Rate of elimination of homologous globulins (including antibody) from the circulation

Abstract

Radioactive antibody and normal globulin were prepared by injecting (carboxy-Cl4) lysine and (carboxy-Cl4) phenylalanine into rabbits hyperimmun-ized against pneumococcus type III. These were transfused to normal and immune rabbits. The specific radioactivity of antibody transfused into normal rabbits remained unchanged for as long as 3 weeks, indicating that molecules of this kind do not exchange their amino acid carbon while they remain in the circulation. The concn. of antibody and the specific radioactivity of transfused globulin declined at a steady rate of approx. 12.5% per day, the globulin rate being fractionally lower than that of the antibody. It is suggested that the true rate of elimination of these globulin-like molecules is given by the decline of the serological label which is irreversibly lost rather than by isoto-pic labelling, even where the isotopically-labelled proteins are transfused. The specific radioactivities of transfused labelled antibody and labelled normal globulin in the plasma of immune rabbits both declined at the same approximate rate of 12.5% per day. The rates of antibody and normal-globulin elimination are shown to be approx. the same and independent of the rate of production. Hence the weight of these proteins produced in a given interval is proportional to their average plasma concn. over the same period. An example is given of the use of this information to calculate absolute rates of antibody production by a rabbit at various stages of hyperimmunization.