The data are representative of two independent experiments performed in duplicate

The data are representative of two independent experiments performed in duplicate. a cascade that leads to inflammation, opsonization and/or lysis of microorganisms (Jack et al., 2001). Three activation pathways are initiated by distinct recognition molecules and converge in a common lytic pathway. The classical pathway is activated by C1q binding to antigen-antibody complexes. The lectin pathway is initiated by mannose-binding lectin (MBL) or Asimadoline ficolin, which recognize sugar moieties on microbial surfaces. Both the classical and lectin pathways activate C4 and C2, resulting in generation of Rabbit polyclonal to ZNF238 the C4bC2a convertase that cleaves C3 to C3b. In the alternative pathway, C3 spontaneously turns over and can bind to pathogens. It then engages factor B, which is cleaved by the serine protease factor D to generate an alternative pathway C3 convertase (C3bBb). The binding of C3b to C4b2a and C3bBb convertases converts them to C5 convertases. These enzymes cleave C5 and promote assembly of C5b-9 membrane attack complex (MAC), which lyses pathogens or infected cells. Complement has a protective role against many viral infections (Avirutnan et al., 2008), and can reduce infectivity by (a) inhibiting attachment to entry receptors, (b) promoting adherence to and ingestion by phagocytes, (c) and through mechanisms that require C5 and do or do not result in virolysis (Friedman et al., 2000). MBL is a C-type multivalent lectin that is synthesized predominantly in the liver and circulates in blood. In humans, a single MBL protein is expressed, whereas mice have two proteins, MBL-A and MBL-C encoded by the genesMBL1andMBL2, respectively. Mouse and human MBL bind specific carbohydrates on the surface of pathogens and necrotic or apoptotic cells (Ip et al., 2009). MBL binds to repeating arrays of mannan, N-acetylglucosamine, lipoteichoic acid, phospholipids, and nucleic acids (Takahashi et al., 2006). MBL has a relatively low affinity for monosaccharide Asimadoline and other carbohydrate ligands, requiring multivalent lectin domain interactions for recognition, specificity, and efficient complement activation (Jack et al., 2001). MBL binding activates C4 and C2 through its associated proteases, MBL-associated serine proteases (MASPs). At least three MASP proteins have been identified (MASP-1, 2, 3), with MASP-2 having a dominant role in cleaving C4 and C2 (Takahashi et al., 2007). Studies usingMBL A/xMBL-C/mice have established roles for MBL in limitingStaphylococcus aureus(Shi et al., 2004) and herpes simplex virus (Gadjeva et al., 2004) infections. In humans, polymorphisms in the MBL gene are well characterized, and individuals with variant alleles have decreased serum levels (Tsutsumi et al., 2005). Low serum MBL concentrations are associated with an increased risk of disseminated disease withNeisseria meningitides(Bathum et al., 2006), and have been suggested to increase susceptibility to HIV (Tan et al., 2009), hepatitis B (Chong et al., 2005), and herpes simplex virus (Seppanen et al., 2009) infections. Flaviviruses are enveloped, positive-polarity RNA viruses that cause significant human disease globally and include West Nile (WNV), Dengue (DENV), yellow fever, and tick-borne encephalitis (TBEV) viruses. Many flaviviruses are arthropod-transmitted and infect humans or other vertebrate animals through insect vectors. The mature flavivirus is a ~50 nm icosahedral particle, composed of a nucleocapsid surrounded by a lipid bilayer that is coated with envelope (E) and membrane (M) proteins. The flavivirus E protein contains a variable number (0, 1, or 2) of N-linked glycans that are believed to contribute to viral attachment and cell tropism. Most WNV strains have only one glycosylation site at E-154 in domain I, whereas virtually all DENV isolates have a second N-linked glycan at position Asimadoline E-67 in domain II. Differences in N-linked glycosylation of E result in differential binding to the viral attachment receptors DC-SIGN and DC-SIGN-R (Davis et al., 2006a;Davis et al., Asimadoline 2006b;Tassaneetrithep.