If you have ever been injured and felt the swelling around the affected area and experienced the scar that develops over time, you are well aware that there is an elaborate immune response immediately following an injury. Is the immune system at all connected to the initiation and process of regeneration? A recent study in zebrafish has demonstrated that a subtype of T cells called regulatory T cells (Treg cells) seems to rapidly invade injured tissues, including the eye, spinal cord, and heart (Hui et al. 2017). Targeted loss of Treg cells in the adult zebrafish prevents regeneration in each of these different organ systems (Figure 1). Most interesting is that these Treg cells recognize the type of tissue injured and respond by upregulating specific growth factors that promote a specific pro-regenerative response in these tissues. For instance, Treg cells in the heart upregulate neuregulin-1, which is capable of inducing cardiomyocyte proliferation even when Treg cells are depleted (Figure 2). This is a remarkable study that demonstrates a clear emergency response from the immune system that appears to provide tailored pro-regenerative care for the specific tissue type injured. Whether this ability is conserved across highly regenerative species remains to be seen. It is nonetheless enticing to explore whether Treg cells and the therapies they provide could be leveraged to enhance pro-regenerative instead of scarring responses in us.
Hui, S. P., D.Z. Sheng, K. Sugimoto, A. Gonzalez-Rajal, S. Nakagawa, D. Hesselson, K. Kikuchi. 2017. Zebrafish Regulatory T Cells Mediate Organ-Specific Regenerative Programs. Dev Cell 43(6):659-672.e5.