Specialized pro-resolving mediators as modulators of immune responses.

Specialized pro-resolving mediators (SPMs) are endogenous small molecules produced mainly from dietary omega-3 polyunsaturated fatty acids by both structural cells and cells of the active and innate immune systems. Specialized pro-resolving mediators have been shown to both limit acute inflammation and promote resolution and return to homeostasis following infection or injury. There is growing evidence that chronic immune disorders are characterized by deficiencies in resolution and SPMs have significant potential as novel therapeutics to prevent and treat chronic inflammation and immune system disorders. This review focuses on important breakthroughs in understanding how SPMs are produced by, and act on, cells of the adaptive immune system, specifically macrophages, B cells and T cells. We also highlight recent evidence demonstrating the potential of SPMs as novel therapeutic agents in topics including immunization, autoimmune disease and transplantation.

Human lung fibroblasts produce proresolving peroxisome proliferator-activated receptor-γ ligands in a cyclooxygenase-2-dependent manner.

Human lung fibroblasts (HLFs) act as innate immune sentinel cells that amplify the inflammatory response to injurious stimuli. Here, we use targeted lipidomics to explore the hypothesis that HLFs also play an active role in the resolution of inflammation. We detected cyclooxygenase-2 (COX-2)-dependent production of both proinflammatory and proresolving prostaglandins (PGs) in conditioned culture medium from HLFs treated with a proinflammatory stimulus, IL-1ß. Among the proresolving PGs in the HLF lipidome were several known ligands for peroxisome proliferator-activated receptor-γ (PPARγ), a transcription factor whose activation in the lung yields potent anti-inflammatory, antifibrotic, and proresolving effects. Next, we used a cell-based luciferase reporter to confirm the ability of HLF supernatants to activate PPARγ, demonstrating, for the first time, that primary HLFs activated with proinflammatory IL-1ß or cigarette smoke extract produce functional PPARγ ligands; this phenomenon is temporally regulated, COX-2- and lipocalin-type PGD synthase-dependent, and enhanced by arachidonic acid supplementation. Finally, we used luciferase reporter assays to show that several of the PGs in the lipidome of activated HLFs independently activate PPARγ and/or inhibit NFκB. These results indicate that HLFs, as immune sentinels, regulate both proinflammatory and proresolving responses to injurious stimuli. This novel endogenous resolution pathway represents a new therapeutic target for globally important inflammatory diseases such as chronic obstructive pulmonary disease.

Resolvin D1 Reduces Emphysema and Chronic Inflammation.

Chronic obstructive pulmonary disease is characterized, in part, by chronic inflammation that persists even after smoking cessation, suggesting that a failure to resolve inflammation plays an important role in the pathogenesis of the disease. It is widely recognized that the resolution of inflammation is an active process, governed by specialized proresolving lipid mediators, including lipoxins, resolvins, maresins, and protectins. Here, we report that proresolving signaling and metabolic pathways are disrupted in lung tissue from patients with chronic obstructive pulmonary disease, suggesting that supplementation with proresolving lipid mediators might reduce the development of emphysema by controlling chronic inflammation. Groups of mice were exposed long-term to cigarette smoke and treated with the proresolving mediator resolvin D1. Resolvin D1 was associated with a reduced development of cigarette smoke-induced emphysema and airspace enlargement, with concurrent reductions in inflammation, oxidative stress, and cell death. Interestingly, resolvin D1 did not promote the differentiation of M2 macrophages and did not promote tissue fibrosis. Taken together, our results suggest that cigarette smoking disrupts endogenous proresolving pathways and that supplementation with specialized proresolving lipid mediators is an important therapeutic strategy in chronic lung disease, especially if endogenous specialized proresolving lipid mediator signaling is impaired.