PreprintCited by 10Immune responses and vaccinationsImmune Response and InflammationNeutrophil, Myeloperoxidase and Oxidative Mechanisms

The DOI matches its Crossref record; 60 of the 61 references it cites were found in a registry or an index, and 1 are not checked yet; none of the 14 sources its claims cite is checked for support yet.

Heme induces innate immune memory

Open access

Abstract

Trained immunity defines long-lasting adaptive responses of innate immunity, mediated by transcriptional and epigenetic modifications of myeloid cells. Here, we report that labile heme, an alarmin released extracellularily upon tissue damage and hemolysis, induces trained immunity in human and murine primary cells and in mice. Heme-trainning in monocytes is associated with epigenetic and transcriptional profiles that overlap to some extent with those seen in β-glucan-training, the prototype agonist of trained immunity. In sharp contrast to β-glucan training however, heme-training relied on activation of the Syk/JNK-pathway. Heme training in mice was associated with long-lasting expansion of myeloid-biased progenitor cells as well as with altered chromatin accessibility in hematopoietic stem and progenitor cells. Finally, heme-induced training was protective against bacterial sepsis in mice. In conclusion, we reveal that heme, a bona fide alarmin, induces innate immune memory regulating host response to infection.

Checked 2026-11-11 · 1 reference not checked yet

Overview

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Written from the paper’s full text.

TL;DR

Labile heme acts as an alarmin that induces trained immunity in human and murine myeloid cells and in mice, with epigenetic and transcriptional overlap but a distinct Syk/JNK-dependent mechanism compared with β-glucan training. Heme training expands myeloid-biased hematopoietic progenitors and is protective in polymicrobial sepsis, yet worsens acute LPS endotoxemia.

Key findings

  • Heme induced trained immunity in human and murine primary macrophages, increasing cytokine release upon secondary LPS or Pam3CSK4 challenge; training was also induced by iron-lacking protoporphyrin (PPIX) and was not prevented by N-acetyl cysteine.
  • ChIP-seq showed that after heme exposure approximately 5% of all H3K27ac-marked regions increased versus untreated controls, with 497 peaks near 308 genes at 24 h; 98.6% of peaks occurred within 0.5 Mb of a gene TSS. RNA-seq at 24 h identified 201 genes commonly induced by heme and β-glucan, 140 heme-specific genes, and 346 β-glucan-specific genes.
  • Heme training required Syk and JNK activation: Syk inhibition with R406 and JNK inhibition with SP600125 abolished training, while mTOR inhibition with rapamycin did not; Tlr4−/− BMDM were equally trained by heme.
  • In mice, heme training increased myeloid-biased LT-HSCs (CD41+ LT-HSC) and MPP3 cells and decreased lymphoid-biased MPP4 cells, persisting 28 days after treatment; single-nuclei ATAC-seq of LSK cells showed altered chromatin accessibility. Heme-trained mice had reduced survival in LPS endotoxemia but faster weight recovery, higher temperature, and higher survival in polymicrobial sepsis.

Methods

  • A 2-hit training model was used with human monocytes/macrophages and murine BMDM: first hit with heme (typically 50 µM) or β-glucan (1 µg/mL) for 24 h, washout and rest, then secondary challenge with LPS (10 ng/mL) or Pam3CSK4; cytokine release was measured by ELISA and LegendPlex.
  • Epigenetic and transcriptional profiling included H3K27ac ChIP-seq, RNA-seq, ChIP-qPCR, Western blot, and single-nuclei ATAC-seq on sorted LSK cells; sequencing data were deposited under GEO accession GSE111003.
  • Mouse experiments used C57Bl/6, Tlr4−/−, and Rag2−/− mice; heme was given at 2 mg/kg i.p., and LPS at 15 mg/kg one week later for survival, temperature, weight, clinical severity, and peritoneal flow cytometry. Statistical tests included log-rank, one-way/two-way ANOVA with Fisher’s LSD, and Student t-test.

Limitations

  • Stated: how heme induces Syk phosphorylation independently of TLR4 is unknown; the authors speculate there may be no specific heme receptor and that Syk autophosphorylation could be enforced by heme–phospholipid interaction. It is also unclear how JNK signaling leads to histone modifications and which cofactors are involved.
  • Stated: whether the observed effects rely on heme-driven modulation of BACH-1 remains to be established, and whether indirect cytokine effects mediate long-term myelopoiesis adaptation as proposed for β-glucan remains to be established. The analysis did not include H3K4me3 or H3K4me1 marks, although innate immune memory also involves histone methylation.
  • Evident: the text is a preprint marked “not certified by peer review”; the single-nuclei ATAC-seq experiments used n = 2 mice per group at each time point, and the in vivo outcomes are context-dependent, with heme training deleterious in acute LPS endotoxemia but protective in polymicrobial sepsis.

