Anti-KC autoantibody:KC complexes cause severe lung inflammation in mice via IgG receptors

The bioactivity of soluble Fas ligand is modulated by key amino acids of its stalk region

We have previously reported that the 26-amino acid N-terminus stalk region of soluble Fas ligand (sFasL), which is separate from its binding site, is required for its biological function. Here we investigate the mechanisms that link the structure of the sFasL stalk region with its function. Using site-directed mutagenesis we cloned a mutant form of sFasL in which all the charged amino acids of the stalk region were changed to neutral alanines (mut-sFasL). We used the Fas-sensitive Jurkat T-cell line and mouse and human alveolar epithelial cells to test the bioactivity of sFasL complexes, using caspase-3 activity and Annexin-V externalization as readouts. Finally, we tested the effects of mut-sFasL on lipopolysaccharide-induced lung injury in mice. We found that mutation of all the 8 charged amino acids of the stalk region into the non-charged amino acid alanine (mut-sFasL) resulted in reduced apoptotic activity compared to wild type sFasL (WT-sFasL). The mut-sFasL attenuated WT-sFasL function on the Fas-sensitive human T-cell line Jurkat and on primary human small airway epithelial cells. The inhibitory mechanism was associated with the formation of complexes of mut-sFasL with the WT protein. Intratracheal administration of the mut-sFasL to mice 24 hours after intratracheal Escherichia coli lipopolysaccharide resulted in attenuation of the inflammatory response 24 hours later. Therefore, the stalk region of sFasL has a critical role on bioactivity, and changes in the structure of the stalk region can result in mutant variants that interfere with the wild type protein function in vitro and in vivo.

Silencing Bruton's tyrosine kinase in alveolar neutrophils protects mice from LPS/immune complex-induced acute lung injury

Previous observations made by our laboratory indicate that Bruton's tyrosine kinase (Btk) may play an important role in the pathophysiology of local inflammation in acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). We have shown that there is cross talk between FcγRIIa and TLR4 in alveolar neutrophils from patients with ALI/ARDS and that Btk mediates the molecular cooperation between these two receptors. To study the function of Btk in vivo we have developed a unique two-hit model of ALI: LPS/immune complex (IC)-induced ALI. Furthermore, we conjugated F(ab)2 fragments of anti-neutrophil antibodies (Ly6G1A8) with specific siRNA for Btk to silence Btk specifically in alveolar neutrophils. It should be stressed that we are the first group to perform noninvasive transfections of neutrophils, both in vitro and in vivo. Importantly, our present findings indicate that silencing Btk in alveolar neutrophils has a dramatic protective effect in mice with LPS/IC-induced ALI, and that Btk regulates neutrophil survival and clearance of apoptotic neutrophils in this model. In conclusion, we put forward a hypothesis that Btk-targeted neutrophil specific therapy is a valid goal of research geared toward restoring homeostasis in lungs of patients with ALI/ARDS.

Interleukin 8 and acute lung injury

Acute lung injury is a complex clinical syndrome involving acute inflammation, microvascular damage, and increased pulmonary vascular and epithelial permeability, frequently resulting in acute respiratory failure culminating in often-fatal acute respiratory distress syndrome. Interleukin 8 (IL-8), a potent neutrophil attractant and activator, plays a significant role in acute lung injury via the formation of anti-IL-8 autoantibody:IL-8 complexes and those complexes' interaction with FcγRIIa receptors, leading to the development of acute lung injury by, among other possible mechanisms, effecting neutrophil apoptosis. These complexes may also interact with lung endothelial cells in patients with acute respiratory distress syndrome. Continuing research of the role of neutrophils, IL-8, anti-IL-8 autoantibody:IL-8 complexes, and FcγRIIa receptors may ultimately provide molecular therapies that could lower acute respiratory distress syndrome mortality, as well as reduce or even prevent the development of acute lung injury altogether.

Fas-deficient mice have impaired alveolar neutrophil recruitment and decreased expression of anti-KC autoantibody:KC complexes in a model of acute lung injury

Background

Exposure to mechanical ventilation enhances lung injury in response to various stimuli, such as bacterial endotoxin (LPS). The Fas/FasL system is a receptor ligand system that has dual pro-apoptotic and pro-inflammatory functions and has been implicated in the pathogenesis of lung injury. In this study we test the hypothesis that a functioning Fas/FasL system is required for the development of lung injury in mechanically ventilated mice.

Methods

C57BL/6 (B6) and Fas-deficient lpr mice were exposed to either intra-tracheal PBS followed by spontaneous breathing or intra-tracheal LPS followed by four hours mechanical ventilation with tidal volumes of 10 mL/kg, respiratory rate of 150 breaths per minute, inspired oxygen 0.21 and positive end expiratory pressure (PEEP) of 3 cm of water.

Results

Compared with the B6 mice, the lpr mice showed attenuation of the neutrophilic response as measured by decreased numbers of BAL neutrophils and lung myeloperoxidase activity. Interestingly, the B6 and lpr mice had similar concentrations of pro-inflammatory cytokines, including CXCL1 (KC), and similar measurements of permeability and apoptosis. However, the B6 mice showed greater deposition of anti-KC:KC immune complexes in the lungs, as compared with the lpr mice.

