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PubMed1985

Reduced function of HLA-DR-positive monocytes in patients with systemic lupus erythematosus (SLE).

Accessory function of monocytes for T-cell activation was studied in patients with systemic lupus erythematosus (SLE). Nylon column-purified T cells alone were not activated to proliferate by stimulation with concanavalin A (Con A), but the addition of dish-adherent monocytes restored the T-cell response in a dose-dependent manner (accessory function). This accessory function is mediated by HLA-DR-positive monocytes. This accessory function of monocytes was markedly impaired in SLE patients. The dysfunction of monocytes was marked in an active stage of SLE but not in an inactive stage of SLE. Furthermore, SLE T cells were not fully activated with Con A in the presence of normal monocytes, suggesting that both monocyte and T-cell functions were impaired in SLE patients. The dysfunction of SLE monocytes was due to neither the development of suppressor monocytes nor the overproduction of prostaglandins, because SLE monocytes did not suppress the accessory function of normal monocytes and indomethacin did not restore the dysfunction of SLE monocytes. The percentage of HLA-DR-positive cells in a monocyte population was markedly decreased in active SLE patients and moderately decreased in inactive SLE patients. Thus, the impairment of accessory function of monocytes in SLE patients seems to be derived from a decrease in HLA-DR-positive monocytes. These results suggest that the dysfunction of HLA-DR-positive monocytes plays an important role in the pathogenesis of SLE.

Autoantibodies↗
PubMed1996

Lipoxin A4 and B4 are potent stimuli for human monocyte migration and adhesion: selective inactivation by dehydrogenation and reduction.

Monocyte recruitment and adherence are important events in inflammatory and vascular diseases. Here, we evaluated the actions of lipoxin A4 (LXA4) and LXB4, a series of lipoxygenase products from arachidonic acid generated by cell-cell interactions, on human monocytes. LXA4 and LXB4 (10(-7) M) each increased monocyte migration in chamber chemotaxis assays and, in migration under agarose, exhibited chemotactic indices similar to those of the chemotactic peptide formyl-methionyl-leucyl-phenylalanine at 10(-10)-10(-8) M and to the chemokine macrophage inflammatory protein-1 alpha (MIP-1 alpha) at 10(-8)-10(-7) M with a rank order of potency: Monocyte chemotactic protein-1 alpha > LXA4 approximately LXB4 approximately MIP-1 alpha. Lipoxins also stimulated monocyte adherence to laminin. In addition, human monocytes rapidly transformed LXA4 and LXB4 to several metabolites. LXB4 (> 80%) was converted within 30 s to new products, in a trend similar to that of LXA4. The novel monocyte-derived LXB4 products were identified as 5-oxo-6,7-dihydro-LXB4 and 6,7-dihydro-LXB4, indicating a role for site-selective dehydrogenation and reduction. Unlike monocytes, intact polymorphonuclear leukocytes (PMN) did not metabolize LXA4 in significant quantities, and only approximately 12% of exogenous LXB4 was omega-oxidized to 20-OH-LXB4 and 20-COOH-LXB4 by PMN. To determine if lipoxin conversion altered bioactivity, we evaluated the actions of these metabolites on monocytes. Each of the novel products of LXA4 and LXB4 from monocytes, namely oxo- and dihydrolipoxins, were essentially inactive in stimulating monocyte adherence. In contrast, the omega-oxidation products of LXB4 isolated from PMN were equipotent with LXB4 for monocyte adherence. Dehydrogenation of LXA4 in monocytes appears to be carried out by a 15-hydroxyprostaglandin dehydrogenase, which is present in human monocytes as determined by reverse transcription PCR and Western blots. Together, these results provide the first evidence that LXA4 and LXB4 are both potent stimulants for migration and adherence of human monocytes. Moreover, they underscore the importance of the major route of lipoxin metabolism in leukocytes, namely, the rapid dehydrogenation and inactivation carried out by monocytes.

Cell Adhesion↗
PubMed1974

Phagocytic and bacterial properties of normal human monocytes.

