Inhibition by cholera toxin of clonal growth of murine granulocyte/macrophage progenitor cells in soft agar cultures

Proliferation in vitro of the committed granulocyte-macrophage progenitor cell (CFUC) is inhibited by cholera toxin (CT) in a dose-dependent manner. This inhibition is reduced and counteracted by higher doses of colony stimulating factor (CSF), an obligatory growth stimulator of CFUC. Mixing of CT with its specific receptor, the monosialoganglioside, GM1, before exposure to bone marrow (BM) cells, blocks the toxin's effect, and a restoration of colony formation is achieved. A dose-dependent inhibition of CSF-induced colony formation is also observed in the presence of choleragenoid, the B subunit of the toxin which binds to the specific receptor on the cell surface, but is biologically inactive. Incubation of BM cells with CT prior to cloning in soft agar cultures supplemented with CSF inhibits clonal proliferation of CFUC, whereas a brief in vitro exposure of BM cells to CSF prior to CT protects the cells against subsequent CT inhibition. The ability of CT to inhibit the CSF-induced clonal proliferation of CFUC and the effectiveness of CSF in reducing and even counteracting CT inhibition suggests that CT, by binding to BM cells through the B subunit, might either directly or indirectly interfere with the stimulatory activity of CSF upon its target cells.     

Regulatory effects of lipopolysaccharide in murine macrophage proliferation

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Progesterone fails to modulate Toxoplasma gondii replication in the RAW 264.7 murine macrophage cell line

Cell mediated immunity is very important for host defence against intracellular pathogens and many studies have shown the role of the production of nitric oxide (NO) by interferon (IFN)-gamma/lipopolysaccharide (LPS)-activated macrophages. As the progesterone level increases during pregnancy in mammals, and as previous studies have shown that progesterone inhibits inducible nitric oxide synthase (iNOS) expression and NO production, we aimed to investigate whether progesterone might modulate intracellular replication of Toxoplasma gondii in macrophages. Our results showed that progesterone does not influence T. gondii replication in non-activated RAW 264.7 cells, and although progesterone inhibits NO production induced by IFN-gamma/LPS, we observed that it fails to restore the growth of T. gondii blocked by IFN-gamma/LPS. After discussing the reasons for this apparent discrepancy, we concluded that progesterone has no direct effect on the macrophage response. The real effect of the sex steroids in T. gondii infection and their implication in clinical toxoplasmosis therefore need to be investigated further to involve wider mechanisms of the immune system.     

Continuous and discontinuous propagation in heart muscle

Although cardiac muscle has been considered as an electrical syncytium for a long time, several aspects of conduction of the electrical impulse in the heart could not be explained by a continuous approach. Even the simple anisotropic nature of cardiac muscle gives rise to a number of conduction characteristics that contradicts with results from continuous models. It is, however, evident that cardiac conduction must be discontinuous in nature owing to recurrent resistive discontinuities caused by the cellular interconnections. In this review, the role of discontinuities at the cellular and macroscopic level on cardiac propagation will be discussed.     

Oxidized low-density lipoprotein induces differentiation of RAW264.7 murine macrophage cell line into dendritic-like cells

Dendtritic cells (DCs) are potent antigen-presenting cells and have an important role in the pathogenesis of atherosclerosis. Recent data suggests oxidized low-density lipoprotein (oxLDL) promotes the transition of a differentiating monocyte to a mature dendritic cell. In this study, we examined whether oxLDL could induce the differentiation of mature macrophages into DCs. After 48 h treatment with oxLDL, RAW264.7 cells increased in cell size and exhibited dendritic morphology. At the optimal oxLDL dose (10 μg/ml), approximately 74% of RAW264.7 cells differentiated into dendritic-like cells. Flow cytometric analysis detected dendritic cell surface markers (CD83, CD40, CD86, MHC Class II, and CD1d), and their expression increased in a dose- and time-dependent manner. Moreover, oxLDL-treated RAW264.7 cells showed functional changes including reduced endocytic activity, increased allostimulatory activity, and IL-12 production. The findings of the present work demonstrate that RAW264.7 cells, incubated with oxLDL, acquire some dendritic cell features.     

