IMMUNOLOGICAL RELATIONSHIP BETWEEN THE CLASS-I EPITOPE OF STREPTOCOCCAL M-PROTEIN AND MYOSIN

The class I epitope of streptococcal M protein is an epidemiological m arker for acute rheumatic fever (ARF)-associated serotypes of group A streptococci and is recognized by anti-M protein monoclonal antibody ( Mab) 10B6. Using MAb 10B6, we determined the relationship between the class I epitope of M protein and the cy-helical coiled-coil protein my osin. MAb 10B6 reacted by enzyme-linked immunosorbent assay and Wester n blotting with human cardiac myosin and rabbit Skeletal myosin and it s heavy meromyosin (HMM) subfragment. Overlapping synthetic peptides o f M5 protein were use to identify the region of M5 protein recognized by MAb 10B6. Two C repeat peptides (C2A and C3) containing the amino a cid sequence KGL RRDLDASREAK reacted with MAb 10B6. Partial sequence i dentity, RRDL, was found in the HMM fragment of myosin, which reacted with MAb 10B6. However, not all peptides of M5 protein and myosin cont aining the RRDL sequence reacted with MAb 10B6. ARF sera and sera from uncomplicated pharyngitis (UNC) reacted with C repeat region peptides of M protein, while acute glomerulonephritis sera were not as reactiv e. Affinity-purified human antibody to peptide C3 reacted with myosin. The data demonstrate that the class I epitope of M protein is immunol ogically cross-reactive with myosin and the HMM subfragment, and antib odies to peptide C3 and myosin were present in ARP and UNC sera.