Complement-Mediated Neutralization of Dengue Virus Requires Mannose-Binding Lectin

Avirutnan, Panisadee; Hauhart, Richard E.; Marovich, Mary A.; Garred, Peter; Atkinson, John P.; Diamond, Michael S.

While MBL has been reported to inhibit infection of several types of viruses, including filoviruses, influenza virus, hepatitis C virus (HCV), herpes simplex virus, human immunodeficiency virus (HIV), severe acute respiratory syndrome coronavirus, and WNV, in most studies, neutralization required complement activation (25, (35) (36) (37) (38) (39) (40) (41) . However, in our experiments, efficient recognition of insect cell-derived DENV by purified human MBL was sufficient to neutralize the virus of all four serotypes independent of complement activation. As MBL is a multimeric molecule that comprises two to six subunits of a triple helix of three identical 32-kDa polypeptide chains (14) , binding of MBL to DENV may impair host cell attachment and/or entry. For example, binding of MBL to the surface glycoproteins of influenza A virus, HCV, and HIV in a complement-free system blocked virus attachment to target cells (36, 42, 43) . Lack of direct neutralization of mammalian cell-derived DENV and insect cell-and mammalian cellderived WNV by MBL (despite saturating concentrations [30 g/ ml]) in the absence of complement suggests that a higher number of MBL-binding sites are available on insect cell-derived DENV, which is sufficient to reach the threshold required for neutralization. In comparison, binding of fewer molecules of MBL (even as low as 30 ng/ml [1,000-fold lower]) could trigger lectin and alternative pathway activation, which deposits C4 and C3 on the virion surface (25) , and promotes neutralization. Deposition of C4b and C3b on virions by MBL-dependent lectin pathway activation inhibited WNV infection, in part, by blocking viral fusion (25) , possibly by interfering with the requisite pH-dependent structural rearrangements.