The molecular and epigenetic mechanisms of innate lymphoid cell (ILC) memory and its relevance for asthma

Repetitive exposure of Rag1^−/− mice to the Alternaria allergen extract generated a form of memory that elicited an asthma-like response upon a subthreshold recall challenge 3–15 wk later. This memory was associated with lung ICOS⁺ST2⁺ ILC2s. Genetic, pharmacologic, and antibody-mediated inhibition and adoptive transfer established an essential role for ILC2s in memory-driven asthma. ATAC-seq demonstrated a distinct epigenetic landscape of memory ILC2s and identified Bach2 and AP1 (JunD and Fosl2) motifs as major drivers of altered gene accessibility. scRNA-seq, gene knockout, and signaling studies suggest that repetitive allergenic stress induces a gene repression program involving Nr4a2, Zeb1, Bach2, and JunD and a preparedness program involving Fhl2, FosB, Stat6, Srebf2, and MPP7 in memory ILC2s. A mutually regulated balance between these two programs establishes and maintains memory. The preparedness program (e.g., Fhl2) can be activated with a subthreshold cognate stimulation, which down-regulates repressors and activates effector pathways to elicit the memory-driven phenotype.

Sprouty2 positively regulates T cell function and airway inflammation through regulation of CSK and LCK kinases

The function of Sprouty2 (Spry2) in T cells is unknown. Using 2 different (inducible and T cell-targeted) knockout mouse strains, we found that Spry2 positively regulated extracellular signal-regulated kinase 1/2 (ERK1/2) signaling by modulating the activity of LCK. Spry2-/- CD4+ T cells were unable to activate LCK, proliferate, differentiate into T helper cells, or produce cytokines. Spry2 deficiency abrogated type 2 inflammation and airway hyperreactivity in a murine model of asthma. Spry2 expression was higher in blood and airway CD4+ T cells from patients with asthma, and Spry2 knockdown impaired human T cell proliferation and cytokine production. Spry2 deficiency up-regulated the lipid raft protein caveolin-1, enhanced its interaction with CSK, and increased CSK interaction with LCK, culminating in augmented inhibitory phosphorylation of LCK. Knockdown of CSK or dislodgment of caveolin-1-bound CSK restored ERK1/2 activation in Spry2-/- T cells, suggesting an essential role for Spry2 in LCK activation and T cell function.

Optimal identification of human conventional and nonconventional (CRTH2-IL7Rα-) ILC2s using additional surface markers

BACKGROUND

Human type 2 innate lymphoid cells (ILC2s) are identified by coupled detection of CRTH2 and IL7Rα on lineage negative (Lin^-) cells. Type 2 cytokine production by CRTH2^-IL7Rα^- innate lymphoid cells (ILCs) is unknown.

OBJECTIVE

We sought to identify CRTH2^-IL7Rα^- type 2 cytokine-producing ILCs and their disease relevance.

METHODS

We studied human blood and lung ILCs from asthmatic and control subjects by flow cytometry, ELISA, RNA sequencing, quantitative PCR, adoptive transfer to mice, and measurement of airway hyperreactivity by Flexivent.

RESULTS

We found that IL-5 and IL-13 were expressed not only by CRTH2⁺ but also by CRTH2^-IL7Rα⁺ and CRTH2^-IL7Rα^- (double-negative [DN]) human blood and lung cells. All 3 ILC populations expressed type 2 genes and induced airway hyperreactivity when adoptively transferred to mice. The frequency of type 2 cytokine-positive IL7Rα and DN ILCs were similar to that of CRTH2 ILCs in the blood and lung. Their frequency was higher in asthmatic patients than in disease controls. Transcriptomic analysis of CRTH2, IL7Rα, and DN ILCs confirmed the expression of mRNA for type 2 transcription factors in all 3 populations. Unexpectedly, the mRNA for GATA3 and IL-5 correlated better with mRNA for CD30, TNFR2, ICOS, CCR4, and CD200R1 than for CRTH2. By using a combination of these surface markers, especially CD30/TNFR2, we identified a previously unrecognized ILC2 population.

