Phenotypic characteristics of human monocytes undergoing transendothelial migration

Identification of a unique intervillous cellular signature in chronic histiocytic intervillositis

INTRODUCTION

Chronic histiocytic intervillositis (CHI) is a rare histopathological lesion in the placenta characterized by an infiltrate of CD68⁺ cells in the intervillous space. CHI is associated with adverse pregnancy outcomes such as miscarriage, fetal growth restriction, and (late) intrauterine fetal death. The adverse pregnancy outcomes and a variable recurrence rate of 25-100% underline its clinical relevance. The pathophysiologic mechanism of CHI is unclear, but it appears to be immunologically driven. The aim of this study was to obtain a better understanding of the phenotype of the cellular infiltrate in CHI.

METHOD

We used imaging mass cytometry to achieve in-depth visualization of the intervillous maternal immune cells and investigated their spatial orientation in situ in relation to the fetal syncytiotrophoblast.

RESULTS

We found three phenotypically distinct CD68⁺HLA-DR⁺CD38⁺ cell clusters that were unique for CHI. Additionally, syncytiotrophoblast cells in the vicinity of these CD68⁺HLA-DR⁺CD38⁺ cells showed decreased expression of the immunosuppressive enzyme CD39.

DISCUSSION

The current results provide novel insight into the phenotype of CD68⁺ cells in CHI. The identification of unique CD68⁺ cell clusters will allow more detailed analysis of their function and could result in novel therapeutic targets for CHI.

Novel Circulating and Tissue Monocytes as Well as Macrophages in Pancreatitis and Recovery

BACKGROUND AND AIMS

Acute pancreatitis (AP) is an inflammatory disease with mild to severe course that is associated with local and systemic complications and significant mortality. Uncovering inflammatory pathways that lead to progression and recovery will inform ways to monitor and/or develop effective therapies.

METHODS

We performed single-cell mass Cytometry by Time Of Flight (CyTOF) analysis to identify pancreatic and systemic inflammatory signals during mild AP (referred to as AP), severe AP (SAP), and recovery using 2 independent experimental models and blood from patients with AP and recurrent AP. Flow cytometric validation of monocytes subsets identified using CyTOF analysis was performed independently.

RESULTS

Ly6C+ inflammatory monocytes were the most altered cells in the pancreas during experimental AP, recovery, and SAP. Deep profiling uncovered heterogeneity among pancreatic and blood monocytes and identified 7 novel subsets during AP and recovery, and 6 monocyte subsets during SAP. Notably, a dynamic shift in pancreatic CD206+ macrophage population was observed during AP and recovery. Deeper profiling of the CD206+ macrophage identified 7 novel subsets during AP, recovery, and SAP. Differential expression analysis of these novel monocyte and CD206+ macrophage subsets revealed significantly altered surface (CD44, CD54, CD115, CD140a, CD196, podoplanin) and functional markers (interferon-γ, interleukin 4, interleukin 22, latency associated peptide-transforming growth factor-β, tumor necrosis factor-α, T-bet, RoRγt) that were associated with recovery and SAP. Moreover, a targeted functional analysis further revealed distinct expression of pro- and anti-inflammatory cytokines by pancreatic CD206+ macrophage subsets as the disease either progressed or resolved. Similarly, we identified heterogeneity among circulating classical inflammatory monocytes (CD14+CD16-) and novel subsets in patients with AP and recurrent AP.

CONCLUSIONS

We identified several novel monocyte/macrophage subsets with unique phenotype and functional characteristics that are associated with AP, recovery, and SAP. Our findings highlight differential innate immune responses during AP progression and recovery that can be leveraged for future disease monitoring and targeting.

Rheumatoid arthritis CD14+ monocytes display metabolic and inflammatory dysfunction, a phenotype that precedes clinical manifestation of disease

Introduction

This study investigates the metabolic activity of circulating monocytes and their impact on pro‐inflammatory responses in RA and explores whether this phenotype is already primed for inflammation before clinical manifestations of disease.

Methods

Blood was collected and CD14⁺ monocytes isolated from healthy control donors (HC), individuals at‐risk (IAR) and RA patients. Monocyte frequency in blood and synovial tissue was assessed by flow cytometry. Inflammatory responses and metabolic analysis ± specific inhibitors were quantified by RT‐PCR, Western blot, migration assays, Seahorse‐XFe‐technology, mitotracker assays and transmission electron microscopy. Transcriptomic analysis was performed on HC, IAR and RA synovial tissue.

