Re: Fibroblast radiosensitivity

["Bjorn Cedervall" <bcradsafers@hotmail.com>]

>Does anyone have information about whether mouse and/or human
>fibroblasts are relatively more or less sensitive to radiation than >human 
>lymphocytes?  If so, by what approximate factor ?

Part of the answer depends on the end-point chosen but I assume that the 
understatement is cell killing:
Lymphocytes are very radiosensitive - a large fraction will be killed by 0.3 
Gy. T cells seem to be more radioresistant than B cells although there is 
some variation. For bone marrow a dose of 4 Gy probably kills more than 99% 
of the cells (mouse or human). A mammalian fibroblast may have less than 90% 
cell killing at 4 Gy (with a more or less pronounced shoulder depending on 
wether the cells are growing logarithmically or not).

DSB repair: All lymphocyte cell lines (about 12 - 15) that I investigated 
have been very sensitive as determined by DSB repair capacity as compared to 
solid tissue cells. That lymphocytes are particularly radiosensitive is no 
news by itself but this work gave me some experience of the DSB repair 
aspect (I was focusing on characteristics of the so called AT 
"complementation groups" - complementation here has been somewhat confusing 
as a concept since only one gene (ATM) has been found - the complementation 
groups may refer to alternative splicing or truncation). The lymphocytes 
seem very prone to apoptotic signalling at relatively low doses (less than 1 
Gy in this context).

Growing/proliferating cells in general are very radiosensitive (like 
cartilage) but there are again variations and exceptions from this rule - 
especially among tumors (here is a special problem with subclones of 
different radiosensitivity). For a closer discussion I would check out the 
group of Dr. E.P. Malaise, Villejuif, France, and their publications on 
"intrinsic radiosensitivity" (which I interpret as a genetic & 
differentiation concept). Please comment or correct if necessary.

Bjorn Cedervall, Associate Professor
bcradsafers@hotmail.com
Departments of Med. Radiation Biology and Med. Radiation Physics,
Karolinska Institutet, Box 260, S-171 76 Stockholm, Sweden
The comments above are my own.


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