The bactericidal and phagocytic capacities of monocytes for E. coli, Staphylococcus, Salmonella, and Listeria, and factors that influence these functions were evaluated and compared with those of the polymorphonuclear leukocytes of 30 normal human subjects. Monocytes killed a significantly smaller proportion of each of the bacterial species than did neutrophils from the same individuals. Whereas the neutrophils of all individuals demonstrated the ability to kill significant numbers of the four bacterial species, there was a marked variation in the effect of monocytes of different individuals on the growth curves of these same bacteria. When the bactericidal capacity of an individual's monocytes to more than one species of bacteria was examined in the same experiment, a significant difference in the effect of monocytes on the growth curve of one bacterial species as opposed to another was noted in 4 of 17 subjects. The bactericidal ability of monocytes of single individuals was consistent on different days in 9 of the 11 subjects whose monocytes were examined more than once against the same bacteria. Studies were performed to determine if the lesser bactericidal capability of monocytes was due to a difference in the ability of monocytes and neutrophils to phagocytize or to a difference in the ability of these cells to kill ingested bacteria or both. The results demonstrated that monocytes phagocytize bacteria significantly less well than neutrophils, but the intracellular killing capacity of both cell types is equal. Addition of phenylbutazone to cell suspensions completely inhibited intracellular killing by both monocytes and neutrophils, suggesting the possibility that the bactericidal mechanisms in both cell types might be similar. Monocyte killing of E. coli, Salmonella, and Listeria, but not of Staphylococcus, was significantly diminished in heat-inactivated autologous serum. Neither increasing the concentration of autologous serum from 10% to 25% nor replacement of autologous serum with pooled human serum had any effect on monocyte killing of any of the four bacteria. These studies demonstrate that peripheral blood monocytes are less bactericidal for the four bacterial species than neutrophils, solely because monocytes are less phagocytic. A baseline for further study of factors that influence monocyte function and for study of this cell in selected patient populations is provided.

Blood↗
PubMed1985

Role of interleukin 1 in promoting human monocyte-mediated tumor cytotoxicity.

Human peripheral blood monocytes from normal donors obtained by separation on a Percoll gradient showed considerable cytotoxicity against tumor cells when preincubated in vitro for 24 hr with human monocyte-derived interleukin 1 (IL 1). In contrast, monocytes after pretreatment in medium alone had low cytotoxic activity. All the IL 1 preparations, including IL 1 which was purified by high-performance liquid column chromatography (HPLC), as well as crude culture supernatant from human monocytes promoted monocyte-mediated cytotoxicity in the same dose-dependent manner as the thymocyte growth-promoting activity. There was no endotoxin or interferon (IFN) activity in the highly purified IL 1, suggesting that IL 1 itself was the active moiety. The effect of IL 1 on monocyte-mediated cytotoxicity was partially inhibited by indomethacin, whereas pretreatment of monocytes with prostaglandin (PG) E1 or E2 rather than IL 1 also resulted in substantial monocyte cytotoxicity. Thus, the effect of IL 1 on monocyte-mediated cytotoxicity is presumably mediated by PGE. Since fresh monocytes that were not preincubated exhibited levels of spontaneous cytotoxic activity similar to that of monocytes preincubated with IL 1, it seemed likely that the effect of IL 1 was to maintain the spontaneous level of activity rather than to induce cytotoxic activity. To elucidate this possibility, monocytes were first preincubated in medium alone for a longer period, and after losing their spontaneous activity they were further incubated with or without IL 1. Such "aged" monocytes did not develop cytotoxic activity in response to IL 1 but did in response to other agents known to induce macrophage cytotoxicity, such as endotoxin or lymphokine-containing supernatants. Therefore, the major effect of IL 1 actually seemed to prolong the cytotoxic state of monocytes. These results also suggest that IL 1 released by macrophages or monocytes may play a role in host defense against neoplastic cells by acting on monocytes as an autostimulating factor.

Cell Adhesion↗
PubMed2006

Migratory fate and differentiation of blood monocyte subsets.

Monocytes are established circulating precursors for tissue macrophages and dendritic cells (DCs). Monocyte-derived macrophages and DCs fulfill critical roles in innate and adaptive immunity during inflammation, and it is believed that monocytes also maintain these populations in peripheral tissues during homeostasis. However, the continuous replenishment of any DC pool by blood monocytes in the steady state remains to be established, and some macrophage populations may be self-renewing in the steady state. Recent identification of mouse monocyte subsets that closely resemble human monocyte subsets has inspired a variety of techniques wherein monocytes can be readily traced in vivo to address these critical questions. There are two major monocyte subsets that vary in chemokine receptor (CCR) and adhesion molecule expression, and in migratory and differentiation properties. In humans, 'classical' CD14+ CD16- monocytes express CCR2, CD64, CD62L, whereas 'non-classical' CD14low CD16+ monocytes lack CCR2. Their counterparts in mice are CCR2+ Gr-1hi and CCR2- Gr-1low monocytes, respectively. Gr-1hi (Ly6Chi) monocytes are recruited to inflammatory sites, e.g. inflamed skin or acutely inflamed peritoneum and give rise to macrophages and DCs in inflammatory or infectious disease models and to epidermal Langerhans cells after skin inflammation. Gr-1low monocytes have been proposed as precursors for steady state DCs, but experimental evidence is as of yet limited. Fortunately, the rate of progress in the study of monocyte fate is rapidly picking up pace, giving rise to the expectation that we will soon know much more about the biology of monocytes in the steady state and inflammation.

