Application of six-color flow cytometry for the assessment of dendritic cell responses in whole blood assays

Comprehensive Phenotyping of Dendritic Cells in Cancer Patients by Flow Cytometry

Dendritic cells (DCs) play a crucial role in the complex interplay between tumor cells and the immune system. During the elimination phase of cancer immunoediting, immunostimulatory DCs are critical for the control of tumor growth. During the escape phase, regulatory DCs sustain tumor tolerance and contribute to the development of the immunosuppressive tumor microenvironment that characterizes this phase. Moreover, increasing evidence indicates that DCs are also critical for the success of cancer immunotherapy. Hence, there is increasing need to fully characterize DC subsets and their activatory/inhibitory profile in cancer patients. In this review, we describe the role played by different DC subsets in the different phases of cancer immunoediting, the function exerted by different activatory and inhibitory molecules expressed on DC surface, and the cytokines produced by distinct DC subsets, in order to provide an overview on the DC features that may be useful to be assessed when dealing with the flow cytometric characterization of DCs in cancer patients. © 2020 International Society for Advancement of Cytometry.

Costimulatory Molecules and Immune Checkpoints Are Differentially Expressed on Different Subsets of Dendritic Cells

Dendritic cells (DCs) play a crucial role in initiating and shaping immune responses. The effects of DCs on adaptive immune responses depend partly on functional specialization of distinct DC subsets, and partly on the activation state of DCs, which is largely dictated by environmental signals. Fully activated immunostimulatory DCs express high levels of costimulatory molecules, produce pro-inflammatory cytokines, and stimulate T cell proliferation, whereas tolerogenic DCs express low levels of costimulatory molecules, produce immunomodulatory cytokines and impair T cell proliferation. Relevant to the increasing use of immune checkpoint blockade in cancer treatment, signals generated from inhibitory checkpoint molecules on DC surface may also contribute to the inhibitory properties of tolerogenic DCs. Yet, our knowledge on the expression of inhibitory molecules on human DC subsets is fragmentary. Therefore, in this study, we investigated the expression of three immune checkpoints on peripheral blood DC subsets, in basal conditions and upon exposure to pro-inflammatory and anti-inflammatory stimuli, by using a flow cytometric panel that allows a direct comparison of the activatory/inhibitory phenotype of DC-lineage and inflammatory DC subsets. We demonstrated that functionally distinct DC subsets are characterized by differential expression of activatory and inhibitory molecules, and that cDC1s in particular are endowed with a unique immune checkpoint repertoire characterized by high TIM-3 expression, scarce PD-L1 expression and lack of ILT2. Notably, this unique cDC1 repertoire was subverted in a group of patients with myelodysplastic syndromes included in the study. Applied to the characterization of DCs in the tumor microenvironment, this panel has the potential to provide valuable information to be used for investigating the role of DC subsets in cancer, guiding DC-targeting treatments, and possibly identifying predictive biomarkers for clinical response to cancer immunotherapy.

Application of ImmunoScore Model for the Differentiation between Active Tuberculosis and Latent Tuberculosis Infection as Well as Monitoring Anti-tuberculosis Therapy

Tuberculosis (TB) is a leading global public health problem. To achieve the end TB strategy, non-invasive markers for diagnosis and treatment monitoring of TB disease are urgently needed, especially in high-endemic countries such as China. Interferon-gamma release assays (IGRAs) and tuberculin skin test (TST), frequently used immunological methods for TB detection, are intrinsically unable to discriminate active tuberculosis (ATB) from latent tuberculosis infection (LTBI). Thus, the specificity of these methods in the diagnosis of ATB is dependent upon the local prevalence of LTBI. The pathogen-detecting methods such as acid-fast staining and culture, all have limitations in clinical application. ImmunoScore (IS) is a new promising prognostic tool which was commonly used in tumor. However, the importance of host immunity has also been demonstrated in TB pathogenesis, which implies the possibility of using IS model for ATB diagnosis and therapy monitoring. In the present study, we focused on the performance of IS model in the differentiation between ATB and LTBI and in treatment monitoring of TB disease. We have totally screened five immunological markers (four non-specific markers and one TB-specific marker) and successfully established IS model by using Lasso logistic regression analysis. As expected, the IS model can effectively distinguish ATB from LTBI (with a sensitivity of 95.7% and a specificity of 92.1%) and also has potential value in the treatment monitoring of TB disease.

