TOLERANT CD8 T-CELLS INDUCED BY MULTIPLE INJECTIONS OF PEPTIDE ANTIGEN SHOW IMPAIRED TCR SIGNALING AND ALTERED PROLIFERATIVE RESPONSES IN-VITRO AND IN-VIVO

The mechanisms responsible for peripheral CD8 T cell tolerance to fore ign Ags remain poorly understood. In this study we have characterized the state of CD8 T cell tolerance induced in F5 TCR transgenic mice by multiple peptide injections in vivo. The tolerant state of CD8 T cell s is characterized by impaired proliferative responses, increased sens itivity to cell death, and failure to acquire cytotoxic effector funct ion after in vitro antigenic challenge. In vivo monitoring of CD8 T ce ll proliferation using 5-carboxyfluorescein diacetate succinimidyl est er showed that a large subset of the tolerant T cell population failed to divide in response to peptide. TCR down-regulation could not accou nt for this loss of responsiveness to Ag since recombination-activatin g gene-1 (RAG-1)(-/-)F5 CD8 T cell responses were similar to those of RAG-1(-/-)F5 x RAG-1(-/-) F-1 T lymphocytes, which express lower level s of the transgenic TCR. Analysis of early signal transduction in tole rant CD8 T cells revealed high basal levels of cytoplasmic calcium as well as impaired calcium mobilization and tyrosine phosphorylation aft er cross-linking of CD3 epsilon and CD8 alpha, Together these data ind icate that repeated exposure to soluble antigenic peptide in vivo can induce a state of functional tolerance characterized by defective TCR signaling, impaired proliferation, and increased sensitivity to cell d eath.