Despite the potential pathogenetic link between PD and RA, patients with RA and PD deal with the same imbalance of cytokines, including higher levels of gingival crevicular fluid of pro-inflammatory cytokines (IL-1β, IL-6, IL-4, and TNF-α) and lower levels of anti-inflammatory cytokines (e.g., IL10) [48,77,78,79]. The gene discussed is IL4; the disease is rheumatoid arthritis.