Animals↗
PubMed1996

Apoptosis of monocytes cultured from long-term hemodialysis patients.

Monocyte apoptosis in vitro was studied in patients on long-term hemodialysis, CAPD, and in predialytic uremia to gain insight into the high susceptibility of these patients to infections. Monocytes from dialysis and control subjects were cultured for 24 to 120 hours in vitro to analyze the level and progression of DNA fragmentation as a hallmark of apoptosis. After an incubation time of 48 hours chromatin fragmentation of 48.5 +/- 7.7% was found in monocytes from dialysis patients, which significantly exceeded DNA fragmentation of control monocytes (23.1 +/- 9.1%; N = 12; P < 0.01). Over longer culture periods of up to 5 days, a continuous progression of apoptosis occurred with a similar slope of percent DNA fragmentation in the two studied groups. Monocyte viability was > 95% both in the dialysis and control group. Hemodialysis patients also showed elevated levels of monocyte apoptosis when programmed cell death was evaluated by transmission electron microscopy or DNA electrophoresis of cleaved chromatin. To test the functional relevance of monocyte apoptosis, a significant reduction of Candida growth inhibition by monocytes of dialysis patients was found with a strong linkage between percentage of DNA fragmentation and impaired microbicidal capacity. Monocytes obtained from patients after the hemodialysis session and from CAPD patients showed normal DNA fragmentation levels similar to controls. Differences of monocyte apoptosis between patients on cuprophane and high-flux polysulphone dialysis were not found. Uremic predialytic patients also exerted an increased monocyte DNA fragmentation of 44.2 +/- 1.5% (N = 7; P < 0.05 compared to controls). Enhanced apoptosis of uremic monocytes was accompanied by a reduced formation of TNF-alpha over 48 hours, revealing a significant negative correlation between chromatin fragmentation and monokine synthesis. Supplementation of monocyte cultures from dialysis patients with exogenous TNF-alpha turned increased apoptosis back to baseline levels, suggesting that inflammatory mediators may modulate monocyte senescence. In summary, the elevated degree of monocyte apoptosis in end-stage renal failure may contribute to the impaired cellular host defense seen in these patients.

Adult↗
PubMed1999

Surface phenotype analysis of CD16+ monocytes from leukapheresis collections for peripheral blood progenitors.

In peripheral blood progenitor cell (PBPC) collections from patients with solid tumour or haematological malignancy, monocytes were separated into two subpopulations. The majority of monocytes expressed CD14 at a high density without CD16 antigen (the CD14+CD16- monocytes). The remaining monocytes co-expressed CD14 and CD16 (the CD14+CD16+ monocytes). These CD14+CD16+ monocytes amounted to 20.6 +/- 15.8%, while those in peripheral blood (PB) obtained from healthy volunteers were 7.3 +/- 3.1% (P < 0.05). When subdividing the CD14+CD16+ monocytes into CD14brightCD16dim and CD14dimCD16bright cells, both populations were found to be increased in PBPC collections. Since typical CD14+CD16+ monocytes are the CD14dimCD16bright population, we compared the additional surface antigens on CD14dimCD16bright monocytes with those of CD14+CD16- monocytes. In PBPC collections, the CD14dimCD16bright monocytes exhibited lower levels of CD11b, CD15, CD33 and CD38 expression and higher levels of CD4, CD11a, CD11c and MHC class II, and also revealed a higher percentage of CD4+ cells and a lower percentage of CD15+ cells and CD38+ cells, compared with the CD14+CD16- monocytes. When compared with the CD14dimCD16bright monocytes in PB, those in PBPC collections exhibited higher expression of CD4 and lower expression of CD11b, and also showed higher percentages of CD4+ cells and CD38+ cells and a lower percentage of CD11b+ cells. These results suggest that PBPC collections may be rich in the CD14+CD16+ monocytes in which the proportion of the immature population is increased. It is likely that these monocytes participate in the haematological and immune recovery after PBPC transplantation.

Adolescent↗
PubMed2002

Increased expression of inducible nitric oxide synthase in circulating monocytes from patients with active inflammatory bowel disease.

