Expression of FasL and Fas protein and their soluble form in patients with hypersensitivity pneumonitis

sFasL-The Key to a Riddle: Immune Responses in Aging Lung and Disease

By dint of the aging population and further deepened with the Covid-19 pandemic, lung disease has turned out to be a major cause of worldwide morbidity and mortality. The condition is exacerbated when the immune system further attacks the healthy, rather than the diseased, tissue within the lung. Governed by unremittingly proliferating mesenchymal cells and increased collagen deposition, if inflammation persists, as frequently occurs in aging lungs, the tissue develops tumors and/or turns into scars (fibrosis), with limited regenerative capacity and organ failure. Fas ligand (FasL, a ligand of the Fas cell death receptor) is a key factor in the regulation of these processes. FasL is primarily found in two forms: full length (membrane, or mFasL) and cleaved (soluble, or sFasL). We and others found that T-cells expressing the mFasL retain autoimmune surveillance that controls mesenchymal, as well as tumor cell accumulation following an inflammatory response. However, mesenchymal cells from fibrotic lungs, tumor cells, or cells from immune-privileged sites, resist FasL⁺ T-cell-induced cell death. The mechanisms involved are a counterattack of immune cells by FasL, by releasing a soluble form of FasL that competes with the membrane version, and inhibits their cell death, promoting cell survival. This review focuses on understanding the previously unrecognized role of FasL, and in particular its soluble form, sFasL, in the serum of aged subjects, and its association with the evolution of lung disease, paving the way to new methods of diagnosis and treatment.

Decreased expression of transmembrane TNFR2 in lung leukocytes subpopulations of patients with non-fibrotic hypersensitivity pneumonitis compared with the fibrotic disease

Hypersensitivity pneumonitis (HP) is an interstitial lung disease, characterized by lung inflammation (non-fibrotic HP) that may often progresses to fibrosis (Fibrotic HP). The tumor necrosis factor (TNF) and its receptors (TNFR1 and TNFR2) can be found as soluble (sol) and transmembrane (tm) forms, playing pro-inflammatory functions but also has been related to immune regulatory functions. Bronchioalveolar lavage from fibrotic and non-fibrotic HP patients was obtained, and immune cells were characterized by flow cytometry, whereas soluble proteins were analyzed by ELISA. Compare to fibrotic HP patients, HP patients with non-fibrotic disease have accumulation of pro-inflammatory CD3+ myeloid cells, cell subpopulations that have decreased tmTNFR2 expression, and low frequency of regulatory-T cells. Whereas solTNF, solTNFR2, and IL-8 are increased. These findings suggest that the TNF pathway may explain, at least partially, the differences between both HP clinical forms. The evaluation of the TNF family molecules may help to develop new therapeutic approaches.

Tumor necrosis factor-alpha and Fas/Fas ligand signaling pathways in chronic spontaneous urticaria

Background

There is increasing evidence pointing to the important role of tumor necrosis factor-alpha (TNF-α), a key inflammatory and apoptotic mediator in urticarial inflammation. However, the role of the TNF-α system and Fas/Fas ligand (FasL) in the apoptosis-inducing pathways in chronic spontaneous urticaria (CSU), remain unclear.

Aim

To determine circulating concentrations of TNF-α, soluble TNF-α receptor type 1 and type 2 (sTNF-R1 and sTNF-R2, respectively) as well as soluble Fas (sFas) and FasL (sFasL) in CSU subjects.

Methods

Serum TNF-α, sTNF-R1, sTNF-R2, sFas, sFasL concentrations were measured using enzyme-linked immunosorbent assay in CSU subjects and in the healthy subjects.

Results

TNF-α concentrations were significantly higher in CSU subjects and moderate-to-severe CSU than in the controls, while there were no significant differences in TNF-α concentrations between subjects with mild CSU and the controls. sTNF-R1 and sTNF-R2 concentrations were significantly higher in all CSU and moderate-severe CSU subjects vs. the controls. Serum concentrations were also significantly higher in mild CSU vs. the controls, but not in moderate-severe CSU vs. mild CSU. No significant differences were observed in sFas and sFasL concentrations between CSU subjects and the healthy controls. Significant correlations were found between concentrations of TNF-α and its receptors, as well as sTNF-R1 and sTNF-R2, but not with the urticaria activity score (UAS). There was no relationship between TNF-α/sTNF-R1/sTNF-R2 and sFas/sFasL pathways in CSU.

