Expression of the bcl-2 protein and bcl-2 mRNA at the individual cell
level was semiquantitatively examined in normal quiescent peripheral b
lood lymphocytes and pokeweed mitogen- or concanavalin A and interleuk
in-2-induced lymphoblasts in vitro by microscopic fluorometry using im
munofluorescence and fluorescein-labeled in situ hybridization. Approx
imately 90% of normal quiescent T and B lymphocytes expressed bcl-2 pr
otein at a level which was compatible with that of bcl-2 mRNA. On the
contrary, most mitogen-induced lymphoblasts showed a posttranscription
al suppression of bcl-2 protein expression. However, bcl-2 protein was
not downregulated by the posttranscriptional suppression in all lymph
ocytes activated in vitro, but approximately 15% of the lymphoblasts s
till expressed bcl-2 protein at a higher level than nontransformed qui
escent small lymphocytes; thus bcl-2 protein expression in lymphoblast
s showed a distinct bimodal pattern. Furthermore, it was supposed that
lymphoblasts with no detectable bcl-2 protein might fall into apoptos
is but the remainder, expressing high levels of bcl-2 protein, could e
scape apoptosis. Thus, the bcl-2 gene may play an important role as a
regulator of apoptosis in the human immune system.