Expression Of Bcl-2 Gene In Reactive And Malignant Lympho-hematopoietic Tissues Is Associated With Modulation Of Susceptibility Of Leukemia To Apoptosis

Enzyme immunohistochemistry and in situ hybridization with a digoxigenin-labeled sense single-strand cDNA probe were used to investigate the expression and localization of Bcl-2 protein and its messenger RNA (mRNA) in reactive and malignant lymphohematopoietic tissues. Our study came to the following results and conclusions. (a)In reactive hyperplastic follicles, Bcl-2 protein was most abundant in the long-lived IgM/IgD B lymphocytes of mantle zones,virtually absent within germinal centers where most cells are dying by apoptosis. In contrast, the distribution of bcl-2 mRNA was roughly reciprocal to that of the protein with intense hybridization signal in germinal centers and almost none in mantle zones. These findings not only support the concept that bcl-2 protein functions as a physiological antidote to apoptosis, but also suggest that posttranscriptional control mechanisms play a significant role in regulating bcl-2 protein levels in germinal center cells. (b)In the thytnus concordant and abundant expression of Bcl-2 protein and mRNA was detected in most of the cells with long-span life in medulla, whereas only scattered positive thymocytes of Bcl-2 protein or mRNA were decorated in cortex in which the majority of thymocytes are destined for a programmed demise. The data here show that cortical thymocytes may be involved in some arrest of bcl-2 gene expression at the transcriptional level. ( c) Enhanced expression of Bcl-2 protein was evidenced in Reed-Sternberg and Hodgkin's cells in approximately 36% of...