Tissue-specific microvascular endothelial cells show distinct capacity to activate NK cells: implications for the pathophysiology of granulomatosis with polyangiitis

Cutaneous vasculitis: insights into pathogenesis and histopathological features

The mechanisms underlying the onset and progression of vasculitis remain poorly understood. This condition is characterized by damage to the vascular wall, recruitment of inflammatory cells, and subsequent structural remodeling, which are hallmarks of vasculitis. The histopathological classification of vasculitis relies on the size of the affected vessel and the predominant type of inflammatory cell involved - neutrophils in acute cases, lymphocytes in chronic conditions, and histiocytes in granulomatous forms. Pathological changes progress in every context, and a single vasculitic pattern can be associated with various systemic conditions. Conversely, a single causative agent may lead to multiple distinct clinical and pathological manifestations of vasculitis. Moreover, many cases of vasculitis have no identifiable cause. A foundational understanding of the normal structure of the cutaneous vascular network is crucial. Similarly, identifying the cellular and molecular participants and their roles in forming the "dermal microvascular unit" is propedeutical.

This review aims to elucidate the complex mechanisms involved in the initiation and progression of vasculitis, offering a comprehensive overview of its histopathological classification, underlying causes, and the significant role of the cutaneous vascular network and cellular dynamics. By integrating the latest insights from studies on NETosis and the implications of lymphocytic infiltration in autoimmune diseases, we seek to bridge gaps in current knowledge and highlight areas for future research. Our discussion extends to the clinical implications of vasculitis, emphasizing the importance of identifying etiological agents and understanding the diverse histopathological manifestations to improve diagnostic accuracy and treatment outcomes.

Natural Killer Cells in Anti-Neutrophil Cytoplasmic Antibody-Associated Vasculitis - A Review of the Literature

Anti-neutrophil cytoplasmic antibody (ANCA)- associated vasculitis (AAV) is a group of systemic autoimmune diseases characterized by inflammation of small- and medium-sized vessels. The three main types of AAV are granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA). A growing number of studies focus on natural killer (NK) cells in AAV. NK cells are innate lymphoid cells with important roles in anti-viral and anti-tumor defense, but their roles in the pathogenesis of autoimmunity is less well established. In this review, we will present a summary of what is known about the number, phenotype and function of NK cells in patients with AAV. We review the literature on NK cells in the circulation of AAV patients, studies on tissue resident NK cells and how the treatment affects NK cells.

Immune Cells Profiling in ANCA-Associated Vasculitis Patients-Relation to Disease Activity

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV) are a group of necrotizing multiorgan autoimmune vasculitides that predominantly affect small blood vessels and are associated with the presence of ANCAs. The aim was to assess regulatory and effector cell populations accompanied by the suPAR biomarker level and link the so-defined immune state to the AAV disease activity. The research involved a multicomponent description of an immune state encompassing a range of B and T cell subsets such as transitional/regulatory B cells (CD19+CD24++CD38++), naïve B cells (CD19+CD24INTCD38INT), Th17 cells, T regulatory cells (CD4+CD25+FoxP3+) and cytotoxic CD4+CD28- cells by flow cytometry. The suPAR plasma level was measured by ELISA. The results indicate that AAV is associated with an increased suPAR plasma level and immune fingerprint characterized by an expansion of Th17 cells and T cells lacking the costimulatory molecule CD28, accompanied by a decrease of regulatory populations (Tregs and transitional B cells) and NK cells. Decreased numbers of regulatory T cells and transitional B cells were shown to be linked to activation of the AAV disease while the increased suPAR plasma level-to AAV-related deterioration of kidney function. The observed immune fingerprint might be a reflection of peripheral tolerance failure responsible for development and progression of ANCA-associated vasculitides.

