Iron is an essential component of the erythrocyte protein hemoglobin and is crucial to oxygen transport in vertebrates. In the steady state, erythrocyte production is in equilibrium with erythrocyte removal1. In various pathophysiological conditions, however, erythrocyte life span is compromised severely, which threatens the organism with anemia and iron toxicity2,3. Here we identify an on-demand mechanism that clears erythrocytes and recycles iron. We show that monocytes that express high levels of lymphocyte antigen 6 complex, locus C1 (LY6C1, also known as Ly-6C) ingest stressed and senescent erythrocytes, accumulate in the liver via coordinated chemotactic cues, and differentiate into ferroportin 1 (FPN1, encoded by SLC40A1)-expressing macrophages that can deliver iron to hepatocytes. Monocyte-derived FPN1+Tim-4neg macrophages are transient, reside alongside embryonically derived T cell immunoglobulin and mucin domain containing 4 (Timd4, also known as Tim-4)high Kupffer cells (KCs), and depend on the growth factor Csf1 and the transcription factor Nrf2 (encoded by Nfe2l2). The spleen, likewise, recruits iron-loaded Ly-6Chigh monocytes, but these do not differentiate into iron-recycling macrophages, owing to the suppressive action of Csf2. The accumulation of a transient macrophage population in the liver also occurs in mouse models of hemolytic anemia, anemia of inflammation, and sickle cell disease. Inhibition of monocyte recruitment to the liver during stressed erythrocyte delivery leads to kidney and liver damage. These observations identify the liver as the primary organ that supports rapid erythrocyte removal and iron recycling, and uncover a mechanism by which the body adapts to fluctuations in erythrocyte integrity.

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This work was supported in part by US National Institutes of Health (NIH) grants 1R01HL095612, R01HL128264, R56AI104695 and the Massachusetts General Hospital's Howard M. Goodman Fellowship (to F.K.S.) and R01DK071837 (to H.Y.L.). I.T. was supported by the Max Kade Foundation and grants by the Austrian Science Fund (FWF) (P28302-B30 and P24749-B13)). I.H. (HI 1573/1-1, HI 1573/2-1) and G.F.W. were supported by the German Research Foundation. M. Nairz was supported by an FWF Erwin Schroedinger Fellowship (J3486-B13). L.M.S.G. and N.K.H. were supported by the Boehringer Ingelheim Fonds. F.W. was supported by the National Natural Science Foundation of China (31530034 and 31225013). We thank D. Capen for help in electron microscopy; N. Bonheur and M. Waring for help with cell sorting; A. Lindau for technical assistance; C. Haerdtner, J. Kornemann, and J. Zou for help with flow cytometry; D. Brown for interpretation of electron microscopy images; C. Robbins for the mouse drawing; and K. Joyes for editing the manuscript.

Author information

Author notes

    • Igor Theurl
    • , Ingo Hilgendorf
    •  & Manfred Nairz

    These authors contributed equally to this work.


  1. Center for Systems Biology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA.

    • Igor Theurl
    • , Ingo Hilgendorf
    • , Manfred Nairz
    • , Shun He
    • , Louisa M S Gerhardt
    • , Ashley M Fenn
    • , Atsushi Anzai
    • , Sara Rattik
    • , Cameron McAlpine
    • , Yoshiko Iwamoto
    • , Georg F Weber
    • , Nina K Harder
    • , Benjamin G Chousterman
    • , Mary McKee
    • , Jodie L Babitt
    • , Matthias Nahrendorf
    • , Ralph Weissleder
    • , Herbert Y Lin
    •  & Filip K Swirski
  2. Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA.

    • Igor Theurl
    • , Ingo Hilgendorf
    • , Manfred Nairz
    • , Shun He
    • , Louisa M S Gerhardt
    • , Ashley M Fenn
    • , Atsushi Anzai
    • , Sara Rattik
    • , Cameron McAlpine
    • , Yoshiko Iwamoto
    • , Georg F Weber
    • , Nina K Harder
    • , Benjamin G Chousterman
    • , Matthias Nahrendorf
    • , Ralph Weissleder
    •  & Filip K Swirski
  3. Department of Internal Medicine VI, Infectious Diseases, Immunology, Rheumatology, Pneumology, Medical University of Innsbruck, Innsbruck, Austria.

    • Igor Theurl
    • , Piotr Tymoszuk
    • , David Haschka
    • , Malte Asshoff
    • , Markus Seifert
    •  & Guenter Weiss
  4. Heart Center Freiburg, University of Freiburg, Freiburg, Germany.

    • Ingo Hilgendorf
  5. Department of Internal Medicine III, Oncology, Hematology and Rheumatology, University Hospital Bonn, Bonn, Germany.

    • Tobias A W Holderried
  6. Department of Internal Medicine V, Medical University of Innsbruck, Innsbruck, Austria.

    • Sieghart Sopper
  7. Department of Ophthalmology and Optometry, Medical University of Innsbruck, Innsbruck, Austria.

    • Milan Theurl
  8. Institute of Neuropathology, Freiburg University Medical Centre, Freiburg, Germany.

    • Peter Wieghofer
    •  & Marco Prinz
  9. Faculty of Biology, University of Freiburg, Freiburg, Germany.

    • Peter Wieghofer
  10. Department of Oncology, Amgen Inc., Thousand Oaks, California, USA.

    • Tara L Arvedson
  11. Program in Membrane Biology, Division of Nephrology, Massachusetts General Hospital, Boston, Massachusetts, USA.

    • Mary McKee
    • , Jodie L Babitt
    •  & Herbert Y Lin
  12. Department of Nutrition, Nutrition Discovery Innovation Center, Institute of Nutrition and Food Safety, School of Public Health, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China.

    • Fudi Wang
  13. Austrian Drug Screening Institute, Innsbruck, Austria.

    • Oliver M D Lutz
  14. Department of Anaesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA.

    • Emanuele Rezoagli
    •  & Lorenzo Berra
  15. BIOSS Centre for Biological Signalling Studies, University of Freiburg, Freiburg, Germany.

    • Marco Prinz
  16. Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, USA.

    • Ralph Weissleder


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I.T., I.H., and M. Nairz conceived the project, designed and performed experiments, analyzed and interpreted data, and wrote the manuscript; P.T., D.H., M.A., S.H., L.M.S.G., T.A.W.H., M.S., S.S., A.M.F., A.A., S.R., C.M., M.T., P.W., Y.I., G.F.W., N.K.H., B.G.C. and M.M. performed experiments; T.L.A., F.W., M.P. and P.W. provided materials and intellectual input; O.M.D.L., J.L.B., M. Nahrendorf, and G.W. provided intellectual input and edited the manuscript; L.B. and E.R. conceived and conducted the clinical trial. R.W. edited the manuscript; H.Y.L. conceived the project, helped interpret data, and edited the manuscript; F.K.S. conceived the project, designed experiments, analyzed and interpreted data, and wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Herbert Y Lin or Filip K Swirski.

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