichoic acid (LTA) and M protein in the adherence of group A streptococci to human cells were investigated. Both M+ and M- streptococci bound to pharyngeal and buccal epithelial cells in similar numbers. Streptococcal attachment was inhibited by LTA, but not by the pepsin-extracted, amino-terminal half of M protein (pep M), suggesting that M protein does not mediate attachment to these cells. However, a purified, recombinant, intact M protein did block attachment of streptococci to buccal cells. Using synthetic peptides, the inhibitory domain was localized to a region of intact M protein that is within or near the bacterial cell wall. Evidence is presented to suggest that on the surface of streptococci this region of the M protein is probably not accessible for interactions with host cell receptors and that M protein does not mediate attachment to buccal or pharyngeal cells. In contrast, approximately 10-times more M+ streptococci bound to Hep-2 cells than did M- streptococci and pep M protein blocked binding of streptococci to Hep-2 cells. The data suggest that at least two streptococcal adhesins, LTA and M protein, are involved in the adherence of streptococci to certain cells and that the relative contributions of these adhesins to the attachment process depends on the type of host cells used to study adherence.

Epitopes of group A streptococcal M protein that evoke cross-protective local immune responses

The present studies were undertaken to identify conserved epitopes of group A streptococcal M proteins that evoke cross-protective mucosal immune responses. Two synthetic peptides copying conserved regions of type 5 M protein, designated SM5(235-264)C and SM5(265-291)C, were covalently linked to carrier molecules and their immunogenicity was tested in laboratory animals. Rabbit antisera against both peptides cross-reacted with multiple serotypes of group A streptococci, indicating that the peptides contained broadly cross-reactive, surface exposed M protein epitopes. Serum antipeptide antibodies adsorbed to the surface of heterologous type 24 streptococci passively protected mice against intranasal challenge infections. Mice that were actively immunized intranasally with each synthetic peptide covalently linked to the B subunit of cholera toxin were protected against colonization and death after intranasal challenge infections with type 24 streptococci in the absence of serum opsonic antibodies. These data confirm and extend previous observations that conserved M protein epitopes evoke cross-protective local immunity and may serve as the basis for broadly cross-protective M protein vaccines.

Epitopes of group A streptococcal M protein that evoke cross-protective local immune responses

The present studies were undertaken to identify conserved epitopes of group A streptococcal M proteins that evoke cross-protective mucosal immune responses. Two synthetic peptides copying conserved regions of type 5 M protein, designated SM5(235-264)C and SM5(265-291)C, were covalently linked to carrier molecules and their immunogenicity was tested in laboratory animals. Rabbit antisera against both peptides cross-reacted with multiple serotypes of group A streptococci, indicating that the peptides contained broadly cross-reactive, surface exposed M protein epitopes. Serum antipeptide antibodies adsorbed to the surface of heterologous type 24 streptococci passively protected mice against intranasal challenge infections. Mice that were actively immunized intranasally with each synthetic peptide covalently linked to the B subunit of cholera toxin were protected against colonization and death after intranasal challenge infections with type 24 streptococci in the absence of serum opsonic antibodies. These data confirm and extend previous observations that conserved M protein epitopes evoke cross-protective local immunity and may serve as the basis for broadly cross-protective M protein vaccines.

Epitopes of group A streptococcal M protein shared with antigens of articular cartilage and synovium

Rabbit antisera evoked by purified pepsin-extracted group A streptococcal M proteins were screened for the presence of joint cross-reactive antibodies by indirect immunofluorescence using thin sections of mouse knee joints. Pep M1, M5, and M18 antisera contained antibodies that cross-reacted with chondrocytes, cartilage, and synovium. Immunofluorescence inhibition assays showed that some of the joint cross-reactive epitopes were shared among the three heterologous serotypes of M protein. The pep M5 joint cross-reactive epitopes were localized to three different synthetic peptides of the C-terminal region of pep M5. Immunoblot analyses showed that the M5 joint cross-reactive antibodies recognized two proteins of human synovium and cartilage of molecular mass 56 and 58 kDa. The cross-reactive antibodies binding to the 56-kDa protein were inhibited by purified vimentin in immunoblot inhibition experiments. M protein-specific antibodies from patients with acute rheumatic fever were also shown to cross-react with joint tissue in a pattern similar to the rabbit antisera. Rabbit and human M protein-specific antibodies that were bound to articular cartilage activated significant levels of complement when compared to control serum, suggesting that M protein joint cross-reactive antibodies could potentially be involved in the pathogenesis of ARF and arthritis.