CONCLUSIONS

The commonly used surface markers for human ILC2s leave a majority of type 2 cytokine-producing ILC2s unaccounted for. We identified top GATA3-correlated cell surface-expressed genes in human ILCs by RNA sequencing. These new surface markers, such as CD30 and TNFR2, identified a previously unrecognized human ILC2 population. This ILC2 population is likely to contribute to asthma.

Experimental asthma persists in IL-33 receptor knockout mice because of the emergence of thymic stromal lymphopoietin-driven IL-9+ and IL-13+ type 2 innate lymphoid cell subpopulations

BACKGROUND

IL-33 plays an important role in the development of experimental asthma.

OBJECTIVE

We sought to study the role of the IL-33 receptor suppressor of tumorigenicity 2 (ST2) in the persistence of asthma in a mouse model.

METHODS

We studied allergen-induced experimental asthma in ST2 knockout (KO) and wild-type control mice. We measured airway hyperresponsiveness by using flexiVent; inflammatory indices by using ELISA, histology, and real-time PCR; and type 2 innate lymphoid cells (ILC2s) in lung single-cell preparations by using flow cytometry.

RESULTS

Airway hyperresponsiveness was increased in allergen-treated ST2 KO mice and comparable with that in allergen-treated wild-type control mice. Peribronchial and perivascular inflammation and mucus production were largely similar in both groups. Persistence of experimental asthma in ST2 KO mice was associated with an increase in levels of thymic stromal lymphopoietin (TSLP), IL-9, and IL-13, but not IL-5, in bronchoalveolar lavage fluid. Expectedly, ST2 deletion caused a reduction in IL-13⁺ CD4 T cells, forkhead box P3-positive regulatory T cells, and IL-5⁺ ILC2s. Unexpectedly, ST2 deletion led to an overall increase in innate lymphoid cells (CD45⁺lin^-CD25⁺ cells) and IL-13⁺ ILC2s, emergence of a TSLP receptor-positive IL-9⁺ ILC2 population, and an increase in intraepithelial mast cell numbers in the lung. An anti-TSLP antibody abrogated airway hyperresponsiveness, inflammation, and mucus production in allergen-treated ST2 KO mice. It also caused a reduction in innate lymphoid cell, ILC2, and IL-9⁺ and IL-13⁺ ILC2 numbers in the lung.

CONCLUSIONS

Genetic deletion of the IL-33 receptor paradoxically increases TSLP production, which stimulates the emergence of IL-9⁺ and IL-13⁺ ILC2s and mast cells and leads to development of chronic experimental asthma. An anti-TSLP antibody abrogates all pathologic features of asthma in this model.

Steroid resistance of airway type 2 innate lymphoid cells from patients with severe asthma: The role of thymic stromal lymphopoietin

BACKGROUND

Type 2 innate lymphoid cells (ILC2s) represent an important type 2 immune cell. Glucocorticoid regulation of human ILC2s is largely unknown.

OBJECTIVE

We sought to assess steroid resistance of human blood and airway ILC2s from asthmatic patients and to examine its mechanism of induction.

METHODS

We studied human blood and lung ILC2s from asthmatic patients and control subjects using flow cytometry and ELISA.

