Heterogeneity among human mononuclear phagocytes in their secretion of lysozyme, interleukin 1 and type-beta transforming growth factor: a quantitative analysis at the single-cell level

Monocyte heterogeneity underlying phenotypic changes in monocytes according to SIV disease stage

Infection by HIV is associated with the expansion of monocytes expressing CD16 antigens, but the significance of this in HIV pathogenesis is largely unknown. In rhesus macaques, at least three subpopulations of blood monocytes were identified based on their expression of CD14 and CD16: CD14(high)CD16(-), CD14(high)CD16(low), and CD14(low)CD16(high). The phenotypes and functions of these subpopulations, including CD16(+) monocytes, were investigated in normal, uninfected rhesus macaques and macaques that were infected with SIV or chimeric SHIV. To assess whether these different monocyte subpopulations expand or contract in AIDS pathogenesis, we conducted a cross-sectional study of 54 SIV- or SHIV-infected macaques and 48 uninfected controls. The absolute numbers of monocyte populations were examined in acutely infected animals, chronically infected animals with no detectable plasma virus RNA, chronically infected animals with detectable plasma virus RNA, and animals that died with AIDS. The absolute numbers of CD14(high)CD16(low) and CD14(low)CD16(high) monocytes were elevated significantly in acutely infected animals and chronically infected animals with detectable plasma virus RNA compared with uninfected controls. Moreover, a significant, positive correlation was evident between the number of CD14(high)CD16(low) or CD14(low)CD16(high) monocytes and plasma viral load in the infected cohort. These data show the dynamic changes of blood monocytes, most notably, CD14(high)CD16(low) monocytes during lentiviral infection, which are specific to disease stage.

Heterogeneous expression of apolipoprotein-E by human macrophages

Apolipoprotein-E (apoE) is expressed at high levels by macrophages. In addition to its role in lipid transport, macrophage-derived apoE plays an important role in immunoregulation. Previous studies have identified macrophage subpopulations that differ substantially in their ability to synthesize specific cytokines and enzymes, however, potential heterogeneous macrophage apoE expression has not been studied. Here we examined apoE expression in human THP-1 macrophages and monocyte-derived macrophages (MDM). Using immunocytochemistry and flow cytometry methods we reveal a striking heterogeneity in macrophage apoE expression in both cell types. In phorbol-ester-differentiated THP-1 macrophages, 5% of the cells over-expressed apoE at levels more than 50-fold higher than the rest of the population. ApoE over-expressing THP-1 macrophages contained condensed/fragmented nuclei and increased levels of activated caspase-3 indicating induction of apoptosis. In MDM, 3-5% of the cells also highly over-expressed apoE, up to 50-fold higher than the rest of the population; however, this was not associated with obvious nuclear alterations. The apoE over-expressing MDM were larger, more granular, and more autofluorescent than the majority of cells and they contained numerous vesicle-like structures that appeared to be coated by apoE. Flow cytometry experiments indicated that the apoE over-expressing subpopulation of MDM were positive for CD14, CD11b/Mac-1 and CD68. These observations suggest that specific macrophage subpopulations may be important for apoE-mediated immunoregulation and clearly indicate that subpopulation heterogeneity should be taken into account when investigating macrophage apoE expression.

Generation of diversity in the innate immune system: macrophage heterogeneity arises from gene-autonomous transcriptional probability of individual inducible genes

Microbial products such as LPS stimulate macrophages to produce a wide diversity of inducible gene products needed for immediate host defense and priming of an appropriate acquired immune response. In this study, we have examined LPS-inducible gene expression in subclones of a mouse macrophage cell line, RAW264, using cDNA microarrays. Even archetypal target genes such as TNF-alpha were not induced in all subclones, and there was no absolute correlation between expression of pairs of genes. Nevertheless, the array analysis revealed clusters of genes that were more likely to be coexpressed. RAW264 cells stably transfected with luciferase reporter genes driven by LPS-responsive promoters revealed the same kind of clonal heterogeneity. The results indicate that each LPS-inducible gene has its own inherent probability of activation in response to LPS.

