Binding of aggregated IgG in the presence of fresh serum: strong association with type 12 group A streptococci.

Highly selected group A streptococci, 108 strains isolated from different groups of individuals, were tested for binding of aggregated human IgG which had been pre-incubated in fresh human serum. All strains displayed resistance to phagocytosis typical of M-producing strains. Among 73 strains isolated from sporadic cases of acute glomerulo-nephritis (AGN), 34 (47 per cent) bound the aggregates. All of 26 type 12 group A streptococci but none of 15 type 49 strains proved positive in the test system. Furthermore, one type 1 and one type 18 strain were positive. All 9 type 49 strains isolated in a minor epidemic of AGN proved negative. Twenty-six strains of type 12 group A streptococci were isolated during three different prospective studies in which no cases of AGN had occurred; all these strains bound aggregates in the presence of fresh serum. Thus, it was found that the capacity to bind aggregates in the presence of fresh serum was strongly associated with — though not limited to — group A streptococci carrying the type 12 antigen. However, this characteristic is not common to all nephritogenic strains, since all type 49 group A streptococci were negative in the test system.