Pit cells--a new type of cell first described here 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 two 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 (Wisse, 1972), Kupffer (Widmann et al., 1972; Wisse and Daems, 1970; Wisse, 1974a, b), and fat-storing cells (Ito, 1973). Pit cells do not phagocytose and do not react to a great number of experimental conditions, to which endothelial and Kupffer cells do react (Wisse, 1972, 1974b). Mitosis has been observed in a pit cell. The function of pit cells remains obscure, but an endocrine function is suggested by the morphology of their highly characteristic granules.

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After stimulation of the mouse peritoneal cavity with newborn calf serum (NBCS), four types of monocyte and macrophage were distinguished on the basis of peroxidase (PO) patterns. These cell types showed heterogeneity in their binding of the lectin wheat-germ agglutinin (WGA). At 16 h after stimulation, monocytes and monocyte-derived macrophages (with PO activity in granules) had a high level of WGA binding; PO-negative macrophages showed moderate WGA binding, and resident macrophages (with PO activity in the RER and nuclear envelope) had low WGA binding. At later time-points after stimulation, each of these cell types lost WGA binding sites. This decrease was related to a process of differentiation and to a modulation, affected by environmental factors. The present results also indicated that PO-negative macrophages can give rise to resident macrophages. Whether these PO-negative cells are monocyte derived or originate otherwise needs further investigation. The fourth type of macrophage, the exudate-resident cell (with PO activity both in granules and in the RER and nuclear envelope), with a WGA binding pattern similar to that of monocytes and monocyte-derived macrophages, was considered not to be a resident precursor cell.

The results of bacteriologic cultures of blood and heparin-lock fluid, both drawn from the central venous catheters of 54 consecutive oncohematologic patients, have been used to determine their value for the diagnosis of systemic and catheter-associated infection. In 30 patients with clinical signs of infection (bacteremia or septicemia), 74 of 1000 (7.4%) heparin-lock fluid cultures, 114 of 542 (21%) catheter-drawn blood cultures, and 36 of 134 (26%) venipuncture blood cultures became positive, whereas in 24 patients without clinical signs of infection the respective values were 5 of 700 (0.7%), one of 220 (0.4%), and none of ten cultures. Comparison of the results of cultures sampled on the same day reveals that the positive and negative predictive values for catheter-drawn blood cultures, with the venipuncture blood cultures taken as the standard for bacteremia, are 82% and 95% respectively. The results of heparin-lock fluid are indicative for clinically relevant colonization of the catheter. Three or more positive heparin-lock fluid cultures, sampled on subsequent days, were correlated with the occurrence of bacteremia or septicemia with a positive predictive value of 100%. The conclusions are supported by the results of scanning electron microscopy.