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Trained immunity is a long-term increase in responsiveness of innate immune cells, induced by certain infections and vaccines. During the last 3 years of the COVID-19 pandemic, vaccines that induce trained immunity, such as BCG, MMR, OPV, and others, have been investigated for their capacity to protect against COVID-19. Further, trained immunity-inducing vaccines have been shown to improve B and T cell responsiveness to both mRNA- and adenovirus-based anti-COVID-19 vaccines. Moreover, SARS-CoV-2 infection itself induces inappropriately strong programs of trained immunity in some individuals, which may contribute to the long-term inflammatory sequelae. In this review, we detail these and other aspects of the role of trained immunity in SARS-CoV-2 infection and COVID-19. We also examine the learnings from the trained immunity studies conducted in the context of this pandemic and discuss how they may help us in preparing for future infectious outbreaks. Trained immunity-inducing vaccines have been suggested to protect against heterologous infections, including COVID-19. This review presents the studies performed during the pandemic that have investigated the effects of vaccines such as BCG, OPV, MMR, and others against COVID-19. In addition, data are reviewed that suggest that COVID-19 itself and the novel COVID-19 vaccines can also induce trained immunity programs. [ABSTRACT FROM AUTHOR]

Objectives: IL-1α/β and TNF are closely linked to the pathology of severe COVID-19 and sepsis. The soluble forms of their receptors, functioning as decoy receptors, exhibit inhibitory effects. However, little is known about their regulation in severe bacterial and viral infections, which we aimed to investigate in this study., Methods: The circulating soluble receptors of TNF (sTNFR1 and sTNFR2) and IL-1α/β (sIL-1R1, sIL-1R2) were evaluated in the plasma of patients with COVID-19, severe bacterial infections, and sepsis and compared with healthy controls. Additionally, IL1R1, IL1R2, TNFRSF1A, and TNFRSF1B expression was evaluated at the single cell level in PBMCs derived from COVID-19 or sepsis patients., Results: Plasma concentrations of sIL-1R1, sTNFR1, and sTNFR2 were significantly higher in COVID-19 patients compared to healthy subjects. Notably, sIL-1R1 levels were particularly elevated in ICU COVID-19 patients, and transcriptome analysis indicated heightened IL1R1 expression in PBMCs from severe COVID-19 patients. In severe bacterial infections, only sTNFR1 and sTNFR2 exhibited increased levels compared to healthy controls. Sepsis patients had decreased sIL-1R1 plasma concentrations but elevated sIL-1R2, sTNFR1, and sTNFR2 levels compared to healthy individuals, reflecting the heightened expression due to the increased numbers of monocytes present in sepsis. Finally, elevated concentrations of sIL-1R2, sTNFR1, and sTNFR2 were moderately associated with reduced 28-day survival in sepsis patients., Conclusion: Our study reveals distinct regulation of plasma concentrations of soluble IL-1 receptors in COVID-19 and sepsis. Moreover, soluble TNF receptors 1 and 2 consistently rise in all conditions and show a positive correlation with disease severity in sepsis., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: M.G.N. is a scientific founder of TTxD, Biotrip and Lemba (none of these entities are involved in sepsis or COVID-19 fields). E. J. Giamarellos-Bourboulis has received honoraria from Abbott CH, bioMérieux, Brahms GmbH, GSK, InflaRx GmbH, Sobi and Xbiotech Inc; independent educational grants from Abbott CH, bioMérieux Inc, InflaRx GmbH, Johnson & Johnson, MSD, Sobi and Xbiotech Inc. All other authors report no potential conflicts., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)