Dengue virus-induced human cytotoxic factor: production by peripheral blood leucocytes in vitro

During dengue type 2 virus (DV) infection of mice a unique cytokine, the cytotoxic factor (CF), is produced which reproduces the pathological lesions seen in patients of dengue haemorrhagic fever (DHF). Recently we have observed a CF-like protein in the sera of DHF cases. The present study was undertaken to investigate whether DV can stimulate human peripheral blood mononuclear cells (PBMC) in vitro to produce human CF (hCF). Cultures prepared from PBMC or its enriched subpopulations were inoculated with 1000 LD50 of DV and controls with normal mouse brain suspension (NMB). Aliquots of cultures were harvested daily from 24 h to 96 h and their supernatant (CS) and cells were separated. CS were screened for viral titres and for the presence of hCF by cytotoxicity assay, inhibition ELISA, dot blot and Western blot tests using anti-mouse-CF antibodies. The RNA from the cells was screened in Northern blot and dot blot tests for the presence of mRNA for CF. It was observed that hCF appeared in the CS of DV-infected culture of PBMC and T-enriched cells at 48 h and was present until 96 h; no CF was detected in CS of B cells or monocyte cultures. The production of hCF was abrogated by pretreatment of the T cells with anti-CD4 antibodies but not with anti-CD8 antibodies, indicating that hCF was produced by CD4+ T cells. The Northern blot analysis using oligonucleotide probes prepared on the basis of amino-terminal sequence of mouse CF, showed presence of mRNA for hCF in PBMC and T cell cultures. DV replicated in PBMC cultures with peak titres at 48 h. The findings of the present study demonstrate that DV-induced hCF is produced by human T cells.