Potential involvement of IL-17F in asthma

The expression of IL-17F is seen in the airway of asthmatics and its level is correlated with disease severity. Several studies have demonstrated that IL-17F plays a pivotal role in allergic airway inflammation and induces several asthma-related molecules such as CCL20. IL-17F-induced CCL20 may attract Th17 cells into the airway resulting in the recruitment of additional Th17 cells to enhance allergic airway inflammation. We have recently identified, for the first time, that bronchial epithelial cells are its novel cell source in response to IL-33 via ST2-ERK1/2-MSK1 signaling pathway. The receptor for IL-17F is the heterodimeric complex of IL-17RA and IL-17RC, and IL-17F activates many signaling pathways. In a case-control study of 867 unrelated Japanese subjects, a His161 to Arg161 (H161R) substitution in the third exon of the IL-17F gene was associated with asthma. In atopic patients with asthma, prebronchodilator baseline FEV1/FVC values showed a significant association with the H161R variant. Moreover, this variant is a natural antagonist for the wild-type IL-17F. Moreover, IL-17F is involved in airway remodeling and steroid resistance. Hence, IL-17F may play an orchestrating role in the pathogenesis of asthma and may provide a valuable therapeutic target for development of novel strategies.

Recent progress in host immunity to avian coccidiosis: IL-17 family cytokines as sentinels of the intestinal mucosa

The molecular and cellular mechanisms leading to immune protection against coccidiosis are complex and include multiple aspects of innate and adaptive immunities. Innate immunity is mediated by various subpopulations of immune cells that recognize pathogen associated molecular patterns (PAMPs) through their pattern recognition receptors (PRRs) leading to the secretion of soluble factors with diverse functions. Adaptive immunity, which is important in conferring protection against subsequent reinfections, involves subtypes of T and B lymphocytes that mediate antigen-specific immune responses. Recently, global gene expression microarray analysis has been used in an attempt to dissect this complex network of immune cells and molecules during avian coccidiosis. These new studies emphasized the uniqueness of the innate immune response to Eimeria infection, and directly led to the discovery of previously uncharacterized host genes and proteins whose expression levels were modulated following parasite infection. Among these is the IL-17 family of cytokines. This review highlights recent progress in IL-17 research in the context of host immunity to avian coccidiosis.

IL-17F Induces CCL20 in Bronchial Epithelial Cells

IL-17F plays a crucial role in airway inflammatory diseases including asthma, but its function has not been fully elucidated. CCL20 is also involved in allergic airway inflammation, while its regulatory mechanisms remain to be defined. To further identify a novel role of IL-17F, the expression of CCL20 by IL-17F in bronchial epithelial cells and the signaling mechanisms involved were investigated. Bronchial epithelial cells were stimulated with IL-17F, and the levels of CCL20 gene and protein measured, with the effects of the addition of various kinase inhibitors and siRNAs also investigated. IL-17F significantly induced the expression of CCL20 gene and protein. Pretreatment with inhibitors for MEK1/2, Raf1 and MSK1, and overexpression of a Raf1 dominant-negative mutant significantly diminished IL-17F-induced CCL20 production. Moreover, transfection of the siRNAs targeting MSK1, p90RSK, and CREB blocked CCL20 expression. These findings suggest that IL-17F is able to induce CCL20 via Raf1-MEK1/2-ERK1/2-MSK1/p90RSK-CREB signaling pathway in bronchial epithelial cells. The IL-17F/CCL20 axis may be a novel pharmacological target for asthma.

Induction of insulin-like growth factor-I by interleukin-17F in bronchial epithelial cells

BACKGROUND

Increased expression of IL-17F has been noted in the airway of asthmatic patients, but its role in asthma has not been fully elucidated. Insulin-like growth FACTOR-I (IGF-I) is known to be involved in airway remodelling and inflammation, while its regulatory mechanisms remain to be defined.

OBJECTIVE

To further clarify the biological function of IL-17F, we investigated whether IL-17F is able to regulate the expression of IGF-I in bronchial epithelial cells.

METHODS

Bronchial epithelial cells were stimulated with IL-17F in the presence or absence of T-helper type 2 cytokines. Various kinase inhibitors were added to the culture to identify the key signalling events leading to the expression of IGF-I, in conjunction with the use of short interfering RNAs (siRNAs) targeting mitogen- and stress-activated protein kinase (MSK) 1, p90 ribosomal S6 kinase (p90RSK), and cyclic AMP response element-binding protein (CREB).

RESULTS

IL-17F significantly induced IGF-I gene and protein expression, and co-stimulation with IL-4 and IL-13 augmented its production. MAP kinase kinase (MEK) inhibitors and the Raf1 kinase inhibitor significantly inhibited IGF-I production, and the combination of PD98059 and Raf1 kinase inhibitor showed further inhibition. Overexpression of Raf1 and Ras dominant-negative mutants inhibited its expression. MSK1 inhibitors significantly blocked IL17F-induced IGF-I expression. Moreover, transfection of the siRNAs targeting MSK1, p90RSK, and CREB blocked its expression.

