Positive reactivity of dysplastic melanocytes with a monoclonal antibody against melanoma melanosomes, MoAb HMSA-2.

A mouse-mouse monoclonal antibody, MoAb HMSA-2, was raised against the melanosomal protein of human malignant melanoma. To characterize the nature of dysplastic melanocytic nevi (DMN), we examined the reactivity of DMN with MoAb HMSA-2 in comparison to that of superficial spreading melanoma (SSM) and common melanocytic nevi (CMN) including junctional melanocytic nevi (JMN) on routine paraffin sections. MoAb HMSA-2 showed several unique immunohistochemical findings: a) MoAb HMSA-2 reacted with melanocytes of DMN in both the epidermis and the dermis, including the pigment granules in the keratinocytes; b) the pigment granules in the keratinocytes of DMN were found to be immature melanosomes transferred from dysplastic melanocytes to keratinocytes; c) the reactivity of epidermal melanocytes in DMN and SSM was stronger than that of junctional component in CMN, though SSM revealed a much stronger reaction than DMN; and d) keratinocytes, especially in a "shoulder" lesion of DMN which was associated with dermal lymphocytic infiltrates, often showed a strong reactivity with MoAb HMSA-2. Thus our study suggested a unique immunohistochemical feature of DMN with deranged melanogenesis as indicated by the reactivity with MoAb HMSA-2.