Fate of homologous antibody in the rabbit

Abstract

The distr. of radioactivity in tissues of a rabbit killed and exsanguinated by perfusion 8 days after receiving a transfusion of (C14) phenylalanine-labelled rabbit pneumococcus antibody was studied, and the radioactivity found predominantly in the form of labelled protein. By extracting the disintegrated tissues with carrier antibody and measuring the amounts of residual lymph by Evans Blue injected before death it is shown that practically all the precipitable radioactive antibody could be accounted for in the residual lymph, inplying that the remainder of the radioactivity present was in the form of protein which had lost its original specific immunological configuration. It is concluded that transfused antibody entered cells in certain organs which became highly labelled, notably in liver, kidney, spleen, bone marrow, lung and gut, whtiout being broken down to the amino acid level, and was rapidly changed into some other kind of intracellular protein. The level of radioactivity in the plasma free amino acid fraction at death was high enough to be consistent with the idea that the protein radioactivities of other poorly labelled tissues, notably muscle, could be due to incorporation of labelled free amino acids. Evans Blue uptake may be a convenient guide to plasma protein assimilation by tissues. This dye is found in high concn. in the highly labelled tissues and hardly at all in the poorly labelled ones, supporting the view that the cells of the latter are impervious to proteins.