E. coli-expressed chicken IL-17A enhances respiratory innate immunity by inducing proinflammatory cytokines and interferons.

Interleukin-17A (IL-17A) is a key pro-inflammatory cytokine that plays a crucial and complex role in immune regulation, infection, and inflammation under both physiological and pathological conditions, demonstrating significant potential in these fields. However, research on its interaction with the avian respiratory system and its potential application as a mucosal immune adjuvant is limited. To investigate its functional relevance, a comparison was first performed of the genetic and structural features of chicken IL-17A (chIL-17A) with those of its mammalian homologs. Recombinant chIL-17A was subsequently produced via a prokaryotic expression system and evaluated through in vitro assays using chicken embryo fibroblasts (CEFs) and peripheral blood mononuclear cells (PBMCs), as well as in vivo experiments in specific-pathogen-free (SPF) chickens. In the in vivo study, 3-week-old SPF White Leghorn chickens (mixed sex) were nebulized with a single or double dose (20 μg/kg per dose, n = 12 per group) of chIL-17A. The results demonstrated that chIL-17A treatment markedly upregulated the transcription of proinflammatory cytokines (e.g., IL-1β, IL-6, and TNF-α), type I interferons, and multiple interferon-stimulated genes in a dose-and time-dependent manner. Notably, a second administration further enhanced its stimulatory effect on these immune mediators. In vivo, nebulized chIL-17A significantly induced pulmonary proinflammatory responses, particularly on day 5 post-treatment, with IL-1β and IL-6 mRNA levels increasing by 67.35-fold (P < 0.001) and 130.19-fold (P < 0.001), respectively, in lung tissues. Modulation of IFN responses was most pronounced in the lower trachea and lung tissues, with minimal effects in the upper tracheal region. These findings unequivocally demonstrate the potent immunomodulatory capacity of chIL-17A and underscore its potential as a mucosal immune enhancer in poultry.