β-Glucan Induces Distinct and Protective Innate Immune Memory in Differentiated Macrophages



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Key Points

  • β-Glucan protects mice from i.p. Pseudomonas aeruginosa infection.

  • Macrophages contribute to β-glucan–induced protection in vivo.

  • β-Glucan rewires macrophage function and metabolism independently of Dectin-1.

Abstract

Bacterial infections are a common and deadly threat to vulnerable patients. Alternative strategies to fight infection are needed. β-Glucan, an immunomodulator derived from the fungal cell wall, provokes resistance to infection by inducing trained immunity, a phenomenon that persists for weeks to months. Given the durability of trained immunity, it is unclear which leukocyte populations sustain this effect. Macrophages have a life span that surpasses the duration of trained immunity. Thus, we sought to define the contribution of differentiated macrophages to trained immunity. Our results show that β-glucan protects mice from Pseudomonas aeruginosa infection by augmenting recruitment of innate leukocytes to the site of infection and facilitating local clearance of bacteria, an effect that persists for more than 7 d. Adoptive transfer of macrophages, trained using β-glucan, into naive mice conferred a comparable level of protection. Trained mouse bone marrow–derived macrophages assumed an antimicrobial phenotype characterized by enhanced phagocytosis and reactive oxygen species production in parallel with sustained enhancements in glycolytic and oxidative metabolism, increased mitochondrial mass, and membrane potential. β-Glucan induced broad transcriptomic changes in macrophages consistent with early activation of the inflammatory response, followed by sustained alterations in transcripts associated with metabolism, cellular differentiation, and antimicrobial function. Trained macrophages constitutively secreted CCL chemokines and robustly produced proinflammatory cytokines and chemokines in response to LPS challenge. Induction of the trained phenotype was independent of the classic β-glucan receptors Dectin-1 and TLR-2. These findings provide evidence that β-glucan induces enhanced protection from infection by driving trained immunity in macrophages.

Footnotes

  • This work was supported by the National Institute of General Medical Sciences, National Institutes of Health (NIH) Grants GM119197 (to E.R.S. and D.L.W.), GM121711 (to J.K.B.), GM141927 (to J.K.B.), GM083016 (to D.L.W.), GM108554 (to N.K.P.), and GM007347 (Vanderbilt Medical Scientist Training Program: C.L.S. and M.A.M.); National Institute of Allergy and Infectious Diseases AI151210 (to E.R.S.); the American Heart Association Grant 19PRE34430054 (to C.L.S.); and Vanderbilt University Medical Center Award VFRS (to N.K.P.). The Agilent Seahorse Extracellular Flux Analyzer is housed and managed within the Vanderbilt High-Throughput Screening Core Facility, an institutionally supported core, and was funded by NIH Shared Instrumentation Grant 1S10OD018015.

  • C.L.S. and E.R.S. wrote the manuscript and designed the figures. C.L.S., D.L.W., and E.R.S. designed experiments. C.L.S., K.R.B., A.M.O., N.K.P., M.A.M., L.L., J.K.B., A.H., and T.K.P. performed experiments. C.L.S., D.L.W., and E.R.S. analyzed data. All authors approved the final manuscript.

  • The online version of this article contains supplemental material.

  • Abbreviations used in this article

    BMDM
    bone marrow–derived macrophage
    2-DG
    2-deoxyglucose
    DKO
    double KO
    3dp
    three-days postgroup
    ECAR
    extracellular acidification rate
    GO
    Gene Ontology
    HSPC
    hematopoietic stem cell precursor
    IkK
    inhibitor of kB kinase
    KO
    knockout
    OCR
    oxygen consumption rate
    PRR
    pattern-recognition receptor
    RNASeq
    RNA sequencing
    ROS
    reactive oxygen species
    Syk
    spleen tyrosine kinase
    TMRM
    tetramethylrhodamine, methyl ester
    WT
    wild-type
  • Received February 3, 2021.
  • Accepted September 27, 2021.



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