Background VISTA is an established T cell immune checkpoint. However, its role in innate immunity is less established, with VISTA regulating cytokine production and chemotaxis by myeloid cells. The role of VISTA in macrophage biology and effector functions such as phagocytosis has not been delineated. Here, we investigated the impact of VISTA on phagocytosis and macrophage polarization.
Methods The frequency of CD14+ monocytes expressing VISTA was determined in peripheral blood mononuclear cells (PBMC) from 37 healthy donors by flow cytometry. Macrophages, differentiated from VISTA overexpressed THP-1 cells and cord blood CD34+ cell-derived monocytes, were used in phagocytosis assay using B-cell lymphoma target cells opsonized with rituximab. PBMC-derived macrophages were used to assess the correlation between phagocytosis and VISTA expression. qRT-PCR and flow cytometry were performed to analyze the impact of VISTA on other checkpoints and M1/M2-like macrophage biology. Enzyme-linked immunosorbent assay was performed to evaluate cytokine secretion of macrophages.
Results VISTA surface expression was identified on CD14+ monocytes of 28 of the 37 healthy donors. On PBMC-derived macrophages, VISTA expression was higher in M2-like macrophages than in M0- or M1-like macrophages, and positively correlated with phagocytic activity in M2-like macrophages. Endogenous VISTA expression on monocytes coincided with the expression on CD3+ T lymphocytes, whereas absence of VISTA on monocytes coincided with the absence on T lymphocytes. Ectopic expression of VISTA in THP-1 cells facilitated differentiation towards macrophage lineage upon PMA treatment. Additionally, VISTA elicited transcriptional and functional changes in THP-1 and CD34+ cell-derived macrophages, increasing M2-like macrophage-related gene expression, while decreasing SIRPα, HLA-ABC, and M1-like macrophage-related gene expression. Further, ectopic VISTA augmented phagocytosis of cancer cells, with a marked decrease in IL-1beta secretion and a significant increase in IL-10 secretion.
Conclusions Collectively, our findings reveal that VISTA expression associates with M2-like activation of macrophages with a high phagocytic capacity, suggesting a role for VISTA in macrophage-mediated immune suppression.
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