The fractional catabolic rate of IgG in the body is regulated with precision in order to maintain appropriate serum concentrations. We have investigated the turnover rate of normal human IgG3, a ...newly identified, naturally occurring, truncated form of IgG3 and a human-mouse chimeric IgG3 antibody in an immunodeficient mouse strain, C.B-17 (SCID), lacking endogenous Ig. The half-life of non-truncated, normal serum IgG3 as well as the chimeric antibody was about 7 days, whereas truncated IgG3 had a shorter half-life of about 5 days. Due to the inherent immune defect, the SCID mouse could represent a versatile animal model for the determination of turnover rates, inasmuch as an immune response will not be mounted against foreign antigens.
