The healing of full-thickness iliac bone grafts over a three-month interval was studied in young adult New Zealand white rabbits focusing on the rates of revascularization and new-bone formation. The former was measured by determining the distribution of ⁵¹Cr labeled erythrocytes while the latter was estimated from the uptake of ⁸⁵Sr.

Revascularization of autografts proceeded rapidly for four weeks and peaked at six weeks, followed by a slow decline. New-bone formation was maximum at three weeks and remained at a high plateau thereafter. The revascularization of allografts in untreated animals did not show an initial rise and remained significantly lower than autografts after the second week of observation (P less than 0.01). New-bone formation was indolent for the first six weeks (P less than 0.001) and rose slowly thereafter. By contrast, the curves for both factors in allografts of animals treated with azathioprine was virtually superimposable on those of autografts.

These studies document and quantitate the barrier imposed on bone implant acceptance by antigenic differences and demonstrate the reversal of this barrier through immunosuppressive treatment.