The in vivo stability of antibody

Our previous studies, concerned largely with antigen retention and the characterization of antigen in tissues, led us to suspect that some antibody, like antigen, may be stabilized in tissue sites (1). The purpose of the present investigation was to study further, such antibody which appeared to be bound with antigen and perhaps normal tissue constituents. The investigation was carried out in the following manner: rabbits were first immunized by a series of intravenous injections of antigen and at the height of precipitin production they were fed S35-labelled yeast cells. Newly produced antibody, like the other plasma proteins, became readily labelled with S35 amino acids within a few hours. After varying lengths of time, when circulating antibody had declined, antigen was again injected. Serum samples were then taken at various intervals and the specific activity of antibody was measured as soon as antibody reappeared in the circulation. The specific activity of antibody was measured in the antigen-antibody precipitates obtained, both in the period when the antibody had been allowed to decline and also after antigen had been reinjected to induce an anamnestic response. A comparison of antibody-specific activity provided evidence that there was a release of antibody which had been made at the time of S35 feeding and stored in some stabilized form in tissues. The results are discussed with respect to the anamnestic response and the retention of antigen in tissues.