Recent insights into the function of hepatic sinusoidal cells.
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Biomedical subjects
L Bouwens
Publications and source records attributed to L Bouwens.
Local proliferation and extrahepatic recruitment of liver macrophages (Kupffer cells) in partial-body irradiated rats.
The relative significance of local proliferation and extrahepatic recruitment of Kupffer cells was investigated by partial-body irradiation before the induction of macrophage hyperplasia by zymosan. There was no difference in growth of the Kupffer cells population between nonirradiated rats and rats irradiated with the liver shielded, whereas irradiation of the liver with the rest of the body (bone marrow) shielded resulted in strong inhibition of growth (-61%). Splenectomy combined with bone marrow irradiation inhibited growth to a lesser extent as compared to liver irradiation (-38%). Monocyte and other leukocyte numbers were strongly reduced in peripheral blood and their accumulation in the liver was completely prevented by bone marrow irradiation. Our results demonstrate that local proliferation of resident Kupffer cells represents the predominant source for their increased number during hyperplasia.
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Cytokinetic analysis of the expanding Kupffer-cell population in rat liver.
Zymosan stimulation in rats provides a useful model for studying the expansion of the Kupffer-cell population in liver, which represents the major population of tissue macrophages. This study, using tritiated-thymidine-labelling experiments, demonstrates that during population expansion at least 90% of the resident macrophages (Kupffer cells) develop proliferative activity. The mean duration of the cell cycle is estimated to be 52 hr, with an S phase of 7 hr. We have calculated that about 75% of population expansion results from local Kupffer-cell replication, whereas the remaining growth results from extrahepatic recruitment of macrophage precursors. These findings conflict with a concept of the mononuclear phagocyte system, which states that resident macrophages are (monocyte-derived) non-dividing end-cells.
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Proliferation, kinetics, and fate of monocytes in rat liver during a zymosan-induced inflammation.
The fate and kinetics of monocytes, recruited to the liver by a single zymosan injection, were investigated by light (LM) and electron (EM) microscopy combined with peroxidase cytochemistry and latex phagocytosis. Ultrastructural and cytochemical differences between these cells and resident Kupffer cells persisted during a 7-day period, demonstrating the existence of two types of hepatic mononuclear phagocytes. Both cell types exhibited a pronounced mitotic activity during their numerical increase. Next to peroxidase-positive (POP) Kupffer cells and monocytes, peroxidase-negative (PON) mononuclear phagocytes were observed. These may represent a monocyte subset and/or possibly Kupffer cell precursors.
Animals↗
Importance of local proliferation in the expanding Kupffer cell population of rat liver after zymosan stimulation and partial hepatectomy.
Partial hepatectomy and a single intravenous injection of zymosan were used to provoke expansion of the Kupffer cell population in rat liver. The number of Kupffer cells per microscopic field increased exponentially for 4 to 5 days after either stimulation. During this exponential growth phase, high mitotic activity of Kupffer cells was observed. The rate of mitosis, based on counts of cells arrested in metaphase by vinblastin, was compared with the increase in total cell population. During the first 3 days after partial hepatectomy, local proliferation was sufficient to explain the increase in population since the mean potential doubling time was 1.3 days compared to an observed doubling time of 3.7 days. During the first 3 days after zymosan stimulation, observed doubling time was 4.3 days compared with the mean potential doubling time of 5.2 days which led to the conclusion that growth is largely due to local proliferation of Kupffer cells. In both experimental situations, extrahepatic recruitment of "resident-type" macrophages was required during the last 2 days of the growth phase, since mitotic activity became too low to explain the observed growth. Proliferating Kupffer cells had characteristics of mature resident macrophages and were, therefore, considered to be different from elicited "exudate-type" cells, such as monocytes.
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Quantitation, tissue distribution and proliferation kinetics of Kupffer cells in normal rat liver.
In normal rat liver, Kupffer cells were unequivocally identified using peroxidase cytochemistry by light microscopy in semithin plastic sections. The Kupffer cell population was found to constitute 31% of the sinusoidal cells and by morphometry and serial sectioning, a mean absolute number of 14 to 20 X 10(6) Kupffer cells per g liver was calculated. The mean distribution of Kupffer cells in the liver lobules was 43% in the periportal, 28% in the midzonal and 29% in the central area of the lobule. Administration of latex particles labeled only 64% of all Kupffer cells, and in particular centrally located cells, showed a lower activity of latex uptake, even at overloading doses. Furthermore, the latter cells were of smaller size than periportal Kupffer cell profiles. The mean number and distribution of latex-labeled Kupffer cells did not change over a period of 3 months, indicating a long lifetime for these resident macrophages. This slow population turnover was supported by the observed small mitotic index, 0.06% after a 6 hr arrest by vinblastine, and by the small [3H]thymidine labeling index which did not change over a period of 3 weeks after administration of the label. It is proposed that the Kupffer cell population, under physiologic conditions, is a long-living and self-renewing population, the kinetics of which substantially differ from those of other sinusoidal cell types.
