Mass cytometry, empowered by CyTOF® technology, utilizes monoisotopic metal-tagged antibodies and a high-sensitivity mass cytometer to allow high-dimensional single-cell analysis in complex biological samples. The 30-marker panel Maxpar® Direct™ Immune Profiling Assay™ (Cat. No. 201325) for suspension mass cytometry provides an unprecedented sample-to-answer solution for detecting and analyzing 30 surface markers in a single experiment. With 18 open mass channels for additional biological markers, the Maxpar Direct Assay facilitates panel expansion and enables flexibility for higher multiplexity and applications. Among the potential complementary applications with the Maxpar Direct Assay, intracellular cytokine staining (ICS) is of particular interest as it may be used to assess infiltrating immune cell phenotypes in the tumor microenvironment. However, for the purpose of assessing cell viability in this workflow, the effectiveness of the Cell-ID™ Intercalator-Rh (Cat. No. 201103) that is included in the Maxpar Direct Assay is in question, since cell permeabilization during ICS can potentially damage the DNA-intercalator bondIn this study, we investigated the compatibility of the Cell-ID Intercalator-Rh (103Rh) with intracellular staining. To do this, we stained either human peripheral blood mononuclear cell (PBMC) or whole blood samples (FLDM-400287) with the Maxpar Direct Assay followed by intracellular staining for the detection of expressed cytokines. The intercalator was evaluated for its ability to discriminate live and dead cells when the sample undergoes surface antibody staining. The monoisotopic Cell-ID Cisplatin-194Pt (Cat. No. 201194) was used as the control to provide benchmark measurement of cell viability of the samples. For both sample types, known percentages of heat-killed PBMC were spiked into the samples in order to evaluate the influence of dead cells. We demonstrate that 103Rh provides equivalent functionality as a cell viability indicator during intracellular staining for cytoplasmic proteins compared to Cell-ID Cisplatin-194Pt. This work was designed to support the use of the Maxpar Direct Immune Profiling Assay in combination with additional intracellular markers. Overall, these findings expand the applicability of Cell-ID Intercalator-Rh (103Rh) to processes that involve cytoplasmic staining. For Research Use Only. Not for use in diagnostic procedures. Citation Format: Noah Saederup, Huihui Yao, Michael Cohen, Leslie Fung. Extending the capabilities of a high-parameter immunophenotyping assay with cytoplasmic staining applications for mass cytometry [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1977.

[This corrects the article DOI: 10.1371/journal.pone.0013693.].

Atrophic age-related macular degeneration (AMD) is associated with the subretinal accumulation of mononuclear phagocytes (MPs). Their role in promoting or inhibiting retinal degeneration is unknown. We here show that atrophic AMD is associated with increased intraocular CCL2 levels and subretinal CCR2(+) inflammatory monocyte infiltration in patients. Using age- and light-induced subretinal inflammation and photoreceptor degeneration in Cx3cr1 knockout mice, we show that subretinal Cx3cr1 deficient MPs overexpress CCL2 and that both the genetic deletion of CCL2 or CCR2 and the pharmacological inhibition of CCR2 prevent inflammatory monocyte recruitment, MP accumulation and photoreceptor degeneration in vivo. Our study shows that contrary to CCR2 and CCL2, CX3CR1 is constitutively expressed in the retina where it represses the expression of CCL2 and the recruitment of neurotoxic inflammatory CCR2(+) monocytes. CCL2/CCR2 inhibition might represent a powerful tool for controlling inflammation and neurodegeneration in AMD.

Microglial cells are difficult to track during development because of the lack of specific reagents for myeloid subpopulations. To further understand how myeloid lineages differentiate during development to create microglial cells, we investigated CX3CR1 and CCR2 transcription unit activation in Cx3cr1+/GFPCCR2+/RFP knockin fluorescent protein reporter mice. The principal findings include: 1) CX3CR1+ cells localized to the aorta–gonad–mesonephros region, and visualized at embryonic day (E)9.0 in the yolk sac and neuroectoderm; 2) at E10.5, CX3CR1 single-positive microglial cells were visualized penetrating the neuroepithelium; and 3) CX3CR1 and CCR2 distinguished infiltrating macrophages from resident surveillant or activated microglia within tissue sections and by flow cytometric analyses. Our results support the contribution of the yolk sac as a source of microglial precursors. We provide a novel model to monitor chemokine receptor expression changes in microglia and myeloid cells early (E8.0–E10.5) in development and during inflammatory conditions, which have been challenging to visualize in mammalian tissues.

CC chemokine receptor 2 (CCR2) is essential to acute skeletal muscle injury repair. We studied the subpopulation of inflammatory cells recruited via CCR2 signaling and their cellular functions with respect to muscle regeneration. Mobilization of monocytes/macrophages (MOs/MPs), but not lymphocytes or neutrophils, was impaired from bone marrow to blood and from blood to injured muscle in Ccr2(-/-) mice. While the Ly-6C(+) but not the Ly-6C(-) subset of MOs/MPs was significantly reduced in blood, both subsets were drastically reduced in injured muscle of Ccr2(-/-) mice. Expression of insulin-like growth factor-1 (IGF-I) was markedly up-regulated in injured muscle of wild-type but not Ccr2(-/-) mice. IGF-I was strongly expressed by macrophages within injured muscle, more prominently by the Ly-6C(-) subset. A single injection of IGF-I, but not PBS, into injured muscle to replace IGF-I remarkably improved muscle regeneration in Ccr2(-/-) mice. CCR2 was not detected in myogenic cells or capillary endothelial cells in injured muscle to suggest its direct involvement in muscle regeneration or angiogenesis. We conclude that CCR2 is essential to acute skeletal muscle injury repair primarily by recruiting Ly-6C(+) MOs/MPs. Within injured muscle, these cells conduct phagocytosis, contribute to accumulation of intramuscular Ly-6C(-) macrophages, and produce a high level of IGF-I to promote muscle regeneration.

