Identification and characterization of tryptophan-kynurenine pathway-related genes involving lamprey (Lampetra japonica) innate immunity

The tryptophan–kynurenine (TRP–KYN) pathway is involved in several biological functions, including immunosuppression, inflammatory response, and tumor suppression. Six TRP–KYN pathway-related genes, tryptophan 2,3-dioxygenase (TDO), indoleamine 2,3-dioxygenase 2 (IDO2), aminoadipate aminotransferase (AADAT), glutamate oxaloacetate transaminase 2 (GOT2), kynurenine monooxygenase (KMO), and kynureninase (KYNU) have been identified and cloned from the jawless vertebrate lamprey (Lampetra japonica) to gain insights into their evolution and characterization. Expression distribution showed that the key gene Lj-TDO was highly expressed in the oral gland. Real-time quantitative PCR showed that TRP–KYN pathway-related genes were significantly overexpressed after multi-stimulation. RNA interference showed that Lj-IDO2 knockdown regulated the expression of inflammatory factors. In conclusion, our study successfully clarified the ancestral features and functions of the TRP–KYN pathway, while providing valuable insights into the involvement of this pathway in the immune responses of a jawless vertebrate.