Natural Killer Cells Regulate the Maturation of Liver Sinusoidal Endothelial Cells Thereby Promoting Intrahepatic T-Cell Responses in a Mouse Model

Functional maturation of liver sinusoidal endothelial cells (LSECs) plays an important role in intrahepatic T-cell activation and control of viral infections. Natural killer (NK) cells have been reported to prompt the maturation of antigen-presenting cells (APCs), especially for dendritic cells (DCs), but the interaction between NK cells and LSECs is elusive. Here, we investigated whether and how NK cells are involved in regulating LSEC maturation and if this has a role in controlling hepatitis B virus (HBV) infection in a mouse model. A chronic HBV replication mouse model was established by hydrodynamic injection (HI) of 6 µg adeno-associated virus plasmid (pAAV)/HBV 1.2. The nucleotide-binding oligomerization domain-containing protein 1 (NOD1) ligand diaminopemelic acid (DAP) was imported into liver by HI at day 14 after plasmid injection. We found that HI of DAP recruited conventional NK cells (cNK) into the liver and promoted tumor necrosis factor alpha (TNF-α) and interferon-gamma (IFN-γ) production of NK cells in a chemokine (C-X-C motif) receptor 3 (CXCR3)-dependent manner. Importantly, the maturation of LSECs and the anti-HBV effects of DAP were impaired in CXCR3^-/- mice; this possibly was associated with the decreased number of intrahepatic cNK cells. Consistently, depleting cNK cells but not liver-resident NK cells also impaired the maturation and antigen-presenting function of LSECs, which reduced intrahepatic HBV-specific T-cell responses and thus inhibited HBV clearance both in wild-type and in Rag1^-/- mice. Moreover, TNF-α or IFN-γ stimulation as well as coculture with intrahepatic NK cells partly promoted LSEC phenotypic and functional maturation in vitro. Conclusion: NOD1-triggered NK cell activation may lead to the enhancement of intrahepatic T-cell responses by promoting maturation of LSECs through soluble cytokines and cell-cell contact, thereby controlling HBV replication and expression.

IFNγ, and to a Lesser Extent TNFα, Provokes a Sustained Endothelial Costimulatory Phenotype

Background

Vascular endothelial cells (EC) are critical for regulation of local immune responses, through coordination of leukocyte recruitment from the blood and egress into the tissue. Growing evidence supports an additional role for endothelium in activation and costimulation of adaptive immune cells. However, this function remains somewhat controversial, and the full repertoire and durability of an enhanced endothelial costimulatory phenotype has not been wholly defined.

Methods

Human endothelium was stimulated with continuous TNFα or IFNγ for 1-48hr; or primed with TNFα or IFNγ for only 3hr, before withdrawal of stimulus for up to 45hr. Gene expression of cytokines, costimulatory molecules and antigen presentation molecules was measured by Nanostring, and publicly available datasets of EC stimulation with TNFα or IFNγ were leveraged to further corroborate the results. Cell surface protein expression was detected by flow cytometry, and secretion of cytokines was assessed by Luminex and ELISA. Key findings were confirmed in primary human endothelial cells from 4-6 different vascular beds.

Results

TNFα triggered mostly positive immune checkpoint molecule expression on endothelium, including CD40, 4-1BB, and ICOSLG but in the context of only HLA class I and immunoproteasome subunits. IFNγ promoted a more tolerogenic phenotype of high PD-L1 and PD-L2 expression with both HLA class I and class II molecules and antigen processing genes. Both cytokines elicited secretion of IL-15 and BAFF/BLyS, with TNFα stimulated EC additionally producing IL-6, TL1A and IL-1β. Moreover, endothelium primed for a short period (3hr) with TNFα mostly failed to alter the costimulatory phenotype 24-48hr later, with only somewhat augmented expression of HLA class I. In contrast, brief exposure to IFNγ was sufficient to cause late expression of antigen presentation, cytokines and costimulatory molecules. In particular HLA class I, PD-1 ligand and cytokine expression was markedly high on endothelium two days after IFNγ was last present.

Conclusions

Endothelia from multiple vascular beds possess a wide range of other immune checkpoint molecules and cytokines that can shape the adaptive immune response. Our results further demonstrate that IFNγ elicits prolonged signaling that persists days after initiation and is sufficient to trigger substantial gene expression changes and immune phenotype in vascular endothelium.

