Yin and yang of interleukin-17 in host immunity to infection

Abstract

The interleukin-17 (IL-17) family cytokines, such as IL-17A and IL-17F, play important protective roles in host immune response to a variety of infections such as bacterial, fungal, parasitic, and viral. The IL-17R signaling and downstream pathways mediate induction of proinflammatory molecules which participate in control of these pathogens. However, the production of IL-17 can also mediate pathology and inflammation associated with infections. In this review, we will discuss the yin-and-yang roles of IL-17 in host immunity to pathogens.

Keywords: IL-17; host immune response; pathogens.

Figure 1.. Yin-and-yang roles of IL-17 during infections.

As the host immune system encounters a pathogen, host immune cells respond by releasing an array of cytokines such as IL-23, IL-6, and IL-1β. ( A) These cytokines elicit IL-17 production from both innate cells (iLC3, NK, iNKT, iTH17, and γδ T) and adaptive cells (Th17 and Tc17). ( B) This IL-17 then acts on responder cells, which express IL-17Rs on the cell surface, such as epithelial cells or myeloid cells. ( C) Through IL-17R signaling, these responder cells produce chemokines which help recruit neutrophils to the site of infection. ( D) These recruited neutrophils destroy the pathogen (mostly extracellular) through the production of cytokines, chemokines, and anti-microbial peptides. ( E) Similarly, myeloid cells are also able to restrict pathogen establishment through activation and recruitment of Th1 cells. These Th1 cells secrete proinflammatory cytokines, chemokines, and anti-microbial peptides to restrict pathogenesis. On the other hand, excessive inflammation at the site of infection may lead to exacerbated disease pathology. IL, interleukin; IL-17R, interleukin 17 receptor; iLC3, group 3 innate lymphoid cell; iNKT, invariant natural killer T; iTH17, innate T helper cell type 17 cell; NK, natural killer; Th, T helper cell type.