Chemical screen for modulators of zebrafish regulatory T cell (zTreg) recruitment in the regenerating tail. (a) Zebrafish tails were amputated at 4 weeks post-fertilization (wpf) along the dotted cut line. (b) Quantification was performed on the region from the amputation site to the tip of the regenerated tail at 3 days post-injury (dpi). (c) foxp3a: RFP+ zTreg cells were visualized by epifluorescence. (d) Normalized numbers of zTreg cells for each compound in the NIH Clinical Collection. Green line, statistical threshold for selecting compounds for retesting. (e) Screen hits were retested at 5 μM and 10 μM. Data presented as mean ± SEM; n = 5 per treatment group, n = 25 for controls. *** p < 0.001. None of the other treatments significantly increased the number of zTreg cells.

Pramipexole (PPX) enhances zebrafish regulatory T cell (zTreg) recruitment in regenerating tail tissue. (a) Regenerating tissue from DMSO- and PPX-treated zebrafish at 3 days post-injury (dpi). White dotted lines represent the amputation line. Cells distal to this line were counted. (b) Dose–response for PPX (0.5–20 μM) in the tail amputation assay. Quantification of foxp3a+ cells (mean ± SEM). (c) Quantification of foxp3a+ cells (mean ± SEM) in uninjured tail tissue from zebrafish treated with PPX or DMSO for 3 days. n.s., non-significant; * p < 0.05, ** p < 0.001. Number of animals in each group indicated in [].

Role of dopamine signaling in zebrafish regulatory T cell (zTreg) recruitment. (a) Dose–response for apomorphine (APO) (2.5–20 μM) and (b) (co)treatments with dopamine antagonists in the tail amputation assay. Quantification of foxp3a+ cells (mean ± SEM). PPX, pramipexole; AMI, amisulpride; SCH, SCH-23390; n.s., non-significant; * p < 0.05.