Biological half-life of normal and truncated human IgG3 in scid mice

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.