BACKGROUND: Inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) synthesis are increased in epithelial cells and in tissue macrophages of the inflamed mucosa from patients with inflammatory bowel disease (IBD). Since tissue macrophages are derived from circulating monocytes, we studied iNOS expression in circulating monocytes and related this expression to disease activity. In view of the possible role of NO in monocyte function, we also studied iNOS expression in relation to markers of monocyte activation. METHODS: The expression of iNOS in circulating monocytes from 15 patients with active IBD, 6 patients who went into remission and 18 healthy controls was quantified by flow cytometry and correlated with surface markers (CD63, CD11b, HLA-DR) for monocyte activation. In addition, iNOS expression in circulating monocytes was assessed by Western blotting, immunocytochemistry and measurement of the NO metabolites nitrite and nitrate in plasma. RESULTS: The expression of iNOS in circulating monocytes and the percentage of iNOS-positive monocytes were increased in patients with active IBD compared to healthy controls (fluorescence index: 1.3 (0.1-6.3) versus 0.8 (0.0-1.8); P < 0.05: percentage of iNOS positive monocytes: 37.3 (1.0-77.0)% versus 5.3 (0.0-43.3)%; P<0.01). The six patients who went into remission all had a marked reduction of iNOS expression. iNOS expression was confirmed by Western blotting and immunocytochemistry. Plasma nitrite and nitrate levels were elevated in three patients with active 1BD. The surface markers for monocyte activation, CD63 and CD11b, were not elevated. HLA-DR expression was decreased on circulating monocytes from patients with active ulcerative colitis. CONCLUSIONS: iNOS is increased in circulating monocytes from patients with active IBD and this increased expression correlates with disease activity. Considering the decreased HLA-DR expression and absence of monocyte activation markers, NO produced by iNOS may have a function in suppressing systemic monocyte activation.

Adult↗
PubMed1981

Activated human monocytes inhibit the intracellular multiplication of Legionnaires' disease bacteria.

We have examined the interaction between virulent egg yolk-grown L. pneumophila, Philadelphia 1 strain, and in vitro-activated human monocytes, under antibiotic-free conditions. Freshly explanted human monocytes activated by incubation with concanavalin A (Con A) and human lymphocytes inhibited the intracellular multiplication of L. pneumophila. Both Con A and lymphocytes were required for activation. Con A was consistently maximally effective at greater than or equal to 4 mug/ml. Monocytes activated by incubation with cell-free filtered supernatant from Con A-sensitized mononuclear cell cultures also inhibited the intracellular multiplication of L. pneumophil a. The most potent supernatant was obtained from mononuclear cell cultures incubated with greater than or equal to 15 mug/ml Con A for 48 h. The degree of monocyte inhibition of L. pneumophila multiplication was proportional to the length of time monocytes were preincubated with supernatant (48 {greater than} 24 {greater than} 12 h) and to the concentration of supernatant added (40 percent {greater than} 20 percent {greater than} 10 percent {greater than} 5 percent). Monocytes treated with supernatant daily were more inhibitory than monocytes treated initially only. With time in culture, monocytes progressively lost a limited degree of spontaneous inhibitory capacity and also lost their capacity to respond to supernatant with inhibition of L. pneumophila multiplication. Supernatant-activated monocytes inhibited L. pneumophila multiplication in two ways. They phagocytosed fewer bacteria, and they slowed the rate of intracellular multiplication of bacteria that were internalized. As was the case with nonactivated monocytes, antibody had no effect on the rate of intracellular multiplication in supernatant-activated monocytes. Neither supernatant-activated nor nonactivated monocytes killed L. pneumophila in the absence of antibody. Both killed a limited proportion of these bacteria in the presence of antibody and complement. We have previously reported that anti-L, pneumophila antibody and complement neither promote effective killing of L. pneumophila by human polymorphonuclear leukocytes and monocytes nor inhibit the rate of L. pneumophila multiplication in monocytes. These findings and our present report that activated monocytes do inhibit L. pneumophila multiplication indicate that cell-mediated immunity plays a major role in host defense against Legionnaires' disease.

Bacteriolysis↗
PubMed2006

Increased expression of monocytic angiotensin-converting enzyme in dialysis patients with cardiovascular disease.

