Background-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. Aims-To investigate which of the two most investigated inductors of apoptosis (Fas ligand (FasL) and tumour necrosis factor (TNF-)) is responsible for the induction of apoptosis in this animal model. Methods-Animals undergoing acute semiallogeneic GvH reaction were treated with neutralising anti-TNF-, two diVerent anti-FasL antibodies, or pentoxifylline.Results-Anti-TNF-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 TNFsecretion in vitro and in vivo, there was significant normalisation of the intestinal morphology accompanied by inhibition of epithelial apoptosis. Conclusions-The FasL-Fas interaction is not involved in the induction of apoptosis during acute GVHD. However, neutralisation of TNF-by an antibody or by pentoxifylline inhibits the occurrence of apoptosis and of mucosal atrophy in this animal model. These results have implications for the treatment of immunologically mediated human atrophic gut diseases-for example, diet refractory cases of coeliac disease. (Gut 1999;45:229-235)

OX40 is highly expressed in the gastrointestinal tissue of patients with immunologically mediated bowel diseases. Together with previous studies in animal models for these diseases, the present results point to a potential role of OX40 in their pathogenesis.