Conclusions

CSU is associated with the activation of the TNF-α/receptors signaling pathway, marked by increased circulating concentrations of TNF-α, sTNF-R1 and sTNF-R2, which are related to each other in this disease. In contrast, the circulating sFas/FasL system is not up-regulated in CSU, and sFas/sFasL may not be a useful marker of the activity/severity of urticarial processes. Considering the lack of significant changes in sFas/sFasL (mainly reflecting systemic apoptosis) in CSU patients, it appears that elevated serum TNF-α concentrations are related to its pro-inflammatory function rather than an enhanced systemic apoptotic response in CSU.

MMP-7 is a predictive biomarker of disease progression in patients with idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease with poor prognosis, which is characterised by destruction of normal lung architecture and excessive deposition of lung extracellular matrix. The heterogeneity of disease progression in patients with IPF poses significant obstacles to patient care and prevents efficient development of novel therapeutic interventions. Blood biomarkers, reflecting pathobiological processes in the lung, could provide objective evidence of the underlying disease. Longitudinally collected serum samples from the Bosentan Use in Interstitial Lung Disease (BUILD)-3 trial were used to measure four biomarkers (metalloproteinase-7 (MMP-7), Fas death receptor ligand, osteopontin and procollagen type I C-peptide), to assess their potential prognostic capabilities and to follow changes during disease progression in patients with IPF. In baseline BUILD-3 samples, only MMP-7 showed clearly elevated protein levels compared with samples from healthy controls, and further investigations demonstrated that MMP-7 levels also increased over time. Baseline levels of MMP-7 were able to predict patients who had higher risk of worsening and, notably, baseline levels of MMP-7 could predict changes in FVC as early as month 4. MMP-7 shows potential to be a reliable predictor of lung function decline and disease progression.

Fas-mediated acute lung injury requires fas expression on nonmyeloid cells of the lung

Fas (CD95) is a membrane surface receptor, which, in the lungs, is expressed in macrophages, neutrophils, and epithelial cells. In mice, Fas activation leads to a form of lung injury characterized by increased alveolar permeability. We investigated whether Fas-mediated lung injury occurs primarily as a result of Fas activation in myeloid cells (such as macrophages) or in nonmyeloid cells (such as epithelial cells). Chimeric mice lacking Fas in either myeloid or nonmyeloid cells were generated by transplanting marrow cells from lpr mice (which lack Fas) into lethally irradiated C57BL/6 mice (MyFas(-) group) or vice versa (MyFas(+) group). Additional mice transplanted with marrow cells from their same strain served as controls (Fas(+) ctr and Fas(-) ctr groups). Sixty days after transplantation, the mice received intratracheal instillations of the Fas-activating mAb Jo2 (n = 10/group), or an isotype control Ab (n = 10/group), and were euthanized 24-h later. Only animals expressing Fas in nonmyeloid cells (Fas(+) ctr and MyFas(-)) showed significant increases in lung neutrophil content and in alveolar permeability. These same mice showed tissue evidence of lung injury and caspase-3 activation in cells of the alveolar walls. Despite differences in the neutrophilic response and lung injury, there was no statistical difference in the lung cytokine concentrations (KC and MIP-2) among groups. We conclude that Fas-mediated lung injury requires expression of Fas on nonmyeloid cells of the lungs. These findings suggest that the alveolar epithelium is the primary target of Fas-mediated acute lung injury, and demonstrate that apoptotic processes may be associated with neutrophilic inflammation.

Expression of apoptosis-related genes after fetal tracheal occlusion in rabbits

BACKGROUND/PURPOSE

Late-gestation lung remodeling is associated with alveolar type II cell apoptosis early in the saccular stage (day 28 in fetal rabbits). Intrauterine tracheal occlusion (TO), a potent stimulus of fetal lung growth and maturation, significantly increases type II cell apoptosis. The aim of this study was to determine the effect of fetal TO on the spatiotemporal expression of key apoptosis-related signaling molecules.

METHODS

Tracheal occlusion of fetal rabbits was performed at gestational day 25 (term, 31 days), and apoptotic gene expression was studied between days 26 and 28.

