Low affinity, antibody binding of an Escherichia coli-derived component

This investigation describes the detection of a component in Escherichia coli capable of binding a large proportion of human antibody variable domains including otherwise highly monospecific antibodies induced by an in vivo antibody response. This interaction is of low affinity, but cross-linking of IgG molecules by, e.g. anti-immunoglobulin preparations, provides a sufficient degree of multivalency to promote a high avidity interaction. This binding which occurs both with kappa and lambda light chain-containing antibodies, appears to involve the variable region of human antibodies making it a superantigen-like activity. This is proposed based on the facts that: (i) different human antibodies of IgG1 isotype appear to bind to different extents suggesting that variable domain differences determine the binding activity; and (ii) addition of soluble antigen abrogates the interaction with the E. coli-derived molecule. Future studies of the nature and possible in vivo consequences of these interactions are warranted since any superantigen activity associated with this binding might affect the human immune response occurring as a consequence of E. coli infections.