Studies on the Fate of Antigens in Vitro

Summary A method is described for studying the fate in vitro of I131-trace labeled human serum albumin in the presence of exudate cells from normal guinea pigs. When the cells were suspended in medium containing normal rabbit serum and normal guinea pig serum only slight breakdown of the albumin occurred. The addition of precipitating rabbit antihuman albumin serum to the system resulted in a greatly increased breakdown of the antigen. Although the amount of antigen precipitated by the antiserum was constant over the range of antiserum dilutions, 1:1 to 1:32, the amount of antigen broken down was greater in tubes to which the antiserum was added at 1:16 dilution than in higher concentrations of antiserum. In the dilutions 1:64 and higher there was a decrease both in the amount of antigen precipitated and in the amount broken down. The mechanism of this effect of antibody is discussed. Evidence is presented that the antigen breakdown occurs intracellularly. Radiochromatographic analysis was carried out in order to identify the radioactive breakdown products, and the presence of a peptide was demonstrated.