Dengue Virus Infection with Highly Neutralizing Levels of Cross-Reactive Antibodies Causes Acute Lethal Small Intestinal Pathology without a High Level of Viremia in Mice

Severe dengue virus (DENV)-associated diseases can occur in patients who have preexisting DENV antibodies (Abs) through antibody-dependent enhancement (ADE) of infection. It is well established that during ADE, DENV-antibody immune complexes (ICs) infect Fc gamma receptor-bearing cells and increase the systemic viral burden that can be measured in the blood. For protection against infection with DENV serotypes 1 to 4, strongly neutralizing Abs must be elicited to overcome the effect of ADE. Clinical observations in infants who have maternal DENV Abs or recent phase II/III clinical trials with a leading tetravalent dengue vaccine suggested a lack of correlation between Ab neutralization and in vivo disease prevention. In addressing this gap in knowledge, we found that inoculation of ICs formed with serotype cross-reactive Abs that are more than 98% neutralized in vitro promotes high mortality in AG129 mice even though peak viremia was lower than that in direct virus infection. This suggests that the serum viremia level is not always correlated with disease severity. We further demonstrated that infection with the ICs resulted in increased vascular permeability, specifically in the small intestine, accompanied with increased tissue viral load and cytokine production, which can be suppressed by anti-tumor necrosis factor alpha (anti-TNF-alpha) Abs. Flow cytometric analysis identified increased infection in CD11b(int) CD11c(int/hi) CD103(-) antigen-presenting cells by IC inoculation, suggesting that these infected cells may be responsible for the increase in TNF-alpha production and vascular permeability in the small intestine that lead to mortality in mice. Our findings may have important implications for the development of dengue therapeutics. IMPORTANCE We examined the relationship between the neutralizing level of Abs at the time of infection and subsequent disease progression in a mouse model in order to understand why patients who are shown to have a neutralizing quantity of Abs still allow sufficient DENV replication to induce severe dengue manifestations, which sometimes do not correlate with viremia level. Strikingly, we found that high mortality was induced in AG129 mice by the increase in TNF-alpha-induced vascular permeability accompanied by an increased viral load, specifically in the small intestine, even when the initial infection level is suppressed to less than 5% and the peak viremia level is not enhanced. This suggests that ADE overcomes the protective efficacy of Abs in a tissue-dependent manner that leads to severe small intestinal pathology. Our findings may serve to address the pathogenic role of Abs on severe dengue disease and also help to develop safe Ab-based therapeutic strategies.