BINDING OF AGGREGATED IgG Fab‐FRAGMENTS AND LIGHT CHAINS TO SOME GROUP A, C and G STREPTOCOCCI

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Abstract
A reaction between group A, C and G streptococci and IgG Fab-parts, not involving the antigen combining sites, is reported. The bacteria proved to bind aggregated, but not monomeric, IgG Fab-fragments, indicating that multivalent interaction was a prerequisite for the binding to occur. Most of the strains exhibiting affinity for aggregated IgG Fab also interacted with aggregated .kappa. and/or .lambda. L chains. The capacity of the single strains to bind aggregated IgG Fab did not correlate with presence of IgG Fc-receptor activity. In contrast to streptococcal Fc-receptors, the streptococcal structure reacting with Fab was highly sensitive to trypsin and phosphatase treatment. The binding of aggregated .lambda.-chains to each of 2 strains tested was inhibited by liquid and aggregated human albumin, suggesting that lipoteichoic acid and/or M protein are responsible for the binding of IgG Fab-fragments. A pronounced binding of aggregated IgG Fab, but not L chains, to Staphylococcus aureus strain Cowan I was also found. Various other bacterial species were tested for binding of the aggregates, with negative results.

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