Elimination and organ distribution of intravenously administered allogeneic and xenogeneic IgG modifications (Standard IgG, F(ab′)₂-fragments and β-propiolactone treated IgG) in dogs

Dog IgG was produced by fractionation procedures used for the production of clinically used i.v. gammaglobulins. Chemical modification of dog IgG was done by pepsin or β-propiolactone treatment. The intravascular half-life of β-propiolactone IgG was 8.5 ± 2.1 days compared to 4.5 ± 1.6 days of pepsin treated IgG. Tissue concentrations of radioactive labelled β-propiolactone IgG were generally higher than of pepsin digested IgG. Pepsin treated IgG was degraded to a significantly higher extent (26% of the administered radioactivity was bound to fragments smaller than 6000 MW after three days) than β-propiolactone IgG (9% fragments after the same interval, P < 0.001). It is concluded that the short intravascular half-life of pepsin IgG cannot be explained by increased extravascular filling, but is due to rapid degradation and excretion via the kidneys. There was no obvious difference in elimination and organ distribution between standard and β-propiolactone IgG.