BACKGROUND: Patients with chronic renal disease suffer from accelerated atherogenesis, which is promoted by inflammation and oxidative stress. Tissue angiotensin converting enzyme (ACE) exerts proinflammatory and prooxidative effects by producing angiotensin II. Monocytes are strongly involved in the pathogenesis of atherosclerosis. They express ACE, which might contribute to their atherogenic potency. We hypothesize that dialysis patients have increased monocytic ACE expression, and that ACE expression on circulating monocytes is associated with prevalent cardiovascular disease. METHODS: In 74 dialysis patients, ACE expression on total monocytes and monocyte subsets was measured flow-cytometrically in a whole-blood assay. A subpopulation of 22 dialysis patients was compared to an age- and gender-matched control group with intact renal function. Cardiovascular risk factors and the prevalence of cardiovascular disease were assessed. In a subgroup of patients (n = 8), monocytic ACE activity was measured in vitro and correlated with monocytic ACE expression. RESULTS: Dialysis patients had an increased expression of monocytic ACE compared to controls. Monocytic ACE expression was higher in dialysis patients with prevalent cardiovascular disease than in those without cardiovascular disease. This association remained significant after correction for classical cardiovascular risk factors. Among monocyte subsets, CD14++CD16+ monocytes had the highest ACE expression. Monocytic ACE activity correlated with ACE surface expression. CONCLUSIONS: The finding of increased ACE expression on monocytes of dialysis patients with cardiovascular disease links monocytes to the activated renin-angiotensin system. ACE expression was found highest among CD14++16+ monocytes, which is in accordance with a prominent role of these proinflammatory cells in atherogenesis.

Aged↗
PubMed2002

Impaired monocyte IL-12 production before surgery as a predictive factor for the lethal outcome of postoperative sepsis.

OBJECTIVE: To investigate whether monocyte paralysis resistant to interferon-gamma (IFN-gamma) costimulation may exist before surgery and postoperative infection and may correlate with the outcome of postoperative sepsis. SUMMARY BACKGROUND DATA: Several studies have correlated monocyte paralysis during the course of sepsis with lethal outcome. Although the authors' previous work indicated that preoperative defects in monocyte interleukin (IL)-12 production are associated with the development of severe postoperative sepsis, the functional state of monocytes before surgery and infection and its significance for sepsis requires further analysis. METHODS: In a prospective study, monocyte functions of 1,113 consecutive patients were examined before major visceral surgery. Monocytes were isolated from peripheral blood and were stimulated in vitro with IFN-gamma and lipopolysaccharide. The secretion of IL-12 p70, IL-12 p40, IL-10, and tumor necrosis factor was measured. RESULTS: Preoperative monocyte secretion of IL-12 p70 and IL-12 p40 was significantly reduced in patients who developed lethal postoperative sepsis compared with sepsis survivors and patients with uneventful postoperative recovery. Moreover, preoperative monocyte IL-12 production was an independent predictive factor for the lethal outcome of postoperative sepsis by multivariate analysis. Preoperative monocyte IL-10 production was impaired in the sepsis group but did not correlate with death from sepsis. Preoperative monocyte tumor necrosis factor secretion was comparable between patients with uneventful recovery, sepsis survivors, and nonsurvivors. Thus, impaired preoperative monocyte IL-12 secretion in patients developing lethal postoperative sepsis did not result from an overproduction of IL-10 or from a generalized monocyte paralysis. The association between impaired preoperative monocyte IL-12 production and death from sepsis was also not explained by gender differences, underlying malignant disease, tumor type, neoadjuvant therapy, or age. CONCLUSIONS: These results identify a selective preoperative defect in monocyte IL-12 production as a predictive factor for the lethal outcome of postoperative sepsis. These data suggest that a partial preoperative monocyte paralysis severely impairs the host defense against postoperative infection, resulting in an increased risk of lethal sepsis.

Adjuvants, Immunologic↗
PubMed1996

Monocyte-induced downregulation of nitric oxide synthase in cultured aortic endothelial cells.