Conclusions

We conclude that a functioning Fas/FasL system is required for full neutrophilic response to LPS in mechanically ventilated mice.

MicroRNA-127 inhibits lung inflammation by targeting IgG Fcγ receptor I

The molecular mechanisms of acute lung injury are incompletely understood. MicroRNAs (miRNAs) are crucial biological regulators that act by suppressing their target genes and are involved in a variety of pathophysiologic processes. miR-127 appears to be downregulated during lung injury. We set out to investigate the role of miR-127 in lung injury and inflammation. Expression of miR-127 significantly reduced cytokine release by macrophages. Looking into the mechanisms of regulation of inflammation by miR-127, we found that IgG FcγRI (CD64) was a target of miR-127, as evidenced by reduced CD64 protein expression in macrophages overexpressing miR-127. Furthermore, miR-127 significantly reduced the luciferase activity with a reporter construct containing the native 3' untranslated region of CD64. Importantly, we demonstrated that miR-127 attenuated lung inflammation in an IgG immune complex model in vivo. Collectively, these data show that miR-127 targets macrophage CD64 expression and promotes the reduction of lung inflammation. Understanding how miRNAs regulate lung inflammation may represent an attractive way to control inflammation induced by infectious or noninfectious lung injury.

Neutrophilic airways inflammation in lung cancer: the role of exhaled LTB-4 and IL-8

BACKGROUND

Recent advances in lung cancer biology presuppose its inflammatory origin. In this regard, LTB-4 and IL-8 are recognized to play a crucial role in neutrophil recruitment into airways during lung cancer.Notwithstanding the intriguing hypothesis, the exact role of neutrophilic inflammation in tumour biology remains complex and not completely known.The aim of this study was to give our contribution in this field by investigating LTB-4 and IL-8 in the breath condensate of NSCLC patients and verifying their role in cancer development and progression.

METHOD

We enrolled 50 NSCLC patients and 35 controls. LTB-4 and IL-8 concentrations were measured in the breath condensate and the blood of all the subjects under study using EIA kits. Thirty NSCLC patients and ten controls underwent induced sputum collection and analysis.

RESULTS

LTB-4 and IL-8 resulted higher in breath condensate and the blood of NSCLC patients compared to controls. Significantly higher concentrations were found as the cancer stages progressed. A positive correlation was observed between exhaled IL-8 and LTB-4 and the percentage of neutrophils in the induced sputum.

CONCLUSION

The high concentrations of exhaled LTB-4 and IL-8 showed the presence of a neutrophilic inflammation in the airways of NSCLC patients and gave a further support to the inflammatory signalling in lung cancer. These exhaled proteins could represent a suitable non-invasive marker in the diagnosis and monitoring of lung cancer.

Does activation of the FcgammaRIIa play a role in the pathogenesis of the acute lung injury/acute respiratory distress syndrome?

ALI (acute lung injury) and its more severe form ARDS (acute respiratory distress syndrome) are inflammatory diseases of the lung characterized by hypoxaemia and diffuse bilateral infiltrates. Disruption of epithelial integrity and injury to endothelium are contributing factors of the development of ALI/ARDS, and alveolar damage is the most pronounced feature of ALI/ARDS. The resulting increase in lung microvascular permeability promotes influx of inflammatory cells to the alveolar spaces. Oedema fluid contains pro-nflammatory mediators and plasma proteins, including Igs (immunoglobulins). Moreover, several reports describe the presence of autoantibodies and immune complexes [anti-IL-8 (interleukin-8) autoantibody/IL-8 complexes] in lung fluids (oedema and bronchoalveolar lavage fluids) from patients with ALI/ARDS. These immune complexes associate with FcgammaRIIa (Fcgamma IIa receptor) in lungs of patients with ARDS. Furthermore, the expression of FcgammaRIIa is substantially elevated in lungs of these patients. FcgammaRIIa appears on virtually all myeloid cells, platelets and endothelial cells. It is a low-affinity receptor for IgG that preferentially binds aggregated immunoglobulins and immune complexes. FcgammaRs regulate phagocytosis and cell-mediated cytotoxicity, and initiate the release of inflammatory mediators. It should be noted that immune complexes formed between either anti-neutrophil autoantibodies and their specific antigens or anti-HLA (human leucocyte antigen) antibodies and target antigens are implicated in the pathogenesis of TRALI (transfusion-related acute lung injury), and importantly, animal studies indicate that FcgammaRs are essential for these complexes to cause damage to the lungs. Therefore, we hypothesize that FcgammaRs such as FcgammaRIIa could contribute to the pathogenesis of ALI/ARDS.

