MEL-5 - A NOVEL ANTIBODY FOR DIFFERENTIAL-DIAGNOSIS OF EPIDERMAL PIGMENTED LESIONS OF THE SKIN IN PARAFFIN-EMBEDDED SECTIONS

Histological evaluation of epidermal melanocytes on routine staining i s difficult and cannot be made with accuracy. Widely known antibodies such as S-100 and HMB-45 are unreliable for normal epidermal melanocyt es. Furthermore, S-100 stains other cells including Langerhans' cells. Results of incubation with DOPA are inconsistent and the procedure is time-consuming. We have evaluated the use of Mel-5, an antibody that was developed against melanoma and melanocytes. This antibody is a mou se monoclonal antibody that specifically detects a 75 kDa glycoprotein usually expressed by normal melanocytes, naevi and melanoma cells in routinely fixed paraffin sections. Histological differentiation betwee n pigmented actinic keratosis in photodamaged skin and lentigo maligna can be difficult. The atypical keratinocytes, particularly in the bas al layer, can be confused with atypical melanocytes, especially if the y are pigmented. Similarly, distinctions between lichen planus-like ke ratosis and lichenoid melanoma in situ and lentigo maligna and lentigo may be difficult. Use of Mel-5 in such cases has shown consistent res ults in separating melanocytic from non-melanocytic lesions. This anti body is also helpful in evaluating biopsies of patients with vitiligo, post-inflammatory pigmentary alteration and regressed or regressing m elanocytic lesions. Furthermore, Mel-5 is an invaluable tool in quanti fication of epidermal melanocytes in research projects.