Helicobacter pylori stimulates inducible nitric oxide synthase expression and activity in a murine macrophage cell line

BACKGROUND & AIMS: Helicobacter pylori uniquely colonizes the human stomach and produces gastric mucosal inflammation. High-output nitric oxide production by inducible nitric oxide synthase (iNOS) is associated with immune activation and tissue injury. Because mononuclear cells comprise a major part of the cellular inflammatory response to H. pylori infection, the ability of H. pylori to induce iNOS in macrophages was assessed. METHODS: H. pylori preparations were added to RAW 264.7 murine macrophages, and iNOS expression was assessed by Northern blot analysis, enzyme activity assay, and NO2- release. RESULTS: Both whole H. pylori and French press lysates induced concentration-dependent NO2- production, with peak levels 20-fold above control. These findings were paralleled by marked increases in iNOS messenger RNA and enzyme activity levels. iNOS expression was synergistically increased with interferon gamma, indicating that the H. pylori effect can be amplified by other macrophage-activating factors. Studies of lipopolysaccharide (LPS) content and polymyxin B inhibition of LPS suggested that the H. pylori effect was attributable to both LPS- dependent and -independent mechanisms. CONCLUSIONS: iNOS expression in macrophages is activated by highly stable H. pylori products and may play an important role in the pathogenesis of H. pylori-associated gastric mucosal disease. (Gastroenterology 1996 Dec;111(6):1524-33)     

Activity of imidazoles against Leishmania tropica in human macrophage cultures

The anti-leishmanial activity of four imidazoles has been determined in Leishmania tropica-infected human monocyte-derived macrophage cultures. One of the imidazoles, hydrolyzed ketoconazole [cis-1-[4-[2-(2,4-dichlorophenyl)-2-(1H-imidazol-1-ylmethyl)-1,3-dioxolan-4-yl] methoxyphenyl]piperazine], eliminated 80 and 95% of the parasites at drug concentrations (2.0 and 2.5 microgram/ml) that are achievable in vivo by a structurally similar compound, ketoconazole. These results demonstrate that an imidazole has anti-leishmanial activity in a model system, and suggests that hydrolyzed ketoconazole should be considered for in vivo trials in animal models of the disease.     

Skeletal myoblasts overexpressing relaxin improve differentiation and communication of primary murine cardiomyocyte cell cultures

The possibility that resident myocardial progenitor cells may be re-activated by transplantation of exogenous stem cells into the post-infarcted heart has been suggested as a possible mechanism to explain the heart's functional improvement after stem cell therapy. Here we studied whether differentiation of mouse neonatal immature cardiomyocytes in vitro was influenced by mouse skeletal myoblasts C2C12, wild type or engineered to secrete the cardiotropic hormone relaxin. The cultured cardiomyocytes formed spontaneously beating clusters and temporally exhibited cardiac immunophenotypical (cKit, atrial natriuretic peptide, troponin T, connexin-43, HCN4) and electrical features (inward voltage-dependent Na⁺, T- and L-type Ca²⁺ currents, outward and inward K⁺ currents, I_f pacemaker current). These clusters were functionally connected through nanotubular structures and undifferentiated cardiac cells in the form of flattened stripes, bridging the clusters through connexin-43-containing gap junctions. These findings suggested the existence of long distance cell-to-cell communications among the cardiomyocyte aggregates involved in the intercellular transfer of Ca²⁺ signals and organelles, likely required for coordination of myocardial differentiation. Co-presence of the myoblasts greatly increased cardiomyocyte differentiation and the amount of intercellular connections. In fact, these cells formed a structural support guiding elongation of nanotubules and stripe-like cells. The secretion of relaxin by the engineered myoblasts accelerated and enhanced the cardiomyogenic potential of the co-culture. These findings underscore the possibility that grafted myoblasts and cardiotropic factors, such as relaxin, may influence regeneration of resident immature cardiac cells, thus adding a tile to the mosaic of mechanisms involved in the functional benefits of cell transplantation for cardiac repair.     

Activated platelets retain their potential to induce osteoclast-like cell formation in murine bone marrow cultures

Supernatants immediately obtained after platelet activation can induce osteoclast-like cell formation in murine bone marrow cultures. Here we report that activated platelets retain their potential to induce osteoclast-like cell formation over a 3-day period with repeated washing, when co-cultured with murine bone marrow cells. Supernatants obtained from washed platelets 3 days following their activation with thrombin, caused the differentiation of haematopoietic progenitors into osteoclast-like cells. The platelet-derived soluble factor(s) responsible for the induction of osteoclastogenesis can be retained in an ultrafilter with a nominal molecular weight limit of 10 kDa, and loose their activity when incubated at 99 degrees C. Indomethacin, which inhibits cyclooxygenase activity, and osteoprotegerin, a decoy receptor for receptor activator of nuclear factor-kappaB ligand (RANKL), suppressed the formation of osteoclast-like cells in this model. The in vitro findings presented here suggest that activated platelets can induce osteoclast-like cell formation via a prostaglandin and RANKL-dependent mechanism over a time period corresponding to the existence of a blood clot.     

