Immunoreactivity of Adventitial Matrix Fibrils of Normal and Aneurysmal Abdominal Aorta with Antibodies against Vitronectin and Fibrinogen

Purpose: We have reported that immunoglobulin G (IgG) harvested from specimens of aneurysmal abdominal aorta (AAA) is immunoreactive with a fibrillar component of the matrix of the aortic adventitia. In further studies we have reported the partial amino acid sequence of a 40-kDa protein, purified from the adventitia of the human aorta, which we have called aortic aneurysm antigenic protein-40 kDa (AAAP-40). AAAP-40 has homologies with bovine microfibril-associated glycoprotein-36 kDa (MAGP-36). Both AAAP-40 and MAGP-36 have homologies to fibrinogen beta (FB-b) and vitronectin (VN). The purposes of the present experiments were (1) to determine whether antibodies against VN and fibrinogen are immunoreactive with elements of the normal and/or aneurysmal aortic wall, and (2) to determine whether these antibodies are immunoreactive with soluble extracts of aortic proteins. Methods: Paraffin-embedded tissue sections of normal and aneurysmal aorta were probed with polyclonal rabbit antihuman VN and antihuman FB-b antibodies. Immunoblots of soluble aortic proteins were evaluated with the same antibodies. Histochemical preparations with Gomori’s aldehyde fuchsin and elastin-von-Gieson solutions were also performed. Results: Anti-VN and FB-b antibodies reacted with matrix fibrils in the aortic adventitia in both normal and aneurysmal specimens, with a distribution that resembles the appearance of fibrils that are stained by Gomori’s reaction. By comparison to normal adventitial fibrils, fibrils in the specimens from AAA appeared fragmented, coiled, and frayed. Antibodies against VN and FB-b were immunoreactive in immunoblots with a soluble aortic protein of molecular weight ∼40 kDa, consistent with the migration of AAAP-40. Conclusions: There appear to be immunodeterminants in AAAP-40 that are recognized by polyclonal antibodies against VN and FB-b.