The Catabolism of Protein Antigens in the Newborn and Maturing Rabbit

The rate of degradation, organ deposition, and blood clearance of SBSA, SRSA, and IRSA has been measured in the newborn, 6-, and 30-day-old rabbits. When the animals were injected with a weight-graded dose of the 3 proteins, differences in their catabolism in the newborns were demonstrable as compared to the 6-, and 30-day-old animals. The capacity to degrade the azo compounds was shown to be incompletely developed at birth. At 6 days of age, however, the rabbits catabolized these proteins much at the same rate as the 30-day-old animals. Addition of the benzenesulfonate moiety determined the rate of degradation organ deposition and excretion rather than the carrier protein when the azo compounds were injected. The biosynthetically labeled S(25) rabbit serum albumin (IRSA) was catabolized at a slower rate than the azoproteins in all age groups. Very little difference in the metabolism and organ deposition of the IRSA was shown to exist between the newborn and maturing animals. A dosage schedule, therefore, designed to test the immunological capacity of developing animals may not be valid when calculated upon body weight. The low level of activity of enzyme systems present at birth which degrade anti-genic material may serve as an explanation as to why this period of development is so vulnerable to the induction of tolerance rather than immunity when compared to the adult.