Characterization of Lamprey IL-17 Family Members and Their Receptors.

IL-17 is an ancient cytokine implicated in a variety of immune defense reactions. We identified five members of the sea lamprey IL-17 family (IL-17D.1, IL-17D.2, IL-17E, IL-17B, and IL-17C) and six IL-17R genes (IL-17RA.1, IL-17RA.2, IL-17RA.3, IL-17RF, IL-17RE/RC, and IL-17RD), determined their relationship with mammalian orthologs, and examined their expression patterns and potential interactions to explore their roles in innate and adaptive immunity. The most highly expressed IL-17 family member is IL-17D.1 (mammalian IL-17D like), which was found to be preferentially expressed by epithelial cells of skin, intestine, and gills and by the two types of lamprey T-like cells. IL-17D.1 binding to rIL-17RA.1 and to the surface of IL-17RA.1-expressing B-like cells and monocytes of lamprey larvae was demonstrated, and treatment of lamprey blood cells with rIL-17D.1 protein enhanced transcription of genes expressed by the B-like cells. These findings suggest a potential role for IL-17 in coordinating the interactions between T-like cells and other cells of the adaptive and innate immune systems in jawless vertebrates.