Epitopes of group A streptococcal M protein shared with antigens of articular cartilage and synovium

Rabbit antisera evoked by purified pepsin-extracted group A streptococcal M proteins were screened for the presence of joint cross-reactive antibodies by indirect immunofluorescence using thin sections of mouse knee joints. Pep M1, M5, and M18 antisera contained antibodies that cross-reacted with chondrocytes, cartilage, and synovium. Immunofluorescence inhibition assays showed that some of the joint cross-reactive epitopes were shared among the three heterologous serotypes of M protein. The pep M5 joint cross-reactive epitopes were localized to three different synthetic peptides of the C-terminal region of pep M5. Immunoblot analyses showed that the M5 joint cross-reactive antibodies recognized two proteins of human synovium and cartilage of molecular mass 56 and 58 kDa. The cross-reactive antibodies binding to the 56-kDa protein were inhibited by purified vimentin in immunoblot inhibition experiments. M protein-specific antibodies from patients with acute rheumatic fever were also shown to cross-react with joint tissue in a pattern similar to the rabbit antisera. Rabbit and human M protein-specific antibodies that were bound to articular cartilage activated significant levels of complement when compared to control serum, suggesting that M protein joint cross-reactive antibodies could potentially be involved in the pathogenesis of ARF and arthritis.

Identification of an epitope of type 1 streptococcal M protein that is shared with a 43-kDa protein of human myocardium and renal glomeruli

The localization of opsonic and tissue-cross-reactive epitopes within the amino terminus of type 1 streptococcal M protein was investigated by using murine mAb raised against synthetic peptides of type 1 M protein. Two mAb (IIIA2 and IIIB8) reacted with epitopes located within amino acid residues 1-12 of type 1 M protein. These antibodies opsonized type 1 streptococci and did not cross-react with human kidney and heart tissue. Another mAb (IC7) reacted with mesangial cells of renal glomeruli and human myocardium. The cross-reactive epitope of mAb IC7 was localized to position 13-19, indicating that it is not the same epitope as the previously described vimentin-cross-reactive epitope at position 23-26 of type 1 M protein. In Western blots of mesangial cell and myocardial proteins, mAb IC7 cross-reacted with a 43-kDa protein. Neither vimentin nor actin inhibited the binding of mAb IC7 to the cross-reactive protein, as determined by Western blot or immunofluorescence inhibition tests. These results provide evidence that type 1 M protein contains at least one autoimmune epitope shared with both human glomeruli and myocardium.

Identification of an epitope of type 1 streptococcal M protein that is shared with a 43-kDa protein of human myocardium and renal glomeruli

The localization of opsonic and tissue-cross-reactive epitopes within the amino terminus of type 1 streptococcal M protein was investigated by using murine mAb raised against synthetic peptides of type 1 M protein. Two mAb (IIIA2 and IIIB8) reacted with epitopes located within amino acid residues 1-12 of type 1 M protein. These antibodies opsonized type 1 streptococci and did not cross-react with human kidney and heart tissue. Another mAb (IC7) reacted with mesangial cells of renal glomeruli and human myocardium. The cross-reactive epitope of mAb IC7 was localized to position 13-19, indicating that it is not the same epitope as the previously described vimentin-cross-reactive epitope at position 23-26 of type 1 M protein. In Western blots of mesangial cell and myocardial proteins, mAb IC7 cross-reacted with a 43-kDa protein. Neither vimentin nor actin inhibited the binding of mAb IC7 to the cross-reactive protein, as determined by Western blot or immunofluorescence inhibition tests. These results provide evidence that type 1 M protein contains at least one autoimmune epitope shared with both human glomeruli and myocardium.

