We have previously demonstrated that administration of the recently described cytokine IL-17 in rat airways in vivo recruits and activates neutrophils locally. In the current study, we examined whether endogenous IL-17 is involved in mediating neutrophil recruitment caused by endotoxin exposure in mouse airways. Our in vivo data show that local endotoxin exposure causes the release of free, soluble IL-17 protein 6 h later. Systemic pretreatment with a neutralizing anti-IL-17 Ab almost completely inhibits neutrophil recruitment 24 h, but not 6 h, after endotoxin exposure in the airways. Pretreatment with neutralizing anti-IL-6 and anti-macrophage inflammatory protein (MIP)-2 Abs inhibits neutrophil recruitment caused by local endotoxin exposure and IL-17, respectively. Our in vitro data show that endotoxin exposure stimulates the release of soluble IL-17 protein in T lymphocytes harvested from lung and spleen, respectively, and that this cytokine release requires coculture with airway macrophages. Intracellular IL-17 protein is detected in T lymphocytes from spleen but not in airway macrophages after coculture and stimulation of these two cell types. Finally, anti-IL-17 does not alter endotoxin-induced release of IL-6 and MIP-2 from T lymphocytes and airway macrophages in coculture. In conclusion, our results indicate that endotoxin exposure causes the release of IL-17 from T lymphocytes and that this cytokine release requires the presence of macrophages. Once released, endogenous IL-17 acts in part by inducing local release of neutrophil-mobilizing cytokines such as IL-6 and MIP-2, from nonlymphocyte, nonmacrophage cells, and this contributes to recruitment of neutrophils in the airways. These IL-17-related mechanisms constitute potential targets for pharmacotherapy against exaggerated neutrophil recruitment in airway disease.

1 Recent data indicate that interleukin (IL)-17 may contribute to neutrophilic airway in¯ammation by inducing the release of neutrophil-mobilizing cytokines from airway cells. The aim of this study was to evaluate the role of mitogen activated protein kinases in IL-17 induced release of IL-8 and IL-6 in bronchial epithelial cells. 4 Ro-31-7549 and LY294002 had no signi®cant e ect on IL-17-induced IL-6 or IL-8 release in bronchial epithelial cells. 5 Taken together, these data indicate a role for p38 and ERK kinase pathways in IL-17-induced release of neutrophil-mobilizing cytokines in human bronchial epithelial cells. These mechanisms constitute potential pharmacotherapeutical targets for inhibition of the IL-17-mediated airway neutrophilia.

The T-cell cytokine interleukin (IL)-17 selectively accumulates neutrophils in murine airways in vivo and may thus constitute a link between activation of T-lymphocytes and accumulation of neutrophils. In this study, the authors evaluated the role of granulocyte macrophage-colony stimulating factor (GM-CSF) in accumulation of neutrophils in the airways caused by IL-17 and tumour necrosis factor (TNF)-a.In vitro, human (h) IL-17 concentration-dependently stimulated the release of GM-CSF protein (enzyme-linked immunosorbent assay) in human bronchial epithelial cells (16HBE). IL-17 also time-dependently stimulated the release of GM-CSF protein in venous endothelial (human umbilical vein endothelial cells) cells in vitro. Co-stimulation with IL-17 plus the pro-inflammatory cytokine TNF-a potentiated the release of GM-CSF protein in 16HBE cells. hIL-17 also enhanced the expression of GM-CSF messenger ribonucleic acid in 16HBE cells (reverse transcriptase polymerase chain reaction), with a similar order of magnitude as TNF-a. Conditioned cell medium from bronchial epithelial cells co-stimulated with hIL-17 plus TNF-a prolonged survival (trypan blue exclusion) of human neutrophils in vitro and this effect was blocked by an anti-GM-CSF antibody. In vivo, local co-stimulation with mouse IL-17 plus TNF-a caused an additive potentiation of the accumulation of neutrophils in bronchoalveolar lavage fluid from mouse airways and this effect was blocked by an anti-GM-CSF antibody given systemically.In conclusion, granulocyte macrophage-colony stimulating factor is involved in the accumulation of neutrophils in the airways caused by interleukin-17 and tumour necrosis factor-a, probably via effects on both recruitment and survival of neutrophils.

The autoimmune regulator (Aire)-directed ectopic expression of tissue-specific antigens (TSAs) by mature medullary thymic epithelial cells (mTECs) has been viewed as an essential mechanism in the induction of central tolerance. Recent data suggest that the survival of mTECs extends beyond the Aire+ cell population to form the post-Aire mTEC population and Hassall’s corpuscles (HCs). The nature and function of these post-Aire epithelial cells and structures, however, have remained unidentified. In this study, we characterized in detail the end-stage development of mTECs and HCs in both Aire-sufficient and Aire-deficient mice. In addition, using a transgenic mouse model in which the LacZ reporter gene is under the control of the endogenous Aire promoter, we purified and analyzed the post-Aire mTECs to characterize their function. We showed that the end-stage maturation of mTECs closely resembles that of keratinocytes and that the lack of Aire results in a marked block of mTEC differentiation, which is partially overcome by ligands for RANK and CD40. We also provide evidence that, during mTEC development, Aire is expressed only once and during a limited 1–2 day period. The following loss of Aire expression is accompanied by a quick downregulation of MHC class II and CD80, and of most of the Aire-dependent and Aire-independent TSAs, with the exception of keratinocyte-specific genes. In the final stage of maturation, the mTECs lose their nuclei to become HCs and specifically express desmogleins (DGs) 1 and 3, which, via cross-presentation by APCs, may contribute to tolerance against these pemphigus vulgaris-related TSAs.

Chronic smoking is characterized by immunosuppressive changes in the airways, leading to chronic colonization with bacteria, which in turn may contribute to the chronic obstructive pulmonary disease. The mechanisms causing this immunosuppression, however, are poorly characterized. This study evaluated whether cigarette smoke can inhibit endotoxin (LPS)-induced inflammatory cytokine production in bronchial epithelial cells and, if so, what the mechanisms are behind this effect. Pretreatment with cigarette smoke extract (CSE) concentration dependently inhibited the LPS-induced GM-CSF and IL-8 protein release, which was accompanied by decreased expression of mRNA in human bronchial epithelial cells (Beas-2B). The increase of neutrophil chemotaxis induced by conditioned medium from LPS-treated Beas-2B cells was also suppressed by CSE. In addition, the activity of LPS-induced transcription factor AP-1, but not NF-κB, was down-regulated by CSE. Notably, at the concentrations used, CSE had no effect on number or viability of Beas-2B cells. These data indicate that cigarette smoke possesses immunosuppressive properties by down-regulating the bacterial pathogen-induced neutrophil-mobilizing cytokine production via suppression of AP-1 activation in the airways. Hence, this study suggests a novel mechanism by which cigarette smoke may contribute to chronic colonization and chronic obstructive pulmonary disease in smokers.