Human B1 cells consist of CD20+CD27+CD43+CD70− cells bearing a skewed B cell receptor repertoire, and are present in umbilical cord and adult peripheral blood.

Background: Coronavirus disease 2019 (COVID-19)–related critical illness and acute illness are associated with a risk of venous thromboembolism (VTE). Objective: These evidence-based guidelines of the American Society of Hematology (ASH) are intended to support patients, clinicians, and other health care professionals in decisions about the use of anticoagulation for thromboprophylaxis for patients with COVID-19–related critical illness and acute illness who do not have confirmed or suspected VTE. Methods: ASH formed a multidisciplinary guideline panel and applied strict management strategies to minimize potential bias from conflicts of interest. The panel included 3 patient representatives. The McMaster University GRADE Centre supported the guideline-development process, including performing systematic evidence reviews (up to 19 August 2020). The panel prioritized clinical questions and outcomes according to their importance for clinicians and patients. The panel used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach, including GRADE Evidence-to-Decision frameworks, to assess evidence and make recommendations, which were subject to public comment. Results: The panel agreed on 2 recommendations. The panel issued conditional recommendations in favor of prophylactic-intensity anticoagulation over intermediate-intensity or therapeutic-intensity anticoagulation for patients with COVID-19–related critical illness or acute illness who do not have confirmed or suspected VTE. Conclusions: These recommendations were based on very low certainty in the evidence, underscoring the need for high-quality, randomized controlled trials comparing different intensities of anticoagulation. They will be updated using a living recommendation approach as new evidence becomes available.

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Human B1 cells can be divided, based on surface CD11b expression, into two transcriptionally and functionally distinct subsets, one of which is more abundant in lupus patients than healthy individuals.

B-1cells play critical roles in defending against microbial invasion and in housekeeping removal of cellular debris. B-1cells secrete natural antibody and manifest functions that influence T cell expansion and differentiation and in these and other ways differ from conventional B-2 cells. B-1-cells were originally studied in mice where they are easily distinguished from B-2cells, but their identity in the human system remained poorly defined for many years. Recently, functional criteria for human B-1cells were established on the basis of murine findings, and reverse engineering resulted in identification of the phenotypic profile, CD20+CD27+CD43+CD70−, for B-1cells found in both umbilical cord blood and adult peripheral blood. Human B-1cells may contribute to multiple disease states through production of autoantibody and stimulation/modulation of T cell activity. Human B-1cells could be a rich source of antibodies useful in treating diseases present in elderly populations where natural antibody protection may have eroded. Manipulation of human B-1cell numbers and/or activity may be a new avenue for altering T cell function and treating immune dyscrasias.

2. Kreienbuehl L, Charbonney E, Eggimann P. Communityacquired necrotizing pneumonia due to methicillin-sensitive Staphylococcus aureus secreting Panton-Valentine leukocidin: a review of case reports.

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