Low-density Monocyte Research Articles

Long-term culture with lipopolysaccharide induces dose-dependent cytostatic and cytotoxic effects in THP-1 monocytes

Monocytes act as a first line of defence against invading pathogens and their dysfunctions seem to be a key factor in many immune disorders. However, the data on mechanisms underlying these dysfunctions remain elusive. In this study, we evaluated the effects of long-term (168h) lipopolysaccharide exposure on monocytes at low density cultures (1×105cells/ml). Treatment with low dose LPS (≤5μg/ml) resulted in oxidative stress induction followed by p21 pathway activation, permanent cell cycle arrest and SASP development. Furthermore, high dose LPS (≥10μg/ml) induced cell death involving mitochondrial pathways, death receptors as well as p21-dependent DNA damage response activation mediated by ROS generation and TNF-α release. Additionally, exposure to high dose of LPS resulted in THP-1 monocytes differentiation to macrophages. In conclusion, long-term culture with LPS exerts in low density monocytes cytostatic/cytotoxic effects in a dose-dependent manner by inducing senescence associated with chronic inflammation at low doses and initiation of cell death at higher doses. These findings shed new light on understanding of monocytes dysfunction, an issue relevant to chronic inflammation and many immune disorders.

Monocyte heterogeneity in angiotensin-converting enzyme induction mediated by autologous T lymphocytes.

The ability of monocyte subpopulations to be induced selectively by T lymphocytes to synthesize enhanced levels of angiotensin-converting enzyme (ACE) was examined using an in vitro model employing normal peripheral blood monocytes and T lymphocytes. Separation of monocytes into subpopulations on the basis of buoyant density indicated no difference in the ability of the resulting monocyte subpopulations to produce basal levels of ACE when cultured in the absence of T lymphocytes. However, the subpopulations differed significantly in their ability to synthesize enhanced levels of ACE in response to the presence of autologous T lymphocytes; low-density monocytes were induced by T lymphocytes to synthesize three-fold more ACE than were high-density monocytes. Surface antigen labelling using MoAbs demonstrated that the low-density monocyte subpopulations also had a significantly higher percentage of Leu-M2+ monocytes compared with the high-density monocyte subpopulations. When monocytes were separated on the basis of the presence of the Leu-M2 antigen using an immune rosetting technique, T lymphocytes were able to induce significantly elevated levels of ACE in the Leu-M2+ enriched monocyte subpopulation but were unable to induce ACE beyond basal levels in the Leu-M2(+)-depleted monocyte subpopulation. These results demonstrate that monocytes are heterogeneous with respect to their ability to be induced by T lymphocytes to synthesize ACE. This raises the possibility that selective accumulation of a monocyte subpopulation in the granulomatous inflammation of sarcoidosis may be one of the factors required for elevated ACE synthesis in the resulting granuloma epithelioid cells.

Identification and characterization of monocyte subpopulations from patients with bronchial asthma

Monocytes are inflammatory cells that accumulate in the airway in asthma. Monocytes constitute a heterogenous cell population in normal subjects. The heterogeneity of monocytes from nine patients with mild asthma and nine normal subjects was studied by means of discontinuous density gradient centrifugation with use of bovine serum albumin. The rate of low-density monocytes recovered from patients with asthma was higher than that obtained from normal subjects. The functional activity of monocyte fractions from asthmatic and control subjects was assessed by using the release of interleukin-1β (IL-1β) and the intensity of lysosomal enzymes, such as acid phosphatase and nonspecific esterase. The low-density cells produced less IL-1β than did cells of higher density in normal subjects. The IL-1β release was increased in low-density monocytes from subjects with asthma when compared with the same fraction from normal subjects ( p < 0.01). The low-density monocytes had a higher activity of lysosomal enzymes than did cells of higher density in both asthmatic and normal subjects. Electron microscopic studies showed that low-density monocytes from the subjects with mild asthma appeared to have the morphologic characteristics of activated cells with more vacuoles in this periphery. This study shows that low-density monocytes from subjects with asthma retain the ability to be activated in vivo and in vitro and may orchestrate immune reactions in mild asthma. (J A LLERGY C LIN I MMUNOL 1995;96:230-8.)

Patients with renal cancer have a larger proportion of high-density blood monocytes with increased lucigenin-enhanced chemiluminescence.

The production of oxygen metabolites is probably important in cancer cell killing. The production of the superoxide anion, O2-, can be measured by lucigenin-enhanced chemiluminescence (Cl). Previous studies have shown that whole-blood lucigenin-enhanced Cl is increased in cancer patients and that this increase is related to blood monocyte activity. The present investigation confirmed these findings and showed that whole-blood lucigenin-enhanced Cl was elevated in 17 patients with renal cell adenocarcinoma (P < 0.001). The activity of the monocytes was studied more in detail, whereby monocytes were separated into different populations based upon differences in densities, i.e., high-density and low-density monocytes. The cancer patients had a significantly larger proportion of high-density monocytes (P < 0.05) than controls. The lucigenin-enhanced Cl of purified high-density monocytes in controls was significantly higher than that of low-density monocytes (P < 0.01). The authors conclude that the increase in the lucigenin-enhanced Cl of whole blood observed in cancer patients may partly reflect the increased activity of a larger proportion of high-density monocytes in these patients.

Cell density-dependent expression of chondroitin sulfate proteoglycan in cultured human monocytes.

Monocytes were isolated and established in vitro at different cell densities. The incorporation of [35S]sulfate into macromolecules in monocytes (day 1 in culture) and monocyte-derived macrophages (day 5 in culture) was found to increase with decreasing cell density in approximately the same way in both day 1 and day 5 cell cultures. [35S]Sulfate was found to be incorporated almost exclusively into chondroitin sulfate proteoglycan (CSPG) in both high and low density monocyte and monocyte-derived macrophage cultures. The molecular size of the [35S]CSPGs produced by the high and low cell density cultures were not found to differ as judged by gel chromatography elution patterns. The molecular size and the structure of the glycosaminoglycan chains were found to be almost similar in high and low density day 1 and day 5 cultures. Only a small degree of proteoglycan degradation could be observed in both high and low density cultures. Furthermore, cell density-dependent differences in CSPG biosynthesis could be observed already 2 h after the establishment of the cultures, indicating that a process of "down-regulation" in high density cultures was already in operation. The glycosaminoglycan synthesis in high cell density day 1 cultures could be increased slightly following exposure to 0.5 mM benzyl-beta-D-xyloside, but not to the same level as that observed in untreated low cell density cultures. By contrast, the expression of 35S-macromolecules by cells cultured at high cell density for 5 days could be increased by xyloside treatment almost to the same level as that observed in the low density cultures.