Precipitating Antibody to Group a Streptococcal Polysaccharide in Humans

Abstract

A simple method for detecting and quantitating antibodies against streptococal group A carbohydrate (A-CHO) is described. Its limits of sensitivity were determined as 0.84 µg Ab N/ml and 0.6 µg/ml A-CHO antigen (Ag). The precipitating activity was specifically inhibited by N-acetyl-glucosamine and was associated with the serum fraction precipitated by half-saturated ammonium sulfate and by the 7S pool obtained by gel filtration on Sephadex G-200. The method was highly reproducible using blind duplicates on the same and subsequent days. Subjects with detectable A-CHO antibody varied in population groups from 30% to 84%. The incidence of positive sera in patients with a history of rheumatic fever with or without rheumatic heart disease (RHD) was intermediate between that observed in populations studied under endemic and epidemic conditions. The antibody content was lower in patients with RHD than in those with history of rheumatic fever but no RHD. The age-specific distribution of A-CHO antibody differed from that of an antiprotein streptococcal antibody, antistreptolysin O (ASO), reaching a maximum titer during the teenage years rather than in the elementary school age group when challenge is greatest. There was evidence that the rise in A-CHO antibody following group A infections is lower than the concurrent rise in ASO.