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Abstract
The classical type of programmed cell death is characterized by its dependence on
de novo RNA and protein synthesis and morphological features of apoptosis. We confirmed
that stimulated 2B4.11 (a murine T-cell hybridoma) and interleukin-3 (IL-3)-deprived
LyD9 (a murine haematopoietic progenitor cell line) died by the classical type of
programmed cell death. Assuming that common biochemical pathways might be involved
in the deaths of 2B4.11 and LyD9, we isolated the PD-1 gene, a novel member of the
immunoglobulin gene superfamily, by using subtractive hybridization technique. The
predicted PD-1 protein has a variant form of the consensus sequence found in cytoplasmic
tails of signal transducing polypeptides associated with immune recognition receptors.
The PD-1 gene was activated in both stimulated 2B4.11 and IL-3-deprived LyD9 cells,
but not in other death-induced cell lines that did not show the characteristic features
of the classical programmed cell death. Expression of the PD-1 mRNA in mouse was restricted
to the thymus and increased when thymocyte death was augmented by in vivo injection
of anti-CD3 antibody. These results suggest that activation of the PD-1 gene may be
involved in the classical type of programmed cell death.