CD107a+ (LAMP-1) Cytotoxic CD8+ T-Cells in Lupus Nephritis Patients

Cytotoxic CD8+ T-cells play a pivotal role in the pathogenesis of systemic lupus erythematosus (SLE). The aim of this study was to investigate the role of CD107a (LAMP-1) on cytotoxic CD8+ T-cells in SLE-patients in particular with lupus nephritis. Peripheral blood of SLE-patients (n = 31) and healthy controls (n = 21) was analyzed for the expression of CD314 and CD107a by flow cytometry. Kidney biopsies of lupus nephritis patients were investigated for the presence of CD8+ and C107a+ cells by immunohistochemistry and immunofluorescence staining. The percentages of CD107a+ on CD8+ T-cells were significantly decreased in SLE-patients as compared to healthy controls (40.2 ± 18.5% vs. 47.9 ± 15.0%, p = 0.02). This was even more significant in SLE-patients with inactive disease. There was a significant correlation between the percentages of CD107a+CD8+ T-cells and SLEDAI. The evaluation of lupus nephritis biopsies showed a significant number of CD107a+CD8+ T-cells mainly located in the peritubular infiltrates. The intrarenal expression of CD107a+ was significantly correlated with proteinuria. These results demonstrate that CD8+ T-cells of patients with systemic lupus erythematosus have an altered expression of CD107a which seems to be associated with disease activity. The proof of intrarenal CD107a+CD8+ suggests a role in the pathogenesis of lupus nephritis.

Natural Killer Cells Exhibit a Peculiar Phenotypic Profile in Systemic Sclerosis and Are Potent Inducers of Endothelial Microparticles Release

The pathophysiology of systemic sclerosis (SSc) involves early endothelial and immune activation, both preceding the onset of fibrosis. We previously identified soluble fractalkine and circulating endothelial microparticles (EMPs) as biomarkers of endothelial inflammatory activation in SSc. Fractalkine plays a dual role as a membrane-bound adhesion molecule expressed in inflamed endothelial cells (ECs) and as a chemokine involved in the recruitment, transmigration, and cytotoxic activation of immune cells that express CX3CR1, the receptor of fractalkine, namely CD8 and γδ T cells and natural killer (NK) cells. We aimed to quantify circulating cytotoxic immune cells and their expression of CX3CR1. We further investigated the expression profile of NK cells chemokine receptors and activation markers and the potential of NK cells to induce EC activation in SSc. We performed a monocentric study (NCT 02636127) enrolling 15 SSc patients [15 females, median age of 55 years (39–63), 11 limited cutaneous form and 4 diffuse] and 15 healthy controls. Serum fractalkine levels were significantly increased in SSc patients. Circulating CD8 T cells numbers were decreased in SSc patients with no difference in their CX3CR1 expression. Circulating γδ T cells and NK cells numbers were preserved. CX3CR1 expression in CD8 and γδ T cells did not differ between SSc patients and controls. The percentage and level of CX3CR1 expression in NK cells were significantly lowered in SSc patients. Percentages of CXCR4, NKG2D, CD69-expressing NK cells, and their expression levels were decreased in NK cells. Conversely, CD16 level expression and percentages of CD16⁺ NK cells were preserved. The exposure of human microvascular dermic EC line (HMVEC-d) to peripheral blood mononuclear cells resulted in similar NK cells degranulation activity in SSc patients and controls. We further showed that NK cells purified from the blood of SSc patients induced enhanced release of EMPs than NK cells from controls. This study evidenced a peculiar NK cells phenotype in SSc characterized by decreased chemokine and activation receptors expression, that might reflect NK cells involvement in the pathogenic process. It also highlighted the role of NK cells as a potent mechanism inducing endothelial activation through enhanced EMPs release.

Clinical Significance of Neutrophil/lymphocyte Ratio in Patients With Granulomatosis With Polyangiitis

OBJECTIVE

To determine to neutrophil-to-lymphocyte ratio (NLR) in granulomatosis with polyangiitis (GPA) patients and to study its relation to disease manifestations and activity.

