C3 and esophageal squamous cell carcinoma: Gingipains produced and secreted by P. gingivalis induces the expression of pro-inflammatory mediator, as matrix metalloproteinases (MMPs), degrades extracellular matrix (ECM), destroys immunoglobulin and complement components C3 and C5, and enables ESCC to escape killing by macrophages and neutrophils, leading to ESCC occurrence and development [50].