IL-1beta mediates diethyldithiocarbamate-induced granulocyte colony-stimulating factor production and hematopoiesis

Diethyldithiocarbamate (DDTC) exhibits chemoprotective effects via reduced myelosuppression in mice treated with various chemotherapeutic agents. The mechanism of DDTC-mediated chemoprotection is believed to involve the induction and release of several cytokines, including interleukin-1 beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and granulocyte colony-stimulating factor (G-CSF). In the present study the roles of IL-1beta and TNF-alpha in DDTC-mediated G-CSF induction were examined using human long-term bone marrow cultures (hLTBMCs). Administration of IL-1 receptor antagonist (IL-1ra) to DDTC-treated hLTBMCs obviated the G-CSF induction profile and blocked the resultant colony proliferation, indicating that IL-1beta mediates DDTC-induced G-CSF release and hematopoiesis. IL-1beta mRNA levels were increased threefold over control following DDTC treatment of hLTBMCs, implying that DDTC induces IL-1beta at the level of transcription. Conversely, studies involving inhibition of DDTC-induced TNF-alpha synthesis, with the inhibitor MNX 160, had no effect on DDTC-induced G-CSF release or colony proliferation. These findings taken together strongly suggest that IL-1beta mediates the chemoprotective effects of DDTC.

Activation of peripheral blood mononuclear cells in bronchoalveolar lavage fluid from patients with sarcoidosis: visualisation of single cell activation products

BACKGROUND

Interstitial lung diseases are characterised by the recruitment of mononuclear cells to disease sites where maturation occurs and activation products, including lysozyme (LZM), are released. Analysis of in vitro cell culture supernatants for activation products masks the functional heterogeneity of cell populations. It is therefore necessary to examine the secretion of activation products by single cells to assess whether the activation of newly recruited mononuclear phagocytes at the sites of disease in the lung is uniform and controlled by the local microenvironment.

METHODS

The reverse haemolytic plaque assay was used to evaluate, at a single cell level, the ability of bronchoalveolar lavage (BAL) fluid from seven patients with sarcoidosis to activate Ficoll-Hypaque-separated peripheral blood mononuclear cells by comparison with BAL fluid from six normal volunteers and nine patients with systemic sclerosis. Monolayers of peripheral blood mononuclear cells and sheep red blood cells were cultured either alone or in the presence of 20% (v/v) BAL fluid with a polyclonal anti-LZM antibody. LZM/anti-LZM complexes bound to red blood cells surrounding the secreting cells were disclosed following complement lysis of red blood cells and quantification of plaque dimensions using microscopy and image analysis.

RESULTS

Bronchoalveolar lavage fluid from all the patients with sarcoidosis increased LZM secretion by peripheral blood mononuclear cells compared with unstimulated mononuclear cells. By contrast, BAL fluid from the other individuals had no effect on LZM secretion.

CONCLUSIONS

Single cells activated by BAL fluid can be evaluated by the reverse haemolytic plaque assay. BAL fluid from patients with sarcoidosis, but not from patients with systemic sclerosis or normal individuals, contains components capable of activating mononuclear phagocytes to secrete lysozyme.

Prevention of the cytotoxic effect of IL-1 by human lysozyme on isolated rat islets

