[Histopathological studies of laryngeal allotransplantation in rats]

The establishment of an animal model for laryngeal allotransplantation in rat has enabled us to correlate clinical impressions of laryngeal allograft rejection with histologic data. In this study we used both clinical and histopathologic criteria to define the sequence and time parameters of rejection in histoincompatible vascularized rat laryngeal allografts. Of the 31 rats receiving vascularized laryngeal allografts, 18 served as experimental group, in which allogeneic transplantations were performed from inbred SD to outbred Wistar rats, 13 rats used as controls receiving laryngeal histocompatible transplants. The clinical phenomena of rejection aas started at 3 days post-operation, characterized by noticeable dermal swelling and lymphadenectasis of the recipient's neck. At this time, the graft appeared slightly edematous. These changes progressed and were more pronounced by 1 week. Two weeks after operation, the recipients exhibited an inflammatory scar tissue encasing the graft, the normal laryngeal architecture of grafts was invisible. Gross clinical evidence of rejection was well correlated with pathologic findings. Three days following transplantation, there was a slight histologic difference between the experimental group and the control group. Five days later, the surface respiratory epithelium exhibited progressive squamoi metaplasia, and minor salivary glands were mostly atrophic, afterwards extensive loss of acini emerged, with predominant lymphocyte and polymorphonuclear leukocyte infiltration throughout the lamina propria, sub-mucosa and the laryngeal adventitia. The arteriolar walls showed fibrinoid changes, with reactive intimal proliferation, and thickening of vessel wall. Focal thrombosis were frequently found. By 2 weeks, the normal architecture of the laryngeal allografts had nearly completely been replaced by fibrovascular connective and granulation tissues. Definition of the time sequence and histopathology of rejection will allow future determination of the efficacy of various immunosuppressive agents.