S100A9 and periodontitis: To determine a potential correlation between calprotectin levels and periodontitis and to examine the mechanism of calprotectin's influence on the behavior of PDLCs, calprotectin levels in the GCF of patients with generalized aggressive periodontitis (AgP) were evaluated and the pro-apoptotic and pro-inflammatory effects of recombinant S100A8, S100A9, and S100A8/A9 in PDLCs were investigated.