Since endothelium-dependent vasodilation is altered in atherosclerosis and enhanced monocyte/endothelial interactions are implicated in early atherosclerosis, we evaluated the effects of monocytes on the endothelial nitric oxide (NO) pathway by estimating release of biologically active NO from cultured endothelial cells and levels of constitutive NO synthase (ecNOS). NO release was estimated in a short-term bioassay using endothelial cell-induced cGMP accumulation in vascular smooth muscle (SM) cells. Exposure of SM cells to porcine aortic endothelial cells (PAECs) and human aortic endothelial cells (HAECs) produced large increases in SM cGMP content; this increase was prevented by NG-nitro-L-arginine methyl ester, the inhibitor of endothelial NOS. Confluent monolayers of PAECs and HAECs cocultured with monocytes also stimulated SM cGMP formation; however, NO release from these cultures was attenuated in a coculture time (2 to 48 hours)- and monocyte concentration (20 to 200 x 10(3) per well)-dependent manner. This effect of monocyte adhesion appeared to be selective for NO release since other biochemical pathways, such as atriopeptin-and isoproterenol-induced cyclic nucleotide accumulation within the endothelial cells, were not altered by monocytes. The effects of adherent monocytes on NO release were mimicked by monocyte-derived cytokines tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 alpha. Furthermore, the conditioned medium of monocytes contained significant quantities of these cytokines. Conditioned medium, as well as monocytes physically separated from the endothelial cells, attenuated NO release, suggesting that soluble factors may mediate the effects of monocytes. An IL-1 beta neutralizing antibody fully prevented the NO dysfunction in response to directly adherent monocytes. Superoxide dismutase, catalase, 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron), and exogenous L-arginine failed to improve NO release, suggesting that oxidant stress-induced inactivation of NO or limited substrate availability were not primarily responsible for the inhibiting effects of monocytes. Western blot analysis revealed reduced quantities of ecNOS in monocyte/endothelium cocultures, as well as in HAECs treated with monocyte-conditioned medium or TNF-alpha. Thus, adhesion of monocytes to endothelial cells and monocyte-derived secretory products downregulate steady state levels of ecNOS, an event associated with attenuated release of biologically active NO. This mechanism may potentially contribute to diminished endothelium-dependent and NO-mediated vasodilation in early atherosclerosis.

Animals↗
PubMed1989

Interferon gamma-activated human monocytes downregulate transferrin receptors and inhibit the intracellular multiplication of Legionella pneumophila by limiting the availability of iron.

We have investigated the role of iron in the intracellular biology of Legionella pneumophila in human monocytes and in the effector arm of cell-mediated immune defense against this intracellular bacterial pathogen. To determine if L. pneumophila intracellular multiplication is iron dependent, we studied the effect of the iron chelator deferoxamine on L. pneumophila infection of monocytes. Deferoxamine at 15 microM completely inhibited L. pneumophila intracellular multiplication. The inhibitory effect of deferoxamine was reversed with equimolar iron-saturated transferrin but not apotransferrin. To examine the potential role of iron in monocyte activation, we investigated the influence of iron-saturated transferrin on L. pneumophila multiplication in IFN gamma-activated monocytes. Iron transferrin, but not apotransferrin, neutralized the capacity of activated monocytes to inhibit L. pneumophila multiplication. To explore a potential mechanism by which activated monocytes might limit the availability of intracellular iron, we examined transferrin receptor expression on nonactivated and activated monocytes cultured in vitro for 5 d. By fluorescence-activated flow cytometry, activated monocytes exhibited markedly fewer transferrin receptors than nonactivated monocytes. By Scatchard analysis of 125I-transferrin binding to monocytes, nonactivated monocytes had 38,300 +/- 12,700 (mean +/- SE) transferrin binding sites, whereas activated monocytes had 10,300 +/- 1,600, a reduction of 73%. Activated and nonactivated monocytes had a similar mean Kd (1.8 +/- 0.2 nM). This study demonstrates that (a) L. pneumophila intracellular multiplication is iron dependent; (b) activated monocytes inhibit L. pneumophila multiplication by limiting the availability of intracellular iron; and (c) transferrin receptors are downregulated on IFN gamma-activated monocytes.

Adult↗
PubMed1995

Granulocyte macrophage colony-stimulating factor contributes to enhanced monocyte survival in chronic atopic dermatitis.

Evidence suggesting that prolonged effector cell survival may contribute to perpetuation of inflammation prompted us to ask whether monocyte macrophages, the predominate inflammatory cell in the lesion of chronic atopic dermatitis (AD), exhibit enhanced survival in AD. Cultures of peripheral blood monocytes from patients with chronic AD, psoriasis, and from normal (NL) donors were examined for morphologic features and DNA fragmentation characteristic of cells undergoing the process of apoptosis (programmed cell death). Cultures of AD monocytes exhibited a significantly lower incidence of apoptosis than did cultures of NL monocytes (45 vs 68%, P < 0.01), or psoriatic monocytes (45 vs 80%, P < 0.01). Furthermore, AD monocytes were unresponsive to both IL-1, an inhibitor of apoptosis, and IL-4, an enhancer of apoptosis, in comparison to cultured NL monocytes. Of note, GM-CSF in a concentration-dependent fashion, decreased the incidence of apoptosis in NL monocyte cultures and rendered them unresponsive to these cytokines. These findings suggested that GM-CSF may enhance monocyte survival in AD. In support of this hypothesis, AD monocyte cultures produced fivefold more GM-CSF than did cultures of NL monocytes or psoriatic monocytes (P < 0.05). Additionally, there was a significantly greater number of GM-CSF mRNA expressing cells detected by in situ hybridization in biopsies of lesions of chronic AD than in acute AD or NL skin (P < 0.05). Finally, NL monocytes incubated with supernatants obtained from monocytes of AD patients exhibited significant inhibition of apoptosis, an effect that could be ablated by a neutralizing antibody to GM-CSF. Taken together, these data strongly suggest that increased production of GM-CSF by cells from patients with AD inhibits monocyte apoptosis and may contribute to the chronicity of this inflammatory disease.