Macrophages are present in the initial phase of the autoimmune process involved in the destruction of the endocrine pancreas in IDDM via the secretion of cytokines such as IL-1 beta. Macrophages also secrete lysozyme. Besides its action on the bacterial cell wall, lysozyme has an important physiological and immunological role. Human lysozyme is an in-situ modulator of the inflammatory reactions. We investigate the protective role of human lysozyme in vitro against the cytotoxic effect of IL-1 beta or of IL-1 beta combined with IFN-gamma on isolated rat islets. Precultured newborn rat islets were incubated with human or chicken lysozyme (50.000 U/ml) over 3 days. Human IL-1 beta (100 U/ml) or IL-1 beta (5 U/ml) + INF-gamma (100 U/ml) was added for the last 2 days and tritiated thymidine for the last 24 hrs. In another set of experiments, islets were exposed simultaneously to human lysozyme and IL-1 beta. Only pretreatment with human lysozyme abolished the lowering of the labelling index of the islet cell induced by IL-1 beta or by IL-1 beta and INF-gamma. Pycnotic nuclei were abundant in islets treated with IL-1 alone while they were not when islets were pretreated with human lysozyme. Chicken lysozyme had no protective effect in the same protocol. Human lysozyme was not protective when applied simultaneously with IL-1. Pretreatment of the islets by human lysozyme does not prevent the reduction of the insulin secretion induced by IL-1 beta. Human and chicken lysozyme differ further in their action when tested on fibroblasts proliferation. Only human lysozyme stimulates the latter. In conclusion, only human lysozyme seems to have a protective effect against the cytotoxicity of IL-1 in combination or not with IFN-gamma on islet cells in vitro. Moreover, to be protected, the islets have to be pretreated with lysozyme before the IL-1 application. Our in vitro results imply that natural aspecific immunity and its relation to the secretory function of the macrophage might be crucial for the prevention of the initial assault responsible for the onset of the immune process leading to insulin dependent diabetes.

Dibutyryl-cAMP modulation of receptor expression and antigen presentation capacity in monocyte subpopulations

Monocyte phenotype heterogeneity is often associated with functional differences between the distinguished Mphi subpopulations. We have previously demonstrated that the Mphi subpopulation separated and stimulated by rosetting Mphi via the Type I Fc gamma R (CD64) are poor antigen presenting cells but can be induced to greater production of TNF alpha, IL-6 and PGE2 than the Fc gamma RI- Mphi population. Here we demonstrate that the Fc gamma RI- Mphi represent the major antigen presenting Mphi population and that APC capacity of the FcRI- Mphi can be further increased by elevating intracellular cAMP levels. Treatment of the Fc gamma RI+ Mphi with db cAMP decreases both their expression of CD64 and their capacity to produce TNF alpha to the levels typical of Fc gamma RI- Mphi. Db cAMP treatment of the Fc gamma RI+ Mphi subpopulation, however, cannot augment the antigen presenting capacity of this low APC Mphi subpopulation to the level of that of the Fc gamma RI- Mphi. Basal expression of the Mo3 activation marker was comparable in the FcRI+/FcRI- Mphi subpopulations, but the FcRI+ Mphi were induced by db cAMP treatment to increase their Mo3 expression to higher levels than the FcRI- Mphi. These results suggest that although elevated intracellular cAMP levels can modulate some Fc gamma RI+ Mphi functions to more closely parallel those of the Fc gamma RI- Mphi, this treatment cannot increase the efficiency of the Fc gamma RI+ Mphi subpopulation as an antigen presenting cell.

Protease production by cultured microglia: substrate gel analysis and immobilized matrix degradation

The production of collagen-degrading proteases by cultured neonatal rat microglia was examined using an immobilized fibronectin-gelatin matrix coupled to a fluorescent marker and by substrate gel analysis. When microglia were plated onto the surface of the matrix and incubated under resting (nonstimulated) conditions, a small but visible amount of immobilized matrix was degraded. Treatment with lipopolysaccharide (LPS) or interleukin-1 (IL-1) significantly increased the number of microglia demonstrating substrate degradation. Substrate-SDS polyacrylamide gel electrophoresis of samples of supernatants from untreated cultured microglia indicated the presence of a 72 and a 92 kD metalloproteinase with characteristics corresponding to collagenases. Supernatants from untreated astrocyte cultures were shown to have primarily a 72 kD metalloproteinase. Proteinase activity increased on stimulation of the microglia with LPS and IL-1 in a dose-dependent fashion. These results indicate that cultured microglia release active proteases capable of degrading the extracellular matrix in a localized region. The production of proteases by activated microglia may have important physiological and pathophysiological consequences within the restricted extracellular matrix of the CNS.

