Inactivated Wild-Type Dengue Virus Type 2

Infection with dengue virus (DENV) results in increased proinflammatory responses, such as nitric oxide (NO) production and TNF-α expression. The studies here show that in addition to TNF-α production in DENV-infected mouse macrophage RAW264.7 cells, inducible NO synthase is also elevated transcriptionally and translationally, accompanied by NO production. NF-κB is known to be activated by DENV infection. Pharmacological inhibition of NF-κB activation abolished iNOS/NO biosynthesis and TNF-α production. By inhibition, the potential role of NF-κB in the regulation of oxidative signaling during DENV infection was prevented. Heat-inactivated DENV (Inactivated Wild-Type Dengue Virus) did not induce the identified inflammatory response. Pharmacological inhibition of TLR3 partially reduced NF-κB activation. However, it effectively abolished inducible iNOS/NO biosynthesis but did not inhibit TNF-α production. In contrast to TLR3, the viral protein NS2B3 also independently promotes NF-κB activation to regulate TNF-α production. These results show distinct pathways of NF-κB activation induced by DENV infection, regulating the expression of iNOS/NO and TNF-α, respectively.

To investigate whether DENV-induced NF-κB activation, followed by TNF-α and iNOS/NO biosynthesis, occurs in a protein-mediated manner, RAW264.7 cells were inoculated with heat-inactivated DENV (HI-DENV) at an MOI of 50. The results showed that HI-DENV induced NF-κB activity less efficiently than live DENV (Figure 1). Similarly, the expression levels of TNF-α, NO, and iNOS were lower in the HI-DENV group compared with the live DENV group. These experiments suggest that DENV activates NF-κB through viral proteins, followed by TNF-α and iNOS/NO biosynthesis.

Figure 1. Heat-inactivated DENV does not efficiently cause NF-κB activation. (Cheng Y L, et al., 2015)