Electron microscopy of human white blood cells and their stem cells

An optimized protocol for the preparation of blood immune cells for transmission electron microscopy

Transmission electron microscopy (TEM) is a powerful technique that enables visualization of structural details inside cells. Prior to TEM imaging, biological samples must undergo several preparation steps that are optimized according to the sample type. Currently, there are limited protocols for the preparation of blood samples for TEM imaging. Here, we provide a detailed step-by-step method for preparing blood samples for TEM imaging. This protocol enables robust visualization of the ultrastructures of blood immune cells. In addition, we describe the typical cellular features that can be used to distinguish between different immune cells in the blood, such as neutrophils, eosinophils, monocytes, and lymphocytes. This protocol is useful for studying ultrastructural changes in blood immune cells under various physiological and disease conditions.

The structure of eosinophil leukocyte granules in rodents and in man

The structure of the specific granules of eosinophil leukocytes has been studied by electron microscopy in sections of tissues, buffy coats, and sediments of peritoneal washings of rats, mice, guinea pigs, and men. The core of eosinophil granules is a crystal which has a cubic lattice with a repeat of approximately 30 A in rodents and approximately 40 A in man. The chemical composition of the core is discussed in connection with recent cell fractionation studies, and the hypothesis that the core is a crystal of peroxidase is considered.

Antigen expression during early human granulocyte development studied with immuno-electron microscopy

Expression of the hapten fucosyl-N-acetyllactosamine was correlated with ultrastructural development in human granulocyte precursors using the monoclonal antibody FMC 10 with immunogold techniques. The antigen was detectable from the myeloblast/early neutrophilic promyelocyte stage onwards and was associated with striking development of the rough endoplasmic reticular system. In addition, low levels of labelling were seen on monocytes, eosinophils and some basophil precursors. Contraction and alignment of the cisternae of the rough endoplasmic reticulum during the promyelocyte stage of neutrophilic differentiation gave the appearance of a plasma cell. However, on closer examination it was apparent that true plasma cells did not react with this antibody.

Genesis, ultrastructure and cytochemical study of the cat eosinophil

Eosinophils from cat bone marrow and peripheral blood were studied by electron microscopy and cytochemical procedures. The maturation of eosinophils and formation of typical granules were described. Contrary to the accepted opinion that the core of animal's eosinophilic specific granules have a crytal-like structure, our observations revealed that the core has a myelin-like cylindrical appearance, whose layered formation proceeds from the inside outwards. Electron microscopic observations revealed that localization of reaction product to potassium pyroantimonate and phosphotungstic acid and to acid phosphatase activity was similar to that of eosinophils of man and other animals. Antimonate deposits and acid phosphatase activity were detected between the layers of the myelin-like structure of the core. Eosinophil granules failed to yield a positive reaction for peroxidase activity. The secretory activity of the eosinophil is discussed.

Light and electronmicroscopic observations on hepatic hematopoiesis of human fetuses. I. Granulocytopoiesis in the hepatic mesenchymal tissue

Focusing on hematopoiesis, especially granulocytopoiesis, livers from ten human fetuses between 7 to 13 weeks of gestation were observed with light and electron microscope. In the hepatic mesenchymal tissue variable number of granulocytes in varying stage of maturation were found from 10 to 13 weeks of gestation. The granules of neutrophils in human fetal livers were classified into three distinct types. The first granules appeared in myeloblasts. The second granules, possibly formed in Golgi complex, were more larger and observed after the promyelocytic stage. The third granules, predominant in mature neutrophils, were pleomorphic. Other than granulocytic, erythrocytic and stromal cells, unclassifiable cells were occasionally encountered. The role of mesenchymal tissues in the granulocytopoiesis, the development of fetal neutrophils and the problem of hematopoietic stem cells were discussed.

Ultrastructure of alcoholic hyalin and fate of the affected hepatocytes

In liver biopsy specimens, foci of satellitosis, i.e., foci of alcoholic hyalin containing hepatocytes surrounded by accumulated leukocytes, were studied by means of electron-microscopic investigation. Within satellitosis hepatocytes, the same morphologic variants of alcoholic hyalin were observed as formerly described in nonsatellitosis liver cells: (1) clusters of randomly oriented smooth filaments of homogenous electron density, (2) bundles of filaments aligned in parallel arrays and exhibiting irregular densities and indistinct boundaries, and (3) masses of a strongly osmiophilic amorphous material, presumably lipidic in nature. The individual hyalin body was composed of one, two, or all three components in varying proportions; an uptake by cytosegresomes was never observed. The leukocytes of satellitosis foci, mostly polymorphonuclear ones without obvious alterations, had close contact to the central hepatocytes, and sometimes covered large holes in the hepatocellular plasma membrane. In other cases, hepatocytes and neutrophils were both destroyed and the hyalin bodies were found unaltered within the sinusoids. It is suggested that alcoholic hyalin represents an inert proteinaceous storage material, deposited at the site of synthesis which in the course of time becomes superimposed by a lipid component. In cases of alcohol-induced hepatocellular lesions, those hepatocytes which produce hyalin bodies may have a special metabolic sensitivity to alcohol which on the one hand may result in hyalin synthesis and accumulation and on the other hand may, under special conditions, lead to plasma membrane destruction with secondary satellitosis formation.

