Disparity between expression of transferrin receptor ligand binding and non‐ligand binding domains on human lymphocytes

D. H. Boldt, J. L. Phillips, O. Alcantara

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

We compared transferrin receptor (TfR) expression on human peripheral blood lymphocytes (PBL) activated by phorbol myristate acetate (PMA) or L‐phytohemagglutinin (LPHA) using two techniques: (1) 125I‐iron‐saturated transferrin (FeTf) binding, (2) reactivity with monoclonal anti‐TfR antibodies—OKT9 and B3/25. These monoclonal antibodies do not block FeTf binding, and therefore bind to TfR domains separate from the ligand binding site. Unstimulated PBL bound fewer than 1,000 molecules of 125I‐FeTf per cell, and < 5% of cells expressed TfR antigens detected by OKT9 or B3/25. 125I‐FeTf binding and antibody binding increased in parallel on LPHA‐activated PBL. After exposure to LPHA for 72 hr, 125I‐FeTf binding increased 100‐fold to 105 molecules per cell and > 50% of cells expressed TfR antigens. By contrast, PMA activation of PBI markedly increased binding of OKT9 and B3/25 but not the binding of 125I‐FeTf. Cell surface expression of TfR antigens seen by OKT9 and B3/25 did not differ between LPHA‐ and PMA‐activated PBL. However, after 72 hr with PMA, 125I‐FeTf binding increased only 6‐fold and consistently remained at < 104 molecules per cell. Therefore, PMA induced a disparity between expression of TfR ligand binding domains and immunological domains at the cell surface. Cell proliferation assessed by fluorescent DNA analysis was similar in cultures stimulated by LPHA or PMA. These data indicate that lymphoid cells may possess a mechanism for modulating TfR expression in which down‐regulation of FeTf binding occurs without receptor internalization. Alternatively, it is possible that this observation may reflect a membrane perturbation effect of PMA.

Original languageEnglish (US)
Pages (from-to)331-336
Number of pages6
JournalJournal of Cellular Physiology
Volume132
Issue number2
DOIs
StatePublished - Aug 1987

ASJC Scopus subject areas

  • Physiology
  • Clinical Biochemistry
  • Cell Biology

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