Phosphorylase-cross-reactive antibodies evoked by streptococcal M protein

Rabbit antisera evoked by type 5 streptococcal M protein (M5) were screened by enzyme-linked immunosorbent assay (ELISA) for immunological cross-reactivity with purified rabbit muscle phosphorylases a and b. Of 10 pep M5 antisera tested, 3 showed significant cross-reactivity with both forms of the enzyme. ELISA inhibition studies using one of the pep M5 antisera showed that all of the phosphorylase b antibodies were inhibited by pep M5, the immunogen, and phosphorylase b, the ELISA antigen. All of the antibodies were also inhibited by pep M6 and pep M19, but not by pep M24, indicating that the cross-reactive epitopes were shared by multiple serotypes of M protein. Western blot (immunoblot) analyses showed that pep M5 antisera reacted strongly with the subunit of phosphorylase b. In addition, purified phosphorylase partially inhibited the binding of pep M5 antibodies to a 95-kilodalton protein of human myocardium. One of the three cross-reactive pep M5 antisera inhibited the enzymatic activity of phosphorylase a in a dose-related fashion, reaching a maximum inhibition of 75%. The enzymatic activity in the presence of antibody was totally restored when the antiserum was first incubated with pep M5.

Human and murine antibodies cross-reactive with streptococcal M protein and myosin recognize the sequence GLN-LYS-SER-LYS-GLN in M protein

Molecular mimicry or epitope similarity between group A streptococcal M proteins and myosin may contribute to the presence of heart reactive antibodies in acute rheumatic fever. In our study overlapping synthetic peptides copying the entire sequence of PepM5 protein were used to map the myosin cross-reactive epitopes of streptococcal M protein recognized by mouse and human mAb and affinity purified myosin-specific antibodies from acute rheumatic fever and rheumatic heart disease sera. Overlapping M protein peptides SM5(164-197)C and SM5(184-197)C inhibited the murine mAb reactions with PepM5 protein. The human mAb and affinity purified myosin-specific antibodies reacted exclusively with SM5(184-197)C. However, one of the five different purified myosin-specific antibodies not only reacted with SM5(184-197)C but also reacted with SM5(84-116)C. The synthetic subpeptides SM5(175-184)C and SM5(188-197C) did not react with any of the antibodies to PepM5 and myosin demonstrating a requirement of the 184-188 amino acid sequence for antibody recognition. A heptapeptide containing the sequence SM5(183-189) was also found to inhibit selected human myosin-specific antibodies and a human antimyosin mAb. Therefore, the majority of mouse and human myosin crossreactive antibodies recognized an epitope within the 14 residue carboxy terminus of PepM5 which appeared to involve the GLN-LYS-SER-LYS-GLN sequence.

Human and murine antibodies cross-reactive with streptococcal M protein and myosin recognize the sequence GLN-LYS-SER-LYS-GLN in M protein

Molecular mimicry or epitope similarity between group A streptococcal M proteins and myosin may contribute to the presence of heart reactive antibodies in acute rheumatic fever. In our study overlapping synthetic peptides copying the entire sequence of PepM5 protein were used to map the myosin cross-reactive epitopes of streptococcal M protein recognized by mouse and human mAb and affinity purified myosin-specific antibodies from acute rheumatic fever and rheumatic heart disease sera. Overlapping M protein peptides SM5(164-197)C and SM5(184-197)C inhibited the murine mAb reactions with PepM5 protein. The human mAb and affinity purified myosin-specific antibodies reacted exclusively with SM5(184-197)C. However, one of the five different purified myosin-specific antibodies not only reacted with SM5(184-197)C but also reacted with SM5(84-116)C. The synthetic subpeptides SM5(175-184)C and SM5(188-197C) did not react with any of the antibodies to PepM5 and myosin demonstrating a requirement of the 184-188 amino acid sequence for antibody recognition. A heptapeptide containing the sequence SM5(183-189) was also found to inhibit selected human myosin-specific antibodies and a human antimyosin mAb. Therefore, the majority of mouse and human myosin crossreactive antibodies recognized an epitope within the 14 residue carboxy terminus of PepM5 which appeared to involve the GLN-LYS-SER-LYS-GLN sequence.