Activated platelets retain their potential to induce osteoclast-like cell formation in murine bone marrow cultures

Supernatants immediately obtained after platelet activation can induce osteoclast-like cell formation in murine bone marrow cultures. Here we report that activated platelets retain their potential to induce osteoclast-like cell formation over a 3-day period with repeated washing, when co-cultured with murine bone marrow cells. Supernatants obtained from washed platelets 3 days following their activation with thrombin, caused the differentiation of haematopoietic progenitors into osteoclast-like cells. The platelet-derived soluble factor(s) responsible for the induction of osteoclastogenesis can be retained in an ultrafilter with a nominal molecular weight limit of 10?kDa, and loose their activity when incubated at 99°C. Indomethacin, which inhibits cyclooxygenase activity, and osteoprotegerin, a decoy receptor for receptor activator of nuclear factor-κB ligand (RANKL), suppressed the formation of osteoclast-like cells in this model. The in vitro findings presented here suggest that activated platelets can induce osteoclast-like cell formation via a prostaglandin and RANKL-dependent mechanism over a time period corresponding to the existence of a blood clot.     

Resistance of the stromal cell in murine long-term bone marrow cultures to damage by ionizing radiation

The ability of bone marrow stromal cells to survive and function after exposure to ionizing radiation remains controversial. Therefore, we used the murine long-term bone marrow culture system to analyze the effects of single doses of ionizing radiation (9-500 Gy) on the function of a preexisting, nearly confluent stroma that was supportive of hematopoiesis. Hematopoiesis ceased promptly in all the irradiated cultures and did not recover unless fresh marrow cells were inoculated. Radiation doses less than or equal to 100 Gy caused no obvious morphologic change in the cells. Total RNA, total protein, and collagen synthesis declined by 35%-60% within two days after even 9 Gy; but radiation doses up to 100 Gy caused minimal or no additional decline. Although RNA synthesis recovered nearly to normal within three weeks after radiation doses less than 100 Gy, total protein and collagen synthesis remained suppressed. Normal adherent layers irradiated with 9-50 Gy supported long-term hematopoiesis by fresh Sl/Sld marrow cells, although Sl/Sld marrow did not demonstrate sustained hematopoiesis when cultured in plain culture dishes or over normal stroma irradiated with 200 Gy. Thus, bone marrow stromal cells in long-term cultures did not show evidence of substantial cell death over at least the six-week period studied after irradiation with as much as 100 Gy, and they maintained hematopoietic supportive functions when irradiated with up to at least 50 Gy.     

Transition from granulocyte to macrophage predominance in bone marrow cultures

These studies examine the mechanisms underlying the transition from granulocytes to macrophages that characterizes cultures of bone marrow cells. Normal mouse marrow was cultured for several weeks in diffusion chambers (DCs) implanted in previously irradiated host mice. Previous studies with this system have shown that there is a period of logarithmic cell growth for 7 d following by a plateau in both total cell number and the numbers of CFU-S and CFU-C. The present studies show that this plateau in cell growth is associated with high cycling rates of both CFU-S and CFU-C. The plateau phase ends with a rapid decrease in the numbers of these progenitor cells. This is associated with a decline in the number of granulocytes, whereas macrophages persist at approximately the plateau level for the entire 48 d of culture. Transplantation of plateau phase cells into secondary DC cultures leads to a more rapid decline in the numbers of CFU-S and CFU-C followed by the total disappearance of granulocytes; in contrast, macrophage number undergoes a small increase which is maintained thereafter. When regular injections of 3H-thymidine are given to host mice bearing late phase secondary cultures, macrophage labelling rises to a plateau of only 30-40%, indicating that most macrophages at this stage of culture are long-lived cells. The kinetics of the stem cell changes implicate the CFU-C as the immediate precursor of granulocyte development in DC cultures but suggest that the CFU-S is the major determinant of overall cell renewal in this system. Macrophages doubtless also originate from CFU-C but, unlike granulocytes, these are often long-lived cells probably with some capacity for continuing cell division. These properties account for the often observed propensity of macrophages to repopulate bone marrow cultures from which stem cells and granulocytes have been depleted.