Objective: Cardiolipin (CL) is found in membranes of bacteria, in the inner membrane of mitochondria and in plasma low-density lipoprotein (LDL). Anticardiolipin antibodies (aCL) are associated with disease states, and we have suggested that many aCL bind to oxidized CL (oxCL) but not native CL. To determine the immunogenicity and origins of oxCL in vivo, we cloned a natural antibody to oxCL.
Methods and results: A monoclonal IgM antibody to oxCL (LRO1) was cloned from a nonimmunized LDLR-/- mouse. The V(H) sequence originated from the V(H)Gam3.8 germline with one nucleotide difference, and the Vkappa was 100% identical to Vkappa19-20 germline gene, making LRO1 a natural antibody. LRO1 bound specifically to oxCL and oxidized-LDL, but not to native CL or native LDL. LRO1 epitopes were demonstrated in apoptotic, but not in viable, Jurkat cells by flow cytometry, immunofluorescence and deconvolution microscopy. Human and rabbit atherosclerotic lesions contained LRO1 epitopes. Human LDL (n=113) showed LRO1 immunoreactivity, which correlated with aCL IgG titers (r=0.32, P=0.0004).
Conclusions: These data demonstrate that some aCL antibodies are highly conserved natural antibodies binding to oxCL in oxLDL, apoptotic cells, and atherosclerotic lesions. This suggests that oxCL is one of the pathogen-associated molecular patterns of innate immunity and gives insight into the pathogenic events of diseases with increased titers of aCL antibodies.