Furthermore, MDSCs can also secrete large amounts of S100A9 in MDS, which on the one hand, can interact with TLR-4 on HSPCs to activate downstream inflammatory signaling pathways, and on the other hand, bind to their cellular surface CD33 to trigger the production of immunosuppressive cytokines IL-10 and TGF-β to directly inhibit hematopoiesis through their immune receptor tyrosine-based inhibitory motifs [119]. Here, CD33 is linked to myelodysplastic syndrome.