Role of the mannose receptor in tumor associated macrophages. Studies in a mouse melanoma model

Abstract

Tumor-associated macrophages (TAMs) play an important role in cancer-related inflammation. TAMs develop M2 polarization which may support tumor growth. Mannose receptor (MR) expression is a hallmark for this cell-subpopulation, and the MR has recently been suggested to be involved in TAM polarization. The aim of the study was to investigate the role of MR in TAM polarization and tumor development in a mouse melanoma model. Tumor growth rate and morphology, and gene expression of markers for different macrophage subpopulations were compared in tumors from MR-knockout (MR-KO) and wild-type (WT) mice. A key question was whether MR is necessary for TAM polarization, or just a marker for M2 polarized cells. Main results: The day of first visible tumor was delayed in MR-KO mice, but from then on the tumors grew with the same rate in both animal groups. There were no marked differences in tumor morphology and histological appearance between groups. TAMs were observed already at an early stage, and some of these cells were already M2 polarized. As M2 polarization happened in both MR-KO and wild-type mice, it is likely that the MR is not a driver of this process. However, it may have a role in early tumor development.