The innate immune regulator MyD88 dampens fibrosis during zebrafish heart regeneration.

The innate immune response is triggered rapidly after injury and its spatiotemporal dynamics are critical for regeneration; however, many questions remain about its exact role. Here we show that MyD88, a key component of the innate immune response, controls not only the inflammatory but also the fibrotic response during zebrafish cardiac regeneration. We find in cryoinjured myd88 ventricles a significant reduction in neutrophil and macrophage numbers and the expansion of a collagen-rich endocardial population.