RESULTS

At days 26 and 27, the protein levels of Fas and Fas-ligand (FasL) in lung lysates were similar in TO fetuses and sham-operated controls. At day 28, however, synchronous with the onset of TO-induced pulmonary distension and type II cell apoptosis, the FasL protein content was 8-fold higher in TO lungs compared with controls (P < .01), whereas Fas levels were comparable. In contrast, Bax and Bcl-2 protein levels were similar in TO and control fetuses at all time-points. TO significantly increased the cellular concentration of immunoreactive FasL in type II cells and bronchial epithelial Clara cells. Furthermore, bronchoalveolar lavage fluid (BAL) from TO fetuses at day 28 induced significantly more type II cell apoptosis in vitro compared with control BAL, an effect that was inhibited by neutralizing anti-FasL antibody.

CONCLUSIONS

Our findings show that TO results in time-specific increase of both cellular and soluble FasL in fetal lungs and implicate the Fas/FasL pathway as a pivotal autocrine and/or paracrine regulator of TO- induced type II cell apoptosis.

Promoter variants in tissue inhibitor of metalloproteinase-3 (TIMP-3) protect against susceptibility in pigeon breeders' disease

BACKGROUND

Tissue inhibitors of metalloproteinases (TIMPs) play a major role in extracellular matrix turnover in the lung. However, in chronic lung disorders such as idiopathic pulmonary fibrosis (IPF) and pigeon breeders' disease (PBD), TIMPs may promote an adverse non-degradative environment. We hypothesised that polymorphisms in TIMP-3 could affect susceptibility to IPF and PBD.

METHODS

Two promoter variants, -915A>G and -1296T>C, were genotyped in 323 healthy subjects, 94 subjects with IPF, 115 with PBD, and 90 exposed to avian antigen but without PBD. The severity of fibrosis in lung tissue and the clinical outcome after 1 year was determined in the PBD group.

RESULTS

The variants did not influence susceptibility to IPF, but the rare alleles of both variants appeared to be protective against susceptibility to PBD (odds ratio (OR) for carriage of at least one rare allele from either variant 0.48, 95% CI 0.30 to 0.76, p = 0.002). Haplotype analysis of positions -915 and -1296 estimated four haplotypes: *A*T, *G*T, *A*C and *G*C, respectively. Their frequencies differed overall between subjects with PBD and healthy subjects (p = 0.0049) and this was attributable primarily to the *G*C haplotype (OR 0.53, 95% CI 0.36 to 0.77, p = 0.001). The severity of fibrosis correlated with poorer outcome in the PBD group (r = 0.73, p<0.01) but no relationship was seen between the *G*C haplotype and outcome or fibrosis. However, PBD subjects with the *G*C haplotype did have proportionally fewer lymphocytes in their bronchoalveolar fluid than those with the common *A*T haplotype (p = 0.029).

CONCLUSIONS

TIMP-3 variants appear to contribute to susceptibility to PBD. This may be through the inflammatory reaction rather than the fibrotic reaction.

Science review: apoptosis in acute lung injury

Apoptosis is a process of controlled cellular death whereby the activation of specific death-signaling pathways leads to deletion of cells from tissue. The importance of apoptosis resides in the fact that several steps involved in the modulation of apoptosis are susceptible to therapeutic intervention. In the present review we examine two important hypotheses that link apoptosis with the pathogenesis of acute lung injury in humans. The first of these, namely the 'neutrophilic hypothesis', suggests that during acute inflammation the cytokines granulocyte colony-stimulating factor and granulocyte/macrophage colony-stimulating factor prolong the survival of neutrophils, and thus enhance neutrophilic inflammation. The second hypothesis, the 'epithelial hypothesis', suggests that epithelial injury in acute lung injury is associated with apoptotic death of alveolar epithelial cells triggered by soluble mediators such as soluble Fas ligand. We also review recent studies that suggest that the rate of clearance of apoptotic neutrophils may be associated with resolution of neutrophilic inflammation in the lungs, and data showing that phagocytosis of apoptotic neutrophils can induce an anti-inflammatory phenotype in activated alveolar macrophages.

