can protein modifications affect immunodetection?

[Allison]

Scientist wrote:
> Hi all!
> im trying to detect a  protein in plants Crude extract using
> polyclonal Abs. These Abs were obtained from rat sorum, The protein
> used to innolculate the rats was expressed in E.coli (thus lacking the
> typical postrasductional modifications occurring in plants) .
> Untill only no positve results were obtained.
> When recombinant form is used as positive control everthing works
> well.
> So the possibilities are :
> a) native form is absent in the plant.
> b) the protien is present but in low concetration
> c) native form is modified in someway , thus the abs cannot recognize
> the epitopes.
> 
> have anyone a suggestions for these items?
> thanks a lot

Try immunizing more than one rat - it's possible that different animals 
will respond differently to the same antigen.  I'm in the middle of a 
project where only one of five mice pick up the endogenous mammalian 
protein on Western after being immunized with the recombinant protein.

Allisoin