Abundant expression of transforming growth factor-beta 1 and -beta 2 by Hodgkin's Reed-Sternberg cells and by reactive T lymphocytes in Hodgkin's disease

The depressed cellular immunity observed in patients with Hodgkin's disease (HD) has been attributed to production of transforming growth factor (TGF)-beta or TGF-beta-like substances by Hodgkin's Reed-Sternberg (H-RS) cells. The TGF-beta produced by L-428 cells (an H-RS cell line) is a 130-kd molecular weight glycoprotein that apparently differs from the TGF-beta (molecular weight, 25 kd) produced by most lymphoid and hematopoietic cells. Among several distinct types of TGF-beta that have been purified, only TGF-beta 1 and TGF-beta 2 have thus far been identified in hematopoietic cells. By using monoclonal antibodies (1D11 and 3C7) and oligonucleotide probes specific for TGF-beta 1 and TGF-beta 2, were confirmed that a cultured H-RS cell line, KM-H2, can produce both TGF-beta types, whereas another line, HDLM-1, produces only TGF-beta 1. Despite the abundance of mRNA in both of these cells, only small amounts of TGF-beta activity were detected, probably because of rapid degradation of TGF-beta 1 mRNA by specific nuclease. No degraded TGF-beta 2 RNA products were observed in KM-H2 cells. The TGF-beta produced by both types of H-RS cells had a molecular weight of approximately 25 kd. In tissues expression of TGF-beta was observed in a small portion (30%) of H-RS cells in 16 of 20 cases examined. A large number of small to medium-sized lymphoid cells (T lymphocytes) in tissues involved by HD also were positive for TGF-beta. These results indicate that there is functional heterogeneity among H-RS cells, and that H-RS cells are not the only source of TGF-beta in tissues involved by HD. Hodgkin's Reed-Sternberg cells are known to secrete several other cytokines, including interleukin (IL)-1, IL-6, and tumor necrosis factor-alpha. These cytokines could be responsible for the increased number of T lymphocytes in tissues involved by HD. Furthermore, T lymphocytes can respond to IL-1 and IL-6 secreted by H-RS cells by increasing their production of TGF-beta. Abundant expression of TGF-beta by T lymphocytes was not observed in lymphoid tissues other than those involved by HD.

Peptide growth factors and wound healing

Growth factors and cytokines are important signal transducers in wound microenvironments. Experimental data are accumulating rapidly which demonstrate their ability to influence populations of polymorphs and macrophages to migrate to the wound, subsequently to be replaced by synthetic cells which produce collagen and matrix; these events are controlled sequentially at cell receptor level by a variety of locally delivered (paracrine and autocrine) peptides. Preliminary results from clinical trials using recombinant human growth factors to improve cutaneous healing are encouraging. Current research aims to produce growth preparations which can be applied to a wound to accelerate healing.

Interleukin 1 is processed and released during apoptosis

Interleukin (IL-) 1 alpha and 1 beta are synthesized as 31- to 34-kDa pro molecules. They are released from monocytes and macrophages as proteolytically processed 17-kDa mature molecules that bind with high affinity to specific receptors on target cells. IL-1 is not released via the classic secretory pathway. The pro molecules are synthesized as cytosolic proteins without signal peptides. Although the proteases that convert the pro molecules to the mature forms are cytosolic enzymes, processed IL-1 is not detected associated with the cell but is found only in culture supernatants. We demonstrate here that release of IL-1 is efficiently induced by cell injury. When the injury causes cellular necrosis, IL-1 alpha is released as a mixture of unprocessed and processed molecules but IL-1 beta is released exclusively as the biologically inactive pro form. In contrast, when cells undergo apoptosis, maturation of both IL-1 alpha and IL-1 beta is efficient. When apoptosis is rapid, as in macrophages that are targets for allospecific cytotoxic T lymphocytes, processing is observed to occur intracellularly. These findings suggest that cell injury is an important physiologic stimulus for release of IL-1. The nature of the injury profoundly affects the forms of IL-1 that are released.

