Decline of passively acquired antibodies in young and adult rats.

The rate of decline (half-life) of passively acquired antibodies was studied in young and adult rats. There was a wide variation in half-life when varying concentrations of diphtheria or tetanus antibody were administered by intraperitoneal injection; half-lives ranged from 1-2 to 12-0 days in both age groups. When different concentrations of diphtheria and tetanus antibody were administered together by the same route, significant differences in half-lives were demonstrated in individuals of each group. Each of the curves describing the relationship between initial antibody titre and half-life took the shape of a rectangular hyperbola; individuals with high initial titres had short half-lifes, whereas in animals with low initial titres antibody declined at a slower rate. The results are in agreement with those previously reported for the decline of maternally acquired antibodies in infants and young rats and for the catabolism of IgG.