QUOTE (miBunny @ Nov 17 2009, 03:35 AM)

Are you using the same antibody for both? Some antibodies recognize the native form of the protein (such as in IHC) but not the denatured form of the protein (such as a western blot where SDS/detergents, reducing agents, and boiling have linearized the protein) and vice versa.
Did your western work? Do you get positive results with a different antibody for a different protien?
Does your protein solubilize with your lysis conditions? Could it have precipitated out (a problem with some of the multipass membrane proteins)?
I doubt this is all the reasons but it is what I could come up with off the top of my head and wouldn't you rather have some ideas than none

Yes I use the same antibody, and I am doing immunofluorescence staining cells and not IHC.
you say about native form of protein, when i treat with 4% of PFA for fixation for my cells that also denatures the protein right
yes western work with other antibody with for the same protein and do solubolize with lysis buffer.
with what scientific points ( theoretically) I can argue or defend my finding when i have this result immunofluorescence positive and western negative