Comparing immunocompetent and immunodeficient mice as animal models for bone tissue engineering.

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To understand the differences and similarities between immunocompetent and immunodeficient mice as ectopic transplantation animal models for bone tissue engineering. Osteogenic cells from mouse leg bones were cultured, seeded on β-TCP granules, and transplanted onto the backs of either immunocompetent or immunodeficient nude mice. At 1, 2, 4, and 8weeks postoperatively, samples were harvested and evaluated by hematoxylin-eosin staining, tartrate-resistant acid phosphatase (TRAP) staining, and immunohistochemical staining and quantitative PCR. In immunocompetent mice, inflammatory cell infiltration was evident at 1week postoperatively and relatively higher expression of TNF-α and IL-4 was observed. In immunodeficient mice, new bone area and the number of TRAP-positive cells were larger at 4weeks than in immunocompetent mice. The volume of new bone area in immunodeficient mice was reduced by 8weeks. Bone regeneration was feasible in immunocompetent mice. However, some differences were observed between immunocompetent and immunodeficient mice in the bone regeneration process possibly due to different cytokine expression, which should be considered when utilizing in vivo animal models.