Modification of Luna's technique for staining eosinophils in the hamster cheek pouch

The cheek pouch is an anatomical peculiarity of hamsters, widely used as an experimental model for oral cancer, and characterization of its normal cell populations and the changes they undergo in pathological conditions is of great interest. Our studies of epithelium-connective tissue interactions have revealed that hamster eosinophils are not easily recognizable because they are small and exhibit a larger nucleus:cytoplasm ratio than those in human and other animal tissues. Luna's technique is the most popular specific staining technique for eosinophils. Owing to the morphology of hamster eosinophils, however, it was necessary to modify Luna's technique to stain these cells selectively against a more contrasting background that would enable their identification and quantitation in the hamster cheek pouch. The modification involved staining the sections with a solution of 0.5% Biebrich scarlet in lithium carbonate followed by counterstaining with 1% metanil yellow in water. The eosinophils were stained selectively red against a yellow background. Our technique avoided nuclear staining and enhanced observation of selectively stained granules in a scarce cytoplasm with a contrasting background, which permits fast, reproducible studies and automated image analysis.