Phorbol esters cause sequential activation and deactivation of complement receptors on polymorphonuclear leukocytes
Phorbol myristate acetate (PMA) exerts a biphasic effect on receptors for C3b and C3bi of human polymorphonuclear leukocytes (PMN). The addition of PMA for 10 min enhances the capacity of these receptors to promote binding and phagocytosis of C3b- and C3bi-coated erythrocytes. Upon additional incubation for 60 min, the capacity of these receptors to bind and ingest ligand-coated erythrocytes decreases the levels below those of resting cells. Although PMA does cause increased expression of cell surface C3b and C3bi receptors, the sequential rise and fall of receptor activity cannot be accounted for the alterations in the number of surface receptors. It appears, rather, that PMA causes qualitative changes in these receptors, first an increase in receptor activity (activation) and then a decrease in receptor activity. To explore the role of phosphorylation in the sequential activation and deactivation of phagocytosis-promoting receptors, the authors loaded PMN with thiophosphate (thioP). This compound is incorporated into cellular nucleotides and proteins, and the resultant (thio)phosphorylated proteins are resistant to phosphatases. thioP-loaded cells show enhanced receptor activity, suggesting that activation of receptors is mediated by a phosphorylation event. Cells loaded with thioP and treated with PMA for 70 min do not deactivate C3 or Fc reactors, suggesting that the deactivation is the result of a dephosphorylation event.
- Research Organization:
- Rockefeller Univ., New York, NY
- OSTI ID:
- 6935962
- Journal Information:
- J. Immunol.; (United States), Vol. 136:5
- Country of Publication:
- United States
- Language:
- English
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