Interdigitating and dendritic reticulum cells in chronic active hepatitis.

An ultrastructural study of the cytology of piecemeal necrosis in 12 liver biopsies from patients with chronic active (aggressive) hepatitis revealed a variety of cell types. This communication deals with two particular cell types, only observed in areas of severe piecemeal necrosis--interdigitating reticulum cells (IDRCs) and dendritic reticulum cells (DRCs). IDRCs are typical components of T-cell regions in lymphoid organs. Cells with the characteristics of IDRCs were found in severe piecemeal necrosis at the periphery of portal tracts and in periportal areas. This suggests that areas of periportal piecemeal necrosis are analogous to the T-cell regions of lymphoid organs during immune reactions. DRCs are typical components of B-cell regions in lymphoid organs. Cells with the characteristics of DRCs were found in the central parts of portal tracts with follicle-like aggregations of lymphocytes, as seen in some cases with pronounced piecemeal necrosis. This finding suggest that follicle-like lymphocytic aggregates in portal tracts are analogous to the B-cell regions of lymphoid organs during immune reactions. A mesenchymal origin of DRCs is suggested. The finding of IDRCs and DRCs in severe piecemeal necrosis emphasizes the fundamental similarity of immune reactions in the liver to those in lymphoid organs. These data are discussed in relation to immunological findings in chronic active hepatitis.