Downregulation of chicken interleukin-17 receptor A during Eimeria infection

Both interleukin-17A (IL-17A) and IL-17F are proinflammatory cytokines that have an important role in intestinal homeostasis via receptor signaling. These cytokines have been characterized in chickens, but very little is known about their receptors and their functional activity. We provide here the first description of the sequence analysis, bioactivity, and comparative expression analysis of chicken IL-17RA (chIL-17RA) in chickens infected with Salmonella and Eimeria, two major infectious agents of gastrointestinal diseases of poultry of economic importance. A full-length chIL-17RA cDNA with a 2,568-bp coding region was identified from chicken thymus cDNA. chIL-17RA shares ca. 46% identity with mammalian homologues and 29.2 to 31.5% identity with its piscine counterparts. chIL-17RA transcript expression was relatively high in the thymus and in the chicken macrophage cell line HD11. The chIL-17RA-specific small interfering RNA inhibits interleukin-6 (IL-6), IL-8, and IL-1β mRNA expression in chicken embryo fibroblast cells (but not in DF-1 cells) stimulated with chIL-17A or chIL-17F. Interaction between chIL-17RA and chIL-17A was confirmed by coimmunoprecipitation. Downregulation of chIL-17RA occurred in concanavalin A- or lipopolysaccharide-activated splenic lymphocytes but not in poly(I·C)-activated splenic lymphocytes. In Salmonella- and Eimeria-infected chickens, the expression levels of the chIL-17RA transcript were downregulated in intestinal tissues from chickens infected with two Eimeria species, E. tenella or E. maxima, that preferentially infect the cecum and jejunum, respectively. However, chIL-17RA expression was generally unchanged in Salmonella infection. These results suggest that chIL-17RA has an important role in mucosal immunity to intestinal intracellular parasite infections such as Eimeria infection.