Must an AGING PROCESS be universal?

Thu Apr 27 07:36:46 EST 1995

This is a repeat (in an abridged form) of a message I sent earlier. I would 
appreciate the response of people working with cell cultures.
In a discussion about the term immortal I recently wrote :
I could agree with calling a cell culture immortal, but there is some
hybris in the word. Isn't it a bit exaggerated? How could we prove it? Things 
that cannot be proven or disproven are outside the realm of science. The term,
therefore, is unscientific.

and Oliver Bogler responded:
> > Immortal in the normal sense means to live forever, and I agree with you
> > this is an unscientific term. However there is a scientific definition of
> > the immortal - which I thought we were all using. In the scientific term a
> > cell is termed immortal if it generates a lineage of descendants that do
> > not undergo senescence at the time when sister cell clones do. We tend to
> > be a little sloppy, if you will, in that we call cells immortal - of
> > course as individual cells they never are, because they need to keep
> > dividing to be termed immortal. As soon as they divide they are gone. What
> > is immortal is in fact the clone which they give rise to. 
> > 
    Since bacteria, for example have
> > lived for millions of years, you could say that they are immortal - all
> > the bacteria alive today are related - they all eventually come from the
> > first bacterial cell division - they are immortal.
> > 
I then responded (I now slightly changed the text):   

*I am very glad that we do agree on one thing: the term immortal, in whatever 
*context we want to use it (either referring to cells or individuals, or to
*cell lines) is unscientific. Cell biologist should try to avoid unscienti-
*fic terms.
*You call bacteria immortal, yet we know that they live for a few days only. It
*is beyond me how we could use one term for two different levels. Level one is 
*that of the individual (cell or multicellular organism), the other the level
*of the cell line, which is actually the population level.  
*As far as I can see it there is a form of circular argument in the terminology
*of people working with cell cultures. They established the very interesting 
*fact that cells undergo a limited number of divisions, then stop dividing 
*unless treated with carcinogenic agents. As cells from older individuals
*showed a lower number of divisions the hypothesis was put forward that a 
*limited number of cell divisions is a main cause of ageing and death. I think
*this is a very plausible thought, but as far as I know there is still quite a 
*debate whether this is true. A cell line then is called senescent when
*it does not show division any more, and immortalized when it goes on dividing.
*Here probably is the fallacy of circular reasoning. Most biologists working 
*with individual organisms would call a cell senescent when it is in a stage 
*of differentiation in which the program leading to cell death is swithed on, 
*this is usually long after its last division.
*To call a cell line senescent when it does not divide any more, while the cells
*are staying alive looks as if the above hypothesis is taken for a fact. Also
*the term immortal can then be understood: a halt to cell division is regarded
*as death (related to the individual the cell line was taken from), and when the 
*cease-division is overcome it is regarded as life (even 'immortal' life).
*Would it not be better to use neutral terms for the stages in cell cultures 
*like a) dividing, b) quiescent, c) nondividing, and d) perpetually dividing, 
*or any other set of terms that just describes the facts.
      Wouter van Doorn
      ATO-DLO, Wageningen, Holland 

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