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autologous blood and marrow transplantation - Blog Science ...

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670 Chapter 14: Radioimmunotherapy<br />

I. Low IgG<br />

Figure 3« Mechanism of y-globulin protection from catabolism. IgG (Y) <strong>and</strong> plasma proteins<br />

(o) (A) are internalized into endosomes of endothelium (B), without prior binding. In<br />

the low pH (H +<br />

) of the endosóme (C), binding of IgG is promoted. D, E, F: IgG retained by<br />

receptor recycles to the cell surface <strong>and</strong> dissociates in the neutral pH of the extracellularfluid,<br />

returning to circulation. G, H: Unbound proteins are shunted to the lysosomes for degrada­<br />

tion. With "Low IgG," receptor efficiently " rescues" IgG from catabolism. With "High IgG,"<br />

receptor is saturated <strong>and</strong> excess IgG passes to catabolism for a net acceleration of IgG catab­<br />

olism. All features excepting the role ofpH in binding <strong>and</strong> endothelial localization were known<br />

to Brambell <strong>and</strong> inherent to his model. 3

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