Erythro-myeloid progenitors can differentiate from endothelial cells and modulate embryonic vascular remodeling

Erythro-myeloid progenitors (EMPs) were recently described to arise from the yolk sac endothelium, just prior to vascular remodeling, and are the source of adult/post-natal tissue resident macrophages. Questions remain, however, concerning whether EMPs differentiate directly from the endothelium or merely pass through. We provide the first evidence in vivo that EMPs can emerge directly from endothelial cells (ECs) and demonstrate a role for these cells in vascular development. We find that EMPs express most EC markers but late EMPs and EMP-derived cells do not take up acetylated low-density lipoprotein (AcLDL), as ECs do. When the endothelium is labelled with AcLDL before EMPs differentiate, EMPs and EMP-derived cells arise that are AcLDL+. If AcLDL is injected after the onset of EMP differentiation, however, the majority of EMP-derived cells are not double labelled. We find that cell division precedes entry of EMPs into circulation, and that blood flow facilitates the transition of EMPs from the endothelium into circulation in a nitric oxide-dependent manner. In gain-of-function studies, we inject the CSF1-Fc ligand in embryos and found that this increases the number of CSF1R+ cells, which localize to the venous plexus and significantly disrupt venous remodeling. This is the first study to definitively establish that EMPs arise from the endothelium in vivo and show a role for early myeloid cells in vascular development

In Situ-Targeting of Dendritic Cells with Donor-Derived Apoptotic Cells Restrains Indirect Allorecognition and Ameliorates Allograft Vasculopathy

Chronic allograft vasculopathy (CAV) is an atheromatous-like lesion that affects vessels of transplanted organs. It is a component of chronic rejection that conventional immuno-suppression fails to prevent, and is a major cause of graft loss. Indirect allo-recognition through T cells and allo-Abs are critical during CAV pathogenesis. We tested whether the indirect allo-response and its impact on CAV is down-regulated by in situ-delivery of donor Ags to recipient's dendritic cells (DCs) in lymphoid organs in a pro-tolerogenic fashion, through administration of donor splenocytes undergoing early apoptosis. Following systemic injection, donor apoptotic cells were internalized by splenic CD11chi CD8α+ and CD8− DCs, but not by CD11cint plasmacytoid DCs. Those DCs that phagocytosed apoptotic cells in vivo remained quiescent, resisted ex vivo-maturation, and presented allo-Ag for up to 3 days. Administration of donor apoptotic splenocytes, unlike cells alive, (i) promoted deletion, FoxP3 expression and IL-10 secretion, and decreased IFN-γ-release in indirect pathway CD4 T cells; and (ii) reduced cross-priming of anti-donor CD8 T cells in vivo. Targeting recipient's DCs with donor apoptotic cells reduced significantly CAV in a fully-mismatched aortic allograft model. The effect was donor specific, dependent on the physical characteristics of the apoptotic cells, and was associated to down-regulation of the indirect type-1 T cell allo-response and secretion of allo-Abs, when compared to recipients treated with donor cells alive or necrotic. Down-regulation of indirect allo-recognition through in situ-delivery of donor-Ag to recipient's quiescent DCs constitutes a promising strategy to prevent/ameliorate indirect allorecognition and CAV

Linear and Branched Glyco-Lipopeptide Vaccines Follow Distinct Cross-Presentation Pathways and Generate Different Magnitudes of Antitumor Immunity

Glyco-lipopeptides, a form of lipid-tailed glyco-peptide, are currently under intense investigation as B- and T-cell based vaccine immunotherapy for many cancers. However, the cellular and molecular mechanisms of glyco-lipopeptides (GLPs) immunogenicity and the position of the lipid moiety on immunogenicity and protective efficacy of GLPs remain to be determined.We have constructed two structural analogues of HER-2 glyco-lipopeptide (HER-GLP) by synthesizing a chimeric peptide made of one universal CD4(+) epitope (PADRE) and one HER-2 CD8(+) T-cell epitope (HER(420-429)). The C-terminal end of the resulting CD4-CD8 chimeric peptide was coupled to a tumor carbohydrate B-cell epitope, based on a regioselectively addressable functionalized templates (RAFT), made of four alpha-GalNAc molecules. The resulting HER glyco-peptide (HER-GP) was then linked to a palmitic acid moiety, attached either at the N-terminal end (linear HER-GLP-1) or in the middle between the CD4+ and CD8+ T cell epitopes (branched HER-GLP-2). We have investigated the uptake, processing and cross-presentation pathways of the two HER-GLP vaccine constructs, and assessed whether the position of linkage of the lipid moiety would affect the B- and T-cell immunogenicity and protective efficacy. Immunization of mice revealed that the linear HER-GLP-1 induced a stronger and longer lasting HER(420-429)-specific IFN-gamma producing CD8(+) T cell response, while the branched HER-GLP-2 induced a stronger tumor-specific IgG response. The linear HER-GLP-1 was taken up easily by dendritic cells (DCs), induced stronger DCs maturation and produced a potent TLR- 2-dependent T-cell activation. The linear and branched HER-GLP molecules appeared to follow two different cross-presentation pathways. While regression of established tumors was induced by both linear HER-GLP-1 and branched HER-GLP-2, the inhibition of tumor growth was significantly higher in HER-GLP-1 immunized mice (p<0.005).These findings have important implications for the development of effective GLP based immunotherapeutic strategies against cancers