The development of neutrophilic polymorphonuclear leukocytes in human bone marrow

Neutrophilic leukocytes (PMN) and their precursors from normal human marrow and blood were examined by histochemical staining and by electron microscopy and cytochemistry in order to determine the origin and nature of their cytoplasmic granules. Human neutrophils contain two basic types of granules, azurophils and specifics, which differ in morphology, contents, and time of origin. Azurophils are large and may be spherical or ellipsoid, the latter with a crystalline inclusion. They are produced in the first secretory stage (promyelocyte), contain peroxidase and various lysosomal enzymes, and thus correspond to modified primary lysosomes. Specifics are smaller, may be spherical or elongated, and are formed during a later secretory stage (myelocyte). They lack lysosomal enzymes and contain alkaline phosphatase and basic protein; their contents remain largely undetermined. Specifics outnumber azurophils in the mature PMN because of reduction in numbers of azurophils per cell by cell division in the myelocyte stage. The findings indicate that the situation is basically the same as described previously in the rabbit, insofar as the origin, enzymic activity, and persistence in the mature cell of the two types (azurophil and specific) of granules are concerned. The main difference between PMN of the two species is in the morphology (size, shape, and density) of the granules, especially the azurophils.

Differentiation of monocytes. Origin, nature, and fate of their azurophil granules

The origin, content, and fate of azurophil granules of blood monocytes were investigated in several species (rabbit, guinea pig, human) by electron microscopy and cytochemistry. The life cycle of monocytes consists of maturation in bone marrow, transit in blood, and migration into tissues where they function as macrophages. Cells were examined from all three phases. It was found that: azurophil granules originate in the Golgi complex of the developing monocyte of bone marrow and blood, and ultimately fuse with phagosomes during phagocytosis upon arrival of monocytes in the tissues. They contain lysosomal enzymes in all species studied and peroxidase in the guinea pig and human. These enzymes are produced by the same pathway as other secretory products (i.e., they are segregated in the rough ER and packaged into granules in the Golgi complex). The findings demonstrate that the azurophil granules of monocytes are primary lysosomes or storage granules comparable to the azurophils of polymorphonuclear leukocytes and the specific granules of eosinophils. Macrophages from peritoneal exudates (72-96 hr after endotoxin injection) contain large quantities of lysosomal enzymes throughout the secretory apparatus (rough ER and Golgi complex), in digestive vacuoles, and in numerous coated vesicles; however, they lack forming or mature azurophil granules. Hence it appears that the monocyte produces two types of primary lysosomes during different phases of its life cycle-azurophil granules made by developing monocytes in bone marrow or blood, and coated vesicles made by macrophages in tissues and body cavities.

Resolution of granules from rabbit heterophil leukocytes into distinct populations by zonal sedimentation

Postnuclear supernates from homogenates of essentially pure rabbit heterophil leukocytes were fractionated by means of zonal differential centrifugation through a discontinuous sucrose gradient at various speeds. Three distinct groups of granules were characterized biochemically and morphologically. They were, in order of decreasing sedimentation coefficient: (a) Large, relatively dense granules, identified morphologically as the azurophil or primary granules, and containing essentially all of the myeloperoxidase activity of the preparations, about one-third of their lysozyme activity, and between 50 and 80% of their content in five acid hydrolases typically associated with lysosomes in other cells; (b) smaller, less dense granules, with the morphological appearance of the specific or secondary granules, and carrying most of the alkaline phosphatase and the remainder of the lysozyme activity of the preparations; (c) a second group of lysosome-like particles, associated with a morphologically heterogeneous fraction, and containing the remainder of the acid hydrolases, but little or no myeloperoxidase. When p-nitrophenyl phosphate was used instead of beta-glycerophosphate for the assay of acid phosphatase, only small proportions of the total activity accompanied the two main lysosomal bands, and considerable activity was found in a zone slightly retarded with respect to the slowly moving band of acid hydrolases.

