Early atherosclerotic lesions in rat aorta. Effect of cholesterol feeding and immunization

Germ-free and conventional rats were fed cholesterol or normal pellets and part of both groups were immunized repeatedly with horseradish peroxidase (HRP). Four days after the last injections all the rats were killed, aortas removed and prepared for immunocytology and chemical analysis. Free peroxidase was not detected in the arterial wall and in all immunized rats only faint staining of free anti-HRP antibodies occurred in the intima. In contrast there was a consistent deposition of HRP-anti-HRP antibody complexes in the inner two thirds of the arterial wall in all HRP-immunized animals. Immunization and cholesterol feeding increased the cholesterol content of the aorta and produced early lesions, whereas cholesterol feeding or immunization alone was less effective.