Complement-fixing antibodies to the cytoplasmic particles (CP) and to the S fraction of streptococcal nucleoproteins are present in normal human sera, the range of concentrations varying among the age groups.
The titer of these antibodies rises between the first half-week and the 3rd week of scarlet fever, in more than 80 per cent of the cases. The titers then remain elevated for at least 4 months.
In children, 91 per cent of the normal sera examined showed anti-CP titers up to 32; 87 per cent of sera in active rheumatic disease had titers above this level. Corresponding data with S fell in the same range of percentage distribution.
Anti-CP and anti-S titers remained elevated long after the rheumatic process had reached quiescence. No correlation of serologic titer with the degree of clinical activity was found in the case of either antibody.