Multiple, heart-cross-reactive epitopes of streptococcal M proteins.

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Abstract
A highly purified pepsin extract of type 5 streptococcal M protein (pep M5) contains at least 3 epitopes that are cross-reactive with sarcolemmal membrane proteins of human myocardium. The tissue-cross-reactive determinants of pep M5 are also partially shared with pep M6 and pep M19. Three rabbits immunized with a single 300 .mu.g dose of pep M5 developed significant levels of heart-cross-reactive antibodies, as determined by indirect immunofluorescence tests. All 3 sera also contained antibodies that cross-reacted with pep M6 and pep M19. The heart tissue-specific antibodies that were eluted from sarcolemmal membranes opsonized types 5, 6 and 19 streptococci, indicating that they were directed against protective M protein epitopes on the surface of virulent organisms. Immunofluorescence inhibition tests, using purified M proteins as soluble inhibitors of heart-cross-reactive antibodies, revealed the number and M protein serotype distribution of the tissue-cross-reactive epitopes. Immunoblot analyses demonstrated the sarcolemmal membrane proteins containing the various cross-reactive antigenic determinants.

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