Journal of Experimental Medicine, Vol 158, 752-766, Copyright © 1983 by Rockefeller University Press
Spontaneous release of the Leu-2 (T8) molecule from human T cells
J Fujimoto, S Levy and R Levy
Sensitive enzyme-linked immunosorbent assays (ELISA) for the detection of
human T cell antigens in soluble form have been developed. The assays use
mouse monoclonal antibodies and specific anti-Leu sera prepared in rabbits
by immunizing with Leu antigens absorbed to monoclonal antibody affinity
columns. With these assays, Leu-1, -2, and -3 antigen signals from extracts
of as few as 5 X 10(3) cells could be detected. When culture supernatants
from various cell lines were tested, Leu-2 antigen, but not Leu-1 or Leu-3,
was found to be present. Leu-2 antigen was present only in supernatants
from T cell lines that expressed Leu-2 on their cell surface. Leu-2 antigen
accumulated progressively in the supernatant of low density culture and its
presence did not depend on cell proliferation or on fetal calf serum in the
culture medium. The Leu-2 antigen in the supernatant was found to have only
one Leu-2a determinant, whereas Leu-2 antigen from cell extracts had at
least two determinants. The Leu-2 molecule was effectively purified from
supernatant with an anti-Leu-2a affinity column. The purified Leu-2 antigen
from supernatant of HPB-ALL cells was a single polypeptide chain of 27,000
mol wt, whereas Leu-2 antigen present on HPB-ALL cell surface was composed
of two or more identical polypeptide chains of 33,000 mol wt linked by
disulfide bonds. Normal human sera and sera from leukemia patients were
also examined for the presence of the Leu-2 antigen. Normal human sera
contained low levels of Leu-2 antigen but sera from Leu-2-positive leukemia
patients had high levels. These results indicate that Leu-2 antigen is
released from human T cells under physiological conditions.
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