Macrophage Fate Mapping

Abstract

Tissue‐resident macrophages are present in all tissues where they perform homeostatic and immune surveillance functions. In many tissues, resident macrophages develop from embryonic progenitors, which mature into a self‐maintaining population through local proliferation. However, tissue‐resident macrophages can be supported by recruited monocyte‐derived macrophages during scenarios such as tissue growth, infection, or sterile inflammation. Circulating blood monocytes arise from hematopoietic stem cell progenitors and possess unique gene profiles that support additional functions within the tissue. Determining cell origins (ontogeny) and cellular turnover within tissues has become important to understanding monocyte and macrophage contributions to tissue homeostasis and disease. Fate mapping, or lineage tracing, is a promising approach to tracking cells based on unique gene expression driving reporter systems, often downstream of a Cre‐recombinase–mediated excision event, to express a fluorescent protein. This approach is typically deployed temporally with developmental stage, disease onset, or in association with key stages of inflammation resolution. Importantly, myeloid fate mapping can be combined with many emerging technologies, including single‐cell RNA‐sequencing and spatial imaging. The application of myeloid cell fate mapping approaches has allowed for impactful discoveries regarding myeloid ontogeny, tissue residency, and monocyte fate within disease models. This protocol outline will discuss a variety of myeloid fate mapping approaches, including constitutive and inducible labeling approaches in adult and embryo tissues. This article outlines basic approaches and models used in mice for fate mapping macrophages. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Adult Fate Mapping Basic Protocol 2: Embryonic Fate Mapping

Tumor-specific CD4 T cells instruct monocyte fate in pancreatic ductal adenocarcinoma

“…Thus, we utilized the CCR2 CreER R26 Tdtomato mouse, which allows for specific labeling of individual waves of blood monocytes following tamoxifen treatment, enabling tracking of their differentiation upon entry into tissue. 31 – 33 Tamoxifen treatment of CCR2 CreER R26 Tdtomato mice revealed robust classical monocyte labeling in the blood, but no labeling of pancreatic tissue-resident macrophages ( Figures S1A – S1D ), consistent with a reported lack of Ccr2. 34 To track monocyte differentiation in PDA in the presence of tumor-specific T cells, we orthotopically implanted KPC2a tumor cells that express a model neoantigen click beetle red luciferase (CB) 30 into the pancreas of CCR2 CreER R26 Tdtomato mice following a single dose of tamoxifen ( Figure 1A ).…”

Adrenal gland macrophages regulate glucocorticoid production through Trem2 and TGF-β

“…Acute cold challenge: All CCR2 creER/+ R26 TdTomato mice were given 200 µL 20 mg/mL tamoxifen (TAM, MilliporeSigma #T5648) in corn oil (MilliporeSigma #C8267) through oral gavage (82,83).…”

Macrophage plasticity: signaling pathways, tissue repair, and regeneration

“… 126 , 127 Contrary to the traditional view that all tissue macrophages are derived from circulating monocytes, recent fate mapping studies have revealed that many TrMΦ are established during embryonic development and maintain themselves through local proliferation, independent of adult monocyte input. 128 , 129 For example, microglia, the resident macrophages of the central nervous system, have been shown to originate from yolk sac‐derived progenitors that seed the brain early in embryonic development. 130 Similarly, Kupffer cells, the resident macrophages of the liver, are derived from a combination of yolk sac and fetal liver progenitors.…”