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Issue 4, Volume 127

Cover Figure: Platelet transactivation by monocytes promotes thrombosis in HIT. Tutwiler et al.

WASHINGTON, January 28, 2016 – Welcome to “This Week in Blood,” a weekly snapshot of the hottest studies from each week’s issue of Blood, the official journal of the American Society of Hematology (ASH), hand-picked by Blood Editor-in-Chief Bob Löwenberg, MD, PhD, and Deputy Editor Nancy Berliner, MD.

Lin- CD34hi CD117int/hi FcεRI+ cells in human blood constitute a rare population of mast cell progenitors
Mast cells are involved in allergic reactions, and increased numbers of mast cells are characteristically found in the lungs of patients with asthma. The cell of origin of the mast cell has been elusive. In this week's plenary paper, Dahlin and colleagues have identified a rare human progenitor cell (CD34hi CD117int/hi FcεRI+) that is committed to mast cell maturation; these immediate mast cell precursors are increased in the lungs of patients with asthma and reduced lung function.

Integration of innate into adaptive immune responses in ZAP-70– positive chronic lymphocytic leukemia
The mechanism by which ZAP-70 positivity in chronic lymphocytic leukemia (CLL) contributes to poor prognosis is not understood. In this week's Blood, Wagner and colleagues demonstrate that signaling through Toll-like-receptor 9 (TLR9) provides a link that may explain this observation. They demonstrate that TLR9 signaling promotes CLL proliferation through a ZAP-70– dependent activation of Syk, which provides an antiapoptotic signal. In the absence of ZAP-70, TLR9 promotes apoptosis. This fascinating integration of the innate immune and adaptive immune response provides new insight into CLL cell survival.

Hemopexin therapy reverts heme-induced proinflammatory phenotypic switching of macrophages in a mouse model of sickle cell disease
Hemolysis leads to release of free hemoglobin and heme into the circulation, leading to heme-iron loading of macrophages. In this week's Blood, Vinchi and colleagues demonstrate that uptake of free heme alters macrophage polarization toward a proinflammatory phenotype and that the heme scavenger hemopexin protects macrophages from heme overload and decreases inflammatory cytokine production. The importance of this pathway is confirmed by demonstrating that administration of hemopexin in sickle mice attenuates the macrophage inflammatory phenotype, suggesting a novel pathway that could be exploited therapeutically.

Detection of septic transfusion reactions to platelet transfusions by active and passive surveillance
Septic transfusion reactions (STRs) are a major hazard of platelet transfusion. In this week's Blood, Hong and colleagues compare active and passive surveillance for bacterial contamination of platelets and correlate the results with reported transfusion reactions. They report the disconcerting results that passive surveillance is inadequate to identify all STRs and that better surveillance methods or pathogen reduction techniques are required to improve platelet transfusion safety, especially in neutropenic patients.

Transfusion of fresher vs older red blood cells in hospitalized patients: a systematic review and meta-analysis
The clinical effect of transfusing fresher vs older red blood cells is a subject of ongoing controversy. In this week's Blood, Alexander and colleagues present a meta-analysis of outcomes from randomized trials. They conclude that there is little or no impact of fresher vs older blood cell transfusions on mortality, suggesting that the evidence does not support changing current transfusion practices.

This week's complete table of contents

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Blood (www.bloodjournal.org), the most cited peer-reviewed publication in the field of hematology, is available weekly in print and online. Blood is the official journal of the American Society of Hematology (ASH) (www.hematology.org), the world’s largest professional society concerned with the causes and treatment of blood disorders.

ASH’s mission is to further the understanding, diagnosis, treatment, and prevention of disorders affecting blood, bone marrow, and the immunologic, hemostatic, and vascular systems by promoting research, clinical care, education, training, and advocacy in hematology.

blood® is a registered trademark of the American Society of Hematology.