Enhancement of T cell apoptosis correlates with increased serum levels of soluble Fas (CD95/Apo-1) in active lupus

Peripheral T cell apoptosis is upregulated in active SLE, in parallel with high expression of both membrane-bound and soluble (s) Fas. Previous studies postulated that sFas down-regulates apoptosis in vitro through its blockade of the Fas-L of cytotoxic cells. We have investigated the extent of apoptosis and sFas levels in 14 patients with active (group A) and 11 with inactive SLE (group B). Fas was predominantly expressed by CD3+ cells from group A, whose increased serological levels of sFas were linearly correlated with the TUNEL positive cell population, whereas low titers paralleled a mild level of apoptosis in group B. This association was also investigated by measuring the effect of sFas on both cell proliferation and caspase activation. We found that incubation with sFas greatly suppressed proliferation of CD3+ cells, especially in group B, and in control cells from healthy donors whose content of CPP32 active products was significantly increased. We postulate that sFas promotes a pro-apoptogen effect, which would explain the high susceptibility to apoptosis in active lupus, and that the apoptosis program itself includes release of sFas to spread the death signal.

The role of apoptosis in acute lung injury

OBJECTIVE

To discuss current aspects of our understanding of the role of apoptosis in lung injury.

DATA SOURCES

Review of English language literature.

DATA SUMMARY

Apoptosis is a process that produces timely death in senescent cells. Apoptosis is important in developmental biology and in remodeling of tissues during repair. Many apoptosis pathways converge in intracellular protease cascades that lead to DNA cleavage and cell death. Apoptosis pathways can be triggered by surface receptors, which interact with soluble proteins or membrane-bound proteins, such as Fas ligand. Fas ligand accumulates in soluble form at sites of tissue inflammation and has the potential to initiate apoptosis of leukocytes, epithelial cells, and other parenchymal cells. Dysregulation of apoptosis pathways could contribute to the epithelial injury that is characteristic of acute lung injury in humans. The effects of Fas ligand are modulated by factors in lung fluids, such as cytokines (e.g., transforming growth factor-beta, surfactant protein A, and angiotensin II) and a specific Fas ligand decoy receptor (DcR3).

CONCLUSION

Strategies to block apoptosis pathways could be useful in limiting some forms of acute lung injury in humans.

Hydrogen peroxide induces upregulation of Fas in human airway epithelial cells via the activation of PARP-p53 pathway

Fas mediates apoptosis following binding with Fas ligand. Fas is expressed in human airway epithelial cells and has a critical role in the pathophysiology of various pulmonary disorders. Hydrogen peroxide (H(2)O(2)) is an important mediator of airway epithelial injury. In this context, we hypothesized that H(2)O(2) would increase the expression of cell surface Fas in human airway epithelial cells. To test this hypothesis, the modulation of Fas expression with H(2)O(2) was assessed in normal human bronchial epithelial cells and A549 cells. The majority of Fas was cytoplasmic in both cell types without any stimulation. Hydrogen peroxide significantly increased Fas in the plasma membrane fraction, while decreasing Fas in the cytoplasmic fraction. Incubation with an agonistic antibody for Fas induced apoptosis in H(2)O(2)-treated cells in proportion to the level of surface Fas expression on those cells. Inhibitors of poly(ADP-ribose) polymerase abrogated the H(2)O(2)-induced Fas translocation to the plasma membrane and p53 activation. Expression of dominant-negative p53 also inhibited the Fas translocation induced by H(2)O(2) in A549 cells. These results indicate that H(2)O(2) induces Fas upregulation by promoting cytoplasmic transport of Fas to the cell surface in human airway epithelial cells, and that the activation of the poly(ADP-ribose) polymerase-p53 pathway may be involved in this mechanism.

Fas and fas ligand are up-regulated in pulmonary edema fluid and lung tissue of patients with acute lung injury and the acute respiratory distress syndrome