Immunomodulatory effects of heat-killed Mycobacterium obuense on human blood dendritic cells

Heat-killed (HK) Mycobacterium obuense is a novel immunomodulator, currently undergoing clinical evaluation as an immunotherapeutic agent in the treatment of cancer. Here, we examined the effect of in vitro exposure to HK M. obuense on the expression of different categories of surface receptors on human blood myeloid (m) and plasmacytoid (p) DCs. Moreover, we have characterized the cytokine and chemokine secretion patterns of purified total blood DCs stimulated with HK M. obuense. HK M. obuense significantly up-regulated the expression of CD11c, CD80, CD83, CD86, CD274 and MHC class II in whole-blood mDCs and CD80, CD123 and MHC class II in whole-blood pDCs. Down-regulation of CD195 expression in both DC subpopulations was also noted. Further analysis showed that HK M. obuense up-regulated the expression of CD80, CD83 and MHC class II on purified blood DC subpopulations. TLR2 and TLR1 were also identified to be engaged in mediating the HK M. obuense-induced up-regulation of surface receptor expression on whole blood mDCs. In addition, our data demonstrated that HK M. obuense augmented the secretion of CCL4, CCL5, CCL22, CXCL8, IL-6, IL-12p40 and TNF-α by purified total blood DCs. Taken together, our data suggest that HK M. obuense exerts potent differential immunomodulatory effects on human DC subpopulations.

β2-1 Fructan supplementation alters host immune responses in a manner consistent with increased exposure to microbial components: results from a double-blinded, randomised, cross-over study in healthy adults

β2-1 Fructans are purported to improve health by stimulating growth of colonic bifidobacteria, increasing host resistance to pathogens and stimulating the immune system. However, in healthy adults, the benefits of supplementation remain undefined. Adults (thirteen men, seventeen women) participated in a double-blinded, placebo-controlled, randomised, cross-over study consisting of two 28-d treatments separated by a 14-d washout period. Subjects' regular diets were supplemented with β2-1 fructan or placebo (maltodextrin) at 3×5 g/d. Fasting blood and 1-d faecal collections were obtained at the beginning and at the end of each phase. Blood was analysed for clinical, biochemical and immunological variables. Determinations of well-being and general health, gastrointestinal (GI) symptoms, regularity, faecal SCFA content, residual faecal β2-1 fructans and faecal bifidobacteria content were undertaken. β2-1 Fructan supplementation had no effect on blood lipid or cholesterol concentrations or on circulating lymphocyte and macrophage numbers, but significantly increased serum lipopolysaccharide, faecal SCFA, faecal bifidobacteria and indigestion. With respect to immune function, β2-1 fructan supplementation increased serum IL-4, circulating percentages of CD282+/TLR2+ myeloid dendritic cells and ex vivo responsiveness to a toll-like receptor 2 agonist. β2-1 Fructans also decreased serum IL-10, but did not affect C-reactive protein or serum/faecal Ig concentrations. No differences in host well-being were associated with either treatment, although the self-reported incidence of GI symptoms and headaches increased during the β2-1 fructan phase. Although β2-1 fructan supplementation increased faecal bifidobacteria, this change was not directly related to any of the determined host parameters.

Analysis of peripheral blood dendritic cells as a non-invasive tool in the follow-up of patients with chronic hepatitis C

Hepatitis C virus (HCV) has a high propensity to establish chronic infections. Failure of HCV-infected individuals to activate effective antiviral immune responses is at least in part related to HCV-induced impairment of dendritic cells (DCs) that play a central role in activating T cell responses. Although the impact of HCV on DC phenotype and function is likely to be more prominent in the liver, major HCV-induced alterations are detectable in peripheral blood DCs (pbDCs) that represent the most accessible source of DCs. These alterations include numerical reduction, impaired production of inflammatory cytokines and increased production of immunosuppressive IL10. These changes in DCs are relevant to our understanding the immune mechanisms underlying the propensity of HCV to establish persistent infection. Importantly, the non-invasive accessibility of pbDCs renders the analysis of these cells a convenient procedure that can be serially repeated in patient follow-up. Accordingly, the study of pbDCs in HCV-infected patients during conventional treatment with pegylated interferon and ribavirin indicated that restoration of normal plasmacytoid DC count may represent an additional mechanism contributing to the efficacy of the dual therapy. It also identified the pre-treatment levels of plasmacytoid DCs and IL10 as putative predictors of response to therapy. Treatment of chronic HCV infection is changing, as new generation direct-acting antiviral agents will soon be available for use in interferon-free therapeutic strategies. The phenotypic and functional analysis of pbDCs in this novel therapeutic setting will provide a valuable tool for investigating mechanisms underlying treatment efficacy and for identifying predictors of treatment response.

Siglec-1-positive plasmacytoid dendritic cells (pDCs) in human peripheral blood: A semi-mature and myeloid-like subset imbalanced during protective and autoimmune responses

Plasmacytoid dendritic cells (pDCs) play a central role in the pathogenesis of systemic lupus erythematosus (SLE) as IFN-α producers and promoters of T-cell activation or tolerance. Here, we demonstrated by flow-cytometry and confocal microscopy that Siglec-1, a molecule involved in the regulation of adaptive immunoresponses, is expressed in a subset of semi-mature, myeloid-like pDCs in human blood. These pDCs express lower BDCA-2 and CD123 and higher HLA-DR and CD11c than Siglec-1-negative pDCs and do not produce IFN-α via TLR7/TLR9 engagement. In vitro, Siglec-1 expression was induced in Siglec-1-negative pDCs by influenza virus. Proportions of Siglec-1-positive/Siglec-1-negative pDCs were higher in SLE than in healthy controls and correlated with disease activity. Healthy donors immunized with yellow fever vaccine YFV-17D displayed different kinetics of the two pDC subsets during protective immune response. PDCs can be subdivided into two subsets according to Siglec-1 expression. These subsets may play specific roles in (auto)immune responses.