Cellular and biochemical responses of human T lymphocytes stimulated with streptococcal M proteins

Purified group A streptococcal M proteins, pep M5 and pep M6, bearing heart cross-reactive epitopes were compared with pep M24, which lacks such epitopes, in their ability to induce functional differentiation of human T lymphocytes. Lymphocytes activated by pep M5 and pep M6 demonstrated cytotoxic activity against cultured heart cells, whereas pep M24-activated cells differentiated into suppressor T cells, which specifically blocked cytotoxic T lymphocytes against cultured human myocardial cells and not NK cell activity against K562 cells. Pep M5 and not pep M24 induced an increase in the number of CD4, 4B4, helper/inducer T cells. In addition, these M proteins appear to induce different biochemical changes in T lymphocytes. Both pep M5 and pep M24 induced the phosphorylation of a 35-kDa cytoplasmic protein; however, only pep M5 induced the phosphorylation of a 28-kDa membrane protein, primarily in CD4 T cells. These data indicate that the virulent M protein Ag of group A streptococci may exert their effect on the human immune system via different mechanisms. Determining these mechanisms and the biochemical pathways involved in T cell differentiation triggered by these Ag may be important in understanding the pathogenesis of post-streptococcal diseases.

Cellular and biochemical responses of human T lymphocytes stimulated with streptococcal M proteins

Purified group A streptococcal M proteins, pep M5 and pep M6, bearing heart cross-reactive epitopes were compared with pep M24, which lacks such epitopes, in their ability to induce functional differentiation of human T lymphocytes. Lymphocytes activated by pep M5 and pep M6 demonstrated cytotoxic activity against cultured heart cells, whereas pep M24-activated cells differentiated into suppressor T cells, which specifically blocked cytotoxic T lymphocytes against cultured human myocardial cells and not NK cell activity against K562 cells. Pep M5 and not pep M24 induced an increase in the number of CD4, 4B4, helper/inducer T cells. In addition, these M proteins appear to induce different biochemical changes in T lymphocytes. Both pep M5 and pep M24 induced the phosphorylation of a 35-kDa cytoplasmic protein; however, only pep M5 induced the phosphorylation of a 28-kDa membrane protein, primarily in CD4 T cells. These data indicate that the virulent M protein Ag of group A streptococci may exert their effect on the human immune system via different mechanisms. Determining these mechanisms and the biochemical pathways involved in T cell differentiation triggered by these Ag may be important in understanding the pathogenesis of post-streptococcal diseases.

Conservation of the D-mannose-adhesion protein among type 1 fimbriated members of the family Enterobacteriaceae

A variety of genera and species of the family Enterobacteriaceae bear surface fimbriae that enable them to bind to D-mannose residues on eukaryotic cells. Until recently, it was thought that the D-mannose binding site was located in the major structural subunit (FimA), of relative molecular mass (Mr) 17,000 (17 K), of these organelles in Escherichia coli. New evidence indicates that this binding site resides instead in a minor protein Mr 28-31 K (FimH) located at the tips and at long intervals along the length of the fimbriae, and is reminiscent of the minor tip adhesion proteins of pyelonephritis-associated pili (Pap) and S fimbriae. In contrast to the antigenic heterogeneity of the major FimA subunit, the antigenic structure of FimH is conserved among different strains of E. coli. Here, we report an even broader conservation of this minor adhesion protein extending to other genera and species of type 1 fimbriated Enterobacteriaceae. Our results may have implications for the development of broadly protective vaccines against Gram-negative bacillary infections in animals and perhaps in man.

