Catabolism of human IgG in mice sensitized to various IgG fragments. Similarities to the catabolism of rheumatoid IgG in mice.

Whole body elimination studies of human serum IgG have showm that C57Bl miceare tolerant to this protein at low concentrations. The present study demonstrates that tolerance to this protein may be broken by presensitization of the mouse with the pepsin-derived fragments of human IgG (F(ab)2 and pFc), in marked contrast to the papain-derived fragments (Fab and Fc). Sensitization with F(ab)2 fragments induced a distinctive elimination pattern of the intact protein which was analogousto that observed in non-sensitized mice injected with serum IgG isolated from patients with rheumatoid arthritis. Since, by circular dichroism studies, we have previouslyimplicated a structural anomaly at or near the hinge region of the 'rheumatoid' IgGmolecule, our observations are discussed in relationship to a possible immune aetiologyfor rheumatoid arthritis.