AZURE-B AS A COUNTERSTAIN IN THE IMMUNOHISTOLOGICAL EVALUATION OF HEAVILY PIGMENTED NEVOMELANOCYTIC LESIONS

Heavily pigmented melanocytes and melanophages are often difficult to distinguish from one another. Several methods have been used to addres s this problem, including bleaching the tissue sections and immunohist ologic stains. The stains are plagued, however, by a resemblance of th e precipitates of common chromogens-such as diaminobenzidine (DAB)-to melanin with hematoxylin counterstains. It has been reported previousl y that azure B allows the distinction between melanin and chromogenic precipitates by metachromatically staining melanin granules. In this s tudy, 35 heavily pigmented lesions, including 27 melanomas, 6 blue nev i, and 2 pigmented spindle-cell nevi, were labeled with an antibody to S-100 protein and with HMB-45, they were then counterstained in paral lel with Harris' hematoxylin and with azure B. Comparison showed that precipitates of DAB could be easily separated from metachromatically l abeled melanin in all azure B-stained cases, whereas that distinction remained difficult when hematoxylin was used as a counterstain. These results confirm the effectiveness of azure B as an aid in interpreting immunohistologic preparations of melanocytic lesions.