Figure 2.

Role of FcRn in determining survival of IgG in the circulation. Left panel: under normal conditions, IgG from the serum binds to FcRn and goes through an endosomal pathway which avoids lysosomal catabolism. The IgG is thus returned intact to the circulation. Right panel: If the serum IgG level is raised by exogenous IgG, FcRn becomes saturated and much of the IgG goes through the default endosomal pathway which results in lysosomal catabolism. Because of the high proportion of exogenous normal IgG, endogenous pathogenic IgG is preferentially degraded (Yu and Lennon, 1999 ). Copyright 1999 Massachusetts Medical Society. Reprinted with permission from Massachusetts Medical Society.