Binding of aggregated IgG to nephritogenic type 12 streptococci: influence of serum, C1 and C4.

The uptake of aggregated IgG by type 12, M protein positive (M + ve) streptococci was high in the presence of fresh serum, while the uptake by type 12, M-ve, type 1 and type 2, M + ve or M-ve streptococci was inhibited. Serum heated to 56 degrees C for 30 min inhibited the uptake of aggregated IgG by all strains tested. Purified C1q or macromolecular C1 added to heat-treated serum restituted the uptake of aggregated IgG. It was shown that C1 and C4 in fresh serum influenced the uptake of aggregated IgG by streptococci, resulting in the distinct reaction patterns observed.