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Integrity signals

Registry

Crossref · 10.1101/2019.12.12.874578

Cites

60 of 61 references verified0 citation errors · 0 not checkable

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Claims the paper makes

47 Own result · 13 Own interpretation · 7 No full text of the sources · 5 Own method · 4 Not checked yet · 1 Check pending

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  • It may state two separate claims as one. 24
  • Probably not a substantial claim. 8
  • The quote only partly states this claim. 1
30 of 30
  • The paper relies on this without support.

    The mouse endotoxemia and polymicrobial sepsis models reflect human acute inflammatory stress and infection sufficiently to support conclusions about host defense.

    “We then assessed the effects of heme training in vivo using a mouse endotoxemia model (Fig. 5a).”
    “we induced a smoldering bacterial sepsis.”
  • The paper relies on this without support.

    Pharmacological inhibitors R406, SP600125, and rapamycin specifically inhibit Syk, JNK, and mTOR, respectively, at the concentrations used.

    “Syk inhibition by R406 38 abolished heme-induced training (Fig. 3b;c).”
    “application of the JNK-Inhibitor SP600125 39 abolished JNK phosphorylation and heme-induced training (Fig. 3g;h).”
    “inhibition of mTOR activity by rapamycin did not abolish heme training”
  • The paper relies on this without support.

    Changes in H3K27ac and chromatin accessibility measured at the assayed time points reflect functional epigenetic memory that mediates the long-lasting trained immunity phenotype.

    “Heme imposes histone modifications and chromatin accessibility patterns”
    “epigenetic alterations in HSPCs may contribute to the persistence of the heme-induced training effects.”
  • The paper relies on this without support.

    Rag2-/- mice, lacking mature B and T cells, isolate innate immune-mediated effects.

    “The deleterious effects of heme training on subsequent LPS-induced systemic inflammation persisted in Rag2 knock-out mice (Rag2 -/-) with a constitutive deficiency of mature B-and T-cells 45”
    “This finding supports that heme-mediated trained immunity is predominantly mediated by effects on innate immune cells.”
4 of 4

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Metadata

Authors
Jentho, E., Novakovic, B., Ruiz-Moreno, C., Kourtzelis, I., Martins, R., Chavakis, T., Soares, M. P., Kalafati, L., Guerra, J., Roestel, F., Bohm, P., Godmann, M., Grinenko, T., Eugster, A., Beretta, M., Joosten, L. A. B., Netea, M. G., Stunnenberg, H. G., Bauer, M., & Weis, S.
Affiliations
  • Jena University Hospital (DE)
  • Radboud University Nijmegen (NL)
  • Princess Máxima Center (NL)
  • German Cancer Research Center (DE)
  • Instituto Gulbenkian de Ciência (PT)
  • Technische Universität Dresden (DE)
  • Friedrich Schiller University Jena (DE)
  • University of Bonn (DE)
Corresponding author
Weis, Sebastian
Venue
bioRxiv (Cold Spring Harbor Laboratory)
Publisher
openRxiv
Published
2019-12-13
OpenAlex
W2995454016
Cited by
10
References
60
Citations by year
2025: 1 · 2024: 1 · 2022: 1 · 2021: 4 · 2020: 3
Type
posted content
Language
en
Open access
Locations
bioRxiv (Cold Spring Harbor Laboratory) (submittedVersion)
Funders
  • East Tennessee State University
  • Deutsche Forschungsgemeinschaft (SFB-TRR 205, FOR1738, SFB1181, 01EO1502, Project A3, GRK1715, 1715/2)
  • Bundesministerium für Bildung und Forschung (FOR 1738, 01EO1502)
  • Universitätsklinikum Jena (01EO1502)
  • Quillen College of Medicine, East Tennessee State University
  • National Health and Medical Research Council (1173314)
  • Center for Sepsis Control and Care (01EO1502)
  • H2020 European Research Council (833247)
Topics
  • Life Sciences › Immunology and Microbiology › Immunology › Immune responses and vaccinations
  • Life Sciences › Immunology and Microbiology › Immunology › Immune Response and Inflammation
  • Life Sciences › Immunology and Microbiology › Immunology › Neutrophil, Myeloperoxidase and Oxidative Mechanisms
Keywords
heme, trained immunity, alarmins, monocytes, epigenetic modifications, chromatin accessibility, hematopoietic stem and progenitor cells, β-glucan, bacterial sepsis, myeloid progenitor cells

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