Dengue hemorrhagic fever (DHF) is observed in individuals that have pre-existing heterotypic dengue antibodies and is associated with increased viral load and high levels of pro-inflammatory cytokines early in infection. Interestingly, a recent study showed that dengue virus infection in the presence of antibodies resulted in poor stimulation of Toll-like receptors (TLRs), thereby facilitating virus particle production, and also suggesting that TLRs may contribute to disease pathogenesis.
We evaluated the expression levels of TLR2, 3, 4 and 9 and the co-stimulatory molecules CD80 and CD86 by flow cytometry. This was evaluated in monocytes, in myeloid and plasmacytoid dendritic cells (mDCs and pDCs) from 30 dengue patients with different clinical outcomes and in 20 healthy controls. Increased expression of TLR3 and TLR9 in DCs of patients with dengue fever (DF) early in infection was detected. In DCs from patients with severe manifestations, poor stimulation of TLR3 and TLR9 was observed. In addition, we found a lower expression of TLR2 in patients with DF compared to DHF. Expression levels of TLR4 were not affected. Furthermore, the expression of CD80 and CD86 was altered in mDCs and CD86 in pDCs of severe dengue cases. We show that interferon alpha production decreased in the presence of dengue virus after stimulation of PBMCs with the TLR9 agonist (CpG A). This suggests that the virus can affect the interferon response through this signaling pathway.
These results show that during dengue disease progression, the expression profile of TLRs changes depending on the severity of the disease. Changes in TLRs expression could play a central role in DC activation, thereby influencing the innate immune response.
Dengue virus (DENV) infections cause a broad spectrum of clinical manifestations, ranging from self-limited fever to severe disease, such as dengue hemorrhagic fever (DHF) that can be fatal. The pathogenesis of severe dengue is associated with an inadequate immune response characterized by the over-production of cytokines and other inflammatory components. However, little is known about the role of the innate immune response in the progression to hemorrhagic manifestations. TLRs are among the most important components of innate immunity and are responsible for initiating a response against a variety of pathogens, including viruses. Recent studies suggest that TLRs may contribute to disease pathogenesis. Here we aimed to explore the role of these receptors in dengue disease progression. To this end, we examined the expression of several TLRs and of co-stimulatory molecules in monocytes and DCs from dengue patients. A link between TLRs expression and the severity of dengue was observed: patients with dengue fever express higher levels of TLR3 and TLR9 than patients with DHF. This could be crucial for the host defense against dengue virus or disease progression. In addition, expression of CD80 and CD86 was altered in DCs of severe dengue cases. We show that interferon type I production is also altered in vitro through TLR9. This suggests that dengue virus affects the interferon response through this signaling pathway.