METHODS

The study included 44 GPA patients and 44 matched age and sex controls. Full history taking, thorough clinical examination with more attention to ocular examination, laboratory and radiological investigations were considered. Disease activity was assessed using the Birmingham Vasculitis Activity Score (BVAS).

RESULTS

The patients (21 males and 23 females) had a mean age of 45.66±7.24 years, disease duration 6.8±3.6 years and BVAS 50.1±14.3. All patients had a positive cytoplasmic anti-neutrophil cytoplasmic antibody (c-ANCA) while only 5 had a positive p-ANCA. The NLR was significantly increased in the GPA patients (5.1±2.4) compared to the control (1.5±0.8) (P<.0001). Ten patients with uveitis had a significantly higher NLR (6.5±1.9) compared to those without (4.7±2.4) (0.03) while those with proptosis (n=10), cutaneous manifestations (n=17) or ischemic heart disease (n=9) had a significantly lower NLR than those without (P=.0001, P=.017 and P=.046 respectively). The NLR did not significantly correlate with any of the patients' characteristics. The NLR inversely yet insignificantly correlated with the disease activity (r=-0.02, P=.93).

CONCLUSION

The NLR may have a significant role in the pathogenesis of GPA, the development of uveitis or proptosis, cutaneous manifestations and ischemic heart disease. NLR may serve as a future potential companion to c-ANCA positivity in diagnosing and evaluating GPA and may play a role in the tissue-specific and clinical characteristics.

Multicolor flow cytometric analysis of TLR2 and TLR9 expression and function in NK cells from patients with ANCA-associated vasculitis

BACKGROUND

The primary objective of this study was to provide an assessment of NK cells in patients with ANCA-associated vasculitis (AAV).

METHODS

Patients were classified based on the presence or absence of ANCAs and compared with healthy controls (HCs). By multiparameter flow cytometry, we evaluated the number and proportion of NK cells (CD3-CD56+) and the CD56^dim , CD56^bright , CD56^dim CD57^bright subsets; TLR2 and TLR9 expression; intracellular IFN-γ production upon stimulation with TLR2 and TLR9 ligands; degranulation activity; serum cytokines; immunohistochemical staining of available biopsies.

RESULTS

No differences in the number and proportion of NK cells between patients and HC were observed, except for a lower proportion of CD56^dim subset in ANCA-negative patients than in HC (P = 0.02). With respect to HC, TLR2 expression levels were reduced in NK cells from ANCA-negative patients (P = 0.03), in the CD56^dim subset of ANCA-positive (P = 0.02) and ANCA-negative patients (P = 0.01), in the CD56^bright subset of ANCA-positive patients (P = 0.007), and in the CD56^dim CD57^bright subset of ANCA-positive (P = 0.04) and ANCA-negative patients (P = 0.03). No differences between patients and HC were found concerning IFN-γ production and degranulation activity. IL-22 levels were lower in ANCA-positive patients than in HC (P = 0.01). The immunohistochemical analysis showed sporadic CD56+ cells in one renal biopsy, and a diffuse and moderate infiltrate of IL-22+ cells in all renal biopsies and in skin tissue.

CONCLUSIONS

Our data suggest a role of infectious stimuli triggering NK cells in AAV pathogenesis. Poor detection of NK cells in affected tissues suggests a marginal involvement in local inflammatory responses. © 2017 International Clinical Cytometry Society.

Active but not inactive granulomatosis with polyangiitis is associated with decreased and phenotypically and functionally altered CD56(dim) natural killer cells

Background

The role of natural killer (NK) cells in granulomatosis with polyangiitis (GPA) is poorly understood. We recently reported that peripheral blood NK cell percentages correlate with the suppression of GPA activity (cohort I). The purpose of the current study was to further characterize NK cell subsets, phenotype and function in a second GPA cohort (cohort II).

