When constructing the expression vector, if I directly connect the IgG2 antibody variable region with the IgG1 constant region, a new antibody protein will be formed. So will the antigen-binding activity of this new antibody be similar to that of the original IgG2 antibody? What will happen to the biological activity of this new antibody protein?
Thanks!
I doubt there'd be any change in antigen binding but please let us know what happens?
The immuno behaviour of an antibody is dictated by the fc portion. This includes it ability to activate complement via the classical cascade as well as the ability to bind to different fcgamma receptor and fcn receptors which on the latter matter may influence Renal clearance and tranplacental delivery. Also be aware that not all igg isotopes bind to protein g with the same affinity so this may influence your purification yields.
Theoretically, there should be no difference, however, the hinge region in different isotypes can impose some level if stearic hinderence and it can alter affinity indirectly fir that reason. I am not sure how this would affect different igg subclasses though, and to be frank. Thus is rather an esoteric point that is more often raised by clinical immunologists comparing iggs to ige.
Dear Min Zeng
i'm my experience when you are preplacing the mouse igG1 with mouse igG2a (constant regions) and vice versa as well as human igG1 and igG4, those are all monomers and differs mainly in the ability of the Fc to bind to the different Fc-receptors, there is no difference in the binding to the antigen.
For example in general when we test, mouse antibodies coming fron hybrodomas with mouse igG1 or igG2a and then we replace its constant region with the human igG1 to generate Mouse/human chimeric mabs, we do not observe main differences in antigen binding.
This may be not true in case of igM or igG3, those are multimeric antibodies.
good luck
Manuele
I agree with Manuele and would add that you should be careful to consider the difference between affinity (one Ab combining site binding to an Ag) and avidity (both combining sites binding to Ags). Add to this the fact that there is potential cooperativity through Ab::Ab attractive energy which can make the apparent avidity even higher.
My best guess is that the affinity would be unaffected, but that the avidity may or may not be impacted. I, too, will be interested in updates.
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