Binding and phagocytosis of fibronectin‐coated beads by BHK cells: Receptor specificity and dynamics

Studies on the receptor specificity and dynamics involved in fibroblast phagocytosis of latex beads revealed the following: (1) Ligands other than fibronectin such as concanavalin A (ConA) and serum spreading factor, when coated on latex beads, were found to promote phagocytosis of the beads. This indicates that fibroblast phagocytosis, like spreading, is a ligand‐receptor mediated phenomenon not specifically requiring fibronectin (pFN); (2) Anti‐pFN antibodies were found to inhibit the ability of cells to ingest pFN‐coated beads that previously were bound on the cell surfaces. Consequently, binding of beads to the cell surfaces per se is not a sufficient signal to promote ingestion of the beads; (3) Finally, divalent cations protected receptor function necessary for phagocytosis of pFN‐coated beads from proteolysis by trypsin, as previously was found for receptors involved in cell attachment and spreading on pFN‐coated culture dishes. Recovery experiments carried out with cells whose surface receptors had been destroyed indicated that there was an internal (or cryptic cell surface) pool of receptors that amounted to at least 50% of the receptors normally found on the cell surface. After complete destruction of the cell surface and cryptic pools of receptors, reappearance of receptors required for bead binding and phagocytosis required several hours and did not occur in the absence of new protein synthesis.