Results

CD14⁺ monocytes from RA patients are hyper‐inflammatory following stimulation, with significantly higher expression of cytokines/chemokines than those from HC. LPS‐induced RA monocyte migratory capacity is consistent with increased monocyte frequency in RA synovial tissue. RA CD14⁺ monocytes show enhanced mitochondrial respiration, biogenesis and alterations in mitochondrial morphology. Furthermore, RA monocytes display increased levels of key glycolytic enzymes HIF1α, HK2 and PFKFB3 and demonstrate a reliance on glucose consumption, blockade of which abrogates pro‐inflammatory mediator responses. Blockade of STAT3 activation inhibits this forced glycolytic flux resulting in metabolic reprogramming and resolution of inflammation. Interestingly, this highly activated monocytic phenotype is evident in IAR of developing disease, in addition to an enhanced monocyte gene signature observed in synovial tissue from IAR.

Conclusion

RA CD14⁺ monocytes are metabolically re‐programmed for sustained induction of pro‐inflammatory responses, with STAT3 identified as a molecular regulator of metabolic dysfunction. This phenotype precedes clinical disease onset and may represent a potential pathway for therapeutic targeting early in disease.

Mass cytometry dissects T cell heterogeneity in the immune tumor microenvironment of common dysproteinemias at diagnosis and after first line therapies

Dysproteinemias progress through a series of clonal evolution events in the tumor cell along with the development of a progressively more “permissive” immune tumor microenvironment (iTME). Novel multiparametric cytometry approaches, such as cytometry by time-of-flight (CyTOF) combined with novel gating algorithms can rapidly characterize previously unknown phenotypes in the iTME of tumors and better capture its heterogeneity. Here, we used a 33-marker CyTOF panel to characterize the iTME of dysproteinemia patients (MGUS, multiple myeloma—MM, smoldering MM, and AL amyloidosis) at diagnosis and after standard of care first line therapies (triplet induction chemotherapy and autologous stem cell transplant—ASCT). We identify novel subsets, some of which are unique to the iTME and absent from matched peripheral blood samples, with potential roles in tumor immunosurveillance as well as tumor immune escape. We find that AL amyloidosis has a distinct iTME compared to other dysproteinemias with higher myeloid and “innate-like” T cell subset infiltration. We show that T cell immune senescence might be implicated in disease pathogenesis in patients with trisomies. Finally, we demonstrate that the early post-ASCT period is associated with an increase of senescent and exhausted subsets, which might have implications for the rational selection of post-ASCT therapies.

Transmigration through venular walls: a key regulator of leukocyte phenotype and function

Leukocyte transmigration is a key event in host defense. As well as delivering leukocytes to sites of inflammation, this response also has an important role in immunity by regulating the responsiveness and behavior of leukocytes in the extravascular tissue. Recent evidence suggests that these events are associated with phenotypic and functional changes in migrating leukocytes mediated by signaling and transcriptional events triggered by the molecular interactions involved in leukocyte transendothelial cell migration. Transfer of membrane proteins from endothelial cells to migrating leukocytes and interaction of leukocytes with components of the perivascular basement membrane might also contribute to this effect. This Review will discuss the characteristics, potential mechanisms and the relevance of transmigration-induced change in leukocyte phenotype and responsiveness both within physiological and pathological scenarios.

Leflunomide inhibits transendothelial migration of peripheral blood mononuclear cells

OBJECTIVES

To test whether the active metabolite of leflunomide (LEF-M), in addition to blocking the proliferation of activated lymphocytes by inhibiting dihydro-orotate dehydrogenase (DHODH), influences the transendothelial migration (TEM) of peripheral blood mononuclear cells (PBMC).

METHODS

In an in vitro model of PBMC transmigration through an endothelial cell (EC) barrier, PBMC were re-collected in three groups: cells not adherent to the EC, cells bound to, and cells which had migrated through, the EC layer. Experiments in which cells were pretreated with LEF-M (in the absence or in the presence of uridine) were compared with parallel experiments in the presence of medium alone.

