An epitope on the transferrin receptor preferentially exposed during tumor
progression in human lymphoma is close to the ligand binding site
S Takahashi, L Esserman and R Levy
Department of Medicine, Stanford University Medical Center, CA 94305.
We have previously reported an anti-transferrin receptor antibody, Trump,
which was originally selected for its ability to discriminate low- and
high-grade lymphomas. This feature was distinct from the other
anti-transferrin receptor antibodies such as OKT9. In the present study,
further immunochemical analysis was performed to define the nature of the
antigenic site recognized by the Trump antibody. Trump was found to block
the binding of transferrin both to solubilized and to surface transferrin
receptors; conversely, transferrin could block the binding of Trump only to
surface transferrin receptors. Therefore, the epitope recognized by Trump
is near but not identical to the transferrin binding site. Stimulation of
peripheral blood lymphocytes with phytohemagglutinin induced both the OKT9
epitope and the Trump epitope, but 12-phorbol 13 myristate acetate induced
only the OKT9 epitope. Growth of some cell lines was inhibited by Trump but
not by OKT9. No structural difference was found between transferrin
receptor molecules reactive with Trump and those reactive with OKT9. In
support of these results, Trump was able to immunoprecipitate transferrin
receptor molecules solubilized from low-grade follicular lymphoma cells
even though it did not bind to the receptors exposed on the surface of
these cells. These findings imply that low-grade lymphoma cells differ from
high-grade lymphoma cells not in the structures of their transferrin
receptors but in their exposure of the molecule on the cell surface.
Volume 77,
Issue 4,
pp. 826-832,
02/15/1991
Copyright © 1991 by The American Society of Hematology
