Effects of S100A8 and S100A9 on AML cell differentiation and proliferation. S100A8 and S100A9 are secreted by a subpopulation of leukemic cells (CD11b⁺Ly6G⁺c-kit⁺) in AML. S100A9 binds to TLR4 and induces signaling pathways, promoting leukemic cell differentiation and proliferation arrest. (1) S100A8 could bind to TLR4 and activate different signaling pathways, leading to the inhibition of cellular differentiation induced by S100A9. (2) Alternatively, S100A8 could interact with a different receptor and induce an antagonizing signal to inhibit S100A9-induced differentiation.