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. Author manuscript; available in PMC: 2019 Jun 11.
Published in final edited form as: Cancer Cell. 2018 Apr 12;33(6):965–983. doi: 10.1016/j.ccell.2018.03.002

Figure 4. Platelet involvement in inflammation and immunity.

Figure 4

Bone marrow derived cell (BMDC) induction and differentiation is stimulated by platelet secretion of CXCL5 and CXCL7 which promotes granulocyte recruitment to tumor cells. Transforming growth factor-beta (TGF-β) released from platelets and microenvironmental PGE2 accumulation also stimulate marrow derived stem cells (MDSC) and T-cell differentiation or inhibition, which encompasses CD8+ cytotoxic T-cells, T-helper1 (TH1), T-helper17 (TH17) and T-regulatory cells (Treg). Secreted TGF-β induces epithelial-mesenchymal-transition (EMT) genes and also facilitates myeloid polarization of macrophages and neutrophils towards immunosuppressive phenotypes. This can generate microenvironmental niches at platelet facilitated arrest sites for cancer cells during the establishment of metastasis. Thus, these platelet-tumor cell microenvironmental niches may direct tumor-associated immune cells to convert from a pro-inflammatory to an immunosuppressive phenotype.