RESULTS

Dexamethasone inhibited (P = .04) chemoattractant receptor-homologous molecule expressed on T_H2 lymphocytes and type 2 cytokine expression by blood ILC2s stimulated with IL-25 and IL-33. However, it did not do so when ILC2s were stimulated with IL-7 and thymic stromal lymphopoietin (TSLP), 2 ligands of IL-7 receptor α. Unlike blood ILC2s, bronchoalveolar lavage (BAL) fluid ILC2s from asthmatic patients were resistant to dexamethasone. BAL fluid from asthmatic patients had increased TSLP but not IL-7 levels. BAL fluid TSLP levels correlated (r = 0.74) with steroid resistance of ILC2s. TSLP was synergistically induced in epithelial cells by IL-13 and human rhinovirus. Mechanistically, dexamethasone upregulated ILC2 expression of IL-7 receptor α, which augmented and sustained signal transducer and activator of transcription (STAT) 5 signaling by TSLP. TSLP induced mitogen-activated protein kinase kinase (MEK), c-Fos, inhibitor of DNA binding 3, phosphorylated signal transducer and activator of transcription (pSTAT) 3, and pSTAT5, molecules linked to steroid resistance. Dexamethasone inhibited c-Fos, inhibitor of DNA binding 3, and pSTAT3 but not pSTAT5 and MEK. The MEK inhibitor trametinib, the Janus kinase-STAT inhibitor tofacitinib, and the STAT5 inhibitor pimozide reversed steroid resistance of BAL ILC2s.

CONCLUSIONS

Dexamethasone inhibited type 2 cytokine production by blood ILC2s. IL-7 and TSLP abrogated this inhibition and induced steroid resistance of ILC2s in a MEK- and STAT5-dependent manner. BAL fluid ILC2s from asthmatic patients with increased TSLP levels were steroid resistant, which was reversed by clinically available inhibitors of MEK and STAT5.

The role of low-level lactate production in airway inflammation in asthma

Warburg and coworkers (Warburg O, Posener K, Negelein E. Z Biochem 152: 319, 1924) first reported that cancerous cells switch glucose metabolism from oxidative phosphorylation to aerobic glycolysis, and that this switch is important for their proliferation. Nothing is known about aerobic glycolysis in T cells from asthma. The objective was to study aerobic glycolysis in human asthma and the role of this metabolic pathway in airway hyperreactivity and inflammation in a mouse model of asthma. Human peripheral blood and mouse spleen CD4 T cells were isolated by negative selection. T cell proliferation was measured by thymidine incorporation. Cytokines and serum lactate were measured by ELISA. Mouse airway hyperreactivity to inhaled methacholine was measured by a FlexiVent apparatus. The serum lactate concentration was significantly elevated in clinically stable asthmatic subjects compared with healthy and chronic obstructive pulmonary disease controls, and negatively correlated with forced expiratory volume in 1 s. Proliferating CD4 T cells from human asthma and a mouse model of asthma produced higher amounts of lactate upon stimulation, suggesting a heightened glycolytic activity. Lactate stimulated and inhibited T cell proliferation at low and high concentrations, respectively. Dichloroacetate (DCA), an inhibitor of aerobic glycolysis, inhibited lactate production, proliferation of T cells, and production of IL-5, IL-17, and IFN-γ, but it stimulated production of IL-10 and induction of Foxp3. DCA also inhibited airway inflammation and hyperreactivity in a mouse model of asthma. We conclude that aerobic glycolysis is increased in asthma, which promotes T cell activation. Inhibition of aerobic glycolysis blocks T cell activation and development of asthma.

Ero1alpha is expressed on blood platelets in association with protein-disulfide isomerase and contributes to redox-controlled remodeling of alphaIIbbeta3

Recent evidence supports a role of protein-disulfide isomerase (PDI) in redox-controlled remodeling of the exofacial domains of α(IIb)β(3) in blood platelets. The aim of this study was to explain whether Ero1α can be responsible for extracellular reoxidation of the PDI active site. We showed that Ero1α can be found on platelets and is rapidly recruited to the cell surface in response to platelet agonists. It is physically associated with PDI and α(IIb)β(3), as suggested by colocalization analysis in confocal microscopy and confirmed by immunoprecipitation experiments. Apart from monomeric oxidized Ero1α, anti-α(IIb)β(3) immunoprecipitates showed the presence of several Ero1α-positive bands that corresponded to the complexes α(IIb)β(3)-PDI-Ero1α, PDI-Ero1α, and Ero1α-Ero1α dimers. It binds more efficiently to the activated α(IIb)β(3) conformer, and its interaction is inhibited by RGD peptides. Ero1α appears to be involved in the regulation of α(IIb)β(3) receptor activity because of the following: (a) blocking the cell surface Ero1α by antibodies leads to a decrease in platelet aggregation in response to agonists and a decrease in fibrinogen and PAC-1 binding, and (b) transfection of MEG01 with Ero1α increases α(IIb)β(3) receptor activity, as indicated by increased binding of fibrinogen.

