Relative gene expression and protein level of pro-inflammatory cytokines (TNF-α, IL-6, IL-8), IL-10, TLR-2 and SERT were measured in fully differentiated Caco-2 monolayers following 24 h of bacterial infection in the presence of different levels of 5-HT (0, 100, 250, 500 ng/mL). The gene discussed is CXCL8; the disease is bacterial infectious disease.