Research ArticleTISSUE REPAIR

Emergence of immunoregulatory Ym1+Ly6Chi monocytes during recovery phase of tissue injury

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Science Immunology  05 Oct 2018:
Vol. 3, Issue 28, eaat0207
DOI: 10.1126/sciimmunol.aat0207

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Monocytes mediate repair

Different subsets of macrophages contribute to inflammation during tissue injury or resolution of inflammation and tissue repair, but the distinct subsets of macrophages that support tissue repair are not well defined. Ikeda et al. now define a role for immunoregulatory Ym1+Ly6Chi monocytes during the recovery phase of tissue injury. Bone marrow–resident precursors of Ly6Chi monocytes express Ym1 during the final stage of differentiation, and these Ym1+Ly6Chi monocytes expand in the bone marrow during late phases of inflammation. These monocytes have an immunoregulatory phenotype and are required for recovery from tissue injury in a mouse model of colitis. These findings highlight a role for bone marrow–originated Ym1+Ly6Chi monocytes in tissue repair.

Abstract

Ly6Chi monocytes migrate to injured sites and induce inflammation in the acute phase of tissue injury. However, once the causes of tissue injury are eliminated, monocyte-derived macrophages contribute to the resolution of inflammation and tissue repair. It remains unclear whether the emergence of these immunoregulatory macrophages is attributed to the phenotypic conversion of inflammatory monocytes in situ or to the recruitment of bone marrow–derived regulatory cells de novo. Here, we identified a subpopulation of Ly6Chi monocytes that contribute to the resolution of inflammation and tissue repair. Ym1+Ly6Chi monocytes greatly expanded in bone marrow during the recovery phase of systemic inflammation or tissue injury. Ym1+Ly6Chi monocytes infiltrating into an injured site exhibited immunoregulatory and tissue-reparative phenotypes. Deletion of Ym1+Ly6Chi monocytes resulted in delayed recovery from colitis. These results demonstrate that a distinct monocyte subpopulation destined to act in immunoregulation is generated in bone marrow and participates in resolution of inflammation and tissue repair.

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