Natural Monoclonal Antibody to Oxidized Low-Density Lipoprotein and Aggregatibacter actinomycetemcomitans.

Natural antibodies are produced by B lymphocytes without exogenous antigenic exposure and are present at the time of birth. They usually bind to conserved epitopes on antigens of different chemical compositions. We cloned and characterized a natural mouse monoclonal IgM antibody (Aa_Mab) by selecting the binding to malondialdehyde acetaldehyde (MAA) adducts on low-density lipoprotein (LDL). The data showed that the Aa_Mab cross-reacted with Aggregatibacter actinomycetemcomitans (Aa) bacteria, an important oral pathogen in periodontitis associated with atherosclerosis. Surprisingly, the binding molecule of Aa bacteria to the Aa_Mab was Aa chaperonin 60 or HSP60, a protein that is not only responsible for maintaining cellular proteins conformation, but also functions as a potent virulence factor prompting bone resorption in periodontitis and as a putative pathogenic factor in atherosclerosis.