Animals↗
Tissue localization and kinetics of pit cells or large granule lymphocytes in the liver of rats treated with biological response modifiers.
The numbers of Kupffer cells (macrophages) and pit cells (large granular lymphocytes) were counted by light and electron microscopy in perfusion-fixed liver sinusoids. After a single intravenous injection of the biological response modifiers zymosan, Propionibacterium acnes and OK-432, a 4- to 6-fold increase in the number of pit cells and a 2- to 4-fold increase in the number of Kupffer cells were observed within a period of 4 to 7 days. The mechanisms of the pit cell accumulation were further studied by the metaphase arrest method and by selective irradiation of the liver, or of the rest of the body, with a dose of 8.5 Gy. Stimulated pit cells showed mitotic activity in the liver and to a lesser extent in peripheral blood. The zymosan-induced increase in pit cell number was inhibited by irradiation of the liver but not by irradiation of the rest of the body (with shielded liver). It is concluded that the hepatic pit cell population, which has been shown to have natural tumoricidal activity, can be induced to expand by biological response modifiers, and local division of preexisting cells contributes significantly to this expansion.
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MRI guided segmentation and quantification of SPECT images of the basal ganglia: a phantom study.
Due to the limited resolution of single-photon emission computed tomography (SPECT) imaging devices, tissue interfaces are not well defined in the reconstructed image, even though resolution recovery techniques may be used during reconstruction. Therefore, segmentation of a particular region and quantification of the tracer uptake in that region is critical due to spillover effects, when based on the SPECT image only. In this study, we present two methods for quantification of tracer uptake in a SPECT image, defined by a matched high resolution structural magnetic resonance image. We show preliminary results of both techniques, when applied for quantifying regional uptake in the different compartments of a phantom simulating the basal ganglia. These results indicate that the quantification method, which takes into account the blurring by the SPECT imaging device, promises to be perform better in the presence of background activity.
Basal Ganglia↗
PET imaging using gamma cameras.
This paper will review the recent advances and future developments in the field of coincidence imaging of positron emitters with a conventional Anger-type gamma camera. FDG imaging has shown high clinical importance in cardiology, neurology and especially oncology. Since access to full ring PET is mainly limited to university hospitals, there have been new developments allowing PET imaging on the standard Anger gamma camera. First the principles of coincidence imaging on a gamma camera will be reviewed. We will discuss the limitations of this technique, and the techniques used to partly overcome these limitations. The different configurations of the gamma camera operating in coincidence mode are pointed out. Different corrections for image degrading effects and reconstruction methods are evaluated in the final part.
Calibration↗
Iterative reconstruction algorithms in nuclear medicine.
Iterative reconstruction algorithms produce accurate images without streak artifacts as in filtered backprojection. They allow improved incorporation of important corrections for image degrading effects, such as attenuation, scatter and depth-dependent resolution. Only some corrections, which are important for accurate reconstruction in positron emission tomography and single photon emission computed tomography, can be applied to the data before filtered backprojection. The main limitation for introducing iterative algorithms in nuclear medicine has been computation time, which is much longer for iterative techniques than for filtered backprojection. Modern algorithms make use of acceleration techniques to speed up the reconstruction. These acceleration techniques and the development in computer processors have introduced iterative reconstruction in daily nuclear medicine routine. We give an overview of the most important iterative techniques and discuss the different corrections that can be incorporated to improve the image quality.
Algorithms↗
Image-correction techniques in SPECT.
This overview takes a look at different correction techniques for Single Photon Emission Computed Tomography (SPECT). We discuss the influence of the detection system followed by the scatter and attenuation caused by the object of investigation. When possible we describe how the correction methods for the different physical effects can be incorporated in the reconstruction method, being either filtered backprojection or iterative reconstruction.
Algorithms↗
Recent insights into hepatic "pit cells" or natural killer cells.
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Animals↗