IDO1 and neoplasm: Similarly, PGE2 impairs the NK cell and DCs interactions, reducing IL-12 secretion by DCs and CD4 T-cell polarization.454 Tumor PGE2 was also reported to inhibit chemokine receptors on cDC cells, preventing their attraction by CCL5 and XCL1 secreted by NK cells.322 IDO metabolizes Tryptophan to L-kynurenine, which inhibits the upregulation of NKp46 and NKG2D under IL-2 stimulation.