Low IL-10/TNFα ratio in patients with coronary artery disease and reduced left ventricular ejection fraction with a poor prognosis after 10 years

Monocytes and dendritic cells (DC) produce tumour necrosis factor (TNF)α during inflammatory processes, but secrete interleukin (IL)-10 simultaneously in order to balance the pro-inflammation. In the present study, we investigated the expression of TNFα and IL-10 by monocytes and DC in patients with a poor cardiovascular prognosis after 10 years. Peripheral blood monocytes were isolated from 30 patients with coronary artery disease (CAD) with stable angina pectoris (SAP), or with an acute coronary syndrome (ACS). Monocytes were differentiated over 7 days to DC. Intracellular accumulation of TNFα and IL-10 in monocytes and DC was analysed by flow cytometry and correlated with the heart function, total and cardiovascular (CV) mortality, as well as with cardiovascular event rate over 10 years. We observed a decreased left ventricular function (LV-EF) for both SAP and ACS patients (p<0.01), as well as a reduced IL-10/TNFα ratio for monocytes (p=0.01) and DC (p<0.01) for both patient groups in comparison to age-matched control group. Only the IL-10/TNFα ratio for monocytes correlated with LV-EF (r=0.4302; p<0.01). Patients with a low LV-EF as well as patients with a low IL-10/TNFα ratio showed an increased cardiovascular mortality over 10 years (both p<0.05). The IL-10/TNFα ratio is decreased in patients with low ejection fraction and poor prognosis. The reduced heart function correlates with an increased proinflammatory state (low monocytic IL-10/TNFα ratio) in patients with CAD. This observed imbalance of IL-10 and TNFα in monocytes might explain pathophysiological processes in atherosclerosis and heart failure.

Immune cell dysfunctions in breast cancer patients detected through whole blood multi-parametric flow cytometry assay

Monitoring functional competence of immune cell populations in clinical routine represents a major challenge. We developed a whole-blood assay to monitor functional competence of peripheral innate immune cells including NK cells, dendritic and monocyte cell subsets through their ability to produce specific cytokines after short-term stimulation, detected through intra-cytoplasmic staining and multi-parametric flow-cytometry. A PMA/ionomycin T cell activation assay complemented this analysis. Comparing cohorts of healthy women and breast cancer (BC) patients at different stages, we identified significant functional alteration of circulating immune cells during BC progression prior to initiation of treatment. Of upmost importance, as early as the localized primary tumor (PT) stage, we observed functional alterations in several innate immune populations and T cells i.e. (i) reduced TNFα production by BDCA-1⁺ DC and non-classical monocytes in response to Type-I IFN, (ii) a strong drop in IFNγ production by NK cells in response to either Type-I IFN or TLR7/8 ligand, and (iii) a coordinated impairment of cytokine (IL-2, IFNγ, IL-21) production by T cell subpopulations. Overall, these alterations are further accentuated according to the stage of the disease in first-line metastatic patients. Finally, whereas we did not detect functional modification of DC subsets in response to TLR7/8 ligand, we highlighted increased IL-12p40 production by monocytes specifically at first relapse (FR). Our results reinforce the importance of monitoring both innate and adaptive immunity to better evaluate dysfunctions in cancer patients and suggest that our whole-blood assay will be useful to monitor response to treatment, particularly for immunotherapeutic strategies.

Change of walking distance in intermittent claudication: impact on inflammation, oxidative stress and mononuclear cells: a pilot study

BACKGROUND

Atherosclerosis is a chronic inflammatory process involving the immune system and formation of reactive oxygen species (ROS). We investigated changes of mononuclear blood cells and ROS production in relation to the walking distance of patients with intermittent claudication during home-based exercise training.

METHODS

Forty patients with intermittent claudication were asked to perform a home-based exercise training for a mean time of 12 months. ROS formation was measured using the luminol analogue L-012. Peripheral blood leucocytes [monocytes, polymorphonuclear neutrophils (PMN) and dendritic cells (DC)] were analysed by flow cytometry and analysed for the expression of major inflammatory surface molecules.

RESULTS

At follow-up, patients showed an increased walking distance and reduced ROS production upon stimulation with a phorbol ester derivative (PDBu) (p < 0.01). Monocytes changed their inflammatory phenotype towards an increased anti-inflammatory CD14(++)CD16(-) subpopulation (p < 0.0001). Adhesion molecules CD11b, CD11c and TREM-1 on monocytes and PMN decreased (all p < 0.01). On DC expression of HLA-DR, CD86 or CD40 decreased at follow-up. Inflammatory markers like fibrinogen, C-reactive protein or soluble TREM-1 (sTREM-1) decreased over the observation period. Finally, we found a close relation of sTREM-1 with the walking distance, fibrinogen and ROS production.

