FIG. 6.

Reaction of affinity-purified anti-C3 antibodies from ARF sera with streptococcal M5 peptide C3 and myosin. Antibodies to M5 peptide C3 were affinity purified from the sera of a patient with rheumatic carditis. The purified antibodies were diluted 1:10 with buffer and reacted with M5 peptides C1C2 and C3 and with skeletal myosin, actin, and tropomyosin by ELISA. Normal human sera (five samples) were pooled and tested as the control. Normal and affinity-purified Igs were reacted at the same Ig concentrations. A second ARF carditis serum was affinity purified and found to react similarly with myosin and peptide C3 as shown. These data show that human anti-C3 antibodies react with myosin following streptococcal infection.