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Establishment of immune tolerance is crucial to protect humans against asthma. Promyelocytic leukemia zinc finger (PLZF) is an emerging suppressor of inflammatory responses. CCL21-CCR7 signaling mediates tolerance development. However, whether PLZF and CCL21-CCR7 are required for the development of asthma tolerance is unknown. Here, we found that Zbtb16 (coding PLZF) and Ccl21 were upregulated in OVA-induced asthma tolerance (OT) lungs by RNA-seq. PLZF physically interacted with GATA3 and its expression was higher in GATA3+ Th2 cells and ILC2s in OT lungs. Zbtb16-knockdown in lymphocytes promoted the differentiation of CD3e+ CD4+ T cells, particularly those producing IL-4 and IL-5. Moreover, iNKT cells with high expression of PLZF were recruited into the lungs via draining lymph nodes during tolerance. Blockade of CCL21-CCR7 signaling in OT mice decreased the PLZF+ cell population, abolished CCR7-induced PLZF+ iNKT recruitment to the lungs, enhanced Th2responses and exacerbated lung pathology. In OT mice, respiratory syncytial virus (RSV) infection impeded PLZF+ cell and CCR7+ PLZF+ iNKT cellrecruitment to the lungs and increased airway resistance. Collectively, these results indicate that PLZF could interact with GATA3 and restrain differentiation of IL-4- and IL-5-producing T cells, iNKT cells with high PLZF expression are recruited to the lungs via CCL21-CCR7 signaling to facilitate the development of asthma tolerance.

Infection of influenza A virus (IAV) can trigger exaggerated pulmonary inflammation and induce acute lung injury (ALI). Limiting IAV replication and alleviation of pulmonary inflammation are two important therapeutic strategies for influenza virus infection. Recent studies have shown that hypoxia inducible factor-1α (HIF-1α) is an essential factor for the development and repair of ALI; however, the role and the underlying mechanisms of HIF-1α in IAV-induced ALI remain elusive. Here, we demonstrated that lung epithelial cell-specific Hif1α knockout mice infected with IAV developed more lung IAV replication and severe lung inflammation, which led to increased mortality compared to IAV-infected control mice. Moreover, knockdown of HIF1A in A549 cells (human alveolar type II epithelial cell line) promoted IAV replication in vitro. Mechanistically, knockdown of HIF1A reduced glycolysis by regulating transcription of glycolysis-related enzymes, which subsequently activated the AMPKα-ULK1 signalling pathway. Interestingly, AMPKα-ULK1 signalling promoted autophagy and augmented IAV replication. Taken together, deficiency of HIF-1α in lung epithelial cells reduces glycolysis and enhances AMPKα-ULK1-mediated autophagy, which finally facilitates IAV replication. These findings have deepened our understanding of the role of HIF-1α in regulating IAV replication and provided us novel therapeutic targets for combating influenza infection.

Airway epithelial cells (AECs) participate in allergic airway inflammation by producing mediators in response to allergen stimulation. Whether ovalbumin (OVA) challenge promotes exosome release from AECs (OVA‐challenged AEC‐derived exosomes (OAEs)), thereby affecting airway inflammation, as well as the underlying mechanisms, is unknown. Our study showed that AECs released an increased number of exosomes after OVA challenge, and the expression of Plexin B2 (PLXNB2; a natural CD100 ligand) was increased by a massive 85.7‐fold in OAEs than in PBS‐treated AEC‐derived exosomes (PAEs). CD100+F4/80+ macrophages engulfed OAEs to trigger the transcription of pro‐inflammatory chemokines and cytokines. Plxnb2 transcripts increased in asthmatic lungs, and similarly, PLXNB2 protein was highly enriched in exosomes purified from asthmatic bronchoalveolar lavage (BAL) fluid. Furthermore, aspiration of PLXNB2 or OAEs increased the recruitment of lung neutrophils, monocytes, eosinophils and dendritic cells in OVA‐challenged mice. Mechanistically, OAE aspiration enhanced the cleavage of CD100 by MMP14, which manifested as an increase in the soluble CD100 (sCD100) level in BAL fluid and lung homogenates. Knockdown of Mmp14 in macrophages prevented the cleavage of CD100 and reduced Ccl2, Ccl5 and Cxcl2 transcription. These data indicate that PLXNB2‐containing OAEs aggravate airway asthmatic inflammation via cleavage of CD100 by MMP14, suggesting potential therapeutic targets of OAE‐mediated asthma exacerbations.

