I'm looking at the IC50 of an checkpoint inhibitor antibody. Several groups have reported varying IC50 values for this antibody, from the picomolar to micromolar range. I have two questions:
1.) What in a dose-dependent response assay could cause such a large variance in IC50 measurement and value?
2.) If I were to use this antibody as a control in my experiment (to compare against my antibody), would the IC50 value I personally calculate be sufficient comparison?
Thanks!
Not all lots of antibodies are the same. Depending on how the antibodies are produces, stored, and used the activity may vary. No matter, you will have to produce your own data on the standard antibody to compare to your test antibody. This way you can say something about the relative activities of the two antibodies, all else being equal (and carefully characterized). It's a lot of work.
I do not know your assay in detail. However, it should be considered that IC50 values are nearly always assay-dependent. Huge differences with the same antibody may indicate multi-valency issues. James Drummond is completely right to stress that the activity of an antibody (preparation) can vary over time. Freezing is often detrimental. The determination of the concentration of active (!) antibody in a solution is not trivial at all. Hence, the direct comparison of two antibodies is usually only sensible, if the concentration is the same.
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