Nonspecific staining problem in birds...

I have recently begun to do IHC on bird tissue, and have come across a
problem on certain cases where the inflammatory cells on the negative
control stain as well.  (This is never a problem with any other mammalian
species on which I've done IHC.)  Is there something unique or unusual about
the avian hematopoietic system that requires an adjustment or change to the
normal blocking protocols?  I've tried extending my 3% hydrogen peroxide
quenching step to 30 minutes, but this doesn't eradicate the problem.  (I
also use a 10% normal serum protein block prior to the primary antibody, and
use the DAKO EnVision detection system with 2% normal avian serum in the
EnVision reagent.)

Helful hints would be MUCH APPRECIATED.

Jan Shivers
IHC Lab