We have also seen cleavage of Caspase 1 and 3 fluorogenic substrates in activated mouse CD8 T cells. The cleavage begins about 12-15 hours following T cell interaction with APC and is present in both those cells which have seen both optimal antigen densities that produce activation but not death (Annexin V and PI negative), as well as in those CTL that have seen supra-optimal antigen densities that result in apoptosis at about 18-20 hours after APC interaction (and which are both Annexin V and PI positive). We suspect, but cannot be entirely sure, that this substrate cleavage is specifically due to caspase activity. This doesn't provide you with an explanation, but at least another example of the same phenomenon, this time in normal mouse CD8 T cells. Mike Derby NCI mderby@nih.gov (In the attached figure, "50 µM I10" refers to an antigen density that activates the T cells while "0 µM I10" is the lack of antigen stimulation.)
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