Delay of LPS-induced acute lung injury resolution by soluble immune complexes is neutrophil dependent

The pathophysiological role of soluble immune complexes (SICXs) and its relationship with neutrophils were investigated in LPS-induced acute lung injury (ALI) animal model (Sprague-Dawley rat) and through the in vitro studies. Results showed that LPS-induced SICX was timely related to changes of tumor necrosis factor alpha and macrophage inflammatory protein 2 (inflammatory cytokines) in bronchoalveolar lavage fluid. In vitro study showed that SICX can bind to Fc gammaR (CD64 and CD32 or CD16) to prevent the apoptosis of neutrophils. The SICX-mediated apoptosis inhibition was extracellular signal-regulated kinase (ERK) or phosphoinositide 3 kinase dependent and was interrupted by PD98059 and LY294002. In vivo, additional amount of SICX exacerbated the lung injury caused by LPS. LPS-induced lung injury and macrophage inflammatory protein 2 release, however, were prevented by CD64 and CD32 blockers (decoy antibodies). In conclusion, excessive amount of SICX in lung can act through Fc gammaRs to protect bronchoalveolar lavage fluid neutrophils from apoptosis that eventually lead to delayed resolution of ALI caused by LPS. Blockade of SICX engagement of CD32 and CD64 (with decoy antibodies) could interrupt SICX-mediated protection of neutrophils and protect lung from LPS-induced injury. The decoy antibodies may therefore have therapeutic utility in ALI.

Alternative Strategies for Toxicity Testing of Species-Specific Biopharmaceuticals

Although toxicology studies should always be conducted in pharmacologically relevant species, the specificity of many biopharmaceuticals can present challenges in identification of a relevant species. In certain cases, that is, when the clinical product is active only in humans or chimpanzees, or if the clinical candidate is active in other species but immunogenicity limits the ability to conduct a thorough safety assessment, alternative approaches to evaluating the safety of a biopharmaceutical must be considered. Alternative approaches, including animal models of disease, genetically modified mice, or use of surrogate molecules, may improve the predictive value of preclinical safety assessments of species-specific biopharmaceuticals, although many caveats associated with these models must be considered. Because of the many caveats that are discussed in this article, alternative approaches should only be used to evaluate safety when the clinical candidate cannot be readily tested in at least one relevant species to identify potential hazards.

Anti-chemokine autoantibody:chemokine immune complexes activate endothelial cells via IgG receptors

Our previous studies revealed that the presence in lung fluids of anti-IL-8 autoantibody:IL-8 immune complexes is an important prognostic indicator for the development and outcome of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Anti-IL-8:IL-8 complexes purified from lung edema fluids trigger chemotaxis of neutrophils, induce activation of these cells, and regulate their apoptosis, all via IgG receptor, FcgammaRIIa. Importantly, increased levels of FcgammaRIIa are present in lungs of patients with ARDS, where FcgammaRIIa is partially associated with anti-IL-8:IL-8 complexes. In the current study, we demonstrate the ability of anti-IL-8:IL-8 complexes to promote an inflammatory phenotype of human umbilical vein endothelial cells via interaction with FcgammaRIIa. Human umbilical vein endothelial cells cultured in the presence of the complexes become activated, as shown by increased phosphorylation of ERK, JNK, and Akt, and augmented nuclear translocation of NF-kappaB. Anti-IL-8:IL-8 complexes also up-regulate expression of intracellular adhesion molecule (ICAM)-1 on the cell surface. Furthermore, we detected increased levels of ICAM-1 on lung endothelial cells from mice in which lung injury was induced by generating immune complexes in alveolar spaces. On the other hand, ICAM-1 expression was unchanged in lungs of gamma chain-deficient mice, lacking receptors that interact with immune complexes. Moreover, in lung tissues from patients with ARDS, anti-IL-8:IL-8 complexes were associated with endothelial cells that expressed higher levels of ICAM-1. Our current findings implicate that anti-chemokine autoantibody:chemokine immune complexes, such as IL-8:IL-8 complexes, may contribute to pathogenesis of lung inflammation by inducing activation of endothelial cells through engagement of IgG receptors.

Anti-interleukin-8 autoantibody:interleukin-8 immune complexes in acute lung injury/acute respiratory distress syndrome

ALI/ARDS (acute lung injury/acute respiratory distress syndrome) is a severe inflammatory lung disease associated with very high mortality. Importantly, no effective therapy has been developed to date for ALI/ARDS. Neutrophils have been implicated in the pathogenesis of ALI/ARDS, and IL-8 (interleukin-8) has been identified as the main chemotactic factor for neutrophils in lung fluids of patients with ALI/ARDS. Significantly, studies from our laboratory have revealed the presence of anti-IL-8 autoantibody:IL-8 immune complexes in lung fluids from patients with ALI/ARDS. Autoantibodies to several cytokines, including IL-8, have been found in human plasma and other tissues. The function of anticytokine autoantibodies is far from clear; however, in some instances, it has been suggested that such autoantibodies may contribute to the pathogenesis of variety of human diseases. In addition, many of these autoantibodies can form immune complexes with target cytokines. Furthermore, immune complexes consisting of anti-IL-8 autoantibodies and IL-8 are very stable due to the high affinity of autoantibodies against IL-8. These complexes are present in various human tissues, including the lung, as they have been detected in lung fluids from patients with ALI/ARDS. In this review, the significance of the latter findings are explored, and the possible involvement of anti-IL-8 autoantibody:IL-8 immune complexes in pathogenesis of ALI/ARDS is discussed.