IL-17A synergistically stimulates TNF-α-induced IL-8 production in human airway epithelial cells: A potential role in amplifying airway inflammation

BACKGROUND

Recent reports have suggested an involvement of neutrophilic inflammation driven by interleukin (IL)-17 from Th17 cells, especially in severe, refractory asthma. It remains unknown about the possible interactions of this cytokine and other proinflammatory cytokines to direct neutrophilic airway inflammation.

MATERIALS AND METHODS

We evaluated the effects of IL-17A, IL-17E, and IL-17F in combination with other stimuli such as tumor necrosis factor (TNF) -α on the production and expression of IL-8 in human bronchial epithelial cells. We also studied their effects on other cytokine production. The possible role of mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signaling pathways was evaluated by specific inhibitors. We examined the effects of anti-asthma drugs, such as steroids or salmeterol.

RESULTS

IL-17A alone induced only a minimal effect on IL-8 expression. IL-17A, but not IL-17E or IL-17F, in combination with TNF-α showed a synergistic effect on IL-8 expression. Similar findings were found when combination with IL-1β and IL-17A were used, but such was not the case with lipopolysaccharide (LPS). In addition, we further found such synergy on GM-CSF production. The synergy with TNF-α and IL-17A was significantly inhibited by MAPKs inhibitors. Corticosteroids such as fluticasone propionate and dexamethasone, but not salmeterol, partially suppressed the IL-17A and TNF-α-induced IL-8 production.

CONCLUSIONS

IL-17A in the combination with TNF-α or IL-1β showed a synergistic augmenting effect on IL-8 and GM-CSF production in human airway epithelial cells.

Comparison of IL-17 production by helper T cells among atopic and nonatopic asthmatics and control subjects

BACKGROUND

T cells, eosinophils, and neutrophils are strongly involved in the pathogenesis of bronchial asthma. Mechanisms that influence neutrophil accumulation and activation in asthma still remain relatively obscure. There is data indicating that IL-17 is produced by T cells and causes the release of neutrophil-mobilizing cytokines from airway epithelial cells, and that in this way it may regulate airway neutrophilia.

METHODS

Peripheral blood mononuclear cells (PBMC) obtained from atopic asthmatics (AA), nonatopic asthmatics (NA), and normal control subjects (NC) were stimulated by immobilized anti-CD3 antibody (Ab) plus soluble anti-CD28 Ab or Dermatophagoidesfarinae (Df) extract. Df-reactive T cell clones were established from PBMC of AA and cultured in the presence of various stimulants. The resulting supernatants were assayed for IL-2, IL-4, IL-5, IL-13, IL-17, and IFN-gamma by specific ELISAs.

RESULTS

PBMC obtained from AA, NA, and NC all produced IL-17 upon immobilized anti-CD3 Ab plus soluble anti-CD28 Ab stimulation. IL-17 production in response to Df extract was significantly induced only in AA. The amount of IL-17 produced by T cell clones stimulated with immobilized anti-CD3 Ab plus soluble anti-CD28 Ab was negatively, but only weakly, correlated with that of IL-4, but not correlated with IL-2, IL-5, IL-13, and IFN-gamma production.

CONCLUSION

T cells producing IL-17 in response to Df antigen exist in the peripheral blood of the sensitized AA. IL-17 production might be regulated by unique mechanisms different from those governing Th1 versus Th2 differentiation.