The Specificity and Function of the Metal-binding Sites in the Integrin β3 A-domain

The A-domains within integrin beta subunits contain three metal sites termed the metal ion-dependent adhesion site (MIDAS), site adjacent to the metal ion-dependent adhesion site (ADMIDAS), and ligand-induced metal-binding site (LIMBS), and these sites are involved in ligand engagement. The selectivity of these metal sites and their role in ligand binding have been investigated by expressing a fragment corresponding to the beta3 A-domain, beta3-(109-352), and single point mutants in which each of the cation-binding sites has been disabled. Equilibrium dialysis experiments identified three Mn2+- and two Ca2+-binding sites with the LIMBS being the site that did not bind Ca2+. Although the ADMIDAS could bind Ca2+, it did not bind Mg2+. These results indicate that the Ca2+-specific site that inhibits ligand binding is the ADMIDAS. Two different assay systems, surface plasmon resonance and a microtiter plate assay, demonstrated that the beta3 A-domain fragment bound fibrinogen in the presence of 0.1 mm Ca2+ but not in 3 mm Ca2+. This behavior recapitulated the effects of Ca2+ on fibrinogen binding to alphavbeta3 but not alphaIIbbeta3. Disabling any of the three cation-binding sites abrogated fibrinogen binding. These results indicate that the specificities of the three metal-binding sites for divalent cations are distinct and that each site can regulate the ligand binding potential of the beta3 A-domain.

Identification and characterization of two cation binding sites in the integrin beta 3 subunit

The midsegment of the beta(3) subunit has been implicated in the ligand and cation binding functions of the beta(3) integrins. This region may contain a metal ion-dependent adhesion site (MIDAS) and fold into an I domain-like structure. Two recombinant fragments, beta(3)-(95-373) and beta(3)-(95-301), were expressed and found to bind fibrinogen. Whereas 0.1 mm Ca(2+) supported ligand binding to both recombinant fragments, 1.0 mm Ca(2+) suppressed binding to the longer but not the shorter fragment. These properties suggest that beta(3)-(95-373) contains both the ligand-competent (LC) and inhibitory (I) cation binding sites, and beta(3)-(95-301) lacks the I site. In equilibrium dialysis experiments, beta(3)-(95-373) contained two divalent cation binding sites, one reactive with either Mg(2+) or Ca(2+) and one Ca(2+)-specific, whereas beta(3)-(95-301) lacked the Ca(2+)-specific site. Mutant forms of beta(3)-(95-373) suggested that the LC site is a MIDAS motif involving Asp(119), Ser(121), Ser(123), Asp(217), and/or Glu(220) as coordination sites, and the I site was dependent upon residues within beta(3)-(301-323). In a molecular model of beta(3)-(95-373), a second Ca(2+) could be docked onto a flexible loop in close proximity to the MIDAS. These results indicate that the ligand competent and Ca(2+)-specific inhibitory cation binding sites are distinct and reside in beta(3)-(95-373).

