Antibodies deposited in abdominal aortic aneurysms(AAA) specifically recognize microfibril-associated glycoprotein(MAGP)

MAGP is a 31kD component of elastin-associated microfibrils produced primarily during early development. Proteolytic destruction of medial aortic elastin is a hallmark of AAA, a disease with features of autoimmunity. To determine if the extensive elastin degradation in AAA might liberate MAGP and thereby initiate the development of autoreactive anti-MAGP antibodies, soluble protein extracts obtained from 6 AAA and 3 normal aortas(NA) were examined in a series of immunoblotting experiments. Five of 6 AAA tissues contained 31- and 60-kD proteins recognized by rabbit antibovine MAGP IgG. but no forms of MAGP were detected in similar extracts of NA. Using IgG extracted from AAA by protein A-sepharose (AAA-IgG) as primary antibody, all 6 samples exhibited autoreactivity with the previously detected 31- and 60-kD MAGP-like proteins. In each case, rabbit antibovine MAGP IgG specifically blocked the binding of AAA-IgG to the 31 and 60-kD MAGP-like proteins in AAA tissue extracts. Neither AAA-IgG nor serum from the same patients consistently recognized recombinant forms of bovine MAGP. These data demonstrate that:(1)soluble forms of MAGP are present in AAA but not NA tissue extracts, (2)IgG deposited in AAA tissues contains antibodies specific for human MAGP-like proteins, and (3)the presence of anti-MAGP antibodies in AAA tissue is not necessarily accompanied by detectable antibody levels in the serum. Further studies will be needed to characterize the antigenic determinants in human MAGP that might be recognized by IgG deposited in AAA tissues and to correlate antibody production with the clinical and histopathologic extent of aneurysmal degeneration.