We have purified and partially sequenced a protein from the adventitia of the human aorta (aortic aneurysm antigenic protein 40 kDa; AAAP-40) that has homologies to bovine aortic microfibril-associated glycoprotein (MAGP-36). It is immunoreactive with immunoglobulin G (IgGs) purified from the serum and aortic wall of patients with abdominal aortic aneurysms. AAAP-40 and MAGP-36 have fibrinogen-like and vitronectin-like motifs. Screening an expression library constructed from human aortic adventitial messenger RNA has resulted in the cloning of three complementary DNAs whose gene products are immunoreactive with immunoglobulin G from patients with abdominal aortic aneurysms. Two strongly resemble each other and have been described separately. The purpose of this article is to report the third clone.

Messenger RNA from a specimen of human aortic aneurysmal adventitia was reverse-transcribed for insertion into the phagemid Uni Zap XR (Stratagene). A strain of Escherichia coli, engineered for expression (XL 1-Blue MFR`, Stratagene), was transfected, and rabbit antihuman vitronectin antibody was used to identify positive clones. Sequencing of the positive clones was performed by the Core Laboratories at Columbia University.

The hypothetical protein of rAAAP-CL4 (clone 4) shares sequence motifs with known microfibril-associated glycoproteins (MAGPs). The recombinant protein (rAAAP-CL4) is immunoreactive with serum from patients (three of four abdominal aortic aneurysm sera). In addition, similarities have been detected with immunoglobulins of the κ family and with a protein from cytomegalovirus that is a potential molecular mimic.

There may several members of a novel family of human aortic autoantigenic proteins implicated in abdominal aortic aneurysm disease. (J Vasc Surg 1997 26:313-8.)