Inhibition of the Complement Membrane Attack Complex bySchistosoma mansoniParamyosin

Abstract

Following partial purification and analysis by mass spectrometry, we have determined SCIP-1 to be a surface-exposed form of the muscle protein paramyosin. As shown by immunofluorescence, anti-paramyosin antibodies label the surface of live schistosomula and adult worms. Like SCIP-1, purified native paramyosin reacts with a polyclonal rabbit anti-human CD59 antiserum, as shown by Western blot analysis. Also, the human complement components C8 and C9 bind to recombinant and native paramyosin. Analysis of paramyosin binding to fragments of C9 generated by thrombin or trypsin has demonstrated that paramyosin binds to C9 at a position located between Gly245 and Arg391. Paramyosin inhibited Zn 2؉ -induced C9 polymerization and poly-C9 deposition onto rabbit erythrocytes (E R ). In addition, paramyosin inhibited lysis of E R and of sensitized sheep erythrocytes by human complement. Finally, anti-paramyosin antibodies enhanced in vitro killing of schistosomula by normal and C4-depleted human complement. Taken together, these findings suggest that an exogenous form of S. mansoni paramyosin inhibits activation of the terminal pathway of complement and thus has an important immunomodulatory role in schistosomiasis.Schistosomiasis is one of the most prevalent parasitic diseases, affecting over 200 million people who live in areas of endemicity in Africa, South America, and Asia (12). Schistosoma mansoni, one of the causative agents of this disease, resides within patients' mesenteric and portal blood systems and successfully evades host immune responses (43). During skin penetration into the mammalian host and shortly afterwards, the larvae convert from exhibiting sensitivity to complement-mediated killing to bearing resistance to complementmediated killing (32, 49). The first step in that conversion is the removal of the glycocalyx coat that contains strong complement activators. Subsequently, the transformed schistosomula and the adult worms employ several strategies to evade the host's complement system (14), thus enabling the parasite to reside for years within the host's circulatory system in direct contact with complement proteins. This parasite contains proteins that bind in vitro to the complement proteins C1 (25) and C2 (22) and C8 and C9 (40) and may thus block the complement cascade at multiple steps. Paramyosin, one of the inhibitory proteins, was shown to bind in vitro to C1q and inhibit C1 and the classical pathway of complement activation (25). Paramyosin is in essence an invertebrate muscle protein (11) that serves as a major component of the thick filament and is thought to play an important role in certain specialized contractile states (7, 23). It has also been found to be an immunogen during infection of mice and humans with helminth parasites (27,37,47). A nonfilamentous membrane-bound form of paramyosin was also found in the tegumental outer layer (16, 33) and on the surface (18, 31) of S. mansoni schistosomes. Analyzed on the basis of its capacity to bind to Fc (31), it has been suggested to have immu...

Proteins Exposed at the Adult Schistosome Surface Revealed by Biotinylation

“…This may explain why we failed to detect the glucose transporter SGTP4 when others using a similar protocol to biotinylate the worm surface and recover tagged proteins were able to locate it on a blot using specific antibody (30). We also failed to detect SmRK-1, a member of the transforming growth factor-␤ family of receptor kinases, reported previously as labeled by sulfo-NHS-LC biotin (15,31), and SCIP-1 (paramyosin), proposed both as an Fc receptor (32) and as an inhibitor of complement C9 polymerization (33).…”

Molecular Cloning and Characterization of a Paramyosin from Clonorchis sinensis

“…rCsPmy likewise demonstrated binding capacity to human C9. Although the mechanism of complement activation in C. sinensis infection is not totally understood, it is well established that S. mansoni paramyosin has an important immuno-modulatory role in schistosomiasis by binding to C8 and C9 and thereby preventing assembly of the C5b-9n membrane attack complex (MAC) [36]. Our finding that CsPmy binds to human collagen and C9 suggests it can possibly inhibit complement activation by binding to the complement components of the host.…”

Live Cell Imaging of Outward and Inward Vesiculation Induced by the Complement C5b-9 Complex

“…Hemolytic Activity of C9-AF488-Antibody-sensitized sheep erythrocytes were prepared with rabbit hemolysin (Difco) as described before (30). The antibody-coated sheep erythrocytes (1.5 ϫ 10 7 ) in 0.1 ml of gelatin/veronal-buffered saline containing 1 mM MgCl 2 and 0.1 mM CaCl 2 (GVB) were incubated with C9-depleted human serum (diluted 1:2,000) and increasing amounts of C9 or C9-AF488 for 30 min at 37°C.…”