Fibrinogen-specific antibody induces abdominal aortic aneurysm in mice through complement lectin pathway activation

Abstract

Abdominal aortic aneurysm (AAA) is a common vascular disease associated with high mortality rate due to progressive enlargement and eventual rupture. There is currently no established therapy known to alter the rate of aneurysmal expansion. Thus, understanding the processes that initiate and sustain aneurysmal growth is pivotal for the development of medical therapies aimed at halting disease progression. Using an elastase-induced AAA mouse model that recapitulates key features of human AAA, we previously reported that a natural IgG antibody directs alternative pathway complement activation and initiates the inflammatory process that culminates in aneurysmal development. The target of this natural antibody, however, was unknown. Herein we identify a natural IgG that binds to fibrinogen deposited in elastaseperfused aortic tissues, activates the complement lectin pathway (LP), and induces AAA. Moreover, we establish that alterations in the glycosylation patterns of this antibody critically affect its ability to activate the LP in vivo. We find that LP activation precedes the alternative pathway and absence of the LP complement protein mannan-binding lectin abrogates elastase-induced AAA. In human AAA tissues the mouse anti-fibrinogen antibody recognizes epitopes that localize to the same areas that stain positively for mannan-binding lectin, which suggests that the complement LP is engaged in humans as well. Lastly, we demonstrate that circulating antibodies in a subset of AAA patients react against fibrinogen or fibrinogen-associated epitopes in human aneurysmal tissues. Our findings support the concept that an autoimmune process directed at aortic wall self-antigens may play a central role in the immunopathogenesis of AAA.A bdominal aortic aneurysm (AAA) is a common vascular disorder that affects ∼5% of men and ∼1.5% of women ages 65 and older (1, 2). Rupture of AAA presents a medical emergency that accounts for 15,000 deaths annually in the United States (3). Currently, surgical repair represents the only treatment option for large AAAs, whereas surgery in small AAAs offers no clear overall long-term survival advantage (4, 5). Thus, medical management, to inhibit or reverse the progression of small AAAs, has received increasing attention. Major challenges remain in the development of therapeutic agents that impede aneurysm expansion, as our understanding of the pathophysiology underlying this disease is incomplete.One of the defining characteristics of AAA is inflammation accompanied by a cellular infiltrate that is predominantly lymphocytic (6-8). The elastase-induced AAA mouse model recapitulates many key features of human AAA, including the inflammatory response (9). We previously established with this model that aneurysm development requires factor B and properdin of the complement alternative pathway (AP) (10, 11). We showed that mice deficient in B cells (and hence antibodies), called μMT mice, are protected against aneurysm formation. Reconstitution with natural IgG, but not IgM, from wild-type mice res...

Anti-Mouse Properdin TSR 5/6 Monoclonal Antibodies Block Complement Alternative Pathway-dependent Pathogenesis

“…The animal protocol is subjected to The generation and purification of a His-tagged mouse TSR5/6 (mTSR5/6) has been previously described. (27) In brief, recombinant mouse properdin cDNA encoding TSRs 5 and 6 was amplified using PCR methodology and cloned into the pET28a + expression vector (EMD/Millipore, Billerica, MA). The resulting plasmids were transformed into E. coli strain BL21(DE3) RIL codon plus (Agilent Technologies, Santa Clara, CA).…”

“…Properdin specificity was confirmed by a Western blot analysis that compared antibody reactivity to normal mouse serum versus serum derived from properdin-deficient mice. (27) Clones H4 and E12 were selected for the studies presented herein. …”

“…(24,27,32,33) Briefly, mice were anesthetized with 55-60 mg/kg intraperitoneal sodium pentobarbital. A laparotomy was performed under sterile conditions.…”

B lymphocytes in abdominal aortic aneurysms

“…Moreover, reconstitution with natural IgG to the WT level rendered uMT mice susceptible to AAA formation accompanied by elastic fiber fragmentation and smooth muscle cell (SMC) depletion [19]. Subsequently, they further found that the natural anti-fibrinogen IgG deposited in elastase-perfused aortic tissues induces AAA by activating the complement lectin pathway [32]. After the three complement pathways converge in the formation of C3 convertase, they proceed on a common pathway that mediates inflammation and immunity through macrophage activation and cell death (the membrane attack complex, MAC).…”

“…AAAP-40, which has homologies with elastin-associated microfibrils, has been shown to be similar to three chains of fibrinogen [30,31]. Zhou et al [32] induced mice AAA with a natural IgG that binds to fibrinogen deposited in elastase-perfused aortic tissues. Furthermore, by using 2-dimensional electrophoresis and western blotting, Takashi et al detected CA1 in AAA wall samples were modified to express neoepitope(s) [33].…”