SURFACE-MEMBRANE VESICLES FROM MONONUCLEAR-CELLS STIMULATE ERYTHROID STEM-CELLS TO PROLIFERATE IN CULTURE

  • 1 January 1982
    • journal article
    • research article
    • Vol. 60  (3) , 583-594
Abstract
To examine the contribution of cell surface materials to erythroid burst-promoting activity (BPA), media conditioned by a variety of human cell types were separated into pellets and supernatants by centrifugation. When added to serum-restricted cultures of nonadherent human marrow cells, pellets contained about half of the total stimulatory activity. Freeze-fracture EM of the pellets revealed the presence of unilamellar membrane vesicles ranging from 0.10-0.40 .mu.M in diameter. The amount of BPA in culture increased with added vesicle concentration in a saturable fashion. Preparation of leukocyte conditioned medium (LCM) from 125I-wheat germ agglutinin labeled cells and studies comparing the glycoprotein composition of vesicles with that of leukocyte plasma membranes suggest that LCM-derived vesicles are of plasma membrane origin. Partially purified leukocyte plasma membrane preparations also contained BPA. While disruption of vesicles by freezing/thawing and hypotonic lysis did not alter BPA, heat, trypsin or pronase treatment removed > 65% of BPA, implying that vesicle surface rather than intravesicular molecules express BPA. Results of BPA assays performed in 2-layer clots indicated that proximity to target cells is required for vesicle BPA expression. Membrane vesicles spontaneously shed from cell surfaces may be important regulators of erythroid burst proliferation in vitro.

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