A large majority of examined
Lyme disease spirochaete isolates were demonstrated to contain one or both of the paralogous genes bapA and eppA. Immunological analyses of serum samples collected from infected patients coupled with comparative sequence analyses indicated that bapA gene sequences are quite stable but the encoded proteins do not provoke a strong immune response in most individuals. Conversely, EppA proteins are much more antigenic but vary widely in sequence between different bacteria. Considerable evidence of insertion, deletion and other mutations within eppA genes was observed. A number of significant recombination events were also found to have occurred in regions flanking bapA genes, while the genes themselves rarely exhibited evidence of mutation, suggesting strong selective pressure to maintain BapA sequences within narrow limits. Data from these and other studies suggest important roles for BapA and EppA during the Borrelia burgdorferi infectious cycle.