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J. Exp. Med.,
Volume 188, Number 1, July 1, 1998 205-210
By


§
From the * Department of Pathology, the Ligation of cytotoxic T lymphocyte antigen 4 (CTLA4) appears to inhibit T cell responses.
Four mechanisms have been proposed to explain the inhibitory activity of CTLA4: competition for B7-1 and B7-2 binding by CD28; sequestration of signaling molecules away from
CD28 via endocytosis; delivery of a signal that antagonizes a CD28 signal; and delivery of a signal that antagonizes a T cell receptor (TCR) signal. As three of these potential mechanisms involve functional antagonism of CD28, an experimental model was designed to determine
whether CTLA4 could inhibit T cell function in the absence of CD28. TCR transgenic/recombinase activating gene 2-deficient/CD28-wild-type or CD28-deficient mice were generated and immunized with an antigen-expressing tumor. Primed T cells from both types of mice
produced cytokines and proliferated in response to stimulator cells lacking B7 expression.
However, whereas the response of CD28+/+ T cells was augmented by costimulation with B7-1,
the response of the CD28
Committee on Immunology, and the § Department of
Medicine, The University of Chicago, Chicago, Illinois 60637
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T cells was strongly inhibited. This inhibition was reversed by
monoclonal antibody against B7-1 or CTLA4. Thus, CTLA4 can potently inhibit T cell activation in the absence of CD28, indicating that antagonism of a TCR-mediated signal is sufficient to explain the inhibitory effect of CTLA4.
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