Natural infection of man with group A streptococci. Levels; restriction in class, subclass, and type; and clonal appearance of polysaccharide-group-specific antibodies.

The level of antibodies specific for the two serologically distinct polysaccharides of group A and group A-variant streptococci was investigated in human sera by a modified Farr technique. Whereas there was an obvious relationship between the anti-streptolysin O titer and the level of group-A-specific antibodies, suggesting a recent streptococcal infection with group A streptococci, this correlation was not apparent for the level of group A-variant antibodies. There is evidence suggesting that children have significantly lower group A polysaccharide antibody levels than adults; this is not true of their group A-variant antibody levels. There was an apparent restriction of groups A- and A-variant-specific antibodies to the kappa light-chain type and IgG2 heavy-chain subclass. Whereas only one serum contained group A-specific antibodies also associated with IgG3 heavy chains, nine sera contained anti-group A-variant-specific antibodies with both IgG2 and IgG3 heavy chains. No anti-polysaccharide activity was detected in the IgM and IgA class of serum antibodies. Anti-group A and anti-group A-variant antibodies of human sera are restricted with respect to the number of clonotypes that are shown by isoelectric focusing. The most heterogeneous sera contained roughly ten clonotypes.