The Experimental Study Of Transforming Growth Factor β₁ Expression During The Incorporation Process Of Cortical Bone Allograft

Objective To investigate the effects of the time, the treatment of the allografts and the degree of matching for major histocompatibility complex antigen between the graft and recipient on the gene expression of transforming growth factor β1 (TGF-β1) during the incorporation process of bone allografts. Methods We used a rat model with bone defect in the left femur. We implanted fresh and frozen cortical bone grafts that were matched and mismatched for major histocompatibility complex antigen, and evaluated the grafts at 1, 2, 4, and 8 weeks after implantation. We assessed the incorporation of the graft with use of histological observation, immunohistochemical staining of TGF-β1, and in situ hybridization of TGF-β1 cDNA probes. We statistically analyzed the effects of and the interactions among time, the degreeof matching for major histocompatibility complex antigen, and the treatment of the graft (whether it was fresh or frozen). Results 1) Antigen-mismatched allografts continued to exhibit a retarded formation of new bone throughout the incorporation process (P<0.05). 2) 1,2, 4, and 8 weeks after implantation, the expression of TGF-β1 mRNA and protein were detected in the area of the implanted bone allografts, but primarily localized to osteoblasts, primitive mesenchymal cells, and extracelluar matrix. 3) TGF-β1 mRNA expression was profoundly affected by time, the treatment of the graft, and the degree of matching for major histocompatibilitcomplex antigen (P<0.05). 4) These factors interacted to affect mRNA expression of TGF-β1 (P<0.05). Conclusion 1) TGF-β1 was intimately involved in the control of incorporation of the graft. 2) Mismatching for major histocompatibility complex antigen between graft and recipient retarded mRNA expression of endogenous TGF-β1 and delayed new bone formation in the grafts. 3) Freezing had two main effects on the process of incorporation of the graft: it muted the effects of histocompatibility mismatching and reduced the biological activityof the graft. 4) There were two-way and three-way interactions among time, the degree of matching for major histocompatibility complex antigen, and the treatment of the graft (whether it was fresh or frozen).