Ultrastructural study of the maturation of peritoneal macrophages in the hamster

Fine structure and endocytic properties of subendothelial macrophages in the bulbus arterious of two bony fish species

The ultrastructure and endocytic properties of the subendothelial macrophages in the bulbus arteriosus of 2 teleosts, Cichlasoma severum and Xiphophorus helleri, are described. These cells show a diameter of 6 to 10 microns and contain a number of membrane-bound inclusion bodies, which vary greatly in size, shape, and electron density. Frequently, these bodies display myelin figures. Further, in the peripheral part of the cell there regularly occur bristle-coated vesicles. In specimens of X. helleri, injected intraperitoneally by a ferritin solution 20 to 400 h before the sacrifice, the subendothelial macrophages in the bulbus arteriosus contain large, ferritin-packed lysosomes. Similar inclusions were also seen in monocytes in the bulbar lumen. In the bulbus arteriosus of C. severum, there regularly occur mast cells beneath the endothelial lining, whereas the bulbar tissue in X. helleri lacks such cells. The present results are discussed and compared with those reported previously on the fine structure of free macrophages in mammals.

Coated pits and coated vesicles in the endothelial cells of trabecular meshwork

Coated pits (CPs) and coated vesicles (CVs) were investigated in the trabecular meshwork of man and rabbit. In both man and rabbit CPs and CVs appear to be randomly distributed throughout the trabecular tissue. CVs are located in the peripheral cytoplasm of the trabecular endothelial cells and show an average diameter of 0 . 16 micron. The ratio between the number of CPs and CVs ranges from 0 . 53 (rabbit) to 0 . 6 (man). The number of CPs and CVs is higher in rabbit than in man. Consequently, the overall CPs surface and CVs volume density estimates are higher in rabbits, where CPs represent about 1% of the cell surface and CVs account for about 0 . 4% of the cell cytoplasm. In man these percentages are 0 . 46 and 0 . 17%, respectively. No significant changes of CPs and CVs were found in rabbits with corticosteroid-induced ocular hypertension. However, changes in length of boundary membrane of CPs, though not statistically significant, were accompanied by proportional changes in CVs diameter.

Molecular characterization of human clathrin

Clathrin extracted from coated vesicles at pH 8.0 sediments as a single boundary with 8.1S sedimentation constant (s020,w) of 8.1 +/- 0.1 S. Sedimentation equilibrium gave a molecular weight (Mr) of 610 000 +/- 30 000. The clathrin frictional ratio (pH 7.5) computed from s020,w and Mr is very large, i.e., 3.06 +/- 0.18. Analysis of the circular dichroic spectrum in the far-ultraviolet showed that about half of the peptide residues are in a alpha-helical conformation. The molecular weight of a preparation of clathrin purified to homogeneity on a Sepharose CL-4B column in 6 M guanidine hydrochloride was 170 000 +/- 26 000 by sedimentation equilibrium, which is in agreement with the values we and others obtained by sodium dodecyl sulfate gel electrophoresis. The 8.1S clathrin species may be regarded as the "native" promoter since (1) it is extracted from coated vesicles by an extremely mild procedure, (2) it is stable over considerable ranges of pH, temperature, and ionic strength, and (3) it readily polymerizes into characteristic closed lattice structures resembling those observed in coated vesicles in the electron microscope. The 8.1S clathrin molecule self-associates at pH 6.3 to form two very high molecular weight species with average sedimentation coefficients of 150 and 300 S. The sedimenting boundaries of both of these species have been analyzed to reveal their molecular heterogeneity. The two species observed by sedimentation velocity may correspond to the two sizes of coated vesicles previously reported to be present in some cells when observed by electron microscopy. Analysis of the sedimentation pattern in the ultracentrifuge also gives the amount of unreacted 8.1S clathrin from which the yield of polymerizable clathrin is obtainable. This methodology can therefore be employed to estimate the quality of the 8.1S preparation of clathrin and thereby affords an assay of its activity.

