IL17A and periodontitis: Garlet (2010) reported that Th1 and Th17 cytokines have intimate involvement in the progression of periodontitis. In addition, Th17 cells and IL-17 might be a key inducer for the alveolar bone breakdown in periodontitis (Eskan et al., 2012). Several studies have observed the IL-17 or IFN-γ producing T cell population of peripheral blood in CP patients (Chen et al., 2016; Chen et al., 2015; Luo et al., 2014; Saraiva et al., 2013); however, the results are inconclusive as to whether these cells are increased or not.