HTR1B and leukemia: Furthermore, AML-secreted kynurenine binds osteoblastic serotonin receptor 1B (HTR1B) to induce proinflammatory serum amyloid A (SAA), which in turn upregulates indoleamine 2,3-dioxygenase 1 (IDO1) in leukemia cells to amplify kynurenine production and establish a self-reinforcing loop, which fosters immune evasion[64].