Methods

Peripheral blood lymphocyte subsets were analyzed at a clinical diagnostic laboratory. Clinical data were extracted from medical records and patients were grouped according to their activity state (remission vs. active/non-remission). Separate analysis (cohort II, n = 22) and combined analysis (cohorts I and II, n = 34/57) of NK cell counts/percentages was performed. NK cell subsets and phenotypes were analyzed by multicolor flow cytometry. Cytotoxicity assays were performed using ⁵¹Cr-labeled K562 target cells.

Results

In cohort II, NK cell counts were lower than the lower limit of normal in active GPA, despite normal percentages due to lymphopenia. NK cell counts, but not other lymphocyte counts, were significantly higher in remission. Combined analysis of cohorts I and II confirmed decreased NK cell counts in active GPA and increased percentages in long-term remission. Follow-up measurements of six patients revealed increasing NK cell percentages during successful induction therapy. Multicolor analysis from cohort II revealed that in active GPA, the CD56^dim subset was responsible for decreased NK cell counts, expressed more frequently CD69, downregulated the Fc-receptor CD16 and upregulated the adhesion molecule CD54, the chemokine receptor CCR5 and the activating receptor NKG2C. In remission, these markers were unaltered or marginally altered. All other receptors investigated (NKp30, NKp44, NKp46, NKG2D, DNAM1, 2B4, CRACC, 41BB) remained unchanged. Natural cytotoxicity was not detectable in most patients with active GPA, but was restored in remission.

Conclusions

NK cell numbers correlate inversely with GPA activity. Reduced CD56^dim NK cells in active GPA have an activated phenotype, which intriguingly is associated with profound deficiency in cytotoxicity. These data suggest a function for NK cells in the pathogenesis and/or modulation of inflammation in GPA. NK cell numbers, phenotype (CD16, CD69, NKG2C) or overall natural cytotoxicity are promising candidates to serve as clinical biomarkers to determine GPA activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1098-7) contains supplementary material, which is available to authorized users.

Concise review: tissue-specific microvascular endothelial cells derived from human pluripotent stem cells

Accumulating evidence suggests that endothelial cells (ECs) display significant heterogeneity across tissue types, playing an important role in tissue regeneration and homeostasis. Recent work demonstrating the derivation of tissue-specific microvascular endothelial cells (TS-MVECs) from human pluripotent stem cells (hPSCs) has ignited the potential to generate tissue-specific models which may be applied to regenerative medicine and in vitro modeling applications. Here, we review techniques by which hPSC-derived TS-MVECs have been made to date and discuss how current hPSC-EC differentiation protocols may be directed toward tissue-specific fates. We begin by discussing the nature of EC tissue specificity in vivo and review general hPSC-EC differentiation protocols generated over the last decade. Finally, we describe how specificity can be integrated into hPSC-EC protocols to generate hPSC-derived TS-MVECs in vitro, including EC and parenchymal cell coculture, directed differentiation, and direct reprogramming strategies.

Peripheral blood natural killer cell percentages in granulomatosis with polyangiitis correlate with disease inactivity and stage

Introduction

The role of CD3−CD56+ natural killer (NK) cells in granulomatosis with polyangiitis (GPA) is poorly understood. Recently, it has been shown that peripheral blood NK cells can kill renal microvascular endothelial cells, suggesting a pathogenic role of NK cells in this disease. So far, subset distribution, phenotype, and function of peripheral blood NK cells in relation to GPA disease activity have not been elucidated. Moreover, it is not known whether NK cells infiltrate GPA tissue lesions.

Methods

Paraffin sections of GPA granulomas and controls were stained with anti-CD56 and anti-CD3 antibodies. Peripheral blood lymphocyte subsets were analyzed by flow cytometry. NK cell degranulation was analyzed using cocultures of patient PBMCs with target cells and surface expression of CD107a. Clinical data were extracted from medical records. Statistical analysis was performed in an exploratory way.