Ultrastructural morphometry of isolated cells: methods, models and applications

Isolated cells constitute a favourable experimental model for the pathologist interested in ultrastructural morphometry. A particular advantage is that the same sampling regime may be appropriate for both normal and pathologically-altered material. Often this is not the case with other model systems. This report reviews alternative methodologies for analysing isolated cells, including free cells and dissociated cells in culture. We begin by attempting to define problems of more general concern: preparative techniques, methods of sampling, selection of stereological parameters and possible sources of error. A generalised morphometric model for isolated cells is followed by descriptions of models devised for specific cell types, notably mononuclear phagocytes and cells of the lymphocyte family. Typical results obtained by stereological analyses of these models are presented.

Quantitative ultrastructural features of maturing mononuclear phagocytes in rat peritoneal fluids

Ultrastructural features of the in vivo transformation of macrophage congeners in resident and adjuvant-induced peritoneal populations are evaluated by sterological methods. Maturation involves an increase in cell size by the differential hypertrophy of subcellular compartments, notably remaining cytoplasm, nucleus and lysosome-like granules. Larger cells have more and larger granules, more mitochondria and a greater plasmalemmal surface. In contrast, adjuvant activation tends to produce fewer granules and a nett loss of surface membrane.

Involvement of vesicle coat material in casein secretion and surface regeneration

The ultrastructure of the apical zone of lactating rat mammary epithelial cells was studied with emphasis on vesicle coat structures. Typical 40-60 nm ID "coated vesicles" were abundant, frequently associated with the internal filamentous plasma membrane coat or in direct continuity with secretory vesicles (SV) or plasma membrane proper. Bristle coats partially or totally covered membranes of secretory vesicles identified by their casein micelle content. This coat survived SV isolation. Exocytotic fusion of SV membranes and release of the casein micelles was observed. Frequently, regularly arranged bristle coat structures were identified in those regions of the plasma membrane that were involved in exocytotic processes. Both coated and uncoated surfaces of the casein-containing vesicles, as well as typical "coated vesicles", were frequently associated with microtubules and/or microfilaments. We suggest that coat materials of vesicles are related or identical to components of the internal coat of the surface membrane and that new plasma membrane and associated internal coat is produced concomitantly by fusion and integration of bristle coat moieties. Postexocytotic association of secreted casein micelles with the cell surface, mediated by finely filamentous extensions, provided a marker for the integrated vesicle membrane. An arrangement of SV with the inner surface of the plasma membrane is described which is characterized by regularly spaced, heabily stained membrane to membrane cross-bridges (pre-exocytotic attachment plaques). Such membrane-interconnecting elements may represent a form of coat structure important to recognition and interaction of membrane surfaces.

Ultrastructural features of proliferating fibroblasts in inflammatory granulomas

Proliferating fibroblasts in subcutaneous connective tissue of rats after injection of peanut oil or implantation of an almost insoluble synthetic material (silicap) were characterized electron microscopically. In tissue samples of both the foreign body granulomas typical fibroblasts with abundant rough endoplasmic reticulum and a peculiar cellular modulation resembling histiocytes concerning their organelle composition were found. The morphological picture of the latter cells does not allow the conclusion that their function must be a merely phagocytic one. True myofibroblasts as detected in other stages of connective tissue proliferation are not present. The capillary vessels show a clear proliferation of their vascular cells and migration of these cells with assumption of fibroblastic features is suggested basing on morphological observations.

The origin of (Kolmer's) epiplexus cells. A combined histomorphological and histochemical study

The morphology and the histochemically proofed enzyme pattern of the (Kolmer's) epiplexus cells found at the telencephalic chorioid plexus of humans indicate that these cells are of monocytogenetic origin, that they are monocytes and monocytogenetic macrophages respectively.

Malignant soft tissue tumors of probable histiocytic origin (malignant fibrous histiocytomas): general considerations and electron microscopic and tissue culture studies

Correlated light and electron microscopic study of four fibrous histiocytomas of proven malignancy has confirmed the presence of histiocyte-like and fibroblast-like cells in this tumor. In addition, an undifferentiated cell type, giant cells, xanthomatous cells, and rare cells with morphological characteristics intermediate between those of histiocytes and fibroblasts were seen. "Nuclear body" type inclusions were commonly present in both principal cell types in all four cases, as were the somewhat less common cytoplasmic inclusion bodies. Electron microscopic study of a tissue culture of one of these tumors demonstrated only fibroblast-like, histiocyte-like, and xanthomatous cells. The possibility is suggested that both principal cell types in this tumor may derive from the same undifferentiated stem cell.