Lymphocyte-epithelium interaction during rejection of nonisogeneic rat tracheal grafts

Rat tracheal tissues were maintained in organ culture for 1 to 2 weeks and then implanted heterotopically into syngeneic and outbred hosts. The grafts and surrounding tissues were removed at regular intervals and examined by light and electron microscopy. Allogeneic grafts were consistently rejected, and a constant pattern of immunologic response was observed during rejection. Infiltration by mononuclear cells occurred initially in the subepithelial region. Subsequently, small lymphocytes migrated through the basal lamina and insinuated themselves between the differentiated epithelial cells. Larger cells resembling activated lymphocytes were also present in the intraepithelial infiltrate. Both type of lymphocytes had cellular processes in contact with epithelial cells, but there was no associated death of epithelial cells. Later, the infiltrate in some areas of the epithelium inclded dividing cells and other large cells exhibiting ultrastructural features suggesting blast transformation. Epithelial cell death was evident during this phase. The sequence of events may reflect a process of recognition and specific cytotoxic action by lymphocytes.