Diagram outlining how ionizing radiation (IR) of tumors leads to anti-tumor responses and how tumor hypoxia can interfere such loop. (A) Ionizing radiation can induce anti-tumor immunity via secreting various danger-associated molecular pattern (DAMP) molecules, which can stimulate dendritic cells and cytotoxic T cells. (B) However tumor hypoxia can mediate various pathways, in which can counteract the antitumor immunity.

Abbreviations: DCs, dendritic cells; HMGB1, high mobility group protein box 1; ATP, adenosine triphosphate; HSPs, heat shock proteins; HIF-1, hypoxia-inducible factor-1; PD-L1, programmed death-ligand 1; VEGF, vascular endothelial growth factor; VEGFR-1, vascular endothelial growth factor receptor-1; CXCL-12, C-X-C motif chemokine ligand 12; CXCR-4, C-X-C motif chemokine receptor-4; MDSCs, myeloid-derived suppressor cells; TAMs, tumor-associated macrophages; MMP, matrix metalloproteinase; S100A8, S100 calcium-binding protein A8; IL-1β, interleukin-1β; IL-6, interleukin-6; TNF-α, tumor necrosis factor-α.