CONCLUSIONS

We observed an amelioration of the proinflammatory phenotype on monocytes, DC and PMN, as well as a reduced ROS production in PAD patients under home-based exercise, paralleled by an increased walking distance. Our data suggest that a reduced inflammatory state might be achieved by regular walking exercise, possibly in a dimension proportionately to changes in walking distance.

Rapid detection of dendritic cell and monocyte disorders using CD4 as a lineage marker of the human peripheral blood antigen-presenting cell compartment

Dendritic cells (DCs) and monocytes are critical regulators and effectors of innate and adaptive immune responses. Monocyte expansion has been described in many pathological states while monocyte and DC deficiency syndromes are relatively recent additions to the catalog of human primary immunodeficiency disorders. Clinically applicable screening tests to diagnose and monitor these conditions are lacking. Conventional strategies for identifying human DCs and monocytes have been based on the use of a lineage gate to exclude lymphocytes, thus preventing simultaneous detection of DCs, monocytes, and lymphocyte subsets. Here we demonstrate that CD4 is a reliable lineage marker for the human peripheral blood antigen-presenting cell compartment that can be used to identify DCs and monocytes in parallel with lymphocytes. Based on this principle, simple modification of a standard lymphocyte phenotyping assay permits simultaneous enumeration of four lymphocyte and five DC/monocyte populations from a single sample. This approach is applicable to clinical samples and facilitates the diagnosis of DC and monocyte disorders in a wide range of clinical settings, including genetic deficiency, neoplasia, and inflammation.

Aerobic training and angiogenesis activation in patients with stable chronic heart failure: a preliminary report

The pathophysiology of chronic heart failure (CHF) involves multiple hystologic and molecular alterations. To determine the effects of physical training on circulating endothelial progenitor cells (EPCs), angiogenesis (angiogenin, angiopoietin-1 and -2, VEGF, Tie-2, SDF-1α) and inflammation (IL-6, CRP), we compared data obtained from 11 CHF pts before and after 3 months aerobic exercise training, to those from 10 non trained CHF pts (CHF-C group, age 64 + 2 years, NYHA 2). At the end of the study, EPCs count and AP-2 serum levels significantly increased in the CHF-TR group. These preliminary data suggest a significant effect of even a short program of physical training on angiogenic activation and endothelial dysfunction.

Plasmodium falciparum-derived uric acid precipitates induce maturation of dendritic cells

Malaria is characterized by cyclical fevers and high levels of inflammation, and while an early inflammatory response contributes to parasite clearance, excessive and persistent inflammation can lead to severe forms of the disease. Here, we show that Plasmodium falciparum-infected erythrocytes contain uric acid precipitates in the cytoplasm of the parasitophorous vacuole, which are released when erythrocytes rupture. Uric acid precipitates are highly inflammatory molecules that are considered a danger signal for innate immunity and are the causative agent in gout. We determined that P. falciparum-derived uric acid precipitates induce maturation of human dendritic cells, increasing the expression of cell surface co-stimulatory molecules such as CD80 and CD86, while decreasing human leukocyte antigen-DR expression. In accordance with this, uric acid accounts for a significant proportion of the total stimulatory activity induced by parasite-infected erythrocytes. Moreover, the identification of uric acid precipitates in P. falciparum- and P. vivax-infected erythrocytes obtained directly from malaria patients underscores the in vivo and clinical relevance of our findings. Altogether, our data implicate uric acid precipitates as a potentially important contributor to the innate immune response to Plasmodium infection and may provide a novel target for adjunct therapies.

Circulating dendritic cell number and intracellular TNF-α production in women with type 2 diabetes

Human dendritic cell (DC) subsets perform specialized functions for surveillance against bacterial and viral infections essential for the management of type 2 diabetes (T2D). Production of tumor necrosis factor-alpha (TNF-α) by DCs acts in autocrine fashion to regulate DC maturation and promotes the inflammatory response. This study was designed to compare circulating DC number and intracellular TNF-α production between post-menopausal women with T2D and healthy women. Blood samples were obtained (n = 21/group) and examined for plasma glucose and TNF-α concentrations, and dendritic cell subset immunophenotype (plasmacytoid, pDC, CD85k(ILT-3)(+)CD123(+)CD16(-)CD14(-) and myeloid, mDC, CD85k(ILT-3)(+)CD33(+)CD123(dim to neg)CD16(-)CD14(dim to neg)). Intracellular production of TNF-α was determined in unstimulated and stimulated DCs. Women with T2D had significantly (P < 0.05) greater plasma glucose and TNF-α concentrations when compared to healthy women. Women with T2D having poor glycemic control (T2D Poor Control, HbA1c ≥ 7%) had fewer circulating pDCs than women with T2D having good glycemic control (T2D Good Control, HbA1c < 7%) and healthy women. A significant interaction (P = 0.011) was observed between the effects of plasma glucose and group for intracellular expression of TNF-α in stimulated pDCs. Intracellular production of TNF-α in pDCs was significantly greater in healthy vs. T2D Poor Control (P < 0.0001) and T2D Good Control (P < 0.0001) but did not differ between T2D subgroups. The mDC number and intracellular production of TNF-α did not differ between groups. These findings indicate that TNF-α production by pDCs was reduced in women with T2D and circulating number of pDCs was associated with glycemic control.

