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Although it is known that impairment of dendritic cells (DC) plays a role in the pathogenesis and immunosuppression of retrovirus-associated diseases, it is not clear whether, or to what extent, these antigen-presenting cells themselves become infected. The realization that the cells can be generated in vitro in larger numbers than can be isolated from circulating blood or bone marrow raised the possibility that they could be used for therapeutic purposes. Therefore, we investigated whether DC generated in vitro from CD34 precursors are susceptible to infection when cocultured with human immunodeficiency virus type 1- or human T-cell leukemia/lymphoma virus-infected cell lines. While there appears to be a remarkable affinity of the viruses for the plasma membranes of the DC, interiorization or budding was not observed in 30 experiments carried out under a variety of conditions.

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A need for hematopoietic stem cells, particularly cells destined to enter the megakaryocyte (MK) series, prompted phenotypic analysis of mononuclear leukocytes in human cord blood. To this end, immunohistochemical, flow cytometric, and ultrastructural techniques were used. The immunogold silver enhancement method (IGS) for the detection of the MK-specific glycoprotein (GP) IIb/IIIa epitopes combined with a monocyte-specific stain for alpha-naphthyl butyrate esterase proved to be superior to flow cytometry (FACS) for precise quantitation of cell types in each sample. Immunoelectron microscopy afforded a description of distinctions between precursors bearing GPIIb/IIIa epitopes and other stem cells of the myeloid series. The number of presumed MK progenitors was surprisingly high, averaging 1.8% +/- 1.3% (range, 0.2% to 4.6%) by IGS and 4.1% +/- 3.0% (range, 0.2% to 9.3%) by FACS analysis. The occurrence of GPIIb/IIIa-positive denuded MK nuclei in cord blood was of interest, but was too small to affect these data. These observations should advocate a greater use of cord blood for restitution of MK/platelet-lineage-depleted patients as well as for experimental studies concerned with MK differentiation.

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Evidence implicates cells belonging to the mononuclear phagocytic system (MPS) in the development of some forms of amyloidosis (10, 22). Whether or not the MPS is involved in central nervous system amyloidosis is not known. As a first step to address this issue, microglial and astroglial cells isolated from mouse brains were cultured and characterized as to the properties they may share with other members of the MPS. It was shown by light and electron microscopy that both cell types phagocytose latex particles, but that only microglial cells engulf immunoglobulin sensitized erythrocytes. By means of immunohistochemical, immunofluorescence, and immunoblotting techniques, it was established that the cells contain and secrete lysozyme as well as the proteinase inhibitor cystatin-C (-gamma trace). Cystatin-C was distributed in the cytoplasm and the nucleus and was strikingly associated with filaments and bundles of fibrils. Another enzyme, commonly used to distinguish cells belonging to the MPS, is alpha-naphthyl butyrate esterase. Shortly after their isolation, only the microglial cells were positive, but on continued culturing, increasing numbers of astroglial cells became positive for alpha-naphthyl butyrate esterase. By day 22, almost all of the cells were positive. Freshly isolated cells were negative for the monocyte-specific antigen Mac-1. However, after 4 days, cells with the morphology of microglia had become positive, whereas astroglia failed to exhibit this antigen with up to 22 days in culture. Thus, both astroglia and microglia have properties in common with cells of the MPS which may be useful for future studies. However, on fresh isolation only microglia were indistinguishable from monocytes for all features tested.

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Ultrastructural cytochemistry of natural killer cells enriched by Percoll gradient centrifugation showed them to possess arylsulfatase (aryl-sulfate sulfohydrolase, EC 3.1.6.1). The enzyme was located in vesicles, granules, and the parallel tubular arrays, organelles characteristic for cytotoxic lymphocytes. Biochemically, peak enzyme activity correlated with the Percoll fractions containing cells with cytotoxicity for melanoma target cells. Treatment of natural killer cells with Na2SO4, a competitive inhibitor of arylsulfatase, suppressed cytotoxicity by almost 50%. Electron microscopy of effector-target cell conjugates, which had been permitted to incubate for only 30 min, disclosed numerous arylsulfatase-positive sites at the points of contact between the effector/target cell membranes. Thus, the enzyme was translocated to the surface before lysis of the target cell was morphologically evident. It is postulated that the parallel tubular arrays play a role in this translocation and that arylsulfatase may function in the degradation of cerebroside sulfate ester components of the target cell membrane to initiate the lytic event.

