IDO expression by human B lymphocytes in response to T lymphocyte stimuli and TLR engagement is biologically inactive

► IDO mRNA and protein are expressed in human B lymphocytes when activated with CD40L and IFN-γ. ► TLR7/8 synergizes with CD40L + IFN-γ stimulation to enhanced IDO mRNA. ► The IDO expressed in human B lymphocytes is enzymatically inactive when tryptophan catabolism is measured by HPLC.