Acute Disease↗
PubMed1999

Circulating CD2+ monocytes are dendritic cells.

Low levels of CD2 have been described on subsets of monocytes, macrophages, and dendritic cells. CD2 is expressed on about one-third of circulating monocytes, at levels one-half log lower than on T or NK cells, representing 2-4% of PBMC. FACS analysis of CD2+ and CD2- monocytes revealed no significant difference in the expression of adhesion molecules (CD11a/b/c), class II Ags (HLA-DR, -DQ, -DP), myeloid Ags (CD13, CD14, CD33), or costimulatory molecules (CD80, CD86). Freshly isolated CD2+ and CD2- monocytes were morphologically indistinguishable by phase contrast microscopy. However, scanning electron microscopy revealed large prominent ruffles on CD2+ monocytes in contrast to small knob-like projections on CD2- monocytes. After 2 days of culture, the CD2+ monocytes largely lost CD14 expression and developed distinct dendrites, whereas the CD2- monocytes retained surface CD14 and remained round or oval. Freshly isolated CD2+ monocytes were more potent inducers of the allogeneic MLR and more efficiently induced proliferation of naive T cells in the presence of HIV-1 gp120 than did CD2- monocytes. After culture in the presence of GM/CSF and IL-4, CD2+ monocytes were up to 40-fold more potent than monocyte-derived dendritic cells or CD2- monocytes at inducing allogeneic T cell proliferation. These findings suggest that circulating CD2+ and CD2- monocytes are dendritic cells and the precursors of macrophages, respectively. Thus, dendritic cells are far more abundant in the blood than previously thought, and they and precursors of macrophages exist in the circulation as phenotypically, morphologically, and functionally distinct monocyte populations.

Antigen Presentation↗
PubMed1991

Characterization of the adherence of human monocytes to cytokine-stimulated human macrovascular endothelial cells.

At sites of inflammation, interactions between monocytes and vascular endothelium play an important role in the margination and extravasation of monocytes. The aim of this study was to investigate the relative contributions of the CD11/CD18 family of leucocyte adhesion molecules on monocytes and ICAM-1 and ELAM-1 molecules on endothelial cells (EC) to the binding of monocytes to EC stimulated with recombinant interleukin-1 alpha (rIL-1 alpha), rIL-6, recombinant tumour necrosis factor-alpha (rTFN-alpha) or recombinant interferon-gamma (rIFN-gamma). The adhesiveness of EC for monocytes increased 1.8-2.3-fold after incubation of monolayers of venous or arterial EC with rIL-1 alpha or rTNF-alpha for 4 hr, and 1.6-2.0-fold after stimulation of both types of EC with rIL-1 alpha, rTNF-alpha or rIFN-gamma for 24 hr. Incubation with rIL-6 was without effect. The monoclonal antibodies (mAb) against CD11a, b, c and CD18 on monocytes did not inhibit the increase in the number of monocytes bound to rIL-1 alpha-, rTNF-alpha-, or rIFN-gamma-stimulated EC. However, mAb against ELAM-1 expressed on the surface of 4 hr rIL-1 alpha-stimulated EC slightly inhibited (15-21%) the enhanced monocyte binding. ICAM-1, which exhibited marked expression on 24 hr rIL-1 alpha-, rTNF-alpha- or rIFN-gamma-stimulated EC, did not contribute to the enhanced monocyte binding. The percentage of EC-bound monocytes which had stretched out over the surface of cytokine-stimulated venous or arterial EC was significantly increased compared to the percentage found for non-stimulated EC. It was observed that mild fixation of EC as well as treatment of EC with cytochalasin B or mAb against ICAM-1 did not affect the number of monocytes that were bound to EC, but considerably reduced the percentage of EC-bound monocytes with a stretched morphology. It is concluded that the binding of monocytes to cytokine-stimulated EC is dependent on the type of cytokine and the duration of cytokine stimulation. The increase in the binding of monocytes to cytokine-stimulated EC occurred as a result of CD11/CD18- and ICAM-1-independent factors. The subsequent morphological changes, i.e. stretching of monocytes over the surface of EC, required viable EC and ICAM-1.