Effect of aging and other factors on monocyte aryl hydrocarbon hydroxylase activity

A measure of the activity of macrophage drug metabolizing enzymes through assay of peripheral monocytes was used to assess the hepatic enzymatic status and thereby evaluate age related changes in drug metabolism. Blood was obtained from elderly subjects (aged 74.8 +/- 5.2, mean +/- S.E., n = 16) and a young control group (aged 23.5 +/- 2.0, n = 27). Monocyte AHH activity was used as an index of liver drug metabolism, ALT activity as an index of liver function, monocyte media IL-1 and as an index of macrophage activation and serum IL-1 levels as a measure of endogenous pyrogenic activity. The medium collected from the cultured monocytes was also assessed for the presence of AHH inhibitory activity. Subjects provided information relating to their age, sex, alcohol consumption, cigarette smoking, recent infection, recent surgery, disease status and medications which could alter drug metabolism. Elderly patients were drawn both from independent seniors living at home and seniors visiting a geriatric day hospital and compared to a control group of young healthy volunteers. Using the experimental design AHH activity did not differ within experimental error between aged (0.832 +/- 0.32 nmol/mg prot. per h, n = 16) and young control subjects (0.452 +/- 0.17, n = 27). ALT activity did not differ between aged (2.83 I.U. +/- 0.46) and young (4.24 +/- 0.82). Monocyte AHH activity did not differ between males (0.45 +/- 0.14, n = 33) compared to females (0.65 +/- 0.18, n = 29), but was significantly higher in smokers (2.5 +/- 1.0, n = 5) compared to non-smokers (0.35 +/- 0.05, n = 52). Mild to moderate alcohol use showed no significant effect on AHH activity. There was no significant difference between the mean level of MCM inhibition of murine hepatocyte AHH between elderly (44.3 +/- 8.32%, n = 8) and control (31.5 +/- 6.21%, n = 15) subjects, but a larger proportion of the elderly population demonstrated such an effect. Serum IL-1 levels (range 0-55.9 pg/ml) were compared to MCM IL-1 and AHH inhibitory activity in the elderly and young group.

Detecting cytokine production at the single-cell level

Cytokines are versatile mediators of intercellular communication. Their functional diversity has aroused considerable interest and prompted the rapid development of a number of techniques for their detection and measurement. However, conventional cytokine assays measure only their bulk release by large numbers of cells and give no indication of the identity or frequency of producer cells. Here, the advantages and disadvantages of a relatively new approach to detect cytokine production by single cells are reviewed.

Role of elevated monocyte transforming growth factor beta (TGF beta) production in posttrauma immunosuppression

We previously reported that increased production of prostaglandin E2 by monocytes is a pivotal mechanism in posttrauma immunopathology. Here we characterize monocyte levels of transforming growth factor beta and examine the effects of elevated transforming growth factor beta on prostaglandin E2 release by patients' monocytes. Trauma patients' and normals' monocyte supernates (+/- stimulation with muramyl dipeptide) were acid treated and assayed for transforming growth factor beta using the mink lung-cell bioassay. Alternatively, human transforming growth factor beta was added to patients' and normals' monocytes and prostaglandin E2 production assayed. Significantly elevated transforming growth factor beta levels (median = 181.7 pmol/10(6) monocytes) were detected in immunosuppressed patients' monocytes but not immunocompetent trauma patients' (median = 32.0 pM) or normals' (median = 20.4 pM) monocytes. Adding transforming growth factor beta to monocytes resulted in a significant elevation of prostaglandin E2 levels. Elevated monocyte transforming growth factor beta levels in trauma patients could be both suppressing T-lymphocyte functions and maintaining elevated monocyte prostaglandin E2 synthesis.

