IL17A and periodontitis: Increasing evidence has shown that T-helper 17 (Th17) cells that produce interleukin (IL)-17 (also known as IL-17A) (Park et al., 2005; Harrington et al., 2005) are involved in the pathogenesis of periodontitis and alveolar bone destruction (Adibrad et al., 2012; Cardoso et al., 2009).