CLASS-II MHC ANTIGEN (IA)-BEARING DENDRITIC CELLS IN THE EPITHELIUM OF THE RAT INTESTINE

Many tissues are found to contain populations of cells with an unusual dendritic shape, high levels of surface expression of MHC class II (l a) gene products, and strong accessory function for the stimulation of specific clones of quiescent T lymphocytes. Dendritic cells (DC) repr esent major population of ''professional'' APC in various lymphoid and nonlymphoid tissues, distinct from cells of the monocyte/macrophage l ineage, Among the best characterized nonlymphoid dendritic cells are e pidermal Langerhans cells, but it has been shown that interstitium and epithelium of other organs also contain irregularly shaped, strongly MHC class II positive cells. In recent years, DC have been localized t o alveolar septa in the lung, as well as within and just beneath airwa y epithelium, comprising a tightly meshed network that is reminiscent of epidermal Langerhans cells. In the gastrointestinal tract, conventi onal immunohistochemical analysis of mucosal class II MHC (la) stainin g reveals a morphologically heterogeneous pattern of staining in the l amina propria. DC that exhibit strong Ag-presenting activity in vitro have been extracted from enzymatic digests of colonic mucosa, but no p revious reports of MHC class Ii-positive cells with pleiomorphic morph ology have been recorded within the epithelium of the intestine. Emplo ying a novel combination of nonconventional section planes, pre-embedd ing fixation, and immunohistochemical techniques, we now demonstrate l a staining of cells with classical DC morphology within the epithelium of the intestine in normal specific pathogen-free rats. Our investiga tion suggests that cells with the morphologic and phenotypical charact eristics of DC are present within the mucosal epithelium of the rat je junum and colon, comprising a significant organized network. The numbe r of DC within epithelium of the colon was 117 +/- 20 per 10-mu m-thic k cross-section. These findings have important theoretical implication s for research on Ag processing and T cell activation in the context o f allergic and infectious diseases in the gastrointestinal tract.