Vesicles (exosomes) released during sheep reticulocyte maturation contain a number of plasma membrane functions. Using an antibody coated, magnetic core bead, it has been shown unequivocally that vesicles that contain the transferrin receptor also contain other plasma membrane activities, such as the nucleoside transporter and acetylcholinesterase. Lysosomal activities, normally found in the same pellet, are excluded from the transferrin receptor-containing exosomes, suggesting that there is a common mechanism to segregate and externalize specific plasma membrane proteins. In addition to the sheep, electron micrographic studies show that exosomes can be retrieved from the circulation of anemic pigs, rats, and rabbits.

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