Human Liver Macrophage Subsets Defined by CD32.

Xia Wu,Ian N Crispe,Ian Strickland,Raymond Yeung,Antony Chen,Jessica Roberto,Heidi Kenerson,Allison Knupp,Helen Horton,Radika Soysa,Nicole Hollingshead

doi:10.3389/fimmu.2020.02108

Abstract

Human liver myeloid cells are imperfectly defined, but it is broadly agreed that cells of stellate appearance in situ, expressing the markers CD11b and CD68, are the liver's resident macrophages, classically termed Kupffer cells. Recent investigations using single cell RNA sequencing and unsupervised clustering algorithms suggest there are two populations of cells with the characteristics of tissue macrophages in human liver. We therefore analyzed dissociated human liver tissue using the markers CD11b and CD68 to define macrophage-like cells and found within this population two subsets that differ in their expression of multiple surface markers. These subsets were FACS-sorted based on CD32 expression, and gene expression analysis identified them with human liver myeloid cell subsets that were previously defined by two independent single cell RNA sequencing studies. Using qRT-PCR we found that the two subsets differed in the expression of genes associated with T cell activation and immunosuppression, suggesting distinct roles in T cell tolerance. In addition, one subset expressed two markers, CD1C and CD11c, more often seen on classical dendritic cells. Criteria used to distinguish macrophages from dendritic cells in other tissues may need to be revised in the human liver.

Highlights

Multiple, independent lines of evidence suggest that there are two populations of macrophages in the mouse and in the human liver, as well as other tissues
We have addressed the issue of human liver macrophage/Kupffer cell heterogeneity starting with the isolation of leukocytes from human liver tissue, obtained from tissue donors undergoing the resection of individual liver lobes
These cells were further stained for CD11b and CD68, and cells expressing both were defined as Kupffer cells

Summary

Introduction

Independent lines of evidence suggest that there are two populations of macrophages in the mouse and in the human liver, as well as other tissues. There is a subset derived from the yolk sac and other early fetal progenitors [9], while other liver macrophages are the differentiation products of peripheral blood monocytes [2, 7]. It is undecided whether the term Kupffer cells should apply only to the fetal-derived cells, or to both subsets. We will use the term to indicate all fully mature tissue macrophages, but this is not intended to pre-judge the issue In mouse these are CD11b+ F4/80+ myeloid cells [10, 11], while in the human their markers include CD68 [12,13,14]

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Results

Conclusion