Pathological effects of autoantibodiesproduced during dengue virus infection

• Main Authors: Chiou-Feng Lin, 林秋烽
• Other Authors: Yee-Shin Lin
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/fw5rnz

博士 === 國立成功大學 === 基礎醫學研究所 === 90 === Dengue virus (DV) infection, an important infectious mosquito-borne disease transmitted by Aedes aegypti, represents a serious public health threat to people throughout the world. Clinical manifestations of patients with DV infection range in severity from dengue fever (DF) to life-threatening dengue hemorrhagic fever and dengue shock syndrome (DHF/DSS). Severe thrombocytopenia, vascular leakage, and hemorrhagic syndrome are the major hallmarks associated with DHF/DSS; the mechanisms are not well understood, although several hypotheses have been suggested. In addition to a direct viral damage to the host, the host immune responses, including immune cell activation, complement activation, and cytokine production, may also play some roles. In the present study, the possible role of host immunity in the pathogenesis of DV infection was investigated. Results show that anti-platelet and anti-endothelial cell autoantibodies are present in DV-infected patient sera, but not in JEV-, HCV-, or Enterovirus 71-infected and normal control sera. The levels of autoantibodies in DHF/DSS patient sera are higher than those in patients with DF. We propose that in addition to the direct effect of DV, the production of autoantibodies in DV infection may also be involved in the pathogenesis and progression of dengue disease. The cDNA that encodes DV nonstructural protein 1 (NS1) protein is constructed in the E. coli expression system. Results show that the cell binding activity of patient sera can be inhibited by pretreatment with DV NS1. The antibodies (Abs) against DV NS1 (anti-DV NS1) produced after DV infection may, at least in part, account for the cross-reactivity of patient sera with platelets and endothelial cells. To provide direct evidence that anti-DV NS1 Abs play a role in the autoimmune response, anti-DV NS1 Abs have been generated from DV NS1-immunized mice. Results show that anti-DV NS1 Abs cross-react with platelets and endothelial cells. Interestingly, both dengue patient sera and mouse anti-DV NS1 Abs cause platelet and endothelial cell lysis in the presence of complement. Furthermore, anti-DV NS1 Abs induce endothelial cell apoptosis in a caspase-dependent manner. The signal transduction triggered by anti-DV NS1 Abs shows an increase in protein tyrosine phosphorylation and NF-kB activation. Further studies show an induction of iNOS expression and NO production, and that treatment with the NOS inhibitor L-NAME blocks cell apoptosis. The mRNA and protein expressions of Bcl-2 and Bcl-xL decrease while Bax and p53 increase after anti-DV NS1 Abs treatment, an effect that could also be inhibited by L-NAME. Taken together, anti-DV NS1 Abs trigger the intracellular signaling that leads to apoptotic cell death in endothelial cells via production of NO, upregulation of Bax and p53, and downregulation of Bcl-2 and Bcl-xL. Based on the results of this study, we suggest that the generation of autoantibodies against platelets and endothelial cells resulting in their dysfunction may play a role in the pathogenesis of dengue virus infection. The findings in the present study may provide valuable information for dengue vaccine development. The possible approaches include gene modifications of DV NS1 to truncate or mutate the epitopes that may cause the pathogenic effects.