Results

CD56+ cells were not detectable in active granulomatous GPA lesions but were found frequently in granulomas from tuberculosis and sarcoidosis patients. In GPA, the proportion of NK cells among peripheral blood lymphocytes correlated negatively with the Birmingham Vasculitis Activity Score (BVAS) (n = 28). Accordingly, NK cell percentages correlated positively with the duration of remission (n = 28) and were significantly higher in inactive GPA (BVAS = 0, n = 17) than in active GPA, healthy controls (n = 29), and inactive control diseases (n = 12). The highest NK cell percentages were found in patients with long-term remission and tapered immunosuppressive therapy. NK cell percentages >18.5 % of peripheral blood lymphocytes (n = 12/28) determined GPA inactivity with a specificity of 100 %. The differentiation into CD56^dim and CD56^bright NK cell subsets was unchanged in GPA (n = 28), irrespective of disease activity. Similar surface expression of the activating NK cell-receptors (NKp30, NKp46, and NKG2D) was determined. Like in healthy controls, GPA NK cells degranulated in the presence of NK cell receptor ligand bearing epithelial and lymphatic target cells.

Conclusions

NK cells were not detectable in GPA granulomas. Peripheral blood NK cell percentages positively correlate with the suppression of GPA activity and could serve as a biomarker for GPA activity. Peripheral blood NK cells in GPA patients are mature NK cells with preserved immune recognition.

Innate immune cells in the pathogenesis of primary systemic vasculitis

Innate immune system forms the first line of defense against foreign substances. Neutrophils, eosinophils, erythrocytes, platelets, monocytes, macrophages, dendritic cells, γδ T cells, natural killer and natural killer T cells comprise the innate immune system. Genetic polymorphisms influencing the activation of innate immune cells predispose to development of vasculitis and influence its severity. Abnormally activated innate immune cells cross-talk with other cells of the innate immune system, present antigens more efficiently and activate T and B lymphocytes and cause tissue destruction via cell-mediated cytotoxicity and release of pro-inflammatory cytokines. These secreted cytokines further recruit other cells to the sites of vascular injury. They are involved in both the initiation as well as the perpetuation of vasculitis. Evidences suggest reversal of aberrant activation of immune cells in response to therapy. Understanding the role of innate immune cells in vasculitis helps understand the potential of therapeutic modulation of their activation to treat vasculitis.

Homing receptor expression is deviated on CD56+ blood lymphocytes during pregnancy in Type 1 diabetic women

Type 1 Diabetes Mellitus (T1DM) is characterized by an augmented pro-inflammatory immune state. This contributes to the increased risk for gestational complications observed in T1DM mothers. In normal pregnancies, critical immunological changes occur, including the massive recruitment of lymphocytes, particularly CD56^bright NK cells, into early decidua basalis and a 2^nd trimester shift towards Type 2 immunity. Decidual CD56^bright NK cells arise at least partly from circulating progenitors expressing adhesion molecules SELL and ITGA4 and the chemokine receptors CXCR3 and CXCR4. In vitro studies show that T1DM reduces interactions between blood CD56⁺ NK cells and decidual endothelial cells by reducing SELL and ITGA4-based interactions. To address the mechanisms by which specific lymphocyte subsets may be recruited from the circulation during pregnancy and whether these mechanisms are altered in T1DM, flow cytometry was used to examine eight peripheral blood lymphocyte subsets (Type 1 (IL18R1⁺) and Type 2 (IL1RL1⁺) CD56^bright NK, CD56^dim NK, NKT and T cells) from control and T1DM women. Blood was collected serially over pregnancy and postpartum, and lymphocytes were compared for expression of homing receptors SELL, ITGA4, CXCR3, and CXCR4. The decline of Type 1/Type 2 immune cells in normal pregnancy was driven by an increase in Type 2 cells that did not occur in T1DM. CD56^bright NK cells from control women had the highest expression of all four receptors with greatest expression in 2^nd trimester. At this time, these receptors were expressed at very low levels by CD56^bright NK cells from TIDM patients. Type 1/Type 2 NKT cell ratios were not influenced by either pregnancy or TIDM. Our results suggest that T1DM alters immunological balances during pregnancy with its greatest impact on CD56^bright NK cells. This implicates CD56^bright NK cells in diabetic pregnancy complications.