Lack of activation of peripheral blood dendritic cells in human pregnancies complicated by intrauterine growth restriction

INTRODUCTION

The state of activation of dendritic cells (DCs) at the feto-maternal interface critically contributes to optimal decidual immune responses needed to support fetal-placental development. We recently demonstrated that during healthy pregnancy also peripheral blood DCs (PBDCs), which are easily accessible, are activated as well. In this study, to investigate a possible involvement of DCs in intrauterine growth restriction (IUGR), we evaluated whether PBDCs in pregnancy complicated by IUGR may be altered compared with PBDCs in healthy pregnancy.

METHODS

PBDCs from 12 pregnant women with primary IUGR, 21 healthy pregnant and 19 nonpregnant women were analyzed by flow cytometric analysis of whole-blood samples collected at a single time point.

RESULTS

The number of plasmacytoid PBDCs was significantly reduced in women with IUGR pregnancy. Myeloid and plasmacytoid PBDCs in IUGR lacked the state of activation (assessed as CD80, CD86, CD40 expression) and the shift to a proinflammatory pattern of cytokine production occurring during healthy pregnancy.

DISCUSSION

To our knowledge, this is the first study investigating the state of PBDC activation in IUGR pregnancy. Our results are in accordance with a previous study reporting a lower expression of activation and maturation markers by decidual DCs in IUGR placentas.

CONCLUSIONS

The reduced activation of PBDCs in IUGR pregnancy may possibly reflect a reduced activation of decidual DCs. If confirmed at the feto-maternal interface, the alterations of DCs described in IUGR pregnancy have the potential to negatively impact on vascular development during gestation. These observations may therefore broaden our understanding of IUGR pathogenesis.

Phenotypic characterisation of pro-inflammatory monocytes and dendritic cells in peripheral arterial disease

Atherosclerosis is a chronic inflammatory process involving antigen-presenting cells like monocytes and dendritic cells (DC). The aim of this study was to perform a phenotypic characterisation of these cell types in patients with different degrees of peripheral arterial disease (PAD). Sixty patients with PAD [N= 30 intermittent claudication (IC), N= 30 critical limb ischemia (CLI)] and 30 controls were included. Peripheral blood leucocytes were analysed from peripheral blood by flow cytometry using different gating strategies to directly identify and analyse monocytes, myeloid DC, (mDC) and plasmacytoid DC (pDC). PAD patients showed a significantly higher proportion of proinflammatory CD14++CD16+ monocytes (p<0.0001) compared with healthy individuals. We found an increased number of mDC/ml and a reduced number of pDC/ml (both p<0.01) in PAD patients, leading to a shift in the mDC/pDC ratio (p<0.01). As compared to patients with intermittent claudication, CLI patients presented a reduced expression of HLA-DR (p<0.01), CD86 and CD40 on both mDCs and pDCs (p<0.01). Peripheral blood monocytes show a proinflammatory phenotype in PAD patients compared to controls. In contrast, CLI patients show a reduced expression of proinflammatory markers. We hypothesise that severe ischaemia and/or prolonged inflammation in CLI might lead to a paradoxical attenuation in the proinflammatory membrane pattern of circulating mononuclear cells, possibly hindering an adequate regulatory function of mDCs and pDCs and favouring the progression of disease.

Toward a reference method for leukocyte differential counts in blood: comparison of three flow cytometric candidate methods

A Complete Blood Count performed by an automated hematology analyzer frequently requires a microscopic slide review. Recently, we and others have proposed combinations of monoclonal antibodies for an extended leukocyte differential by flow cytometry. The aim of this study was to compare the performance of these proposals. Ninety-two samples were analyzed at 2 sites to compare the accuracy of three published methods. Reference methods used were i) cell counter for leukocyte count and ii) microscopic review as defined by CSLI H20-A2 for cell subsets. Comparison of flow cytometers from 2 manufacturers (FC500 and CANTO/LSRII) was performed. Published protocols were adapted to three different models of flow cytometer and each provided similar results in leukocyte subset enumeration, although some discrepancies were noted for each protocol in comparison with the reference method. The conclusion is that each protocol carries advantages and disadvantages and there is no clear "winner". This study supports the fact that flow cytometry is a candidate to become a reference method for the leukocyte differential. None of the tested protocols clearly demonstrated superiority and each had demonstrable deficiencies. Additional work to develop a consensual 8 to 10 color panel is concluded to be necessary for a satisfactory reference method.