Lysosomal and ultrastructural changes in human "toxic" neutrophils during bacterial infection

"Toxic" neutrophils from humans with severe bacterial infections, identified by the presence of Döhle bodies, "toxic" granules, and vacuoles were shown to differ from normal neutrophils both in ultrastructure and in lysosome activity. Döhle bodies were identified as lamellar aggregates of rough endoplasmic reticulum. Toxic granules corresponded to the azurophilic granules usually identified by Romanowsky stains only in neutrophil precursors. By electron microscopy such granules were large, electron-dense, and peroxidase positive; they could usually be distinguished from the smaller, less dense, "specific" granules also present in control neutrophils, but in the latter they became visible by light microscopy only after prolonged staining or following fixation with glutaraldehyde. These observations suggest that toxic granules represent an abnormal staining reaction of the large dense granules in the toxic cells, and not phagocytized material, newly formed abnormal granules or autophagic bodies. Alkaline phosphatase activity was significantly greater in toxic neutrophils than in normal ones; 80% of the activity of both was located in the lysosome fraction. Beta glucuronidase was normal. Total acid phosphatase was normal, but the percentage located in the nonlysosome fraction of toxic neutrophils was increased, suggesting that lysosomes were "labilized." Formation of neutral red vacuoles in supravitally stained preparations, an index of lysosome activity, occurred more rapidly in toxic neutrophils. This reaction paralleled degranulation and the formation of clear vacuoles in unstained wet mounts and could be blocked by colchicine, a lysosome stabilizer, or enhanced by procedures which activate lysosomes. "Autophagic" vacuoles were observed by electron microscopy in some toxic neutrophils. These observations are discussed in relation to the concept that the "toxic" neutrophils in severe bacterial infection reflect cellular immaturity and/or stimulation or degeneration.

Ultrastructure of human leukocytes after simultaneous fixation with glutaraldehyde and osmium tetroxide and "postfixation" in uranyl acetate

Human leukocytes in suspension or in monolayer cultures have been processed for electron microscopy by fixation in a freshly made cold mixture of glutaraldehyde and osmium tetroxide and by "postfixation" in uranyl acetate. Simultaneous exposure to glutaraldehyde and osmium tetroxide eliminates many of the shortcomings seen when either of these agents is used alone as the initial fixative. Specimens are processed to the stage of dehydration as single cell suspensions or as very small clumps to assure rapid penetration of fixatives and efficient washing. The technique is rapid and reproducible. Electron micrographs presented in this report illustrate the ultrastructural features of human white cells prepared by this method.

Studies on lysosomes. XI. Characterization of a hydrolase-rich fraction from human lymphocytes

Pure suspensions of human lymphocytes were separated from peripheral blood by means of nylon wool, homogenized in 0.34 M sucrose-0.01 M EDTA solution, and fractionated by differential centrifugation. The bulk of acid hydrolase activity was found to be concentrated in a 20,000 g x 20 min granular fraction, whereas nuclear, debris, and supernatant fractions contained lesser concentrations of hydrolases. Acid hydrolase activity present in the granular fraction showed appropriate "latency" as judged by its dose-dependent release into the 20,000 g x 20 min supernatant after exposure to membrane-disruptive agents such as streptolysin S, filipin, and lysolecithin. Heparin proved to be necessary in the suspending medium so that reproducible homogenization and cell fractionation could be obtained. Even excessive contamination of lymphocyte suspensions with platelets did not appreciably alter the acid hydrolase activity of lymphocyte homogenates or the distribution of enzymes in subcellular fractions. Discontinuous density-gradient centrifugation of a 500 g x 10 min supernatant, containing both acid hydrolase-rich organelles and mitochondria, resulted in partial resolution of hydrolase-rich organelles from mitochondria. Fine structural studies of the intact lymphocytes showed the presence of acid phosphatase-positive, membrane-bounded organelles. Electron microscopy of the "large granule" (20,000 g x 20 min) fraction of such lymphocytes demonstrated 80-90% mitochondria, 5-10% platelets, and 5-10% membrane-bounded acid phosphatase-positive structures. The data indicate the presence in human peripheral blood lymphocytes of acid hydrolase-rich granules which possess many of the biochemical and structural characteristics of lysosomes in other tissues.

Acid phosphatase localization in rabbit eosinophils

Eosinophil (and heterophil) leukocytes of glycogen-induced rabbit peritoneal exudates were fixed for 1(1/2) min in 2% glutaraldehyde and examined for acid phosphatase activity both biochemically and cytochemically. Biochemical assays showed that enzymatic activity had been inhibited by only approximately 10% under these conditions. The cytochemical reaction in the eosinophil was confined to the granules in which the reaction product appeared in the matrix, not in the crystalline core (or in the core region after the latter's extraction). Granules wherein the matrix was disrupted and the crystalline core degraded or extracted showed the most intense deposition of reaction product, whereas well preserved granules with morphologically intact matrix and crystals were unreactive. Yet, not all disrupted granules gave a positive reaction, indicating that disruption was a necessary but not sufficient condition for reactivity. In many eosinophil leukocytes, most if not all granules were acid phosphatase-positive, provided they had become disrupted to a certain degree. Factors possibly involved in converting the granules from an unreactive to a reactive state are discussed.