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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2006;26:2096.)
© 2006 American Heart Association, Inc.

Atherosclerosis and Lipoproteins

A Natural Antibody to Oxidized Cardiolipin Binds to Oxidized Low-Density Lipoprotein, Apoptotic Cells, and Atherosclerotic Lesions

Anu Tuominen; Yury I. Miller; Lotte F. Hansen; Y. Antero Kesäniemi; Joseph L. Witztum; Sohvi Hörkkö

From the Department of Internal Medicine and Biocenter Oulu (A.T., Y.A.K., S.H.), University of Oulu, Finland; Department of Medicine (Y.I.M., L.F.H., J.L.W., S.H.), University of California San Diego, San Diego, Calif.

Correspondence to Sohvi Hörkkö, University of California San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0682. E-mail shorkko{at}ucsd.edu

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_HGam3.8 germline with one nucleotide difference, and the V was 100% identical to V19–20 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.

A natural anticardiolipin antibody (LRO1) binding to oxidized cardiolipin (oxCL), oxidized LDL, apoptotic cells, and atherosclerotic lesions was cloned from a nonimmunized LDLR^–/– mouse. These data demonstrate that oxCL is an important antigenic determinant in vivo and gives insight into the pathogenic events of diseases with increased titers of aCL antibodies.

Key Words: autoantibody • cardiolipin • lipoproteins • oxidized phospholipids

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