Quantitative pathology of oral mucosal allografts in the rabbit

Abstract

Quantitative analysis of four morphological components of the rejection reaction revealed differences between skin and mucosal allografts and between allografts and autografts of these tissues. Orthotopic skin or mucosal allografts were exchanged between pairs of rabbits matched or mismatched at the RLA locus of the major histocompatibility complex. Similar autografts were placed as controls. Quantitative microscopic examination of paraffin sections of all grafts, in which a standardized microscopic field was analysed, gave mean values for: (1) percentage of vessels with damaged walls; (2) fraction of vessel lumen occupied by blood cells or thrombus; (3) extravascular lymphocyte counts; (4) extravascular granulocytes counts. Significant differences were found between mismatched mucosal and mismatched skin allografts for all variables except lymphocyte counts. Mucosal and skin autografts differed significantly only in lymphocyte and granulocyte counts. Comparisons between mismatched allografts and autografts showed significant differences in all four variables in both mucosa and skin, whereas matched allografts and autografts of both tissues differed significantly for all variables except for the granulocyte count. Differences between autografts and allografts, whether RLA matched or mismatched, are clearly attributable to histocompatibility barriers in allografts. If the RLA locus had a significant effect on the 4 pathological components analysed, differences between matched and mismatched allografts would be evident. There being no such differences it is concluded that the minor histocompatibility loci play an important role in this type of immunological reaction. Differences in the reaction in oral mucosa and skin may be due to differences in the expression of histocompatibility antigens or tissue-specific antigens in these tissues and to factors of the local environment.