Dengue virus infection induces selective expansion of V4 and V6TCR æ T cells in the small intestine and a cytokine storm driving vascular leakage in mice

Dengue is a major health problem in tropical and subtropical regions. Some patients develop a severe form of dengue, called dengue hemorrhagic fever, which can be fatal. Severe dengue is associated with a transient increase in vascular permeability. A cytokine storm is thought to be the cause of the vascular leakage. Although there are various research reports on the pathogenic mechanism, the complete pathological process remains poorly understood. We previously reported that dengue virus (DENV) type 3 P12/08 strain caused a lethal systemic infection and severe vascular leakage in interferon (IFN)-alpha/beta and gamma receptor knockout mice (IFN-alpha/beta/gamma RKO mice), and that blockade of TNF-alpha signaling protected mice. Here, we performed transcriptome analysis of liver and small intestine samples collected chronologically from P12/08-infected IFN-alpha/beta/gamma RKO mice in the presence/absence of blockade of TNF-alpha signaling and evaluated the cytokine and effector-level events. Blockade of TNF-alpha signaling mainly protected the small intestine but not the liver. Infection induced the selective expansion of IL-17A-producing V gamma 4 and V gamma 6 T cell receptor (TCR) gamma delta T cells in the small intestine, and IL-17A, together with TNF-alpha, played a critical role in the transition to severe disease via the induction of inflammatory cytokines such as TNF-alpha, IL-1 beta, and particularly the excess production of IL-6. Infection also induced the infiltration of neutrophils, as well as neutrophil collagenase/matrix metalloprotease 8 production. Blockade of IL-17A signaling reduced mortality and suppressed the expression of most of these cytokines, including TNF-alpha, indicating that IL-17A and TNF-alpha synergistically enhance cytokine expression. Blockade of IL-17A prevented nuclear translocation of NF-kappa B p65 in stroma-like cells and epithelial cells in the small intestine but only partially prevented recruitment of immune cells to the small intestine. This study provides an overall picture of the pathogenesis of infection in individual mice at the cytokine and effector levels. Dengue fever can lead to severe illness in some cases, which can be fatal. The number of severe cases is increasing. There are currently no effective therapeutic drugs or vaccines available for widespread use. Vascular leakage is the physiological basis of the pathology leading to severe disease, and it is widely believed that vascular leakage is directly or indirectly driven by an excessive immune response, that is, a cytokine storm. Although many hypotheses have been proposed, a complete understanding of disease progression has been missing. Therefore, we performed a comprehensive analysis of gene expression in the mouse model and found that the changes in the small intestine are critical for severe disease. In the small intestine, among six types of gamma delta T cells, IL-17A-producing V gamma 4 and V gamma 6 T cell receptor (TCR) gamma delta T cells were selectively expanded following infection. IL-17A played a critical role, through NF-kappa B activation, in inducing the production of IL-6 and neutrophil collagenase/matrix metalloprotease 8 (not previously considered an inducer of vascular leakage), as well as STAT-3 phosphorylation, acting synergistically with TNF-alpha to promote vascular leakage. This study both reinforces and challenges some of the previous observations, while highlighting the need for new perspectives in this field.