Immunohistochemical staining of sections of zebrafish kidney with anti-GFP Ab. Staining was performed on paraffin-embedded kidney sections using a 1:1500 dilution of anti-GFP Ab and peroxidase-conjugated secondary Ab. Brown-staining cells were observed in panels A, C, and D. (A) In donor Tg(CD41:GFP) kidney, representative CD41-GFP⁺ cells are indicated by pink arrows. (B) In wild-type untransplanted fish, there was no staining detected. (C) Irradiated fish that were transplanted with 0.5 × 10⁶ β-actin:GFP⁺ cells from Tg(β-actin:GFP) WKM showed engrafted cells of multiple lineages throughout the renal tubules and interstitium, as exhibited by brown signals galore in the kidney section. (D) In transplanted fish that received 10³ flow-sorted CD41-GFP^lo cells, engrafted cells were marked by red arrows in the hematopoietic cell portion of the recipient kidney.