Background Monocyte subpopulations distinguished by differential expression of chemokine receptors CCR2 and CX3CR1 are difficult to track in vivo, partly due to lack of CCR2 reagents. Methodology/Principal Findings We created CCR2-red fluorescent protein (RFP) knock-in mice and crossed them with CX3CR1-GFP mice to investigate monocyte subset trafficking. In mice with experimental autoimmune encephalomyelitis, CCR2 was critical for efficient intrathecal accumulation and localization of Ly6Chi/CCR2hi monocytes. Surprisingly, neutrophils, not Ly6Clo monocytes, largely replaced Ly6Chi cells in the central nervous system of these mice. CCR2-RFP expression allowed the first unequivocal distinction between infiltrating monocytes/macrophages from resident microglia. Conclusion/Significance These results refine the concept of monocyte subsets, provide mechanistic insight about monocyte entry into the central nervous system, and present a novel model for imaging and quantifying inflammatory myeloid populations.

CX 3 CR1 expression is associated with the commitment of CSF-1R + myeloid precursors to the macrophage/dendritic cell (DC) lineage. However, the relationship of the CSF-1R + CX 3 CR1 + macrophage/DC precursor (MDP) with other DC precursors and the role of CX 3 CR1 in macrophage and DC development remain unclear. We show that MDPs give rise to conventional DCs (cDCs), plasmacytoid DCs (PDCs), and monocytes, including Gr1 + infl ammatory monocytes that differentiate into TipDCs during infection. CX 3 CR1 defi ciency selectively impairs the recruitment of blood Gr1 + monocytes in the spleen after transfer and during acute Listeria monocytogenes infection but does not affect the development of monocytes, cDCs, and PDCs.

CX3CR1 expression is associated with the commitment of CSF-1R+ myeloid precursors to the macrophage/dendritic cell (DC) lineage. However, the relationship of the CSF-1R+ CX3CR1+ macrophage/DC precursor (MDP) with other DC precursors and the role of CX3CR1 in macrophage and DC development remain unclear. We show that MDPs give rise to conventional DCs (cDCs), plasmacytoid DCs (PDCs), and monocytes, including Gr1+ inflammatory monocytes that differentiate into TipDCs during infection. CX3CR1 deficiency selectively impairs the recruitment of blood Gr1+ monocytes in the spleen after transfer and during acute Listeria monocytogenes infection but does not affect the development of monocytes, cDCs, and PDCs.

CX 3 CR1 expression is associated with the commitment of CSF-1R + myeloid precursors to the macrophage/dendritic cell (DC) lineage. However, the relationship of the CSF-1R + CX 3 CR1 + macrophage/DC precursor (MDP) with other DC precursors and the role of CX 3 CR1 in macrophage and DC development remain unclear. We show that MDPs give rise to conventional DCs (cDCs), plasmacytoid DCs (PDCs), and monocytes, including Gr1 + infl ammatory monocytes that differentiate into TipDCs during infection. CX 3 CR1 defi ciency selectively impairs the recruitment of blood Gr1 + monocytes in the spleen after transfer and during acute Listeria monocytogenes infection but does not affect the development of monocytes, cDCs, and PDCs.

Background - Monocyte-derived foam cells are the hallmark of early atherosclerosis, and recent evidence indicates that chemokines play important roles in directing monocyte migration from the blood to the vessel wall. Genetic deletions of monocyte chemoattractant protein-1 (MCP-1, CCL2), fractalkine (CX3CL1), or their cognate receptors, CCR2 and CX3CR1, markedly reduce atherosclerotic lesion size in murine models of atherosclerosis. The aim of this study was to determine whether these 2 chemokines act independently or redundantly in promoting atherogenesis.Methods and Results - We crossed CX3CL1(-/-) ApoE(-/-) and CCR2(-/-) ApoE(-/-) mice to create CX3CL1(-/-) CCR2(-/-) ApoE(-/-) triple knockouts and performed a 4-arm atherosclerosis study. Here, we report that deletion of CX3CL1 in CCR2(-/-) mice dramatically reduced macrophage accumulation in the artery wall and the subsequent development of atherosclerosis. Deletion of CX3CL1 did not reduce the number of circulating monocytes in either "wild-type" ApoE(-/-) mice or CCR2(-/-) ApoE(-/-) mice, which suggests a role for CX3CL1 in the direct recruitment and/or capture of CCR2-deficient monocytes.Conclusions - These data provide the first in vivo evidence for independent roles for CCR2 and CX3CL1 in macrophage accumulation and atherosclerotic lesion formation and suggest that successful therapeutic strategies may need to target multiple chemokines or chemokine receptors.