The transport and distribution of colloidal iron and its relation to the ultrastructure of the cell

Intracellular ferritin accumulation in neural and extraneural tissue characterizes a neurodegenerative disease associated with a mutation in the ferritin light polypeptide gene

Abnormal accumulation of ferritin was found to be associated with an autosomal dominant slowly progressing neurodegenerative disease clinically characterized by tremor, cerebellar ataxia, parkinsonism and pyramidal signs, behavioral disturbances, and cognitive decline. These symptoms may appear sequentially over a period of 4 decades. Pathologically, intranuclear and intracytoplasmic bodies were found in glia and subsets of neurons in the central nervous system as well as in extraneural tissue. Biochemical analyses of these bodies isolated from the striatum and cerebellar cortex revealed that ferritin light polypeptide (FTL) and ferritin heavy polypeptide (FTH1) were the main constituents. Molecular genetic studies revealed a 2-bp insertion mutation in exon 4 of the FTL gene. The resulting mutant polypeptide is predicted to have a carboxy terminus that is altered in amino-acid sequence and length. In tissue sections, the bodies were immunolabeled by anti-ferritin and anti-ubiquitin antibodies and were stained by Perls' method for ferric iron. Synthetic peptides homologous to the altered and wild-type carboxy termini were used to raise polyclonal antibodies. These novel antibodies as well as an antibody recognizing FTH1 immunolabeled the bodies. This study of this disorder has provided additional knowledge and insights in the growing area of ferritin-related neurodegeneration.

Electron microscopy and x-ray scanning microanalysis of needle biopsy material from human liver

A study has been made of the fine structure of hepatic parenchymal cells of human biopsy material in a case of pancreatic tumor with obstructive jaundice. Dense particles about 60 A in diameter have been found in the cytoplasm, which are considered to be ferritin molecules by electron microscopy. They are encountered throughout the cytoplasmic matrix and are often aggregated in electron-transparent areas, most of which are enclosed by an apparently single-layered membrane. Identification of the elemental iron has been pursued by the application of the x-ray scanning microanalyser which reveals a quantitative value within 1.0 per cent of the pure iron sample. The use of x-ray scanning microanalysis enables one to obtain accurate data from extremely small and precisely defined volumes of biological specimens.

The nuclear annuli as pathways for nucleocytoplasmic exchanges

Colloidal gold particles, 25 to 55 A in diameter, which had been coated with polyvinylpyrrolidone, were microinjected into the ground cytoplasm of amebas (Chaos chaos). At time intervals of 1 minute, 2 minutes, 10 minutes, and 24 hours after injection the cells were fixed for electron microscopy. After 24 hours, gold particles were found in both the nuclei and the ground cytoplasm, the concentration being higher in the nuclei. Colloidal particles were also present in the nuclei after 10 minutes, but at this time interval the concentration did not appear to be greater than that in the ground cytoplasm. One and 2 minutes after injection, the gold particles were located almost exclusively in the ground cytoplasm; however, individual particles were often found within the annuli of the nuclear envelope, and were located specifically in the centers of these structures. The results suggest that at least some of the gold particles which enter the nuclei pass through the annuli, and that passage through these structures may be restricted to a central channel.

Characterization and accumulation of ferritin in hepatocyte nuclei of mice with iron overload

After a single subcutaneous dose of iron-dextran (600 mg of iron/kg), iron overload developed in C57BL/10ScSn mice. At 4, 24 and 78 wk liver nonheme iron concentrations were 67-, 42- and 21-fold higher than controls, respectively. Much of the iron was in macrophages, but hepatocytes were also strongly positive for Perls' stainable iron. One feature was the development of iron-positive nuclear inclusions in hepatocytes. After a delay of at least 8 wk when no stainable iron was evident, a maximum of 37% of periportal hepatocytes contained inclusions by 24 wk. Although this proportion remained constant for the remainder of the study, the size of the inclusions (which were not membrane-limited) increased to greater than 3 microns in diameter, occupying greater than 25% of the nuclear volume. The presence of iron in the inclusions was confirmed by energy dispersive x-ray microanalysis. Immunocytochemical studies showed that the iron was present as aggregates of ferritin. Quantitation of nonaggregated ferritin molecules by image analyses after electron microscopy demonstrated that within 4 wk ferritin levels in cytoplasm and nucleoplasm had greatly increased but that there was a concentration gradient of approximately one order of magnitude across the nuclear envelope. These findings are consistent with the hypothesis that in iron-loaded mouse hepatocytes there is a slow passage of ferritin-molecules through the nuclear pores; the gradient is maintained by the continual aggregation of ferritin within the nucleus. Intranuclear ferritin may provide a source of iron for catalyzing hydroxyl radical formation in nuclei during some toxic, carcinogenic and aging processes.

Antigens in immunity. XIV. Electron microscopic radioautographic studies of antigen capture in the lymph node medulla

Details of antigen trapping and processing in the rat lymph node have been investigated by the technique of high resolution radioautography. A series of 24 adult rats was injected with 20 microg of (125)I-labeled Salmonella adelaide flagella, given as either a primary or a secondary stimulus into one hind foot-pad. At intervals ranging from 3 min to 3 wk, rats were killed and the popliteal nodes were processed for electron microscopic radioautography using Kodak NTE emulsion. The present paper deals with events in the lymph node medulla, and an accompanying report describes the radically different behavior of antigen in the cortical follicles. In the medulla, lightly labeled granulocytes were transiently encountered, but by far the greatest bulk of antigen was in macrophages. Antigen entered these cells in two ways: by direct penetration of the plasma membrane; and by pinocytosis. In either case, the antigen rapidly became surrounded by tiny vesicles which may have represented Golgi-derived "protolysosomes." Vacuolar fusion ensued and a series of progressively larger and more complex antigen-containing "phagolysosomes" was formed. Substantial amounts of antigen could be detected in such bodies for at least 3 wk. The antigen injection, as expected, caused extensive plasma-cytopoiesis. No evidence of label in plasma cells was obtained. No special anatomic relationship between plasma cells and antigen depot sites was discovered. These results are briefly discussed in relation to current theories of immune induction.