Apoptosis mediated by Fas/Fas ligand (FasL) interaction has been implicated in human disease processes, including pulmonary disorders. However, the role of the Fas/FasL system in acute lung injury (ALI) and in the acute respiratory distress syndrome (ARDS) is poorly defined. Accordingly, we investigated both the soluble and cellular expression of the Fas/FasL system in patients with ALI or ARDS. The major findings are summarized as follows. First, the soluble expression of the Fas/FasL system was assessed in undiluted pulmonary edema fluid and simultaneous plasma. Pulmonary edema fluid obtained from patients with ALI or ARDS (n = 51) had significantly higher concentrations of both soluble Fas (27 ng/ml; median; P < 0.05) and soluble FasL (0.125 ng/ml; P < 0.05) compared to control patients with hydrostatic pulmonary edema (n = 40; soluble Fas, 12 ng/ml; soluble FasL, 0.080 ng/ml). In addition, the concentrations of both soluble Fas and soluble FasL were significantly higher in the pulmonary edema fluid of the patients with ALI or ARDS compared to simultaneous plasma samples (soluble Fas, 16 ng/ml; soluble FasL, 0.058 ng/ml; P < 0.05), indicating local release in the lung. Higher soluble Fas concentrations were associated with worse clinical outcomes. Second, cellular expression of the Fas/FasL system was assessed by semiquantitative immunofluorescence microscopy in lung tissue obtained at autopsy from a different set of patients. Both Fas and FasL were immunolocalized to a greater extent in the patients who died with ALI or ARDS (n = 10) than in the patients who died without pulmonary disease (n = 10). Both proteins were co-expressed by epithelial cells that lined the alveolar walls, as well as by inflammatory cells and sloughed epithelial cells that were located in the air spaces. Semiquantitative immunohistochemistry showed that markers of apoptosis (terminal dUTP nick-end labeling, caspase-3, Bax, and p53) were more prevalent in alveolar wall cells from the patients who died with ALI or ARDS compared to the patients who died without pulmonary disease. These findings indicate that alveolar epithelial injury in humans with ALI or ARDS is in part associated with local up-regulation of the Fas/FasL system and activation of the apoptotic cascade in the epithelial cells that line the alveolar air spaces.

TGF-beta 1 as an enhancer of Fas-mediated apoptosis of lung epithelial cells

Transforming growth factor-beta 1 (TGF-beta 1) has important roles in lung fibrosis and the potential to induce apoptosis in several types of cells. We previously demonstrated that apoptosis of lung epithelial cells induced by Fas ligation may be involved in the development of pulmonary fibrosis. In this study, we show that TGF-beta1 induces apoptosis of primary cultured bronchiolar epithelial cells via caspase-3 activation and down-regulation of cyclin-dependent kinase inhibitor p21. Concentrations of TGF-beta 1 that were not sufficient to induce apoptosis alone could enhance agonistic anti-Fas Ab or rFas ligand-mediated apoptosis of cultured bronchiolar epithelial cells. Soluble Fas ligand in the bronchoalveolar lavage fluid (BALF) from patients with idiopathic pulmonary fibrosis (IPF) also induced apoptosis of cultured bronchiolar epithelial cells that was significantly attenuated by anti-TGF-beta Ab. Otherwise, BALF from patients with hypersensitivity pneumonitis (HP) could not induce apoptosis on bronchiolar epithelial cells, despite its comparable amounts of soluble Fas ligand. The concentrations of TGF-beta 1 in BALF from patients with IPF were significantly higher compared with those in BALF from patients with HP or controls. Furthermore, coincubation with the low concentration of TGF-beta 1 and HP BALF created proapoptotic effects comparable with the IPF BALF. In vivo, the administration of TGF-beta 1 could enhance Fas-mediated epithelial cell apoptosis and lung injury via caspase-3 activation in mice. Our results demonstrate a novel role of TGF-beta 1 in the pathophysiology of pulmonary fibrosis as an enhancer of Fas-mediated apoptosis of lung epithelial cells.

Recombinant human Fas ligand induces alveolar epithelial cell apoptosis and lung injury in rabbits

This study investigated whether recombinant human soluble Fas ligand (rh-sFasL) induces apoptosis of primary type II pneumocytes in vitro and lung injury in vivo. Type II cells isolated from normal rabbit lung expressed Fas on their surface and became apoptotic after an 18-h incubation with rh-sFasL. Fas expression in normal rabbit lungs was localized by immunohistochemistry to alveolar and airway epithelia and alveolar macrophages. The administration of 10 microg of rh-sFasL into the right lungs of rabbits resulted 24 h later in both significantly more bronchoalveolar lavage fluid total protein and significantly more tissue changes compared with those in the left lungs, which received rh-sFasL plus Fas:Ig (a fusion protein that binds and blocks sFasL). Tissue changes included thickening of the alveolar walls, neutrophilic infiltrates, apoptotic (terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling-positive) cells in the alveolar walls, and increased expression of interleukin-8 by alveolar macrophages (as determined by immunohistochemistry). We conclude that the alveolar epithelium of normal rabbits expresses Fas and that sFasL induces lung injury and inflammation in rabbits.