Cell Adhesion↗
PubMed1991

Monokines released during short-term Fc gamma receptor phagocytosis up-regulate polymorphonuclear leukocytes and monocyte-phagocytic function.

Freshly explanted monocytes phagocytosing IgG antibody-coated erythrocyte targets (EIgG) release a factor(s) that stimulates phagocytosis by neighboring monocytes and polymorphonuclear leukocytes (PMN). Culture supernatants obtained after 30-min incubation of adherent monocytes with EIgG, but not unopsonized sheep erythrocytes, markedly up-regulated the extent of PMN phagocytosis and enhanced the rate at which monocytes ingested EIgG. The presence of this factor(s) was first evident in phagocytic studies in which monocytes were prepared by a colloidal silica-based continuous gradient technique (Sepracell-Mn). After introduction of erythrocyte targets, there was a 20- to 30-min delay before initiation of phagocytosis that was not observed with monocytes prepared by the standard Percoll-gradient technique. Experiments suggest that, when compared with monocytes prepared by the Percoll-gradient method, Sepracell-Mn monocytes are closer to a base line state of activation with regard to the expression of Fc gamma RI and the ability to ingest EIgG. The mechanism of PMN upregulation by the monocyte factor(s) was explored. Monocyte supernatants did not induce an increase in the surface expression of PMN Fc gamma RI, II, or III. Neither anti-TNF, anti-IL-2, nor anti-GM-CSF had any significant effect on monocyte supernatant activity. Neutrophil activating protein-1 was not detected by ELISA. In contrast, anti-IL-1 completely blocked the effect of the supernatant on subsequent monocyte phagocytosis, and partially inhibited its effect on PMN phagocytosis. Furthermore, it was shown that RIL-1 as well as TNF markedly enhanced monocyte and PMN ingestion of EIgG. These results suggest that monocytes, after Fc gamma R-mediated phagocytosis, release monokines, including at least IL-1, which enhance the phagocytic function of neighboring PMN and monocytes to augment the host defense process.

Antigens, Differentiation↗
PubMed1990

Characterization of monocyte adherence to human macrovascular and microvascular endothelial cells.

The interaction of monocytes with cultured large vessel venous and arterial endothelial cells (EC) and with cultured microvascular EC was studied. Analysis of time-lapse microcinematographic video recordings showed that monocytes adhere rapidly to the surface of EC and subsequently remain spherical and fixed to the initial site of adherence. Some monocytes adherent to EC stretch out within 30 to 90 min and migrate over the EC surface or become stretched for about 10 to 30 min and then detach from the EC surface and move rapidly over the EC monolayer. It was shown that the interaction of monocytes with EC is dynamic, that the morphology of monocytes adherent to EC changes constantly, and that stretching of the monocytes over the surface of the EC is not an inevitable and irreversible consequence of binding. A quantitative adherence assay was developed in which both the morphology and the number of monocytes bound to EC were determined. For each type of EC the number of monocytes bound to a single EC was found to be linearly related to the number of monocytes added and was lower for smaller EC. The adherence of monocytes to venous and arterial EC followed a different time course than the adherence to capillary EC and adherence to both types of macrovascular EC was higher than adherence to microvascular EC was higher than adherence to microvascular EC. The percentage of adherent monocytes with a stretched morphology was lower when these cells were adherent to capillary EC than to both types of macrovascular EC and increased upon addition of serum. Adherence of monocytes to venous, arterial, and capillary EC was partially inhibited by mAb directed against the alpha-chain of lymphocyte function-associated Ag-1 or C3bi receptor (with mAb LM2/1, but not with mAb OKM1) and by mAb against the common beta-chain of the three leukocyte adhesion molecules. The degree of inhibition of monocyte adherence to EC by mAb against lymphocyte function-associated Ag-1 alpha and the common beta-chain was dependent on the type of EC and was higher for venous EC (57 to 70% inhibition) than for arterial (40 to 44% inhibition) and capillary (44 to 49% inhibition) EC. Inhibition of monocyte adherence obtained with anti-C3bi receptor-alpha mAb was similar for each EC type. mAb against p150, 95 did not affect adherence. None of the mAb could block binding completely; combinations of the mAb also did not result in increased inhibition of monocyte adherence to EC.

Antibodies, Monoclonal↗