CONCLUSIONS

In bronchial epithelial cells, IL-17F is able to induce the expression of IGF-I via the Raf1-MEK1/2-ERK1/2-MSK1/p90RSK-CREB pathway in vitro.

The IL-17F signaling pathway is involved in the induction of IFN-gamma-inducible protein 10 in bronchial epithelial cells

BACKGROUND

IL-17F is involved in airway inflammation, but its biologic activity and signaling pathway remain incompletely defined. Interferon-gamma-inducible protein 10 (IP-10) is widely expressed and plays a role in airway inflammatory diseases.

OBJECTIVE

We sought to investigate the functional linkage between IL-17F and IP-10 expression in bronchial epithelial cells.

METHODS

Bronchial epithelial cells were cultured in the presence or absence of IL-17F, and/or a T(H)1 cytokine, T(H)2 cytokines, proinflammatory cytokines, various kinase inhibitors, or a Raf1 dominant-negative mutant to analyze the expression of IP-10. Moreover, the involvement of p90 ribosomal S6 kinase (p90RSK) and cyclic AMP response element-binding protein (CREB) in IL-17F-induced IP-10 expression were investigated.

RESULTS

IL-17F induces the gene and protein expression of IP-10. The addition of IFN-gamma, IL-1beta, and TNF-alpha augmented IL-17F-induced IP-10 expression. The mitogen-activated protein kinase kinase (MEK) inhibitors PD98059, U0126, and Raf1 kinase inhibitor I significantly inhibited its production. In contrast, a p38 inhibitor, a JNK inhibitor, protein kinase C inhibitors, and a phosphatidylinositol 3-kinase inhibitor, showed no inhibitory effect. Furthermore, overexpression of a Raf1 dominant-negative mutant inhibited its expression. Of interest, IL-17F phosphorylated p90RSK and CREB, and transfection of the cells with a short interfering RNA for p90RSK or CREB inhibited its expression, suggesting p90RSK and CREB as novel signaling molecules of IL-17F.

CONCLUSION

IL-17F is a potent inducer of IP-10 in bronchial epithelial cells through the activation of the Raf1-MEK1/2-extracellular signal-regulated kinase 1/2-p90RSK-CREB pathway, supporting its regulatory role in airway inflammation.

CLINICAL IMPLICATIONS

The IL-17F-IP-10 axis might be a novel and critical therapeutic target for airway inflammatory diseases.

IL-17 cytokine family

A new family of cytokines, IL-17, has recently been defined that reveals a distinct ligand-receptor signaling system. Functional studies have provided evidence for its importance in the regulation of immune responses. Notably, 3 members, IL-17A, IL-17E (IL-25), and IL-17F, have been best characterized both in vitro and in vivo , and have been shown to be proinflammatory in nature. This proinflammatory activity is exemplified by their involvement in pulmonary inflammatory responses, in which both IL-17A and IL-17F are involved in the recruitment of neutrophils, and IL-17E is able to induce T H 2 cytokine production and eosinophilia. Although the elucidation of a detailed mechanism of action continues to be an active area of research, the potent inflammatory activity and its association with various human disease states suggest this new cytokine family as an important contributor to the pathophysiology of human disease conditions, in particular the pulmonary diseases.

Interleukin-17F induces pulmonary neutrophilia and amplifies antigen-induced allergic response

Interleukin (IL)-17F is a recently described human cytokine belonging to the IL-17 gene family, but its in vivo function remains to be determined. To this end, a full-length mouse IL-17F cDNA sequence with a 483-bp coding region sequence was first identified. Pulmonary gene transfer of an IL-17F expression construct (pcDNAmIL-17F) in mice was used to investigate its regulatory role. The results showed first that a significant increase in the number of neutrophils was seen in the bronchoalveolar lavage fluids of IL-17F-transduced mice, concomitant with increased expression of genes encoding C-X-C chemokines and inflammatory cytokines when compared with mock and phosphate-buffered saline control animals. Mucosal transfer of the IL-17F gene in ovalbumin (OVA)-sensitized mice before antigen (Ag) challenge enhanced the levels of Ag-induced pulmonary neutrophilia, but not eosinophilia, goblet cell hyperplasia, and mucin gene expression. However, no significant change in the levels of Th2 cytokine expression was noted. A significant enhancement of ventilatory timing in response to inhaled methacholine was also seen in IL-17F-transduced, Ag-sensitized mice, whereas a small but significant increase was found in IL-17F-transduced, naive mice. These results suggest a role for IL-17F in the induction of neutrophilia in the lungs and in the exacerbation of Ag-induced pulmonary inflammation.