The use of [14C]amino acids to study sites and rates of antibody synthesis in living hyperimmune rabbits

Abstract

Intracellular antibody was recovered from tissues of rabbits hyperimmunized by intravenous injections of type 3 pneumococci, and perfused free of blood at various time intervals after administration of C14-labeled amino acids. Allowance was made for pre-formed extracellular antibody by injecting I131-labeled antibody 2-3 days beforehand and allowing it to come into equilibrium with antibody in the extracellular fluid. C14-labeled antibody was found in lungs, bone marrow, spleen, lymph glands and appendix (but not in liver or kidneys) within a few minutes of administering the label, and before C14 was detectable in plasma antibody. The amounts of intracellular antibody recovered from tissues were: lungXxbone marrowspleenlymph glands^appendix. The time course was determined of the specific Cl4-activities of intracellular antibody and of the intracellular free amino acids. From the results the "turnover time" of intracellular antibody in the lung was calculated to be of the order of 2 hours. From consideration of the total amounts of intracellular antibody recovered, and of the daily production of antibody required to maintain the observed plasma levels, the average "turnover time" of all tissue antibody was calculated to be of the order of 3 hours. Consideration of the time course of plasma-free amino acid specific activities during the first few minutes after injection of a mixture of C14-labeled amino acids suggests (for a 2.5 kg rabbit) that (1) the rate of exchange of amino acids between cells and tissue fluids is of the order of 100 mg/minute and (2) the size of the "intracellular free amino acid pool" with which this rapid exchange occurs is of the order of 100 times the plasma-free amino acid pool.