FIG. 1.
Compartmental model. The model consists of two equivalent systems (one for the labeled and one for the unlabeled antibody), which are connected by the same number of antigens and the physical decay λphys. The antibody is administered into the main plasma compartment. There is a certain capacity of readily accessible antigens (Agra), where the antibody can directly bind from the serum because of discontinuous capillary structures. To bind to most of the antigens in the tumor (Agtu), first the antibody has to pass the capillary walls. Degradation takes place wherever the antibody is bound. Degradation of unbound antibody is simplified by a linear degradation rate from the plasma compartment. AgAbi, bound antibody (i = tu or ra), Ab, free antibody; tu, tumor; ra, readily accessible; int, interstitial spaces; mono, monovalently bound; bi, bivalently bound.