DC-HL had considerably lower binding of the antibody than DC-NL (Fig. differentiation, we unexpectedly observed accumulation of lipids in DCs generated in the presence of tumor cell conditioned medium (Supplementary Fig. 1). These findings prompted us to investigate the potential role of lipid accumulation in DC function in cancer. Lipids represent a diverse group of low molecular weight molecules. Most lipid molecules contain fatty acid moieties3. Lipids are an important energy resource and a major structural component of the membrane matrix. Signaling functions of fatty acids are now considered a core component of the network, Talabostat mesylate TNFSF8 regulating different cells (rev in. 4). The factors affecting storage, uptake and metabolism of different fatty acids in DC may impact the function of the immune system5. A number of studies have shown the negative effect of dietary lipids on DC function6C14 (see supplementary material). These data indicate that lipids could be an important factor regulating DC function. However, their exact role in DC activity remains unclear. There is very little information regarding the biological or clinical significance of lipid accumulation in DCs in cancer. Here, we report our novel finding that accumulation Talabostat mesylate of lipids in DCs is not only a consistent phenomenon found in tumor-bearing hosts, but also has a profound effect on DC function. Results Lipid accumulation in DCs To evaluate the level of lipids in DCs we used the lipophilic fluorescent dye Bodipy 493/503. CD11c+ DCs isolated from spleens of mice bearing EL-4 tumor displayed higher fluorescence than their control counterparts (Fig. 1a). Using flow cytometry we detected two populations of CD11c+ DCs in Talabostat mesylate tumor-bearing (TB) mice. One population termed DCs with normal lipid content (DC-NL) representing 30C50% of cells had a similar level of fluorescence to that in control DCs. The other population (50C70% of cells) referred to as DCs with high lipid content (DC-HL) had fluorescence higher than that in control DCs (Fig. 1b). The level of lipids in spleen DCs was elevated in all 4 tested tumor models in C56BL/6 and BALB/c mice as compared with DCs from control Talabostat mesylate mice (Fig. 1c) and it increased with tumor progression (Fig. 1d). Increased lipid levels were observed in CD11c+CD8+ DCs and CD11c+CD11b+B220? conventional DCs (cDC) but not in CD11c+CD11b?B220+ plasmacytoid DCs (pDC) (Fig. 1e). DCs isolated from tumors had higher levels of lipids than DCs from blood and lymph nodes (LN) (Fig. 1f). DCs from the LN, bone marrow (BM), and blood from TB mice had higher levels of lipids than DCs from control mice (Fig. 1g). The lipid content was equally elevated in DCs from tumor-draining and distant LNs (Fig. 1h). Open in a separate window Figure 1 Lipid levels in DCs from TB micea. Staining of CD11c+ from the spleens of na?ve and EL-4 TB Talabostat mesylate mice with Bodipy 493/503. 10m scale bar shown. b. A typical example of the analysis of lipid level in CD11c+ DCs from spleens of control (red) or EL-4 TB mice (blue). c. Cumulative results of lipid staining of splenocytes from different tumor models. Geomean fluorescence intensity (MFI) of Bodipy 493/503 in CD11c+ DCs was measured. Each group includes 4-8 mice. Control and TB mice were evaluated in parallel in each experiment. d. Proportion of DCs with high lipid content in spleens during progression of CT-26 tumors. Each time point included 3 mice. Mean SD are shown. e. Lipid levels in different populations of DCs from the spleens of control or EL-4 TB mice..