Besides viral infection, the expression of TLR2 was significantly induced by lipopolysaccharide (LPS) and Aeromonas hydrophila in the head kidney, liver, gill, trunk kidney, and spleen of Qihe crucian carp (Carassius auratus), indicating that various PRRs could trigger TLR2-mediated immune response in main tissues of fish [39]. The gene discussed is TLR2; the disease is viral infectious disease.