Central memory CD4+ T cells dominate the normal cerebrospinal fluid

BACKGROUND

To use cerebrospinal fluid (CSF) immune phenotyping as a diagnostic and research tool, we have set out to establish reference values of white blood cell (WBC) subsets in CSF.

METHODS

We assessed the absolute numbers and percentages of WBC subsets by 6-color flow cytometry in paired CSF and blood samples of 84 individuals without neurological disease who underwent spinal anaesthesia for surgery. Leukocyte (i.e., lymphocytes, granulocytes, and monocytes), lymphocyte (i.e., T [CD4(+) and CD8(+) ], NK, NKT and B cells), T cell (i.e., naïve, central memory, effector memory, and regulatory) and dendritic cell subsets (i.e., myeloid and plasmacytoid) were studied.

RESULTS

CSF showed a predominance of T cells, while granulocytes, B and NK cells were relatively rare compared to blood. The majority of T cells in CSF consisted of CD4(+) T cells (∼70%), most of them (∼90%) with a central memory phenotype, while B cells were almost absent (<1%). Among the small population of dendritic cells in CSF, those of the myeloid subtype were more frequent than plasmacytoid dendritic cells (medians: 1.7% and 0.4% of leukocytes, respectively), whilst both subsets made up 0.2% of leukocytes in blood.

CONCLUSIONS

This study reports reference values of absolute numbers and percentages of WBC subsets in CSF, which are essential for further investigation of the immunopathogenesis of neuro-inflammatory diseases. Furthermore, the relative abundance of CD4(+) T cells, mainly with a central memory phenotype, and the presence of dendritic cells in CSF suggests an active adaptive immune response under normal conditions in the central nervous system (CNS).

Incomplete activation of peripheral blood dendritic cells during healthy human pregnancy

Successful pregnancy relies on the adaptation of immune responses that allow the fetus to grow and develop in the uterus despite being recognized by maternal immune cells. Dendritic cells (DCs) are central to the control of immune tolerance, and their state of activation at the maternal-decidual interface is critical to the feto-maternal immunological equilibrium. So far, the involvement of circulating DCs has been investigated poorly. Therefore, in this study we investigated whether, during healthy human pregnancy, peripheral blood DCs (PBDCs) undergo changes that may be relevant to the adaptation of maternal immune responses that allow fetal tolerance. In a cross-sectional study, we analysed PBDCs by six-colour flow cytometry on whole blood samples from 47 women during healthy pregnancy progression and 24 non-pregnant controls. We demonstrated that both myeloid and plasmacytoid PBDCs undergo a state of incomplete activation, more evident in the third trimester, characterized by increased expression of co-stimulatory molecules and cytokine production but lacking human leucocyte antigen (HLA)-DR up-regulation. To investigate the contribution of soluble circulating factors to this phenomenon, we also performed culture experiments showing that sera from pregnant women added to control DCs conditioned a similar incomplete activation that was associated with reduced DC allostimulatory capacity, supporting the in vivo relevance of our findings. We also obtained evidence that the glycoprotein hormone activin-A may contribute to DC incomplete activation. We suggest that the changes of PBDCs occurring during late pregnancy may aid the comprehension of the immune mechanisms operated by the maternal immune system to maintain fetal tolerance.

Decreased numbers of peripheral blood dendritic cells in patients with coronary artery disease are associated with diminished plasma Flt3 ligand levels and impaired plasmacytoid dendritic cell function

We investigated whether activation of circulating DCs (dendritic cells) or levels of Flt3L (FMS-like tyrosine kinase 3 ligand) and GM-CSF (granulocyte/macrophage colony-stimulating factor), haematopoietic growth factors important for DC differentiation, could account for reduced blood DC numbers in CAD (coronary artery disease) patients. Concentrations of Flt3L and GM-CSF were measured in plasma from CAD patients (n = 15) and controls (n = 12). Frequency and phenotype of mDCs (myeloid dendritic cells) and pDCs (plasmacytoid dendritic cells) were analysed by multicolour flow cytometry in fresh blood, and after overnight incubation with TLR (Toll-like receptor)-4 or -7 ligands LPS (lipopolysaccharide) or IQ (imiquimod). DC function was measured by IL (interleukin)-12 and IFN (interferon)-α secretion. Circulating numbers of CD11c+ mDCs and CD123+ pDCs and frequencies of CD86+ and CCR-7+ (CC chemokine receptor type 7) mDCs, but not pDCs, were declined in CAD. In addition, plasma Flt3L, but not GM-CSF, was lower in patients and positively correlated with blood DC counts. In response to LPS, mDCs up-regulated CD83 and CD86, but CCR-7 expression and IL-12 secretion remained unchanged, similarly in patients and controls. Conversely, pDCs from patients had lower CD83 and CCR-7 expression after overnight incubation and had a weaker IQ-induced up-regulation of CD83 and IFN-α secretion. In conclusion, our results suggest that reduced blood DC counts in CAD are, at least partly, due to impaired DC differentiation from bone marrow progenitors. Decreased levels of mDCs are presumably also explained by activation and subsequent migration to atherosclerotic plaques or lymph nodes. Although mDCs are functioning normally, pDCs from patients appeared to be both numerically and functionally impaired.

