Immunogenicity of human serum albumin: decay in the normal mouse.

The disappearance of immunogenicity of human serum albumin (HSA) was measured by injection of 1 μg of this protein in normal mice and by transferring to them, at intervals, a fixed number of HSA-sensitized syngeneic spleen cells: subsequently the antigen binding capacity of the serum was determined. This system served to reveal the residual amount of immunogen present in the animal, since under these conditions the adoptive secondary response is proportional to the HSA available, and no antibody is formed by the host. The half-life of HSA immunogenicity was 17½ hours. A similar rate of decline (T = 16½ hours) was found by following (131)I coupled to the HSA in the circulation of the same mice. This demonstrates that the albumin antigen is not stored in an active form in non-pre-immunized mice.