['Murine T cell mediated acute semiallogeneic graft versus host disease (GVHD) is characterised by lymphocytic infiltrates, crypt hyperplasia, and villous atrophy. It has been shown that programmed cell death (apoptosis) of the crypt epithelium takes place during the intestinal manifestation of acute GVHD.', 'To investigate which of the two most investigated inductors of apoptosis (Fas ligand (FasL) and tumour necrosis factor alpha (TNF-alpha)) is responsible for the induction of apoptosis in this animal model.', 'Animals undergoing acute semiallogeneic GvH reaction were treated with neutralising anti-TNF-alpha, two different anti-FasL antibodies, or pentoxifylline.', 'Anti-TNF-alpha application inhibited the appearance of apoptotic cells in the intestinal mucosa, whereas anti-FasL antibodies had no influence on mucosal apoptosis. In addition, the transfer of FasL deficient (gld) donor lymphocytes still induced crypt cell apoptosis, villous atrophy, and crypt hyperplasia. Furthermore, when the animals were treated with pentoxifylline, a known inhibitor of TNF-alpha secretion in vitro and in vivo, there was significant normalisation of the intestinal morphology accompanied by inhibition of epithelial apoptosis.'] Is intestinal crypt cell apoptosis in murine acute graft versus host disease mediated by tumour necrosis factor alpha and not by the FasL-Fas interaction : effect of pentoxifylline on the development of mucosal atrophy?