IL17A and atrial fibrillation: Additionally, various factors influence the level of CRP expression in serum, making CRP a nonspecific inflammatory secretory factor in the inflammatory immune regulation of AF.[16–18] Interleukin-17 (IL-17) is a cytokine secreted by T helper cells 17 (Th17).[34] Th17 cells primarily mediate the differentiation of naïve T cells, a process predominantly driven by IL-6,[35–37] a cytokine primarily secreted by macrophages.