The hepatic lobule consists of parenchymal cells (epithelial cells) and nonparenchymal cells associated with the sinusoids: endothelial cells (ECs), Kupffer cells, pit cells, dendritic cells, and stellate cells (also known as vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells, Ito cells) (1–3) (Figure 67.1). ECs (4,5) express lymphocyte costimulatory molecules (6) and form the greater part of the extremely thin lining of the sinusoids, which are larger than ordinary capillaries and more irregular in shape. Kupffer cells are tissue macrophages and components of the diffuse mononuclear phagocyte system. They usually are situated on the endothelium, with cellular processes extending between the underlying ECs. The greater part of their irregular cell surface is exposed to the blood in the lumen of the sinusoid. Pit cells are natural killer cells. Dendritic cells (located in the portal triad in human, and in periportal and central areas in rats) capture and process antigens, migrate to lymphoid organs, and secrete cytokines to initiate immune responses (7). Hepatic stellate cells (1–3,8–11) lie in the space between sinusoidal ECs and parenchymal cells (perisinusoidal space or space of Disse) and, like ECs, are mesenchymal in origin. Recently, retinoid-storing stellate cells have been reported to exist in extrahepatic organs including the kidney, intestine, lung, and pancreas (2,12,13). The goal of this chapter is to review the structure and function of the hepatic stellate cell and to discuss its interactions with neighboring ECs.

HEPATIC STELLATE CELL

Hepatic stellate cells distribute regularly within hepatic lobules. The cell consists of a spindle-shaped or angular cell body and long, branching cytoplasmic processes that encompass the endothelial tubes of sinusoids (14,15).