Human herpesvirus-8 infection leads to expansion of the preimmune/natural effector B cell compartment

Background

Human herpesvirus-8 (HHV-8) is the etiological agent of Kaposi's sarcoma (KS) and of some lymphoproliferative disorders of B cells. Most malignancies develop after long-lasting viral dormancy, and a preventing role for both humoral and cellular immune control is suggested by the high frequency of these pathologies in immunosuppressed patients. B cells, macrophages and dendritic cells of peripheral lymphoid organs and blood represent the major reservoir of HHV-8. Due to the dual role of B cells in HHV-8 infection, both as virus reservoir and as agents of humoral immune control, we analyzed the subset distribution and the functional state of peripheral blood B cells in HHV-8-infected individuals with and without cKS.

Methodology/Principal Findings

Circulating B cells and their subsets were analyzed by 6-color flow cytometry in the following groups: 1- patients HHV-8 positive with classic KS (cKS) (n = 47); 2- subjects HHV-8 positive and cKS negative (HSP) (n = 10); 3- healthy controls, HHV-8 negative and cKS negative (HC) (n = 43). The number of B cells belonging to the preimmune/natural effector compartment, including transitional, pre-naïve, naïve and MZ-like subsets, was significantly higher among HHV-8 positive subjects, with or without cKS, while was comparable to healthy controls in the antigen-experienced T-cell dependent compartment. The increased number of preimmune/natural effector B cells was associated with increased resistance to spontaneous apoptosis, while it did not correlate with HHV-8 viral load.

Conclusions/Significance

Our results indicate that long-lasting HHV-8 infection promotes an imbalance in peripheral B cell subsets, perturbing the equilibrium between earlier and later steps of maturation and activation processes. This observation may broaden our understanding of the complex interplay between viral and immune factors leading HHV-8-infected individuals to develop HHV-8-associated malignancies.

Evaluation of a 12-color flow cytometry panel to study lymphocyte, monocyte, and dendritic cell subsets in humans

Monitoring changes in human immune cell populations such as lymphocytes, monocytes, and dendritic cells (DCs) during infectious diseases like human immunodeficiency virus (HIV) is crucial. However, difficulties to identify rare or heterogeneous cell populations can be limiting. For example, to accurately measure DC subsets, eight flow cytometry parameters are ideal. The aim of this work was to analyze the phenotype of human lymphocyte, monocyte, and DC subsets using a single 12-color flow cytometry panel. After erythrocyte lysis, blood from healthy human volunteers was washed and labeled with a cocktail of 12 antibodies. Samples were analyzed on a Becton-Dickinson FACSAria equipped with three lasers. Data were compared with lineage-specific panels using 5-8 Ab combinations per lineage. Acquired data were analyzed using FlowJo software. Our 12-color panel allows for the identification of the following major subsets of circulating cells in a single tube: CD4+ and CD8+ T lymphocytes, B lymphocytes, NK cells, NKT cells, monocyte subsets (CD14 and/or CD16), and five nonoverlapping HLA-DR+Lin- subsets: CD34+ hematopoietic stem cells, CD123+ plasmacytoid DC, and three subsets of CD11c+ myeloid DC expressing either CD16, CD1c (BDCA-1), or CD141 (BDCA-3). We have developed a single flow cytometry panel that allows for simultaneous detection of the lymphocyte and monocyte cell populations and all known DC subsets. Studying these major players of the immune system in one single panel may give us a broader view of the immune response during HIV infection and the ability to better define the role of individual cell types in Acquired Immune Deficiency Syndrome (AIDS) pathogenesis. (c) 2010 International Society for Advancement of Cytometry.

Association of two clones allows for optimal detection of human FOXP3

FOXP3 is a key transcription factor expressed by regulatory T cells (Treg cells). However, differences in staining and analysis protocols have led to conflicting results. Moreover, the transient upregulation of FOXP3 that follows activation in non-Treg cells renders the interpretation of FOXP3 data more difficult in humans than in mice. Human peripheral blood mononuclear cells (PBMCs), isolated CD25(-) or CD25(+)CD4(+) T cells were stained with three different anti-FOXP3 clones (PCH101, 206D, and 259D) alone or in combination, and using different permeabilization methods. FOXP3 expression was evaluated following T cell activation by several pathways. Gating based on a population that did not express FOXP3 (such as CD3(-)CD4(-) T cells) allowed for the optimal characterization of Treg cells. The 206D clone detected a lower percentage of cells than PCH101 or 259D. In contrast, 259D stained a population of activated T cells that PCH101 did not. Staining with two clones together consistently increased the proportion of FOXP3(+) cells. However, it is likely that only the double positive cells are Treg cells, as they expressed the highest CD25 and lowest CD127 levels. Our results emphasize that the choice of staining protocol leads to very different results concerning the frequency of Treg cells in humans. A more consistent identification of these cells will improve the knowledge of their biology, particularly during disease processes.