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Previous studies from this laboratory have shown actin to be a major protein of human lymphocytes (Stark, R., Liebes, L. F., Nevrla, D., and Silber, R. Biochem. Med., 27: 200-206, 1982). We now report the purification to homogeneity and characterization of actin from blood lymphocytes of normal subjects and patients with chronic lymphocytic leukemia. The recovery of the purified protein was about 20%. The properties of the lymphocyte actins were compared to each other and to those of rabbit skeletal muscle actin. Lymphocyte actin consisted of beta and gamma forms in a 2:1 ratio. The Mr 42,000 was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Normal and leukemic lymphocyte actin had similar polymerization properties as assessed by viscosity measurements at 25 degrees and 4 degrees, and the ultrastructural appearance of the filaments was the same. Similar patterns were observed between normal and chronic lymphocytic leukemia actin tryptic digests analyzed by high-performance liquid chromatography. The Vmax of the actin-activated myosin Mg2+ ATPase activity was compared using rabbit skeletal muscle heavy meromyosin and subfragment 1 preparations. The values obtained with rabbit skeletal muscle and normal lymphocyte actin were identical. The Vmax observed with chronic lymphocytic leukemia lymphocyte actin was 70% of that obtained with normal lymphocyte actin. The amount of actin needed to produce half-maximal activation (Kapparent) of heavy meromyosin and subfragment 1 were, respectively, 26 and 25 microM for normal lymphocytes and 18 and 24 microM for chronic lymphocytic leukemia lymphocytes. The anomalous ATP activation by actin did not reflect differences in B-:T-cell subpopulations between chronic lymphocytic leukemia and normal lymphocytes. The possible significance of the observed differences between the myosin Mg2+ ATPase activation by chronic lymphocytic leukemia and normal lymphocyte actin is discussed.

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In order to examine whether morphologically unidentifiable precursors of Reed-Sternberg cells (RSC) may circulate in the blood of patients with untreated Hodgkin's Disease (HD), mononuclear leukocytes were isolated from the blood of 33 consecutive patients and cultured in soft agar. Abnormal colonies containing multinucleated giant cells developed in the specimens of 12 patients. These cells had the light and electron microscopic appearance of RSC. They were positive for alpha-naphthyl acetate and alpha-naphthyl butyrate esterases, acid phosphatase and lysozyme, bespeaking their monocyte/macrophage lineage. The observations suggest that unidentifiable precursors of RSC could be responsible for hematogenous spread of the disease in some cases. Moreover, since RS-like cells developed in the specimens of 8 patients with stage I and II HD, it may be useful to evaluate whether soft agar colony culture would yield data of prognostic significance in patients with early disease.

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Soft agar culture of mononuclear cell fractions prepared from rat peripheral blood yielded numerous colonies consisting of mast cells. The mast cell nature of the cells was established by ultrastructural and histochemical analyses as well as by the demonstration the the colonies contained histamine and that the cells possessed receptors for the Fc component of IgE. Stringent criteria for the distinction of mast cells from monocytes/macrophages that could have metachromatic inclusions were applied. The alcian-blue-safranin technique delineated the maturation of mast cell granules by showing the loss of alcian-blue and increase in safranin-positive organelles presumed to reflect the increase in N-sulfated polysaccharides representing heparin. The mast cells exhibited low or absent reactions for peroxidase, alpha-naphthyl butyrate, periodic acid Schiff, and Sudan black reacting lipid, whereas macrophages stained in parallel were positive for these substances. Since it is known that extracellular conditions may cause variations in phenotypic expression, the observations have led to the hypothesis that mast cells and macrophages may have a common precursor.

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Human peripheral blood leukocytes, when cultured in soft agar give rise to giant (100 to 500 micrometer.) "foam cells." Investigation of the origin and properties of the cells proved that they were derived from monocytes in that the cells adherent to glass after 24 hours in culture were phagocytic, elaborated lysozyme and bore receptors for complement and immunoglobulin. The increment in size was accounted for primarily by large inclusions which on histochemical and biochemical analyses were shown to consist predominantly fo neutral fat. Transformation to fat cells took place in the absence of mitosis. Fc receptors were retained but complement receptors were lost. These observations suggest a role for monocytes in the replacement of hematopoietic tissue by fat in certain hypoplastic states. The cultured monocytes may also serve to facilitate the study of fat synthesis and metabolism in vitro.

