Effect of monoamine oxidase- A on the anti- tumor immunity of tumor- associated macrophages in biliary tract cancers

Abstract

Objective To investigate the effect of monoamine oxidase- A(MAO- A)in biliary tract cancers(BTCs) on the immunity of tumor- associated macrophages. Methods MAO- A expression plasmid and control plasmid were constructed and transiently transfected into BTC cell lines respectively. Macrophages were derived from peripheral blood mononuclear cells donated by healthy volunteers. Macrophages were then cocultured with aforementioned transfected cancer cell lines for 48 h respectively, Western blotting and enzyme linked immunosorbent assay(ELISA) were applied to assess the expression of immune effector proteins and the excretion of cytokines from cocultured macrophages.24 h priming of macrophages with human recombinant interferon-γ(IFN -γ) were performed after their first stage of coculture; then the second stage of coculture with corresponding transfected cancer cell lines for 48 h were followed.Flow cytometry was employed to detect necrosis and apotosis of cancer cells induced by cocultured macrophages. Results The expression of MAO- A was down- regulated in BTC cell lines, which polarized the cocultured macrophages into M2 type tumor- associated macrophages, and promoted their excretion of interleukin(IL)- 10 and expression of PD- L1, while suppressed their excretion of tumor necrosis factor-α(TNF-α), IL- 1βand IL-12p70(18.8±2.3 vs.31.7±1.9,75.0±0.4 vs.150.2±17.0 and 49.1±15.2 vs.135.2±1.0, respectively, P<0.05),as well as the expression of Human leukocyte antigen- DR(HLA- DR).On the contrary, however, macrophages cocultured with MAO- A overexpressing BTC cells exhibited pro- inflammatory phenotype(M1 type) which opposite to above suppressive immunity phenotype (M2 type).After priming of IFN-γ, macrophages cocultured with MAO- A overexpressing BTC cells induced tumor necrosis and apoptosis more effectively than those cocultured with control BTC cells[(84.85±5.66)% vs.(1.56±0.46)% and(76.73±6.31)% vs.(1.28±0.57)%, respectively, P<0.05]. Conclusion Down- regulation of MAO- A in BTC can promote the development of M2 type tumor- associated macrophages, while restoration of MAO- A in BTC can recover antitumor immunity of macrophages.Present study supports MAO- A as a promising target in the immunotherapy of BTC. Key words: Monoamine oxidase-A; Biliary tract cancer; Immune microenvironment; Tumor-associated macrophages; Tumor immune escape