CCL7 and CXCL10 orchestrate oxidative stress-induced neutrophilic lung inflammation

Oxidative stress from ozone (O(3)) exposure augments airway neutrophil recruitment and chemokine production. We and others have shown that severe and sudden asthma is associated with airway neutrophilia, and that O(3) oxidative stress is likely to augment neutrophilic airway inflammation in severe asthma. However, very little is known about chemokines that orchestrate oxidative stress-induced neutrophilic airway inflammation in vivo. To identify these chemokines, three groups of BALB/c mice were exposed to sham air, 0.2 ppm O(3), or 0.8 ppm O(3) for 6 h. Compared with sham air, 0.8 ppm O(3), but not 0.2 ppm O(3), induced pronounced neutrophilic airway inflammation that peaked at 18 h postexposure. The 0.8 ppm O(3) up-regulated lung mRNA of CXCL1,2,3 (mouse growth-related oncogene-alpha and macrophage-inflammatory protein-2), CXCL10 (IFN-gamma-inducible protein-10), CCL3 (macrophage-inflammatory protein-1alpha), CCL7 (monocyte chemoattractant protein-3), and CCL11 (eotaxin) at 0 h postexposure, and expression of CXCL10, CCL3, and CCL7 mRNA was sustained 18 h postexposure. O(3) increased lung protein levels of CXCL10, CCL7, and CCR3 (CCL7R). The airway epithelium was identified as a source of CCL7. The role of up-regulated chemokines was determined by administering control IgG or IgG Abs against six murine chemokines before O(3) exposure. As expected, anti-mouse growth-related oncogene-alpha inhibited neutrophil recruitment. Surprisingly, Abs to CCL7 and CXCL10 also decreased neutrophil recruitment by 63 and 72%, respectively. These findings indicate that CCL7 and CXCL10, two chemokines not previously reported to orchestrate neutrophilic inflammation, play a critical role in mediating oxidative stress-induced neutrophilic airway inflammation. These observations may have relevance in induction of neutrophilia in severe asthma.

Comparison of platelet aggregability and P-selectin surface expression on platelets isolated by different methods

Three methods commonly used for isolation of blood platelets from plasma were compared. Platelets were isolated by: 1) a washing method; 2) a method of metrizamide-gradient centrifugation; 3) a modified method of gel-filtration. The last method employed BSA-Sepharose gel instead of routinely used Sepharose gel saturated with BSA. BSA-Sepharose gel was prepared by covalent binding of thermally deactivated BSA to CNBr-activated Sepharose 2B. In contrast to platelets isolated by the other methods, an aggregability of the gel-filtered platelets and control platelets in plasma, both activated with ADP, were comparable. When expression of P-selectin on the surface of freshly isolated platelets was examined, the gel-filtered platelets exhibited the same extent of fluorescence signal as platelets in the citrated blood, whereas platelets isolated by the other methods exhibited twice the extent of the signal. The methods involving the centrifugation process cause a low but a significant platelet activation.

Microplate reader--a convenient tool in studies of blood coagulation

Results of platelet aggregation measured with a dual channel aggregometer and with a microplate reader are compared. Platelets in plasma were activated by ADP and by collagen, and thrombin was used for the aggregation study of gel filtered platelets. The results obtained with both instruments were quantitatively and qualitatively similar. A microplate reader allowed a simultaneous measurement of a high number of samples with a high degree of reproducibility. The same instrument can be useful in other coagulology studies. Results of citrated plasma clotting by thrombin or by recalcination together with results of platelet counting, both obtained with a microplate reader, are presented in this report as well.

Platelet membrane fluidity and intraplatelet Ca2+ mobilization are affected in uraemia

