High levels of interleukin-21(IL-21) are produced during primary dengue infections. (VIR8P.1067)

Introduction: IL-21 is produced by CD4 T cells, mainly follicular T cells and exerts multiple and pleiotropic effects on innate and adaptive immune as well as on non-immune cells. IL-21 is involved in various viral infections but has not been described in dengue virus (DENV) infection context. Objective: The aim of this study was to investigate the IL-21 level production during the clinical course of primary DENV infections. Material and Methods: We collected 122 serum samples of primary DENV-infected patients at different days after the onset of symptoms and classified according to their phase of disease (acute vs. convalescent phases), and the clinical severity (dengue fever vs. dengue hemorrhagic fever). IL-21 levels were measured using a quantitative capture ELISA. Results: IL-21 levels were significantly elevated in the disease group compared with the control group (P < 0.0001). IL-21 was detected in primary DENV infections with a significantly higher concentration in the convalescent phase. Conclusions: Our results show for the first time the involvement of IL-21 during the clinical course of DENV infections. We speculate that IL-21 may play a protective role in primary infections.