The availability of eosinophil-specific antibodies capable of identifying infiltrating eosinophils in formalin-fixed paraffin-embedded FF-PE) tissues from humans and most animal model systems is limited. However, the omnipresence of eosinophils in mammals suggests that antibody reagents targeting conserved regions of granule proteins from any one mammal may have pan-species specificity.

Eosinophil secondary granule proteins (ESGPs) were purified from eosinophils of IL-5 transgenic mice and used, together with Freund's adjuvant, as the antigen to immunize rabbits. The resulting polyclonal serum was assessed by ELISA and immunohistochemistry with FF-PE sections.

The polyclonal anti-mouse ESGP antisera displayed a unique ability to detect infiltrating tissue eosinophils from all of the mammalian species tested, including mice, rats, non-human primates, and guinea pigs. In addition, it was shown that this antisera was capable of specifically detecting eosinophils lung sections from asthma patients, even in cases where the blocks were collected more than 20 years ago.

Sequence conservation exists between one or more of the mouse ESGP genes and orthologues in other mammals as to allow pan-species epitope recognition by mouse total ESGP polyclonal antisera. This reagent uniquely recognizes eosinophils regardless of the species examined, including FF-PE human biopsy samples. This reagent is a novel and previously unavailable tool for the study of diseases associated with eosinophils.