Ultrastructural alterations in canine lung allografts

Morphologic alterations in transplanted dog lungs undergoing acute rejection were studied with the electron microscope. Earliest changes were swelling of the type I alveolar cells and cytoplasmic vacuolization in the capillary endothelial cells. Later, there was progressive infiltration of macrophages which contained large osmiophilic inclusions. Type II alveolar cells increased in number and showed vacuolization, fraying and membrane disruption of their lamellar inclusions. A decrease in the relative number of type II cell inclusions and extensive endothelial damage were observed in preterminal biopsies. The significance of these cellular changes in relation to pulmonary rejection requires further investigation.