Endocytosis and exocytosis of phytohemagglutinin (PHA) cell surface receptors of human lymphocytes during blast transformation

Linthicum, D.S.; Elson, E.; Mendelsohn, J.; Sell, S.

Experimental Cell Research 110(2): 237-250


ISSN/ISBN: 0014-4827
PMID: 304009
DOI: 10.1016/0014-4827(77)90289-0
Accession: 068525739

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The ultrastructural distribution of T thymidine incorporation. Over the course of a 72 h incubation period, cell samples were harvested at regular intervals and examined by transmission electron microscopy. Within several minutes of culture at 37.degree. C the majority of the ferritin (Fe)-labeled PHA surface receptors on almost all cells undergo rapid endocytosis; some Fe label remains at the cell surface. After several hours, endocytotic vesicles containing Fe-labeled receptors coalesce and undergo condensation. Within 36-48 h, most endocytotic vesicles transform into multivesicular bodies (MVB). After 48-72 h, 70-80% of the cells had the ultrastructural appearance of blast transformation as characterized by increased size, euchromatic nuclei, nucleolonema and polyribosomes. In 40% of the blast cells the Fe-labeled MVB are exocytosed to the cell surface; cytoplasmic MVB in the remaining portion of the blasts and non-blast lymphocytes do not appear to undergo exocytosis. Although endocytosis and exocytosis of lymphocyte surface receptors during mitogen-induced blast transformation are observed, the role and significance of receptor redistribution to cell activation remains unclear.