Elevated phagocytic capacity directs innate spinal cord repair.

Immune cells elicit a continuum of transcriptional states after spinal cord injury (SCI). In mammals, inefficient debris clearance and chronic inflammation impede recovery and overshadow pro-regenerative immune functions. We found that zebrafish SCI elicits transient immune activation and efficient debris clearance. Transcriptomics and genetic ablation showed zebrafish macrophages are highly phagocytic and required for regeneration. Comparisons between zebrafish and mammalian macrophages identified transcription and immune response regulator (tcim) as an immune-enriched regenerative gene. Deletion of zebrafish tcim impairs phagocytosis and regeneration and activates a pro-inflammatory signature in leukocytes. Tcim expression in zebrafish and mouse macrophages establishes its conserved roles by promoting lipid metabolism and the reprogramming of myeloid precursors into activated phagocytes. This study underscores a requirement for elevated phagocytic capacity to achieve innate spinal cord repair and identifies a gene with conserved function in mammalian cells.