Dengue virus infection-enhancing activity of undiluted sera obtained from patients with secondary dengue virus infection

Background: Dengue virus (DENV) infection-enhancing activity of pre-existing antibody has been suggested to be one of the factors responsible for the pathogenesis of the severe form of DENV infection, dengue haemorrhagic fever. Although studies of infection-enhancement activity using diluted serum sera are informative, infection-enhancement activity determined using undiluted sera may better reflect in vivo conditions. Methods: We determined whether serum samples collected from dengue patients possessed the ability to enhance DENV infection without dilution using Fc gamma R-expressing cells. Results: Serum samples obtained at the early phase of secondary infection enhanced DENV infection without dilution. In contrast, sera obtained at the late stage of secondary infection demonstrated low levels or absence of infection-enhancing activity. Conclusion: The results indicate that human sera obtained from patients with secondary infection possess the ability to enhance DENV infection without dilution, and suggest that antibody-dependent enhancement may occur in vivo during secondary DENV infection to infecting DENV serotypes.