Interleukin 17A (IL-17A) is the founding member of the IL-17 family, which is composed of six members with different patterns of expression. The IL-17 family is characterized by a common disulfide-linked homodimeric structure, and different family members can also form heterodimers, such as IL-17A/IL-17F. IL-17 family members act as pro-inflammatory agents involved in the immunity against extracellular pathogens, but they are extensively studied mainly for their pathogenic role in autoimmunity and allergy. IL-17F is expressed by Th17 cells, NK cells, monocytes, basophils, and mast cells, and plays a chemotactic role for neutrophils. Both IL-17A and IL-17F act on a specific receptor complex formed by IL-17RA and IL-17RC, expressed on different stromal cells in several tissues, such as endothelial cells, fibroblasts, and immune cells. IL-17F also plays a regulatory role as inhibitor of angiogenesis, and participates in the regulation of cartilage matrix modeling. A strong association between IL-17F and asthma has been found, and IL-17F is investigated as therapeutic target for the cure of allergic airway inflammation.
