Interleukin-26 in antibacterial host defense of human lungs. Effects on neutrophil mobilization.

RATIONALE: The role of the presumed Th17 cytokine IL-26 in antibacterial host defense of the lungs is not known. OBJECTIVES: To characterize the role of IL-26 in antibacterial host defense of human lungs. METHODS: Intrabronchial exposure of healthy volunteers to endotoxin and vehicle was performed during bronchoscopy and bronchoalveolar lavage (BAL) samples were harvested. Intracellular IL-26 was detected using immunocytochemistry and immunocytofluorescence. This IL-26 was also detected using flow cytometry, as was its receptor complex. Cytokines and phosphorylated signal transducer and activator of transcription (STAT) 1 plus STAT3 were quantified using ELISA. Gene expression was analyzed by real-time polymerase chain reaction and neutrophil migration was assessed in vitro. MEASUREMENTS AND MAIN RESULTS: Extracellular IL-26 was detected in BAL samples without prior exposure in vivo and was markedly increased after endotoxin exposure. Alveolar macrophages displayed gene expression for, contained, and released IL-26. Th and cytotoxic T cells also contained IL-26. In the BAL samples, IL-26 concentrations and innate effector cells displayed a correlation. Recombinant IL-26 potentiated neutrophil chemotaxis induced by IL-8 and fMLP but decreased chemokinesis for neutrophils. Myeloperoxidase in conditioned media from neutrophils was decreased. The IL-26 receptor complex was detected in neutrophils and IL-26 decreased phosphorylated STAT3 in these cells. In BAL and bronchial epithelial cells, IL-26 increased gene expression of the IL-26 receptor complex and STAT1 plus STAT3. Finally, IL-26 increased the release of neutrophil-mobilizing cytokines in BAL but not in epithelial cells. CONCLUSIONS: This study implies that alveolar macrophages produce IL-26, which stimulates receptors on neutrophils and focuses their mobilization toward bacteria and accumulated immune cells in human lungs.

Interleukin-22 produced by alveolar macrophages during activation of the innate immune response.

OBJECTIVE AND DESIGN: Interleukin (IL)-22 is important for mucosal host defense. Whereas previous studies focus on lymphocytes as sources of IL-22, we determined whether IL-22 is produced by inflammatory cells in the lungs other than T-lymphocytes during the activation of the innate immune response. MATERIAL, METHODS AND TREATMENT: Inflammatory cells in the lungs of Balb/c mice were primed by endotoxin (LPS, 10 µg) or peptidoglycan (PG, 40 µg) intranasally (3 days). After CD3 + cell depletion, lung homogenates were re-stimulated 24 h with LPS (100 ng/ml), PG (10 µg/ml), IL-23 (100 ng/ml) or vehicle. Human BAL macrophages were stimulated 24 h with PG (50 µg/ml) and IL-23 (100 ng/ml) or vehicle. The release of IL-22 was measured with ELISA and intracellular IL-22 with immunostaining. For statistics, either Dunnett or Students t test method was employed (n = 3-8). RESULTS: Re-stimulation in vitro increased concentrations of mouse IL-22 protein irrespective of priming in vivo. A majority of macrophages in mouse lung and BAL samples displayed immunostaining for IL-22. In analogy, human BAL macrophages released IL-22 protein, and a third of these cells displayed immunostaining for IL-22. CONCLUSIONS: Alveolar macrophages can produce and release IL-22 during the activation of the innate immune response and thereby constitute a potentially important regulator of mucosal host defence in the lungs.

Negative feedback on IL-23 exerted by IL-17A during pulmonary inflammation.

It is now established that IL-17 has a broad pro-inflammatory potential in mammalian host defense, in inflammatory disease and in autoimmunity, whereas little is known about its anti-inflammatory potential and inhibitory feedback mechanisms. Here, we examined whether IL-17A can inhibit the extracellular release of IL-23 protein, the upstream regulator of IL-17A producing lymphocyte subsets, that is released from macrophages during pulmonary inflammation. We characterized the effect of IL-17A on IL-23 release in several models of pulmonary inflammation, evaluated the presence of IL-17 receptor A (RA) and C (RC) on human alveolar macrophages and assessed the role of the Rho family GTPase Rac1 as a mediator of the effect of IL-17A on the release of IL-23 protein. In a model of sepsis-induced pneumonia, intravenous exposure to Staphylococcus aureus caused higher IL-23 protein concentrations in cell-free bronchoalveolar lavage (BAL) samples from IL-17A knockout (KO) mice, compared with wild type (WT) control mice. In a model of Gram-negative airway infection, pre-treatment with a neutralizing anti-IL-17A Ab and subsequent intranasal (i.n.) exposure to LPS caused higher IL-23 and IL-17A protein concentrations in BAL samples compared with mice exposed to LPS, but pre-treated with an isotype control Ab. Moreover, i.n. exposure with IL-17A protein per se decreased IL- 23 protein concentrations in BAL samples. We detected IL-17RA and IL-17RC on human alveolar macrophages, and found that in vitro stimulation of these cells with IL-17A protein, after exposure to LPS, decreased IL-23 protein in conditioned medium, but not IL-23 p19 or p40 mRNA. This study indicates that IL-17A can partially inhibit the release of IL-23 protein during pulmonary inflammation, presumably by stimulating the here demonstrated receptor units IL-17RA and IL-17RC on alveolar macrophages. Hypothetically, the demonstrated mechanism may serve as negative feedback to protect from excessive IL-17A signaling and to control antibacterial host defense once it is activated.

IL-17 in human asthma.

