PROS1 and neoplasm: When the macrophages were isolated from the peritoneum of the Mertk-/- or Tyro3-/- mouse, the suppression was also lost, suggesting that PROS1 acting via MERTK inhibits macrophage M1 cytokine production which in the TME would be deleterious to anti-tumor immune stimulation (the suppression was not lost in peritoneal macrophages elicited from the Axl-/- mouse).