Enhanced resolution of experimental ARDS through IL-4-mediated lung macrophage reprogramming.

Despite intense investigation, acute respiratory distress syndrome (ARDS) remains an enormous clinical problem for which no specific therapies currently exist. In this study, we used intratracheal lipopolysaccharide or Pseudomonas bacteria administration to model experimental acute lung injury (ALI) and to further understand mediators of the resolution phase of ARDS. Recent work demonstrates macrophages transition from a predominant proinflammatory M1 phenotype during acute inflammation to an anti-inflammatory M2 phenotype with ALI resolution. We tested the hypothesis that IL-4, a potent inducer of M2-specific protein expression, would accelerate ALI resolution and lung repair through reprogramming of endogenous inflammatory macrophages. In fact, IL-4 treatment was found to offer dramatic benefits following delayed administration to mice subjected to experimental ALI, including increased survival, accelerated resolution of lung injury, and improved lung function. Expression of the M2 proteins Arg1, FIZZ1, and Ym1 was increased in lung tissues following IL-4 treatment, and among macrophages, FIZZ1 was most prominently upregulated in the interstitial subpopulation. A similar trend was observed for the expression of macrophage mannose receptor (MMR) and Dectin-1 on the surface of alveolar macrophages following IL-4 administration. Macrophage depletion or STAT6 deficiency abrogated the therapeutic effect of IL-4. Collectively, these data demonstrate that IL-4-mediated therapeutic macrophage reprogramming can accelerate resolution and lung repair despite delayed use following experimental ALI. IL-4 or other therapies that target late-phase, proresolution pathways may hold promise for the treatment of human ARDS.

The role of post-transcriptional regulation in chemokine gene expression in inflammation and allergy.

The aim of this review is to discuss recent advances in the understanding of the regulation of chemokine expression occurring during chronic inflammatory conditions, such as allergic diseases. The focus will be on current data, which suggest that post-transcriptional regulation plays a larger role in chemokine gene regulation than previously recognised. In particular, a growing body of data indicates that mechanisms controlling mRNA stability may be relevant in determining, or maintaining, the increased levels of chemokine gene expression in this context. Such regulatory pathways may be important targets of novel anti-inflammatory strategies.

Assessment of signal transducer and activator of transcription 6 as a target of glucocorticoid action in human airway epithelial cells.

BACKGROUND: Activation of signal transducer and activator of transcription (STAT)6 by IL-4 and IL-13 is essential in many key epithelial responses in the asthmatic airway including expression of numerous chemokines, goblet cell differentiation and mucus production and expression of other allergic inflammatory genes. While these responses are all inhibited by glucocorticoids (GC) administered systemically or by inhalation, the inhibitory mechanisms are unknown. OBJECTIVE: To test the hypothesis that GC suppress allergic responses by blocking IL-4-induced STAT6 signalling in airway epithelial cells. METHODS: Western blotting and reporter gene assays were used to determine whether GC could inhibit STAT6 production, phosphorylation or nuclear translocation, or whether GC could affect STAT6 transcriptional activity in the BEAS-2B airway epithelial cell line. RESULTS: Our results showed that GC had no inhibitory effect on the total cellular or nuclear levels of STAT6 or phospho-STAT6. GC did not inhibit transcription from three different STAT6-driven reporter constructs, indicating that GC also did not inhibit STAT6 function. CONCLUSION: We conclude that airway epithelial STAT6 is not the central target of GC in allergic inflammation and that the inhibitory effect of GC on STAT6-mediated IL-4- and IL-13-induced responses is exerted by targeting pathways distinct from STAT6.