GENE-EXPRESSION AT GRAFT HOST INTERFACES OF CORTICAL BONE ALLOGRAFTS AND AUTOGRAFTS

The healing processes of autogenous and frozen allogeneic cortical bon e grafts were compared in rats. Two unicortical defects created in the proximal metaphysis of the tibia were autografted or allografted with blocks of cortical bone. The biomechanical properties of the graft-ho st junction and the time-related changes of the expression of genes co ding for Type I, II, III, and X collagens and osteonectin were determi ned at one, two, four, and eight weeks. The strength of the allograft host bone union was lower than that of autografts at the early stage o f incorporation but the difference diminished by eight weeks. Northern analysis of graft mRNAs demonstrated a strong expression of Type I co llagen and osteonectin genes at the beginning of autograft incorporati on. The allografts showed a lower expression of the corresponding gene s at one and two weeks, but the difference diminished thereafter. The gene coding for Type III collagen showed a temporary expression at two weeks both in allografts and autografts, probably because of the form ation of inflammatory fibrovascular stroma provided by the host borne at the graft-host interface. No expression of cartilage-specific Type II and Type X collagens were observed, demonstrating that the healing in both grafts proceeded through primary bone healing. Compared with c ortical-cortical junctions of autografts, the graft-host interfaces of allografts exhibited a reduced osteoinductive process and a slower in crease of union strength.