Person:

Thiriot, Aude

Background: Intravascular leukocyte recruitment in most vertebrate tissues is restricted to postcapillary and collecting venules, whereas capillaries and arterioles usually support little or no leukocyte adhesion. This segmental restriction is thought to be mediated by endothelial, rather than hemodynamic, differences. The underlying mechanisms are largely unknown, in part because effective tools to distinguish, isolate, and analyze venular endothelial cells (V-ECs) and non-venular endothelial cells (NV-ECs) have been unavailable. We hypothesized that the atypical chemokine receptor DARC (Duffy Antigen Receptor for Chemokines, a.k.a. ACKR1 or CD234) may distinguish V-ECs versus NV-ECs in mice. Methods: We generated a rat-anti-mouse monoclonal antibody (MAb) that specifically recognizes the erythroid and endothelial forms of native, surface-expressed DARC. Using this reagent, we characterized DARC expression and distribution in the microvasculature of murine tissues. Results: DARC was exquisitely restricted to post-capillary and small collecting venules and completely absent from arteries, arterioles, capillaries, veins, and most lymphatics in every tissue analyzed. Accordingly, intravital microscopy showed that adhesive leukocyte-endothelial interactions were restricted to DARC+ venules. DARC was detectable over the entire circumference of V-ECs, but was more concentrated at cell-cell junctions. Analysis of single-cell suspensions suggested that the frequency of V-ECs among the total microvascular EC pool varies considerably between different tissues. Conclusions: Immunostaining of endothelial DARC allows the identification and isolation of intact V-ECs from multiple murine tissues. This strategy may be useful to dissect the mechanisms underlying segmental microvascular specialization in healthy and diseased tissues and to characterize the role of EC subsets in tissue-homeostasis, immune surveillance, infection, inflammation, and malignancies. Electronic supplementary material The online version of this article (doi:10.1186/s12915-017-0381-7) contains supplementary material, which is available to authorized users.

Healthy individuals of African ancestry have neutropenia that has been linked with the variant rs2814778(G) of the gene encoding atypical chemokine receptor 1 (ACKR1). This polymorphism selectively abolishes the erythroid cell expression of ACKR1, causing Duffy-negative phenotype. Here we describe an unexpected fundamental role that ACKR1 plays in hematopoiesis and provide the mechanism linking its absence with neutropenia. Nucleated erythroid cells highly expressed ACKR1, which facilitated their direct contacts with the hematopoietic stem cells. The absence of erythroid ACKR1 altered murine hematopoiesis, including stem and progenitor cells, ultimately giving rise to phenotypically distinct neutrophils, which readily left the circulation, causing neutropenia. Duffy-negative individuals developed a distinct profile of neutrophil effector molecules closely reflecting that in the ACKR1-deficient mice. Thus, alternative physiological patterns of hematopoiesis and bone marrow cell outputs depend on the expression of ACKR1 in the erythroid lineage providing major implications for the selection advantages that have resulted in the paramount fixation of the rs2814778(G) polymorphism in Africa.