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J. Exp. Med.,
Volume 186, Number 10, November 17, 1997 1787-1791
By
From the Michael Heidelberger Division of Immunology, Department of Pathology and Kaplan Cancer
Center, New York University Medical Center, New York 10016
It has been proposed that some bystander T cell activation may in fact be due to T cell antigen
receptor (TCR) cross-reactivity that is too low to be detected by the effector cytotoxic T lymphocyte (CTL). However, this hypothesis is not supported by direct evidence since no TCR
ligand is known to induce T cell proliferation and differentiation without being recognized by
the effector CTL. Here we report that transgenic T cells expressing a T cell receptor to influenza virus A/NT/68 nucleoprotein (NP) 366-374:Db complexes clonally expand and become
effector CTLs in response to homologous peptides from either A/PR8/34 (H1N1), A/AA/60
(H2N2), or A/NT/68 (H3N2). However, the effector T cells induced by each of the three
peptides kill target cells pulsed with NP peptides from the H3N2 and H2N2 viruses, but not
from the H1N1 virus. Thus, NP366-374 from influenza virus H1N1 is the first TCR ligand
that can induce T cell proliferation and differentiation without being recognized by CTLs.
Since induction of T cell proliferation was mediated by antigen-presenting cells that express
costimulatory molecules such as B7, we investigated if cytolysis of H1N1 NP peptide-pulsed
targets can be restored by expressing B7-1 on the target cells. Our results revealed that this is
the case. These data demonstrated that costimulatory molecule B7 modulates antigen specificity
of CTLs, and provides a missing link that explains some of the bystander T cell activation.
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