TCR ligation on CD8+ T cells creates double-negative cells in vivo.

The lack of CD95 in mice is associated with an accumulation of TCR alphabeta+ CD4- CD8- (double-negative (DN)) cells in the lymph nodes (LNs) and other organs. To test the hypothesis that these DN cells arise from TCR alphabeta+ CD8+ cells after activation via the TCR, we have crossed an MHC class I-restricted TCR transgene (tg) onto the lpr genotype to generate two TCR-transgenic experimental groups, TCRtg+ lpr/+ (CD95-intact) and TCRtg+ lpr/lpr (CD95-deficient). Specific peptide administration resulted in peripheral deletion of TCR alphabeta cells from the LNs of CD95-intact and CD95-deficient mice. On day 3 after peptide administration in the CD95-deficient but not the CD95-intact mice, there was a ninefold increase in the percentage of DN cells in the LN; this increase returned to control levels by day 10. Peripheral deletion was associated with an accumulation of TCR alphabeta+ CD8high cells in the livers of mice of both genotypes by day 3, which returned to control levels by day 10 without an increase in the percentage or total number of DN cells. Our data show that the in vivo stimulation of TCR alphabeta+ CD8+ cells in the absence of CD95 results in an initial accumulation and an eventual loss of DN cells. This identifies a role for CD95 after TCR alphabeta stimulation in the efficient removal of TCR alphabeta+ CD8+ cells after the down-regulation of CD8. CD95 is not essential for this process, because other mechanisms can compensate, but such mechanisms are less efficient in the LN.