Protective immunity evoked by locally administered group A streptococcal vaccines in mice

The present studies were undertaken to determine the pathogenicity of group A streptococci introduced intranasally (i.n.) into mice in an attempt to mimic mucosal infections in humans and to determine the efficacy of streptococcal vaccines administered via the mucosal route. The LD50 of type 24 streptococci (M24 strep) administered i.n. was 3 x 10(4) CFU. Throat cultures were performed in M24 strep-inoculated mice. Of 11 mice that died, 9 had positive throat cultures 3 or 4 days after i.n. challenge, and of 9 mice that survived, only 1 had a positive throat culture, indicating an association between mucosal infection and death. Postmortem examination performed on 35 mice that died after i.n. challenge showed that all had evidence of disseminated infections, and group A streptococci were recovered from the cervical lymph nodes, blood, spleen, liver, and brain. To determine vaccine efficacy, heat-killed M24 strep or pep M24 were administered i.n. to groups of mice. Whole, heat-killed streptococci and pep M24 administered locally protected mice against death from i.n. challenge infections with homologous M24 strep. The whole cell vaccine also protected against i.n. challenge infections with heterologous type 6 streptococci. Our data suggest that streptococcal vaccines administered locally evoke protective immunity against streptococcal infections.

Protective immunity evoked by locally administered group A streptococcal vaccines in mice

The present studies were undertaken to determine the pathogenicity of group A streptococci introduced intranasally (i.n.) into mice in an attempt to mimic mucosal infections in humans and to determine the efficacy of streptococcal vaccines administered via the mucosal route. The LD50 of type 24 streptococci (M24 strep) administered i.n. was 3 x 10(4) CFU. Throat cultures were performed in M24 strep-inoculated mice. Of 11 mice that died, 9 had positive throat cultures 3 or 4 days after i.n. challenge, and of 9 mice that survived, only 1 had a positive throat culture, indicating an association between mucosal infection and death. Postmortem examination performed on 35 mice that died after i.n. challenge showed that all had evidence of disseminated infections, and group A streptococci were recovered from the cervical lymph nodes, blood, spleen, liver, and brain. To determine vaccine efficacy, heat-killed M24 strep or pep M24 were administered i.n. to groups of mice. Whole, heat-killed streptococci and pep M24 administered locally protected mice against death from i.n. challenge infections with homologous M24 strep. The whole cell vaccine also protected against i.n. challenge infections with heterologous type 6 streptococci. Our data suggest that streptococcal vaccines administered locally evoke protective immunity against streptococcal infections.

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

M protein was purified to homogeneity from limited pepsin digests of intact type 19 streptococci (pep M19). The purified pep M19 when emulsified in CFA and injected into rabbits evoked type-specific and crossreactive opsonic antibodies, as well as heart-crossreactive antibodies. The NH2-terminal primary structure of pep M19 was determined and a peptide copying the first 24 amino acids [SM19(1-24)C] was chemically synthesized. Rabbits that were immunized with the unconjugated peptide developed antibodies that recognized the native pep M19, as determined by ELISA, and opsonic antibodies against type 19 streptococci, as determined by in vitro opsonophagocytosis tests. The synthetic peptide also evoked antibodies that crossreacted with a 60-kD sarcolemmal membrane protein of human myocardium. By using overlapping synthetic subpeptides as immunoinhibitors, the opsonic and heart-crossreactive epitopes of SM19(1-24)C were localized to SM19(11-24)C. Our data confirm the presence of heart-crossreactive epitopes within the primary structure of pep M19 and show that these potentially harmful autoimmune epitopes may be located in the NH2-terminal regions of certain M proteins. We conclude that continued efforts to identify the primary structures of protective and heart-crossreactive epitopes will be necessary to elucidate the pathogenesis of acute rheumatic heart disease and to develop safe and effective streptococcal vaccines.

Comparison of the leader sequences of four group A streptococcal M protein genes

The 5' portions and flanking sequences of genes encoding types 1, 12, 24, and 6 M proteins were compared. Although the DNA sequences encoding the amino-termini of the mature M proteins had no obvious similarity, upstream sequences, and those encoding the signal peptides (leader sequences) of the four M protein genes had considerable similarity. In general, the 5' ends of all the leader sequences were more conserved than the 3' ends, although the M6 and M24 leader sequences had identical 3' ends. Sequence similarity among the deduced amino acid sequences of the four signal peptides was more extensive than the corresponding DNA sequences. We found that strict DNA similarity among all four sequences extended only to the ends of the hydrophilic amino-terminal regions of the signal peptides, but that amino acid sequence conservation continued to the ends of the respective hydrophobic cores. With the exception of the M6 and M24 sequences, the regions adjacent to the signal peptidase cleavage sites were highly variable.