Basic fibroblast growth factor and interleukins 4 and 6 stimulate the release of IFN-gamma by individual NK cells

Both the secretory and cytotoxic activity of natural killer (NK) cells are known to be regulated by such cytokines as interleukin-2 (IL-2) and interferon-gamma (IFN-gamma). In the present study we have used the reverse hemolytic plaque assay to investigate either the direct effects of the protein kinase activator, phorbol myristate acetate (PMA), or exposure to recombinant human interleukins 2, 4, and 6 (IL-2, IL-4, and IL-6) tumour necrosis factor alpha (TNF-alpha) and basic fibroblast growth factor (bFGF) on the release of IFN-gamma by individual, immunoidentified NK cells isolated from peripheral blood. This sensitive immunoassay was adapted and coupled with immunocytochemistry not only to immunophenotype and enumerate cells secreting IFN-gamma in a given cell population, but also to quantify the amount of this cytokine released per individual cell. These studies have confirmed mononuclear cells with the morphology of large granular lymphocytes and the immunophenotype of CD3-/CD16+ NK cells to be the predominant source of spontaneously released IFN-gamma in vitro. In contrast to this, fewer than 2% of the CD3+ T cells secreted detectable levels of this cytokine during the assay, irrespective of the stimulus applied. Whilst TNF-alpha had no significant effect on IFN-gamma release by NK cells, a 6-hr exposure to IL-2 or PMA stimulated an increase in the amount secreted per single cell. Furthermore, bFGF and interleukins 4 and 6 elicited a marked, dose-dependent stimulation of IFN-gamma secretion by this cell type. However, exposure to these cytokines did not alter the number of cells capable of releasing detectable levels of IFN-gamma during the assay. These studies demonstrate that (i) both the spontaneous and stimulated release of IFN-gamma by NK cells can be visualized and quantified at the single-cell level using this sensitive immunoassay, and (ii) bFGF and interleukins 2, 4, and 6, but not TNF-alpha, are potent stimulants of IFN-gamma secretion by CD3-/CD16+ NK cells.

Measurement of cytokine release by human cells. A quantitative analysis at the single cell level using the reverse haemolytic plaque assay

The reverse haemolytic plaque assay has been adapted to detect and measure the release of such cytokines as interleukin-1, -2 and -6, GM colony-stimulating factor or interferon-gamma by individual human cells derived from either peripheral blood or enzymatically dispersed breast carcinomas. Since each of these peptides is released by more than one cell type, this in vitro assay has been coupled with immunocytochemistry to identify the particular cell type(s) contributing to the release of each cytokine. This technique is useful in (i) obviating the need for purification of a given cell type prior to estimating cytokine release, and (ii) evaluating quantitative differences in secretion amongst cells of a particular type. Such a method has the additional advantage over most alternative methods applied at the single cell level in that the cells remain viable at the end of the assay and can be used in further studies. This assay thus provides a powerful new tool in the investigation of the role of cytokines in both the normal modulation of the immune system and the development of such diseases as neoplasia.

Effects of ethanol on human monocyte/macrophage lysozyme storage and release. Implications for the pathobiology of alcoholic liver disease

The effect of ethanol on the release and/or intracellular accumulation of lysozyme (LZM) by human monocytes and monocyte-derived macrophages (mø) was investigated in vitro. A reverse haemolytic plaque assay, to detect and quantify LZM release by individual cells was combined with quantitative immunocytochemistry using LZM and the pan-macrophage monoclonal EBM/11 as markers. Ethanol had no effect on monocytes; however it reduced secretion of LZM by a mø subpopulation. Ethanol also reduced both the total number of mø immunoreactive for LZM, (but not EBM/11), and the proportion of LZM-secreting mø containing detectable LZM. The latter was correlated with an increase in the proportion of LZM-secreting mø that were not immunoreactive for this enzyme. These data suggest functional heterogeneity amongst human macrophages with a mø subpopulation which responds to ethanol exposure with a drop in both content and release of LZM. This might have implications for macrophage function in alcoholic liver disease.