RESULTS

Preincubation of EC with LEF-M led to a 36 (SEM 16)% reduction in PBMC TEM (p<0.05). Likewise, preincubation of PBMC induced a reduction in their TEM of 39 (9)% (p<0.005). Incubation of both PBMC and EC with LEF-M had an additive effect (mean reduction of 48 (6)%, p<0.005). Incubation of PBMC with LEF-M also decreased monocytic CD44 expression (p<0.005) and PBMC-hyaluronan binding (p<0.05). Incubation of cells with LEF-M and uridine in addition to LEF-M reversed the inhibition of migration, suggesting that the observed effects were due to DHODH inhibition. Fluorocytometric analysis of PBMC subsets within the migrated population showed a decrease of monocytes, but not of B or T cells, after LEF-M treatment.

CONCLUSIONS

LEF-M reduces monocytic adhesion molecule expression and TEM and may thus interfere with monocyte and EC activities in RA. Thus, the clinical effects of leflunomide may, at least in part, be due to blocking cell traffic into the inflamed synovia.

Increased transendothelial migration of scleroderma lymphocytes

BACKGROUND

CD4+ T lymphocytes play an important part in the pathogenesis of scleroderma (systemic sclerosis, SSc) and predominate in perivascular SSc skin lesions. Both soluble and membrane bound adhesion molecules are overexpressed in SSc, possibly influencing lymphocyte/endothelial cell (EC) contact.

OBJECTIVE

To assess the transendothelial migration capacity of peripheral lymphocytes in vitro.

PATIENTS AND METHODS

Collagen was covered with human umbilical vein endothelial cells (HUVEC), and peripheral blood mononuclear cells (PBMC) of patients and matched healthy controls (HC) were added in parallel experiments. Before and after fractionated harvest of non-adherent, bound, and migrated lymphocytes, the CD4/CD8 ratio and the lymphocytic expression of activation markers and adhesion molecules were analysed by fluorocytometry.

RESULTS

13 (SD 12)% of the SSc PBMC migrated compared with only 5 (5)% HC PBMC (p<0.0002); this increase was primarily due to the migration of CD3+ T lymphocytes and mainly to a larger proportion of CD4+ cells within this CD3+ fraction (71 (SD 14)% for SSc v 56 (14)% for HC, p<0.03), leading to an increased CD4/CD8 ratio among migrated SSc lymphocytes in comparison with controls (3.3 (1.5) v 1.62 (0.93), p<0.006). Among migrated SSc CD4+ T lymphocytes, the frequency of HLA-DR+ cells was increased; migrated lymphocytes highly expressed the adhesion molecules CD11a, CD49d, CD29, and CD44.

CONCLUSION

Transendothelial migration of CD4+ T lymphocytes is enhanced in SSc, and migrating cells exhibit an activated phenotype. The data suggest that activated CD3+CD4+ lymphocytes as found in SSc peripheral blood are prone to transvascular migration, thus contributing to the formation of typical perivascular lymphocytic infiltrates.

Regulation and functional effects of monocyte migration across human brain-derived endothelial cells

We have used human brain-derived endothelial cells (HBECs) maintained under basal culture conditions in a Boyden chamber assay system as an in vitro model of migration of cells of systemic immune origin across the blood brain barrier (BBB) during the initiation of a CNS-directed inflammatory response. In this study we evaluated the molecular mechanisms that regulate passage of ex vivo peripheral blood-derived monocytes across this barrier and the effects of such migration on the properties of both the HBECs and the monocytes. Our results indicate that monocytes can migrate across HBECs in the absence of inflammatory conditions, at rates exceeding those of lymphocytes. Monocyte migration could be significantly inhibited by the addition of blocking antibodies to intercellular adhesion molecule (ICAM)-1, very late antigen (VLA)-4 integrin, and monocyte chemoattractant protein (CCL-2/MCP-1), or treatment with tissue inhibitor of metalloproteinase (TIMP-1). Following monocyte migration there was a significant increase in permeability of soluble molecules and an enhanced rate of T cell migration across HBECs. The enhanced permeability could be partially prevented with anti-TNF-alpha antibody. The migration process did not induce the upregulation of either co-stimulatory molecules or chemokine receptors on the monocytes. These studies emphasize the functional role of monocyte-endothelial interactions in permitting target access of a CNS-directed cell-mediated immune response.