GM-CSF: How to convert U/mL value in pg/mL ? - (Sep/30/2006 )

Hi all,
I just want to know, if it´s possible to convert the U/mL values for GM-CSF in pg/mL - just as it´s possible for the endotoxin units with 1 EU/mL corresponding about 100pg/mL Endotoxin ?
It´s really confusing: why is U/mL used anyway with cytokines => I always thought that U/mL is used only in the context of enzyme activity ???????

Alex

I think it has something to do with purity and biological activity;

for biologic high active compounds or actors such as enzymes or messenger compounds which often have to be purified from biological sources, there might be some impurities or loss of biological activities during enrichment or purification process; therefore, it is better to declare biological activity (f.i. in U/vol) instead of mass/vol or absolute mass, especially if in crude samples the relative amount of compound of interest is only vague to determine...

The entity EU describes the biological activity of an endotoxin and was introduced by the U.S. Food and Drug Administration (FDA).
The biological activity causing pyrogenic effects depends on a variety of factors like polysaccharide chain length, aggregation status, solubility in biological fluids, bacterial source, associated substances, etc.
For example, 100 pg of the standard endotoxin EC-5, 200 pg of EC-2 and 120 pg of endotoxin from Escherichia coli 0111:B4 have an activity of 1 EU.

It is taken as a rule of thumb that 1 EU corresponds to 100 pg of endotoxin.