Antigenic cross-reactivity and sequence homology between Actinobacillus actinomycetemcomitans GroEL protein and human fibronectin

The immunologic cross‐reactivity between human fibronectin and Actinobacillus actinomycetemcomitans GroEL was examined. Analyses by SDS‐PAGE/Western immunoblotting and ELISA showed that a polyclonal antibody directed against the purified GroEL protein of A. actinomycetemcomitans, but not against the Escherichia coli GroEL, cross‐reacts with human fibronectin. No antigenic cross‐reactivity was observed between anti‐A. actinomycetemcomitans GroEL antibody and type IV collagen, another important constituent of the basement membrane. A comparative analysis of the amino acid sequences of A. actinomycetemcomitans GroEL and human fibronectin revealed eight instances of four‐amino acid sequence homology between the two proteins. Six of these tetrapeptide sequences were also shared with E. coli GroEL, suggesting that the remaining two tetrapeptides, GQLI (Glycine‐Glutamine‐Leucine‐Isoleucine) and TGLE (Threonine‐Glycine‐Leucine‐Glutamic acid), may be associated with the epitope that the anti‐A. actinomycetemcomitans GroEL antibody specifically recognizes. Reactivity between TGLE, but not GQLI, with anti‐A. actinomycetemcomitans GroEL antibody was confirmed by a biospecific interaction analysis using a biosensor technology. Although additional investigations are required, the observed phenomenon may lead to an autoimmune response and thus contribute to tissue destruction during periodontitis.