Abstract
Background
Chronic lymphocytic leukemia (CLL) is characterized by accumulation of clonal, malignant CD5^+^, CD23^+^ B cells. In vivo, these cells have an antiapoptotic phenotype (high levels of Bcl‐2 and low levels of proapoptotic Bcl‐2 family proteins, such as Bax). Abnormal B cells accumulate due to altered apoptosis regulation rather than to increased proliferation. However, it is unclear whether there are inherent Bcl‐2 apoptotic pathway defects. With in vitro culture, these B cells rapidly apoptosis.
Methods
To investigate apoptosis regulation, Bcl‐2, Bax, mitochondrial membrane potential, annexin V, and caspase activation were simultaneous monitored in individual cells during in vitro apoptosis.
Results
With in vitro culture, 30% to 50% of B cells were apoptotic at 24 h compared with fewer than 10% of T cells. Apoptotic B cells showed dramatic Bax upregulation and slight Bcl‐2 decreases accompanied by decreased mitochondrial membrane potential and increased activated caspase‐3 protein levels. Caspase‐3 and caspase‐9 activities were increased 18‐ to 51‐fold and 6‐ to 11‐fold, respectively, after 24 h of culture. Caspase‐8 showed limited or no activation (less than fourfold).
Conclusions
These data show that in vitro apoptosis of CLL B cells occurs through a well‐characterized Bcl‐2 regulatory pathway consistent with that pathway being functional. Further, these cells' antiapoptotic phenotype is dependent on the in vivo environment, potentially involving paracrine/autocrine interactions. © 2004 Wiley‐Liss, Inc.