IL-23 and Th17 cells not only induce Th17-cell-mediated neutrophilic airway inflammation but also up-regulate Th2-cell-mediated eosinophilic airway inflammation.

No abstract

In order to determine the role of CD4+ and CD8+ T-cells and of interleukin-5 (IL-5) in causing antigen-induced eosinophil infiltration into the site of airway late-phase reaction, we examined the effect of the in vivo depletion of CD4+ and CD8+ T-cells on the eosinophil infiltration of the trachea induced by antigen inhalation in mice. We also studied the effect of anti-murine IL-5 monoclonal antibody (mAb) on the antigen-induced eosinophil infiltration in the trachea. The eosinophil infiltration into the trachea of ovalbumin (OVA)-sensitized BALB/c mice began to increase 9 h after OVA inhalation and persisted for more than 48 h. The in vivo depletion of CD4+ T-cells by pretreatment with anti-L3T4 mAb significantly decreased the eosinophil infiltration induced by OVA inhalation in the trachea of sensitized mice. However, the in vivo depletion of CD8+ T-cells by pretreatment with anti-Lyt-2 mAb had no significant effect on OVA-induced eosinophil infiltration in the trachea. Pretreatment with anti-murine IL-5 mAb also decreased OVA-induced eosinophil infiltration in the trachea. In contrast, neither disodium cromoglycate nor a selective antagonist for platelet-activating factor CV-6209 decreased OVA-induced airway eosinophilia in the mouse. Our results provide direct evidence that CD4+ but not CD8+ T-cells mediate antigen-induced eosinophil recruitment in the airways and that IL-5 mediates this eosinophil recruitment.

It has recently been shown that interleukin (IL)-21 is produced by Th17 cells, functions as an autocrine growth factor for Th17 cells, and plays critical roles in autoimmune diseases. In this study, we investigated the differentiation and characteristics of IL-21–producing CD4+ T cells by intracellular staining. Unexpectedly, we found that under Th17-polarizing conditions, the majority of IL-21–producing CD4+ T cells did not produce IL-17A and -17F. We also found that IL-6 and -21 potently induced the development of IL-21–producing CD4+ T cells without the induction of IL-4, IFN-γ, IL-17A, or IL-17F production. On the other hand, TGF-β inhibited IL-6– and IL-21–induced development of IL-21–producing CD4+ T cells. IL-2 enhanced the development of IL-21–producing CD4+ T cells under Th17-polarizing conditions. Finally, IL-21–producing CD4+ T cells exhibited a stable phenotype of IL-21 production in the presence of IL-6, but retained the potential to produce IL-4 under Th2-polarizing conditions and IL-17A under Th17-polarizing conditions. These results suggest that IL-21–producing CD4+ T cells exhibit distinct characteristics from Th17 cells and develop preferentially in an IL-6–rich environment devoid of TGF-β, and that IL-21 functions as an autocrine growth factor for IL-21–producing CD4+ T cells.

IL-17 is overproduced by T cells from the peripheral blood and fibrotic lesions of the skin and lungs in SSc patients. These results suggest that IL-17 overproduction plays an important role in the pathogenesis of SSc, especially in the early stages of the disease, by inducing the proliferation of fibroblasts and the production of IL-1 and the expression of adhesion molecules on endothelial cells.