Regulation of p26-bcl-2 protein levels in human peripheral blood lymphocytes.

BACKGROUND: The protein encoded by the bcl-2 (B cell lymphoma/leukemia-2) proto-oncogene has been implicated in the regulation of lymphocyte cell survival and has been shown to interfere with programmed cell death (apoptosis). Recently, controversy has emerged regarding the expression of bcl-2 in circulating peripheral blood lymphocytes (PBL) and its correlation with lymphocyte proliferation. Using immunohistochemical methods, Pezzella et al. (Pezzella F, Tse G, Cordell J, Pulford K, Gatter K, Mason D. Am J Pathol 1990; 137:225-32) detected abundant amounts of Bcl-2 protein in resting PBLs and observed an inverse correlation between bcl-2 expression and cellular proliferation in lymphoid tissues. In contrast, previous in vitro studies of bcl-2 mRNAs showed that expression of this gene is very low in unstimulated PBLs but can be markedly induced when lymphocytes are stimulated to proliferate in culture (Reed JC, Tsujimoto Y, Alpers JD, Croce CM, Nowell PC. Science 1987; 236:1295-9; Granniger W, Seto M, Boutain B, Goldman P, Korsmeyer S. J Clin Invest 1987; 80:1512-5). EXPERIMENTAL DESIGN: To resolve this issue, the regulation of p26-Bcl-2 protein levels was examined in freshly isolated and in cultured human PBLs by immunoblotting using two different polyclonal antisera specific for the human Bcl-2 protein. RESULTS: When freshly isolated from whole blood, resting PBLs contained easily detectable amounts of p26-Bcl-2 protein that did not significantly change in culture when cellular proliferation was stimulated with mitogenic lectins and lymphokines. If processing of the blood was delayed, however, p26-Bcl-2 protein was low or undetectable in resting PBLs and underwent marked increases in its relative levels after in vitro stimulation of PBLs by mitogenic lectins and lymphokines. CONCLUSIONS: The findings indicate that bcl-2 is normally expressed in quiescent circulating lymphocytes, consistent with a role for this gene in the maintenance of lymphocyte survival, and illustrate the importance of correlating in vitro and in vivo expression data.