THE PROPENSITY TO APOPTOSIS OF CENTROCYTES AND CENTROBLASTS CORRELATES WITH ELEVATED LEVELS OF INTRACELLULAR MYC PROTEIN

In this study, we investigated the c-myc expression by tonsillar germi nal center (GC) B cells using reverse transcriptase-polymerase chain r eaction, flow cytometry, Western blot and in situ immunohistochemical methods. The results obtained demonstrate elevated levels of c-myc mRN A and of Myc protein in GC B cells compared to those of the other rest ing or activated tonsillar B cells. Separation of GC B cells into cent roblasts and centrocytes revealed that, while differing in their cell cycle status, surface marker expression and morphology, the two cell t ypes had the same propensity to apoptosis and elevated Myc protein exp ression, thus reinforcing the notion of a close correlation between th ese two events. Based upon these observations and other considerations it is proposed that elevation of Myc proteins confers to GC B cells a particular propensity to apoptosis, while the subsequent decision bet ween progression into the cell cycle or programmed cell death is dicta ted by other signals that are delivered in the GC and perhaps operate at the level of other proto-oncogenes.