Nevertheless, the findings raised here with respect to atherosclerosis are not without precedent in the cancer literature. Recent work has shown, for example, that dendritic cells with high lipid content are less effective at presenting tumor-associated antigens; this appears to be due to a selective defect in antigen processing while the cells continue to take up soluble proteins 33. Several other studies have also supported a role for nuclear receptors 34 and the NLRP3 inflammasome 35–37 in cancer progression. Many questions remain, however. What is the role of the cholesterol efflux pathways in the macrophage cancer response? Do lipid-loaded monocytes/macrophages traffic to tumor sites and influence

cancer progression? Is atherosclerosis-associated Sunitinib in vivo leukocytosis a major mechanism by which myeloid-derived suppressor cells (MDSCs, discussed in the next section)

arise? Harnessing some Sorafenib ic50 of these atherosclerosis-related studies to better understand how metabolism and inflammation converge in cancer may provide unexpected insights and strengthen common threads between these two pathologies. Ly6Chigh CCR2high (but not Ly6Clow CCR2−) mouse monocytes represent a sizeable fraction of a heterogeneous population of cells called Gr-1+ CD11b+ MDSCs, which are defined operationally by their capacity to regulate T-cell responses 38. MDSCs are widely talked about in the context of cancer and have Interleukin-3 receptor been also shown to control immune responses during pathogen infection, transplantation and trauma 39, 40. Whether they participate during atherosclerosis remains largely unknown. MDSCs produce immunosuppressive factors, such as nitric oxide and reactive oxygen species, that suppress anti-tumor effector

T-cell activity 41, enhance regulatory T-cell responses 42 and collectively support tumor progression. Accumulating evidence also supports a key role for T cells in atherosclerosis 6. In this context, however, effector T cells exert proatherogenic effects, whereas regulatory T cells dampen inflammation and are antiatherogenic. Consequently, when merely considering their impact on T cells, Ly6Chigh monocytes/MDSCs might exert antiatherogenic functions. This notion is unexplored because Ly6Chigh monocytes are well-known precursors of macrophages and lipid-rich foam cells in atheromata. Future studies should define the spectrum of MDSC-mediated functions (beside modulation of T-cell responses) and the relative importance of these activities in distinct disease settings. MDSCs (and TAMs) also often activate STAT3 upon recruitment to tumors. This transcription factor, by triggering the NF-κB and JAK pathways, typically activates the production of enzymes (metalloproteinases), cytokines (IL-6, IL-10, IL-17, IL-23) and growth factors (VEGF, FGF) that elicit and sustain angiogenic and metastatic programs 43, 44.