Fig. 2.

Stability of peptide antigen-specific CD4 T cell lines over time: peptide-specific CD4 T cell lines are stable only until 8–10 weeks. The data are shown as stimulation indices (SIs) derived from proliferation assays performed as described above. As shown for four different CD4 T cell lines, an increase in peptide-specific stimulation occurs over the initial 6–7 weeks, followed by a sharp decline in activation. This is reminiscent of antigen-induced apoptotic cell death described in various other systems, including stimulation of CD4 T cells by superantigens.