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From the * Department of Immunology, IMM4, The Scripps Research Institute, La Jolla, California
92037; and The requirements for inducing downregulation of
R.W. Johnson Pharmaceutical Research Institute, San Diego, California 92121
/
T cell receptor (TCR) molecules on
naive major histocompatibility complex class I-restricted T cells was investigated with 2C
TCR transgenic mice and defined peptides as antigen. Confirming previous results, activation
of 2C T cells in response to specific peptides required CD8 expression on the responder cells
and was heavily dependent upon costimulation provided by either B7-1 or ICAM-1 on antigen-presenting cells (APC). These stringent requirements did not apply to TCR downregulation. Thus, TCR downregulation seemed to depend solely on TCR/peptide/interaction and
did not require either CD8 or B7-1 expression; ICAM-1 potentiated TCR downregulation,
but only with limiting doses of peptides. TCR downregulation was most prominent with high
affinity peptides and appeared to be neither obligatory nor sufficient for T cell activation. In
marked contrast to T cell activation, TCR downregulation was resistant to various metabolic inhibitors. The biological significance of TCR downregulation is unclear, but could be a device for protecting T cells against excessive signaling.
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