Immunophenotyping of lymphocyte, monocyte and dendritic cell subsets in normal rhesus macaques by 12-color flow cytometry: clarification on DC heterogeneity

Monitoring changes in rhesus macaque immune cell populations during infectious disease is crucial. The aim of this work was to simultaneously analyze the phenotype of rhesus macaque lymphocyte, monocyte and dendritic cell (DC) subsets using a single 12-color flow cytometry panel. Blood from healthy non-infected rhesus macaques was labeled with a cocktail of 12 antibodies. Data were compared to three smaller lineage specific panels and absolute and relative percentages of cells were compared. Our 12-color panel allows for the identification of the following major subsets: CD4+ and CD8+ T lymphocytes, B lymphocytes, natural killer (NK) cells, natural killer T (NKT) cells, monocyte subsets and four non-overlapping Lin-HLA-DR+ cell subsets: CD34+ hematopoietic stem cells, CD11c- CD123+ plasmacytoid DC, CD11c+ CD16+ and CD11c(-)(/dim) CD1c+ myeloid DC. The development of a multiparameter flow cytometry panel will allow for simultaneous enumeration of mature lymphocyte, NK cells, monocyte and DC subsets. Studying these major players of the immune system in one panel may give us a broader view of the immune response during SIV infection and the ability to better define the role of each of these individual cell types in the pathogenesis of AIDS.

Enumeration and phenotypic assessment of human plasmacytoid and myeloid dendritic cells in whole blood

Traditionally, flow cytometry analysis of dendritic cells (DC) has followed a negative selection procedure, often limiting the characterization of individual DC subsets to enumeration. We demonstrate the development, evaluation, and clinical application of a novel 6 color/8 parameter flow cytometry panel to allow enumeration and monitoring of activation status of circulating human myeloid (MDC1) and plasmacytoid (PDC) dendritic cells in human whole blood. Enumeration showed a trend of greater numbers of MDC1s and PDCs being collected for fresh whole blood than frozen PBMCs, with this difference being statistically significant (P = 0.04) for unstimulated PDC enumeration. Intra-assay variation had a coefficient of variation <10% and interassay results between operators showed good correlation (r > 0.95). Our results on fresh whole blood showed a significant up regulation of CD83 on both MDC1 and PDC at 4 h post Toll-like ligand stimulus and this activity was comparable in frozen PBMC samples. Comparison for the late activation marker CCR7 showed a significant difference (P <0.05) in expression between fresh and frozen samples, precluding its use for batch analysis of frozen samples. In addition, the level of activation is dependent on the anticoagulant used for sample collection. For CD83 expression at 4 h both EDTA and lithium heparin samples are comparable for MDC1 and PDC populations. Whereas for CCR7 expression, lithium heparin is preferable as EDTA increases the background expression in PDC, preventing further functional assessments. We demonstrate the importance of establishing the kinetic profile of activation marker expression and the importance of evaluating sample collection tubes and sample type before application of novel cytometry panels to a clinical study. We have shown that this DC enumeration flow cytometry panel is a robust analysis system that allows the flexibility of including activation markers.

[Dendritic cells in sepsis: an approach to post-infectious immunosuppression]

Dendritic cells (DCs) play a decisive role in the immune system, especially in the initial events that determine coordination between the innate and adaptive response. Moreover, they are antigen-presenting cells which, through contact with T cells, determine the type of immune responses towards inflammatory or anti-inflammatory. Currently, the hypothesis that attributes importance to the development of a post-infectious immunosuppression in the prognosis of the septic patient is growing stronger. It has been possible to verify the role played by these cells in this type of immunosuppression by the significant decrease in the number of DCs and by the dysfunctions in the functional capacity that include, on the one hand, the abnormal cytokine production and, on the other hand, the alterations in communication between the DCs and T cells that constitute an essential immunological fact. Further research into the knowledge regarding the DCs, in the context of severe infection, may help to consolidate some encouraging data that indicate these cells as: 1) an effective tool for monitoring the acute infection, 2) a discriminatory variable that may help determine the risk of nosocomial infection and 3) in a longer term, a treatment target that would restore the immunological abnormalities that occur in sepsis.

The role of CD40 and CD154/CD40L in dendritic cells

In this review, we focus on the function of CD40-CD40L (CD154) interactions in the regulation of dendritic cell (DC)-T cell and DC-B cell crosstalk. In addition, we examine differences and similarities between the CD40 signaling pathway in DCs and other innate immune cell receptors, and how these pathways integrate DC functions. As research into DC vaccines and immunotherapies progresses, further understanding of CD40 and DC function will advance the applicability of DCs in immunotherapy for human diseases.