Fatty acids secreted from head and neck cancer induce M2-like Macrophages.

Tumor-infiltrating monocytes can mature into Macrophages that support tumor survival or that display antitumor properties. To explore mechanisms steering Macrophage maturation, we assessed the effects of supernatants from squamous cell carcinoma cell lines (FaDu and SCC) on monocyte-derived Macrophage maturation. Purified monocytes were incubated in medium or medium supplemented with supernatants from FaDu and SCC9 or the leukemia monocytic cell line, THP-1. Macrophages were examined for markers of maturation (CD14, CD68), activation (HLA-DR, CD86, IL15R), scavenger receptor (CD36), toll-like receptor (TLR4), M2 marker (CD206), immune checkpoint (PD-L1), and intracellular chemokine expression (IP-10). Compared to other conditions, cells incubated with FaDu or SCC9 supernatants displayed enhanced survival, down-regulation of cell surface HLA-DR, CD86, IL-15R, CD36, and intracellular IP-10 expression, and increased cell surface PD-L1, CD14, and CD206 expression. Despite expressing TLR4 and CD14, Macrophages matured in tumor supernatants failed to respond to stimulation with the canonical TLR4 agonist, LPS. These changes were accompanied by a decrease in intracellular phospho-p38 expression in tumor supernatant conditioned Macrophages. Depletion of fatty acids from tumor supernatants or treatment of cell cultures with an inhibitor of fatty acid oxidation, Etomoxir, reversed a number of these phenotypic changes induced by tumor supernatants. Additionally, Macrophages incubated with either palmitic acid or oleic acid developed similar phenotypes as cells incubated in tumor supernatants. Together, these data suggest that fatty acids derived from tumor cells can mediate the maturation of Macrophages into a cell type with limited pro-inflammatory characteristics.

Endosomal toll-like receptors play a key role in activation of primary human monocytes by cowpea mosaic virus.

The plant virus, cowpea mosaic virus (CPMV), has demonstrated a remarkable capacity to induce anti-tumour immune responses following direct administration into solid tumours. The molecular pathways that account for these effects and the capacity of CPMV to activate human cells are not well defined. Here, we examine the ability of CPMV particles to activate human monocytes, dendritic cells (DCs) and macrophages. Monocytes in peripheral blood mononuclear cell cultures and purified CD14+ monocytes were readily activated by CPMV in vitro, leading to induction of HLA-DR, CD86, PD-L1, IL-15R and CXCL10 expression. Monocytes released chemokines, CXCL10, MIP-1α and MIP-1ß into cell culture supernatants after incubation with CPMV. DC subsets (pDC and mDC) and monocyte-derived macrophages also demonstrated evidence of activation after incubation with CPMV. Inhibitors of spleen tyrosine kinase (SYK), endocytosis or endocytic acidification impaired the capacity of CPMV to activate monocytes. Furthermore, CPMV activation of monocytes was partially blocked by a TLR7/8 antagonist. These data demonstrate that CPMV activates human monocytes in a manner dependent on SYK signalling, endosomal acidification and with an important contribution from TLR7/8 recognition.