[Histonet] F4/80 Ab clone CI:A3-1 not working for foam cells - why?

From:GT Hebert

Hello again,
I just worked out my F4/80 antibody on mouse tissue.  The mouse tissue, aortic arch with athrosclerotic lesions came up negative though.  I would think that the foam cells (macrophages??) would light up as the do when I stain with CD68 ... but only 1 or 2 cells outside the lesion lit up.  The Kupffer cells in the liver and the red pulp in the spleen (my + controls) came out great and the negative isotype controls on all samples are clear.  Any idea why this may be happening?  I have seen this antibody used on a number of literature papers staining foam cells in AT lesions (same clone - just different dilutions (1:25, 1:200m etc -- all paraffin) -- and they showed staining of foam cells.  
My tissues are all treated the same: 24 hour fixation in 4%PF, routine processed and embedded, 4 micron sections, deparaffinized ... and then IHC (optimal conditions).
I'm sort of lost with this one ... I know the antibody works.  Just the results are not what I expected.  Any information would be greatly appreciated.
Gustave Hebert
Wyeth Cambridge

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