Mucosal cell-mediated immunological changes associated with experimental graft-versus-host disease

This study examined the histological changes and local cellular immune response induced within the lingual mucosa in an allogeneic F1 hybrid rat model of graft-versus-host disease (GvHD) with a view to studying oral lymphocyte-epithelial cell reactions. Highest levels of disease, as reflected by both a GvHD index and the extent of the oral mucosal changes, were obtained using primed donor (Lewis rats) splenocytes and irradiated hosts (Lew/Da rats). The lingual mucosae of test animals were characterised by irregular epithelial keratosis, an absence of basal cell liquefaction and a diffuse inflammatory cell infiltrate, histological features consistent with an oral lichenoid tissue reaction. Immunohistochemical studies showed that mucosal involvement was characterised by infiltration of the lamina propria by NK cells (CD8+, CD5-), "activated" cells (CD25+) and T cells (CD5+) with selective migration of the latter, including a CD5+, CD8- subset (helper/inducer T cell), into the epithelium. Epithelial expression of Ia was invariably associated with these inflammatory cell infiltrates and correlated with the GvHD index. These findings suggest the presence of local mucosal T cell activation in the absence of detectable epithelial cell damage, which may be equivalent to the early initiating events in the pathogenesis of oral lichen planus. However, whilst experimental graft-versus-host disease appears to be a useful model for studying lymphocyte-epithelial interactions, the induced oral mucosal changes are more consistent with a lichenoid reaction rather than lichen planus.