When a tissue is transplanted from one site to another in the same individual, immunologic complications usually do not occur.’ The immune system is not triggered, because the tissue is recognized as “self.” However, when a tissue is transplanted from one individual to another or from one species to another, the immune system may present a formidable obstacle, to the success of the grafting procedure. If the’ graft is recognized as a foreign substance by the host, it will mount an intense response in an a tempt to destroy the graft. The type of response theirnn, -ne svstem mounts against “foreign” grafts is primarily a cell-mediated response by ‘l-lymphocytes. It may not ccur imrucdiatpIy, however, and \n the ea ly period the incorporation of a bone graft into the host may appear to be progressing normally. The length of this latent period depends on the Similarity between the host and the recipient. The more similar they are (antigenically), the longer an immunologic reaction may take to appear. This type of immunologic reaction is th most common reason for rejection of hearts, kidneys, and other organs transplant- “ed to another individual. Tissue-typing procedures, in which a donor and recipient are genetically compared for similarities before transplantation, are currently ommonplace for organ transplantation but never for bone grafts.
Because of the immunologic rejection of transplants between individuals or between species, methods have been devised to improve the success of grafting procedures in these instances. Two basic approaches are used
clinically: The first is the suppression of the host individual ‘s0 immune response. Immunosuppression with various medications is most commonly used in organ transplant patients. This approach is not used routinely in oral andmaxillofacial surgical bone grafting procedures because of
the potential complications from immunosuppression. Another approach that has been used extensively in oral arid maxillofacial surgical procedures is the alteration of the antigenicity of the graft so that the host’s immune response will not be stimulated. Several methods of treating grafts
‘have been used.rincluding boiling, deproteinizjng, rnerthiolating,
freezing, freeze-drying, irradiating, and dry heating. All of these methods, potentially helpful for use in bone grafts, are obviously not helpful in organ transplants.’