IFNG and neoplasm: The expression of IFN-γ mRNA was decreased in Lee1 cells co-cultured with DF-1 expressing PD-L1, suggesting that in case of chickens, PD-L1 also interacts with PD-1, and then induces the immunosuppression in PD-1-expressing cells, although further functional analysis concerning the involvement of chickens PD-1/PD-L1 pathway in immunosuppression and tumor formation is required.