Protective and autoimmune epitopes of streptococcal M proteins

Several rheumatogenic serotypes of streptococcal M protein have been shown to contain both protective and cardiac tissue crossreactive epitopes. By synthesizing peptides copying different regions of M protein polypeptides, we were able to localize the protective and heart crossreactive epitopes. Some epitopes are only opsonic, some are only crossreactive, whereas others are both opsonic and tissue crossreactive. Multivalency of vaccines can be obtained by synthesizing protective peptides of one M serotype in tandem with protective peptides of other M serotypes. Such hybrid peptides evoke protective immune responses against the related streptococci without evoking tissue crossreactive immunity.

Human cytotoxic T lymphocytes evoked by group A streptococcal M proteins

Purified group A streptococcal M proteins were used to stimulate peripheral blood lymphocytes from normal adult volunteers. The activated lymphocytes were cytotoxic against cultured human heart cells, as well as liver cells, fibroblasts, and K562 cells, but showed only minimal cytotoxicity against several animal cell types. The cytotoxic activity evoked by type 5 M protein was dose and time dependent. Rabbit antisera against pep M5 that contained heart-crossreactive antibodies partially inhibited cytotoxicity against heart cells, but had no effect on other target cells, suggesting that a fraction of the effector lymphocytes may be recognizing M protein-crossreactive cell surface antigens. All of the cytotoxic activity was recovered from a CD3+ population of lymphocytes obtained from a fluorescence-activated cell sorter, and CD4+ and CD8+ cells were also cytotoxic. M protein-responsive T cell clones were generated that showed specificity for heart and K562 cells, in addition to clones that were cytotoxic against both cell lines. Our data show that streptococcal M protein evokes cytotoxic T lymphocytes against multiple human but not animal target cells. Some of the effector cells may be specific for cultured myocardial cells, but their role in the pathogenesis of rheumatic carditis will require further studies of lymphocytes from patients with acute rheumatic fever and carditis.

Sequence and type-specific immunogenicity of the amino-terminal region of type 1 streptococcal M protein

The NH2-terminal sequence of type 1 M protein was determined by automated Edman degradation of purified polypeptide fragments extracted from whole streptococci by limited digestion with pepsin. Three polypeptide fragments were purified by slab gel electrophoresis on sodium dodecyl sulfate (SDS) polyacrylamide followed by electroelution. The purified fragments migrated as 28-, 25-, and 23.5-kDa fragments, respectively. Each of the fragments inhibited opsonization of a diluted antiserum prepared in rabbits by immunization with whole type 1 streptococci. The amino-terminal sequences of the peptide fragments were confirmed by comparison with the primary structure predicted from the nucleotide sequence of the type 1 M protein structural gene. The 28-kDa fragment contained the NH2-terminal asparagine residue of the processed type 1 M protein, whereas the NH2-terminal sequences of the 25- and 23.5-kDa peptides began at residues 27 and 36, respectively. A seven-residue periodicity with respect to polar and nonpolar residues was observed beginning at residue 22 and, therefore, the secondary structural potential of type 1 M protein is similar to that reported for other M proteins. In contrast to the other M proteins, however, identical repeats were rare, the longest sequence identity consisting of a three-amino acid acid sequence Lys-Asp-Leu at positions 30-32 repeated once at positions 65-67. A 23-residue synthetic peptide of the amino-terminus of the type 1 M protein evoked opsonic antibodies against type 1 streptococci. These results indicate that the NH2-terminal region of type 1 M protein retains the secondary structural characteristics of other M serotypes. Moreover, it contains epitopes that evoke protective immune responses. Our studies may have bearing in the development of safe and effective vaccines against group A streptococcal infections.