Mesenchymal stem cells (MSCs) have been used in cell-based therapies for a variety of disorders. Some factors such as inflammatory mediators in the diseased area might damage the survival of MSCs and affect their efficacy. Pyroptosis is a form of programmed necrosis as a response for immune cells to cytosolic pathogenic stimuli. Whether MSCs develop pyroptosis under pathological stimulation, its underlying mechanism and biological significance are still unclear. Here, we found that LPS, flagellin, dsDNA, nigericin (NIG), or LPS combined with nigericin (LPS/NIG) could not induce pyroptosis in adipose-tissue-derived mesenchymal stem cells (ASCs). However, when applied the culture media collected from LPS/NIG-induced pyroptotic bone marrow-derived macrophages (BMDMs) to incubate ASCs, ASCs developed pyroptosis. Inhibition of caspases or deletion of Caspase-1/11 in ASCs did not affect the pyroptotic macrophage media-triggered ASC pyroptosis while ablation of Caspase-1/11 abolished BMDM pyroptosis induced by LPS/NIG. Media collected from LPS/NIG stimulated Gsdmd−/− or Caspase-1/11−/− BMDMs could not induce pyroptosis of ASCs. In addition, RNA-seq analysis showed that interferon (IFN)-stimulated genes were upregulated in pyroptotic ASCs. Adding IFNβ could boost LPS/NIG stimulated BMDM media-induced ASC pyroptosis. Surprisingly, the pyroptotic ASCs had a lower bactericidal ability to P. Aeruginosa. Taken together, induction of ASC pyroptosis requires gasdermin D or caspase-1/11-dependent mediators and IFNβ from pyroptotic macrophages.

Vagal circuits-α7 nAChR (α7 nicotinic acetylcholine receptor, coded by Chrna7) signaling utilizes spleen as a hub to dampen systemic inflammatory responses. Vagal innervations also extend to the distal airways and alveoli. Vagotomy and deficiency of α7 nAChR deteriorate E. coli and lipopolysaccharide (LPS)-induced acute lung inflammatory responses; however, the underlying mechanisms remain elusive. Here, we hypothesized that vagal circuits would limit splenic release and lung recruitment of α7 nAChR+CD11b+ cells (CD11b is coded by Itgam, a surface marker of monocytes and neutrophils) via phosphorylation of AKT1 and that this process would define the severity of lung injury. Using both E. coli and LPS-induced lung injury mouse models, we found that vagotomy augmented splenic egress and lung recruitment of α7 nAChR+CD11b+ cells, and consequently worsened lung inflammatory responses. Rescue of vagotomy with an α7 nAChR agonist preserved α7 nAChR+CD11b+ cells in the spleen, suppressed recruitment of these cells to the lung and attenuated lung inflammatory responses. Vagal signals via α7 nAChR promoted serine473 phosphorylation of AKT1 in α7 nAChR+CD11b+ cells and stabilized these cells in the spleen. Deletion of Akt1 enhanced splenic egress and lung recruitment of α7 nAChR+CD11b+ cells, which elicited neutrophil-infiltrated lung inflammation and injury. Vagotomy and double deletion of Chrna7 and Itgam reduced serine473 phosphorylation of AKT1 in the spleen and BAL (bronchoalveolar lavage) Ly6CintGr1hi neutrophils and Ly6Chi monocytes, and they facilitated the recruitment of neutrophils and monocytes to the airspaces of E. coli-injured lungs. Double deletion of Chrna7 and Itgam increased lung recruitment of monocytes and/or neutrophils and deteriorated E. coli and LPS-induced lung injury. Thus, signals of vagal circuits engaging with AKT1 in α7 nAChR+CD11b+ cells attenuate E. coli and LPS-induced acute lung inflammatory responses. Targeting this signaling pathway could provide novel therapeutic strategies for treating acute lung injury.

