Complement in Human Serum Suppresses Antibody- Dependent Enhancement and Potentiates Neutralization of Dengue Virus

Objective: Antibody-dependent enhancement (ADE), in which pre-existing antibodies increase viral infection, is a major concern in dengue virus (DENV) pathogenesis and vaccine development. While conventional ADE models are well-established, the role of the complement system in modulating this process remains underexplored. This study investigated how complements in human serum influence DENV infection in the presence of enhancing and neutralizing antibodies. Materials and Methods: U937 and K562 cells were infected with DENV serotype 2 (DENV-2). The virus was pre-incubated with various concentrations of dengue antibodies, purified from pooled convalescence serum, under three conditions: culture medium, heat-inactivated human serum, or fresh human serum (as a source of active complement). After 48 hours, infectious virus production was quantified by a focus-forming assay, and infection rates were measured by flow cytometry. Results: Both fresh and heat-inactivated human serum significantly reduced DENV infection. In the presence of antibodies, complement activation in fresh serum was significantly more effective at decreasing infection than conditions with inactive complement, particularly at antibody concentrations that mediate ADE and partial neutralization. Conclusion: Human serum limits DENV infection, and active complement amplifies this neutralizing effect under conditions that typically promote ADE. These findings support incorporating complement into in-vitro assessments and motivate validation in primary FcγR/complement receptor-expressing target cells.