PIT CELL - DESCRIPTION OF A NEW TYPE OF CELL OCCURRING IN RAT-LIVER SINUSOIDS AND PERIPHERAL-BLOOD

Pit cells, a new type of cell first described and so named because they contain highly characteristic granules, are situated in the wall of rat liver sinusoids, and have hyaloplasmic pseudopodia intermingling with the microvilli of the parenchymal cells. The characteristic granules are mainly situated at one side of the nucleus, the other side showing organelle-free hyaloplasm. Pit cells are also found in portal tracts and in granuloma-like cellular aggregates. They also occur in rat peripheral blood, although there are morphological differences between cells in these 2 sites. Pit cells can be regarded as regular inhabitants of the sinusoidal wall, and therefore belong to the series of sinusoidal cells, i.e., the endothelial, Kupffer and fat-storing cells. Pit cells do not phagocytose and do not react to a great number of experimental conditions, to which endothelial and Kupffer cells do react. Mitosis was observed in a pit cell. The function of pit cells remains obscure, but an endocrine function is suggested by the morphology and their highly characteristic granules.