Induction of TRAIL and TNF-alpha-dependent Apoptosis in Human mDCs by Microfilariae of Brugia Malayi

Dysregulation of professional APC has been postulated as a major mechanism underlying Ag-specific T cell hyporesponsiveness in patients with patent filarial infection. To address the nature of this dysregulation, dendritic cells (DC) and macrophages generated from elutriated monocytes were exposed to live microfilariae (mf), the parasite stage that circulates in blood and is responsible for most immune dysregulation in filarial infections. DC exposed to mf for 24–96 h showed a marked increase in cell death and caspase-positive cells compared with unexposed DC, while mf exposure did not induce apoptosis in macrophages. Interestingly, 48 h exposure of DC to mf induced mRNA expression of the pro-apoptotic gene TRAIL and both mRNA and protein expression of TNF-alpha. mAb to TRAIL-R2, TNF-R1, or TNF-alpha partially reversed mf-induced cell death in DC, as did knocking down the receptor for TRAIL-R2 using small interfering RNA. Mf also induced gene expression of BH3-interacting domain death agonist (Bid) and protein expression of cytochrome c in DC; mf-induced cleavage of Bid could be shown to induce release of cytochrome c, leading to activation of caspase 9. Our data suggest that mf induce DC apoptosis in a TRAIL- and TNF-alpha-dependent fashion. Keywords: Dendritic Cell, Parasite, Human, Microfilariae Microfilariae and human monocyte derived-DCs were cultuted at a multiplicity of infection of 1:1 for 24hrs for four independent donors. Matching samples exposed to media alone were used for controls The four experimental and 4 control samples were then pooled to create one experoimental and one healthy pool used for microarray analysis.