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There has been a need to easily quantitate the incidence of eosinophil colonies within soft agar cultures. This has been realized by layering of the agar with benzidine dihydrochloride that permits detection of peroxidase activity in cells. Eosinophil colonies can be specifically identified by the addition to the substrate of potassium cyanide, an inhibitor of enzyme activity in neutrophils and monocytes. The enumeration of eosinophil colonies can be accomplished by scanning fresh or embedded cultures with low power magnification.

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The enzyme, 5'-nucleotidase (5'N) (E.C.-3.1.3.5) is present in lymphocytes isolated from the blood of normal subjects. This activity is markedly decreased or not detectable in the cells from three-quarters of patients with chronic lymphocytic leukemia (CLL), while supranormal levels are found in less than 10% of the cases. To determine whether the decreased 5'N value in CLL represents a lower activity per cell or fewer enzyme-containing cells than in the normal, conditions were established for the histochemical measurement of 5'N in human lymphocytes. It was found that the cells isolated from the blood of normal subjects or patients with CLL consist of 5'N-positive and 5'N-negative subpopulations. Normal subjects who had high 5'N specific activity were shown to have a greater percentage of 5'N-positive cells than individuals with low 5'N activity. Patients with CLL who had no activity by standard chemical assay had no 5'N-positive cells, while the exceptional patient with CLL with a higher than normal specific activity showed an percentage of 5'N-positive cells. It is suggested that the selective proliferation of 5'N-positive and 5'N-negative populations may account for the heterogeneity of 5'N in CLL.

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The ultrastructure of granulocyte colonies derived from normal human peripheral blood leukocytes cultured in semisolid media has been studied by a new method developed for this purpose. Fixation, dehydration, and embedding of the whole content of the Petri dish resulted in a block of Epon containing colonies made up of cells with the spatial orientation of those observed in living cultures. This permitted serial sectioning through entire colonies. Cell maturation in vitro appeared to parallel that of normal marrow. However, even the most mature cells retained cytoplasmic characteristics of more immature cells. This was particularly true for eosinophils which only rarely possessed granules with electron-dense crystalline "cores," a feature typical for mature eosinophils. In addition to the normal-appearing hematopoietic cells found within colonies, very large round or spindle-shaped cells were present between colonies and firmly attached to the bottom of the culture dish. Although the histochemical and functional characterization of these cells awaits further study, it is suggested that they are related to histiocytes or macrophages. The technique described here should prove valuable in studies of the development, differentiation, and interaction of many types of cells.

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Granulocyte colonies can be grown from leukocyte-rich plasma obtained from normal human peripheral blood. Purification of lymphocytes by the Ficoll-Hypaque gradient method and subsequent removal of monocytes achieved a 10-fold increase in the number of colonies formed, suggesting that the colony-forming cell is nonadherent, nonphagocytic, and morphologically difficult to distinguish from a lymphocyte. Ultrastructural analysis of intact colonies by a new method developed for this purpose showed orderly differentiation and maturation. Only undifferentiated cells were seen in colonies on day 5, promyelocytes with developing primary lysosomes were present on day 9, whereas myelocytes and metamyelocytes were most prevalent on days 15 and 21, respectively. The studies suggest where further concentration of precursor cells may be attempted, and where further functional and histochemical analysis of colonies on the ultrastructural level will be possible.

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The contractility of platelets has been attributed to an actomyosin-like protein which has been well defined on a physicochemical basis. Moreover, platelets contain +/-80 A filaments which resemble actin filaments in smooth muscle. Studies were undertaken on human and bovine platelets to better define the morphologic structures which may subserve this contractile function. In order to identify actin, the ability of the filaments to react with heavy meromyosin (HMM) was tested. Accordingly, platelets were glycerinated and treated with HMM. In addition, platelet actin was extracted, reacted with HMM, and examined by negative staining. In both instances typical arrowhead structures with clearly defined polarity and a periodicity of +/-360 A formed. As is the case with purified muscle actin, the complexes were dissociable with Mg-ATP. The formation of myosin-like filaments was observed when osmotically shocked platelets were incubated with MgCl(2) and excess ATP. These "thick" filaments measured 250-300 A in width, tapered at both ends and often occurred in clumps. They resembled aggregates of thick filaments described in contracted smooth muscle. Extraction of platelets by methods suitable for the demonstration of myosin showed filaments with an average length of 0.3 mu, a smooth shaft, and frayed or bulbous ends. These appeared identical to those seen in synthetically prepared myosin of striated muscle. It is suggested that the filaments described here represent the actin and myosin of platelets.

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