FIG. 2.

Clusters of human spectrin-positive myofibers are detected in mice never injected with human cells; these are regenerating myofibers. (A–C) NOD/Rag1^nullmdx5^cv muscle tissue sections from animals not injected with human cells. Myofibers reactive to the human-spectrin antibody are detected. (D–F) The human spectrin-reactive myofibers are regenerating myofibers. Consecutive sections stained for laminin and embryonic myosin heavy chain (eMHC) reveal the identity of the spectrin-reactive myofibers in NOD/Rag1^nullmdx5^cv mice. (G–L) NSG mouse muscles from 6-month-old animals never injected with human cells and injured with cardiotoxin show expression of human spectrin in regenerating myofibers. (G–I) Human spectrin-positive myofibers are negative for dystrophin. (J–L) In consecutive sections, the spectrin-reactive myofibers are within the injured area, as documented by coexpression of laminin and eMHC. Scale bar: 50 μm.