In present investigations, platelet membrane fluidity and intraplatelet Ca2+ mobilization were analysed in uraemic platelets by fluorescence techniques. Thirteen non-dialyzed uraemic patients and 16 control subjects were examined. Anisotropy of DPH-probe, measured at 37 degrees C, was significantly higher in control (0.2236 +/- 0.0050) than in uraemic platelets (0.1969 +/- 0.0082; p < 0.01). There was no difference between control (109.8 +/- 6.0 nM) and uraemic platelets (100.0 +/- 7.3 nM) when the basal [Ca2+]i in resting platelets was determined. Activation of platelets by ADP (12.5 microM) or by thrombin (0.1 U/ml) resulted in an increase in [Ca2+]i. It was significantly higher (p* < 0.003 for ADP and p* < 0.009 for thrombin, respectively) in control platelets (383.6 +/- 56.3 nM and 2031.0 +/- 298.8 nM, respectively) than in uraemic ones (191.0 +/- 21.3 nM and 838.7 +/- 144.1 nM, respectively). The amount of released Ca2+ was higher in control platelets activated by both ADP and thrombin (157.6 +/- 21.4 nM and 409.3 +/- 71.0 nM, respectively) than in uraemic platelets (76.7 +/- 15.7 nM and 203.0 +/- 29.3 nM, respectively) and the differences were significant (p < 0.01 and p* < 0.01, respectively). These results indicate an abnormal intracellular Ca2+ mobilization in uraemic platelets. Both increased membrane fluidity and decreased Ca2+ mobilization should be considered as a possible reason of reduced fibrinogen receptor exposure on uraemic platelets.

Changes in platelet response to adenosine 5'-diphosphate caused by verapamil

Verapamil is widely used in the treatment of patients with coronary artery disease. The effect of verapamil on vascular smooth muscle cells is well documented. This effect is mediated by the inhibition of calcium fluxes across plasma membranes. Some data suggest that verapamil may affect platelet functions in thrombosis, but those observations were made for much higher verapamil concentration than could be achieved in vivo. Our current investigations are focused on an influence of low doses of verapamil (0.1-1.0 microM) on platelet response to ADP. We have found that verapamil at concentration of 0.1 microM can inhibit platelet aggregation (by 10%) evoked in PRP by 1.0-1.5 microM ADP. Moreover, the inhibitory effect is potentiated by prolonged time of platelet preincubation with verapamil. On the other hand, we have found a significant reduction in the number of fibrinogen receptors exposed on the platelet surface of patients (n = 21) treated with therapeutic doses (240 mg/day) of verapamil during two weeks of drug administration. The mean number of exposed receptors was reduced from 75,000 to 40,000 per platelet, with significance p < 0.0001. In vitro platelet preincubation with verapamil, even in much higher concentrations, did not affect fibrinogen binding to ADP activated platelets. It suggests, that in vitro exposure of platelets to verapamil for a short time has no effect on the expression of fibrinogen receptors on platelets, but prolonged in vivo interaction of this drug with platelets results in reduction of the fibrinogen receptor exposition. Thus, observed inhibition of platelet aggregation does not relay on a simple reduction of the number of exposed receptors, but intraplatelet signalling has to be affected. In fact, we have observed, in platelets pretreated with low doses of verapamil, significantly reduced release of calcium ions upon activation by ADP, whereas the calcium influx under such conditions does not seem to be affected.

Platelet membrane fluidity and intraplatelet Ca2+ homeostasis are affected in uremia

Recently we have described a dependence of platelet disability in thrombosis upon the progression in renal failure and an elevated level of RGDS-containing degradation products in uremic plasma, which is also correlated with progression in renal failure. Based on fluorescence techniques, our present investigations concerned possible changes in platelet membrane fluidity and intraplatelet calcium homeostasis in uremic platelets. Washed platelets loaded with DPH or with Fura-2 were examined with LS-50 luminescence spectrometer. Light anisotropy of DPH measured at 37 degrees C was significantly higher in control platelet membranes than in uremic ones. It can be considered as more fluidic membranes of uremic platelets. No difference between the basal intraplatelet calcium level was found for uremic and control platelets, but in the presence of 5 mM EGTA, the basal level was reduced significantly deeper in uremic platelets. Activation of platelets by both ADP (12.5 microM) and thrombin (0.1 U/ml) resulted in rapid increase in the intraplatelet calcium level in the examined platelets, but this increase was significantly higher for control platelets. The results indicate an abnormal intracellular calcium homeostasis in uremic platelets, which is associated with an increased fluidity of platelet membranes in uremia.