Previous studies have revealed the clinical relevance of pro-inflammatory
cytokine production during dengue virus (DENV)
infections. In this study, we evaluated the production of
interleukin-21 (IL-21), a key soluble mediator mainly produced by CD4+ T cells. The aim of this study was to investigate the role of
IL-21 production during the
clinical course of primary and secondary DENV
infections and the potential association of
IL-21 serum levels with the disease pathogenesis. Blood samples from DENV-infected patients were collected on different days after the onset of symptoms. Patients were classified according to their phase of
disease (acute vs. convalescent phases), the type of
infection (primary vs. secondary), and the clinical severity of their disease (
dengue fever (DF) vs.
dengue hemorrhagic fever (DHF)).
IL-21 levels were measured using a quantitative capture ELISA assay. The levels of
IL-21 were significantly elevated in the disease group compared with the control group.
IL-21 was detected in primary and secondary DENV
infections, with a significantly higher concentration in the convalescent phase of primary
infections.
IL-21 levels were significantly higher in patients with secondary acute DHF
infections when compared with those with secondary acute DF
infection. There was a relationship between the elevated serum levels of
IL-21 and the production of DENV-specific
IgM and
IgG antibodies. Taking together, 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 the context of the convalescent phase of primary
infections and the acute phase of
secondary infections.