Acute and modified rejection of heterotopic canine cardiac allotransplants studied by serial needle biopsy.

Serial histological changes in heterotopic canine cardiac allografts are reported using a percutaneous needle biopsy technique. This procedure can be performed without general anaesthesia or major complications and gives a high success rate (over 98%) with representative sampling of the organ. A pattern of acute rejection is described and compares well with the findings in other orthotopic and heterotopic studies. Histological differences between a group of untreated dogs and a group receiving azathioprine and hydrocortisone, in amounts that would permit subacute rejection in treated human transplants, suggest that immunotherapy causes greater reduction in local cellular immunological activity than in graft necrosis. It is concluded that although major graft damage in acute and subacute rejection appears to be cell mediated other factors may also be concerned in the pathogenesis of graft necrosis.