In order to reveal the mechanisms underlying nurse cell formation during Trichinella spiralis infection, the expression of the factors of tumor necrosis factor-alpha (TNF-α)/TNF receptor 1 (TNFR-1) signalling pathway mediating apoptosis was investigated. The analysed factors included TNF-α, TNFR-1, TNF receptor-associated death-domain (TRADD), caspase 3, caspase 8, TNF receptor associated factor-2 (TRAF2) and receptor interactive protein (RIP), all of which are involved in the TNF-α/TNFR-1 signalling pathway-mediated apoptosis. The quantitative RT-PCR indicated that the infected muscle tissues up-regulate the expression of pro-apoptosis genes (TNF-α, TNFR-1 and TRADD, caspase 3 and caspase 8), and anti-apoptosis genes (TRAF2 and RIP) at the beginning of cyst formation. The expression returned to the normal level after cyst formation. The quantitative RT-PCR analysis of mRNA from tissue samples isolated by laser capture micro-dissection confirmed that the up-regulation of these genes was restricted in infected muscle cells, was not in the inflammation cells around infected muscle cells nor in normal muscle cells. The in situ localization study of pro-apoptosis (TRADD, caspase 3) and anti-apoptosis gene products (TRAF2) indicated that these were expressed in the basophilic cytoplasm (infected muscle cell origin) of the nurse cells. Thus the present study suggests that the TNF-α/TNFR-1 signalling pathway is involved in nurse cell formation.
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