Evaluation of the protective ability of plasma from Japanese individuals against mosquito-borne viral infections.

Background: Most of the Japanese population is seropositive for anti-Japanese encephalitis virus (JEV) anti-bodies because of previous JEV vaccination or natural infection. Because the virological characteristics of JEV are similar to those of West Nile virus (WNV) and dengue virus (DENV), we hypothesized that anti-JEV anti-bodies can cross-react with WNV and DENV antigens, leading to protection against infection by these viruses. Methods: Using isolated intravenous immunoglobulin (IVIG) from plasma collected in Japan, neutralizing activities against WNV and DENV and antibody-dependent enhancement (ADE) of these viral infections were evaluated using an in vitro assay to determine the potency of immunity against these viruses. Results: The prepared IVIG showed considerable neutralizing activity of 2.57 log10 reduction factor against WNV infection but showed little effect against DENV infection. A strong correlation was observed between the neutralizing activity of individual plasma samples against JEV and WNV (rho=0.768). Moreover, IVIG showed no significant ADE of WNV infection. Conclusions: Based on these results, we presume that the Japanese population is generally protected from WNV infection. Furthermore, IVIG prepared from plasma donations from Japanese individuals is expected to be an effective therapeutic agent based on its neutralizing activity against JEV and WNV.