What is the role of eosin in a staining protocol that includes hematoxylin?

In histopathology, eosin plays a crucial role as a counterstain in the staining protocol that includes hematoxylin. Hematoxylin primarily stains the nuclei of cells, imparting a blue or purple hue to them due to its affinity for nucleic acids. However, hematoxylin does not effectively stain the cytoplasm or extracellular components, which is where eosin comes in.

Eosin, which is an acidic dye, contrasts with the basic nature of hematoxylin by staining cytoplasmic components and other structures within the tissue sections. It typically imparts a pink or red color to the areas that are not stained by hematoxylin, thereby allowing for a clear differentiation between the nucleus and the surrounding cytoplasm. This combination of hematoxylin staining for nuclei and eosin staining for the cytoplasm is known as H&E staining, widely used in histology and pathology for visualizing tissue morphology.

The other options do not accurately describe the role of eosin in this context. Eosin does not specifically stain nuclei, decolorize specimens, or enhance lipid staining. Its primary function is to provide contrast, enabling a more comprehensive examination of the tissue structure.