Differential expression of apoptosis, Bcl-x and c-Myc in normal and malignant lymphoid tissues.

Bcl-x and c-Myc have an important role for the immune response by regulating the programmed cell death (apoptosis) of lymphocytes. Dysfunction of these selection processes can lead to the development of malignant lymphoma. The present study aimed at defining the differential expression of apoptosis, Bcl-x and c-Myc in normal and in malignant lymphoid tissues. Follicular centre lymphoma (FCL-F) and mantle cell lymphoma (MCL) contained the lowest apoptotic indices (AIs), whereas Burkitt's lymphoma (BL) had the highest AIs. The AIs correlated significantly with the growth rates of the tumours and with the extent of Bcl-x expression. Bcl-x was expressed in almost all BL cells, but in few tumour cells in FCL-F and in MCL. c-Myc, in contrast, was found in the majority of the tumour cells in FCL-F and in MCL, but not in BL. Whereas the extent of Bcl-x expression correlated positively with the growth rates, an inverse correlation was observed between the percentages of c-Myc-positive tumour cells and the growth rates of the tumours. We conclude that normal and malignant lymphoid tissues have a distinct pattern of apoptosis and that expression of Bcl-x and c-Myc in B cell lymphoma is differentially regulated.