Barrier Tissue Macrophages: Functional Adaptation to Environmental Challenges

Macrophages are found throughout the body, where they have crucial roles in tissue development, homeostasis and remodeling, as well as being sentinels of the innate immune system that can contribute to protective immunity and inflammation. Barrier tissues, such as the intestine, lung, skin and liver, are exposed constantly to the outside world, which places special demands on resident cell populations such as macrophages. Here we review the mounting evidence that although macrophages in different barrier tissues may be derived from distinct progenitors, their highly specific properties are shaped by the local environment, which allows them to adapt precisely to the needs of their anatomical niche. We discuss the properties of macrophages in steady-state barrier tissues, outline the factors that shape their differentiation and behavior and describe how macrophages change during protective immunity and inflammation

Long-lived self-renewing bone marrow-derived macrophages displace embryo-derived cells to inhabit adult serous cavities

Peritoneal macrophages are one of the most studied macrophage populations in the body, yet the composition, developmental origin and mechanisms governing the maintenance of this compartment are controversial. Here we show resident F4/80(hi)GATA6(+) macrophages are long-lived, undergo non-stochastic self-renewal and retain cells of embryonic origin for at least 4 months in mice. However, Ly6C(+) monocytes constitutively enter the peritoneal cavity in a CCR2-dependent manner, where they mature into short-lived F4/80(lo)MHCII(+) cells that act, in part, as precursors of F4/80(hi)GATA6(+) macrophages. Notably, monocyte-derived F4/80(hi) macrophages eventually displace the embryonic population with age in a process that is highly gender dependent and not due to proliferative exhaustion of the incumbent embryonic population, despite the greater proliferative activity of newly recruited cells. Furthermore, although monocyte-derived cells acquire key characteristics of the embryonic population, expression of Tim4 was impaired, leading to cumulative changes in the population with age

Macrophage biology in development, homeostasis and disease

Macrophages the most plastic cells of the hematopoietic system are found in all tissues and exhibit great functional diversity. They have roles in development, homeostasis, tissue repair, and immunity. While anatomically distinct, resident tissue macrophages exhibit different transcriptional profiles, and functional capabilities, they are all required for the maintenance of homeostasis. However, these reparative and homeostatic functions can be subverted by chronic insults, resulting in a causal association of macrophages with disease states. In this review, we discuss how macrophages regulate normal physiology and development and provide several examples of their pathophysiologic roles in disease. We define the “hallmarks” of macrophages performing particular functions, taking into account novel insights into the diversity of their lineages, identity, and regulation. This diversity is essential to understand because macrophages have emerged as important therapeutic targets in many important human diseases

The interstitium in cardiac repair: role of the immune-stromal cell interplay

Cardiac regeneration, that is, restoration of the original structure and function in a damaged heart, differs from tissue repair, in which collagen deposition and scar formation often lead to functional impairment. In both scenarios, the early-onset inflammatory response is essential to clear damaged cardiac cells and initiate organ repair, but the quality and extent of the immune response vary. Immune cells embedded in the damaged heart tissue sense and modulate inflammation through a dynamic interplay with stromal cells in the cardiac interstitium, which either leads to recapitulation of cardiac morphology by rebuilding functional scaffolds to support muscle regrowth in regenerative organisms or fails to resolve the inflammatory response and produces fibrotic scar tissue in adult mammals. Current investigation into the mechanistic basis of homeostasis and restoration of cardiac function has increasingly shifted focus away from stem cell-mediated cardiac repair towards a dynamic interplay of cells composing the less-studied interstitial compartment of the heart, offering unexpected insights into the immunoregulatory functions of cardiac interstitial components and the complex network of cell interactions that must be considered for clinical intervention in heart diseases