Asthma is perceived as a heterogeneous disease with several clinical phenotypes and triggering factors. In general, cytokines from T-helper 2 cells are believed to be critical contributors of asthma. In recent years, IL-17, another T-helper lymphocyte-associated cytokine, has been put forward as another potentially important mediator of asthma. Currently, several drugs that target IL-17 signaling are being tested in clinical trials. With the aim to find whether there are any specific features of this heterogeneous disease that potentially could be relieved by the use of IL-17-targeting drugs, this review scrutinizes the evidence for an involvement of IL-17 in human asthma.

Impact of interleukin-17 on macrophage phagocytosis of apoptotic neutrophils and particles.

There is now substantial evidence that the cytokine interleukin-17 orchestrates the accumulation of neutrophils in mammals and thereby contributes to host defense. However, the role of IL-17 in controlling neutrophil turnover is not fully understood. Here, we demonstrate that IL-17 stimulates the apoptosis of mouse neutrophils and, simultaneously, the release of the microbicidal compound, myeloperoxidase. IL-17 also stimulates mouse macrophages to phagocytose aged neutrophils and latex beads, and it induces an increase in a soluble form of the phagocytic receptor, lectin-like oxidized low-density lipoprotein receptor-1 as well. In contrast, IL-17 does not markedly increase the release of the archetype neutrophil-recruiting cytokine, macrophage inflammatory protein-2 in mouse macrophages. Importantly, IL-17 also stimulates the phagocytosis of latex beads in human monocyte-derived macrophages. Thus, IL-17 bears the potential to control both phagocytosis and neutrophil turnover during activation of host defense.

Interleukin-17A during local and systemic Staphylococcus aureus-induced arthritis in mice.

Staphylococcus aureus is one of the dominant pathogens that induce septic arthritis in immunocompromised hosts, e.g., patients suffering from rheumatoid arthritis treated with immunosuppressive drugs. S. aureus-induced arthritis leads to severe joint destruction and high mortality despite antibiotic treatment. Recently, interleukin-17A (IL-17A) has been discovered to be an important mediator of aseptic arthritis both in mice and humans, but its function in S. aureus-induced arthritis is largely unknown. Here, we investigated the role of IL-17A in host defense against arthritis following systemic and local S. aureus infection in vivo. IL-17A knockout mice and wild-type mice were inoculated systemically (intravenously) or locally (intra-articularly) with S. aureus. During systemic infection, IL-17A knockout mice lost significantly more weight than the wild-type mice did, but no differences were found in the mortality rate. The absence of IL-17A had no impact on clinical arthritis development but led to increased histopathological erosivity late during systemic S. aureus infection. Bacterial clearance in kidneys was increased in IL-17A knockout mice compared to the level in wild-type mice only 1 day after bacterial inoculation. During systemic S. aureus infection, serum IL-17F protein levels and mRNA levels in the lymph nodes were elevated in the IL-17A knockout mice compared to the level in wild-type mice. In contrast to systemic infection, the IL-17A knockout mice had increased synovitis and erosions and locally decreased clearance of bacteria 3 days after local bacterial inoculation. On the basis of these findings, we suggest that IL-17A is more important in local host defense than in systemic host defense against S. aureus-induced arthritis.

IL-17-producing T lymphocytes in lung tissue and in the bronchoalveolar space after exposure to endotoxin from Escherichia coli in vivo--effects of anti-inflammatory pharmacotherapy.

Interleukin (IL)-17 may play a critical role for the innate immune response in mammals. However, little is known about its production in T lymphocytes in comparison with other cells, in lung tissue and in the bronchoalveolar space in vivo. Even less is known about the effects of anti-inflammatory pharmacotherapy on this IL-17 production. In this study on mice we show that one single, intranasal exposure to endotoxin from Escherichia coli increases extracellular IL-17 protein in bronchoalveolar (BAL) samples during 3 days, and is accompanied by a local increase in neutrophils and other inflammatory cells. This endotoxin exposure also elevates IL-17 mRNA in lung tissue samples. Moreover, after endotoxin exposure, the absolute number of CD3-positive cells containing intracellular IL-17 protein is increased as well; from a moderate cell number in lung tissue samples and from virtually none in BAL samples; with the number in lung tissue exceeding that observed in BAL samples. Notably, we also demonstrate that among the cells that contain intracellular IL-17 protein after endotoxin exposure, the percentage of CD3-positive cells is similar to that of CD3-negative cells in lung tissue. In contrast, CD3-negative cells dominate among IL-17-containing cells in BAL samples. A high systemic dose of a glucocorticoid receptor agonist attenuates the endotoxin-induced increase in extracellular IL-17 protein in BAL samples, IL-17 mRNA in lung tissue samples, and in IL-17-containing CD3-positive cells in BAL and lung tissue samples. This is also true for the endotoxin-induced accumulation of neutrophils and other inflammatory BAL cells in vivo. A systemic dose of a calcineurin phosphatase inhibitor exerts a less complete and more selective effect on the endotoxin-induced increase in extracellular IL-17 protein and on neutrophils in BAL samples. In vitro, endotoxin also increases extracellular IL-17 protein in a co-culture of CD3-positive spleen cells and adherent mononuclear BAL cells; an increase that was inhibited by a glucocorticoid as well as by a calcineurin phosphatase inhibitor. In conclusion, endotoxin-induced IL-17 production and release from T lymphocytes originates from cells that reside in lung tissue and from cells that have been recruited to the bronchoalveolar space. In both compartments, there is also a substantial number of cells other than T lymphocytes that contain IL-17 after endotoxin exposure. The sustained IL-17 production from T lymphocytes and the associated neutrophil accumulation may be inhibited non-selectively through glucocorticoid receptor stimulation and more selectively through calcineurin phosphatase inhibition.