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. 2020 Jan 22;9:1556. doi: 10.3389/fonc.2019.01556

Figure 1.

Figure 1

The intricate interplay within the K-ras mutant lung cancer tumor microenvironment. Tumors are constantly infiltrated with immune cells which make up important components of the TME. Tumor cells attract immunosuppressive immune cells such as M2 macrophages, neutrophils, MDSCs, Th17 and Treg cells through secretion of soluble factors (CCL2, CCL3, CXCL1, CXCL2, IL-1β, IL-6, IL-8, IL-10, TGFβ, G-CSF, etc.). These cells promote tumor growth, angiogenesis, and at the same time, protect tumor cells from cytotoxic effects. CD8+ T cells and NK cells attack tumor cells through secretion of perforin, granzyme B and IFNγ, and Th1 cells act as important assistants for CD8+ T cells. However, tumor cells, MDSCs and Treg cells could render cytotoxic immune cells incompetent through expressing immune checkpoint molecules. Moreover, immunosuppressive cells also produce soluble factors that exhaust CD8+ T cells and NK cells, such as arginase, IDO, iNOS, TGFβ, etc.