Early myeloid cell infiltration and subset-specific macrophage responses in murine corneal nerve injury

Corneal nerve fibers and resident macrophages form a specialized microenvironment essential for tissue integrity and recovery after injury. This study aims to elucidate the early immune dynamics following corneal nerve injury, focusing on myeloid cell infiltration and resident macrophage subset shifts.

Using a murine circular nerve-cut model, we tracked immune responses for 21 days, with a focus on the first 12 h post-injury. Confocal imaging was used to assess corneal nerve density, while flow cytometry quantified infiltrating and resident immune cell populations. Transcriptomic profiling was performed at 3 and 6 h post-injury to analyze inflammatory gene expression, and in vitro experiments examined the effects of short-term nerve growth factor (NGF) exposure on macrophage polarization.

Confocal imaging showed a rapid decrease in corneal nerve density, followed by progressive regeneration. Flow cytometry revealed a surge in Ly6C⁺ myeloid cells at 3-6 h post-injury, predominantly in the central cornea, with an early tendency toward M2-like polarization. Resident macrophages exhibited distinct responses: M2-like and undifferentiated subsets declined, while M1-like cells were proportionally maintained, indicating divergent but complementary roles during the initial inflammatory phase. Transcriptomic profiling showed significant upregulation of inflammatory genes along with a transient increase in Ngf and compensatory anti-inflammatory signaling. In vitro, short-term NGF exposure enhanced both M1-and M2-like polarization, mirroring in vivo activation patterns.

Early myeloid cell infiltration and macrophage subset dynamics contribute to the initial neuroinflammatory response and may influence subsequent repair processes, highlighting the potential for immune modulation in corneal nerve regeneration.