Three studies only assessed the serum IgG levels of the oral bacteria associated with periodontopathic biofilms (Kamer et al., 2009; Stein et al., 2012; Noble et al., 2014); one study evaluated periodontitis by clinical parameters and also assessed pro-inflammatory cytokines levels (IL-1, IL-6, and TNF-α) in serum (Cestari et al., 2016). The gene discussed is IL6; the disease is periodontitis.