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Background: As the adverse effects of blood transfusions are better understood, recommendations support single-unit red blood cell (RBC) transfusions (SRBCT). However, an isolated SRBCT across the entire index admission suggests even the single unit may be avoidable. We sought to identify the characteristics of cardiac surgery patients receiving an isolated SRBCT and analyze the impact on outcomes., Methods: The Society of Thoracic Surgeons Adult Cardiac Surgery Database was queried for the period between January 1, 2010, and December 31, 2019. Patients aged >18 years undergoing isolated coronary artery bypass grafting or isolated aortic valve replacement were included. A total of 2,151,430 encounters were analyzed., Results: Of the 847,442 patients (39.3%) receiving any RBC transfusion during their index admission, 206,555 (24.4%) received only 1 unit. Propensity-matching analysis determined SRBCT patients were significantly older (67.26 vs 64.02 years; odds ratio [OR], 1.02; P < .001), female (39.1% vs 17.8%; OR, 1.57; P < .001), non-White (18.2% vs 13.1%; OR, 0.81; P < .001), and had a smaller body surface area (1.94 vs 2.07 m 2 ; OR, 0.20; P < .001). They also had higher mortality (1.4% vs 1.0%, P < .001), stroke (1.7% vs 1.2%, P < .001), prolonged ventilation (6.4% vs 3.4%, P < .001), renal failure (1.8% vs 0.9%, P < .001), and reoperations (1.3% vs. 0.5%, P < .001) than patients who received 0 RBCs., Conclusions: SRBCT is a common occurrence in adult cardiac surgery. This low-volume transfusion is strongly associated with higher morbidity, even after controlling for preoperative risk factors., (Copyright © 2023 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

The cytokine IL-9, derived primarily from T-helper 9 (Th9) lymphocytes, promotes expansion of the Th2 subset and is implicated in the mechanisms of allergic asthma. We hypothesize that IL-9 also has a role in human allergic contact dermatitis (ACD). To investigate this hypothesis, skin biopsy specimens of positive patch-test sites from non-atopic patients were assayed using quantitative PCR and immunohistochemistry. The cytokines IFN-γ, IL-4, IL-17A, IL-9, and PU.1, a Th9 associated transcription factor, were elevated when compared with paired normal skin. Immunohistochemistry on ACD skin biopsies identified PU.1+ CD3+ and PU.1+ CD4+ cells, consistent with Th9 lymphocytes, in the inflammatory infiltrate. Peripheral blood mononuclear cells from nickel-allergic patients, but not nonallergic controls, show significant IL-9 production in response to nickel. Blocking studies with mAbs to HLA-DR (but not HLA-A, -B, -C) or chloroquine significantly reduced this nickel-specific IL-9 production. In addition, blockade of IL-9 or IL-4 enhanced allergen-specific IFN-γ production. A contact hypersensitivity model using IL-9(-/-) mice shows enhanced Th1 lymphocyte immune responses, when compared with wild-type mice, consistent with our human in vitro data. This study demonstrates that IL-9, through its direct effects on Th1 and ability to promote IL-4 secretion, has a regulatory role for Th1 lymphocytes in ACD.