Distribution and morphological characteristics of the pit cells in the liver of the rat.

Pit cells, on which almost no further contributions have been presented since the first report by Wisse et al. (1976), are described in detail in the rat liver. These cells show several characteristic features: 1) "rod-cored vesicles", a new type of vesicular inclusion observed first in our study; 2) electron-dense granules, which we consider to arise from multivesicular bodies by the accumulation of dense material; and 3) well-developed pseudopodia. Although these features clearly differentiate pit cells from conventional lymphocytes, these two cell types display similarities (i) in a number of ultrastructural features, (ii) in the pattern of their intralobular distribution, and (iii) in their presence in the spleen and peripheral blood.