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Tendon injuries heal by scar, leading to poor function. To date, the role of immune cells remains underexplored. Using a neonatal mouse model of functional tendon healing compared to adult scar–mediated healing, we identified a regenerative immune profile that is associated with type 1 inflammation followed by rapid polarization to type 2, driven by macrophages and regulatory T cells (T reg cells). Single-cell and bulk RNA sequencing also revealed neonatal T reg cells with an immunomodulatory signature distinct from adult. Neonatal T reg cell ablation resulted in a dysregulated immune response, failed tenocyte recruitment, and impaired regeneration. Adoptive transfer further confirmed the unique capacity of neonatal T reg cells to rescue functional regeneration. We showed that neonatal T reg cells mitigate interleukin-33 (IL-33) to enable tenocyte recruitment and structural restoration, and that adult IL-33 deletion improves functional healing. Collectively, these findings demonstrate that T reg cells and IL-33 immune dysfunction are critical components of failed tendon healing and identify potential targets to drive tendon regeneration.
Arvind et al. (Wed,) studied this question.