Postnatal decline of maternally acquired antibodies in the rat.

The decline (half-life) of maternally acquired antibodies of two different specificities (diphtheria and tetanus) was studied in rats. Essentially similar half-lives for antibody of each specificity were found in young rats from the same litter. In contrast, half-lives varied from 2 to 10 days in individuals of different litters. Significant differences in half-lives were demonstrated in young rats possessing markedly different initial titres of antibodies of the two specificities. It was established that there was a relationship between the half-life and the initial titre of antibody of each specificity which could be described by a rectangular hyperbola. These findings are in close aggreement with previous studies in human infants.