More about Apoptosis

wzhou at wzhou at
Mon Apr 11 12:21:37 EST 1994

Thank you all for your response to my previous post seeking your opinion about 
the distinctions between apoptosis and necrosis.   

I asked "Is it true that apoptotic cells maintain their membrane intergrity?"

Most people said "yes".  Some people said, specifically, that apoptotic cells 
exclude trypan blue.  But, many published papers, especially those 
demonstrating the protective effect of bcl-2, used trypan blue exclusion as a 
measurement of cell death.  Are those types of cell death really apoptotic or 
should they be considered as necrotic?

In normal intestinal cell lines, I can detect DNA fragmentation.  I call it 
spontaneous cell death and it is somehow cell density dependent.   I can see 
very few trypan blue stained cells even though I can identify and then purify 
detergent-insoulbe envelope (apoptotic bodies).  I assumed apoptotic cells 
were engulfed by neigboring cells before they lost their membrane intergrity.

In some transformed cell lines, such as HT-29, most dead cells detach from the 
monolayer.  Detached cells can be judged as apoptotic by acridine organe 
staining and are all stained well with trypan blue, even the cells maintaining 
good morphology (I assume they are in the early stage of cell death) .   I got 
beautiful DNA ladder from those cells.  

Is it possible that apoptotic cells, when not engulfed by other cells,  
can not maintain their membrane intergrity?  Also, what do you think is the 
function of apoptotic bodies?
I would appreciate your comments.

Wei Zhou
Emory University
wzhou at

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