In this review, we first analyzed the current status of cholinergic anti-inflammatory pathway and then put forward a novel regulatory machinery-pulmonary parasympathetic inflammatory reflex, which is composed by lung vagal sensors at afferent arm, α7 nAChR (α7 nicotinic acetylcholine receptors)-expressing cells at efferent arm and the brain information integrating center. This modulatory circuit might loop the lungs, immune and nervous systems and play a very important role in regulating lung infection, inflammation and immunity through the neural innervations and signals when the lungs encounter pathogenic challenges.

CFTR (cystic fibrosis transmembrane conductance regulator) is expressed by both neutrophils and platelets. Lack of functional CFTR could lead to severe lung infection and inflammation. Here, we found that mutation of CFTR (F508del) or inhibition of CFTR in mice led to more severe thrombocytopenia, alveolar neutrocytosis and bacteriosis, and lower lipoxin A4/MIP-2 (macrophage inhibitory protein-2) or lipoxin A4/neutrophil ratios in the BAL (bronchoalveolar lavage) during acute E. coli pneumonia. In vitro, inhibition of CFTR promotes MIP-2 production in LPS-stimulated neutrophils; however, lipoxin A4 could dose-dependently suppress this effect. In LPS-induced acute lung inflammation, blockade of PSGL-1 (P-selectin glycoprotein ligand-1) or P-selectin, antagonism of PAF by WEB2086, or correction of mutated CFTR trafficking by KM11060 could significantly increase plasma lipoxin A4 levels in F508del relevant to wildtype mice. Concurrently, F508del mice had higher plasma platelet activating factor (PAF) levels and PAF-AH activity compared to wildtype under LPS challenge. Inhibiting hydrolysis of PAF by a specific PAF-AH (PAF-acetylhydrolase) inhibitor, MAFP, could worsen LPS-induced lung inflammation in F508del mice compared to vehicle treated F508del group. Particularly, depletion of platelets in F508del mice could significantly decrease plasma lipoxin A4 and PAF-AH activity and deteriorate LPS-induced lung inflammation compared to control F508del mice. Taken together, lipoxin A4 and PAF are involved in E. coli or LPS-induced lung inflammation in CFTR-deficient mice, suggesting that lipoxin A4 and PAF might be therapeutic targets for ameliorating CFTR-deficiency deteriorated lung inflammation.

Mutation of CFTR (cystic fibrosis transmembrane conductance regulator) leads to cystic fibrosis (CF). Patients with CF develop abnormalities of blood platelets and recurrent lung inflammation. However, whether CFTR-mutated platelets play a role in the development of lung inflammation is elusive. Therefore, we intratracheally challenged wildtype and F508del (a common type of CFTR mutation) mice with LPS to observe changes of F508del platelets in the peripheral blood and indexes of lung inflammation (BAL neutrophils and protein levels). Furthermore, we investigated whether or not and how F508del platelets modulate the LPS-induced acute lung inflammation by targeting anti-platelet aggregation, depletion of neutrophils, reconstitution of bone marrow or neutrophils, blockade of P-selectin glycoprotein ligand-1 (PSGL-1), platelet activating factor (PAF), and correction of mutated CFTR trafficking. We found that LPS-challenged F508del mice developed severe thrombocytopenia and had higher levels of plasma TXB2 coincided with neutrophilic lung inflammation relative to wildtype control. Inhibition of F508del platelet aggregation or depletion of F508del neutrophils diminished the LPS-induced lung inflammation in the F508del mice. Moreover, wildtype mice reconstituted with either F508del bone marrow or neutrophils developed worse thrombocytopenia. Blocking PSGL-1, platelet activating factor (PAF), or rectifying trafficking of mutated CFTR in F508del mice diminished and alveolar neutrophil transmigration in the LPS-challenged F508del mice. These findings suggest that F508del platelets and their interaction with neutrophils are requisite for the development of LPS-induced lung inflammation and injury. As such, targeting platelets might be an emerging strategy for dampening recurrent lung inflammation in cystic fibrosis patients.