Immunoperoxidase staining for Ia-like antigens in paraffin-embedded tissues from human melanoma and lung carcinoma.

The human Ia-like antigens that are predominantly expressed by cells associated with immunologic function has been considered as a diagnostic marker of malignant transformation of some nonlymphoid tissues. Immunoperoxidase staining of formalin-fixed and paraffin-embedded tissue sections with a monoclonal antibody to Ia-like antigens was chosen for assessment of the value of this marker for diagnosis in surgical pathology. Monoclonal antibody LK8D3 developed against a human melanoma cell line bearing Ia-like antigens was found to react in serologic and immunochemical studies with an antigenic determinant of Ia-like antigens that was relatively stable to formalin fixation and paraffin embedding. Avidin-biotin complex peroxidase staining of formalin-paraffin sections with LK8D3 showed focal expression of Ia-like antigens in 3 of 12 melanomas, whereas all 8 cases of intradermal nevi were negative. Immunoperoxidase staining of formalin-paraffin sections of lung carcinomas with antibody LK8D3 was related to the histologic subtype of tumors. Thus, squamous cell carcinomas showed only very focal staining for Ia-like antigens in 5/9 cases, while widespread and intense Ia-like immunoreactivity was seen in 3/5 cases of lung adenocarcinomas, including two bronchioalveolar carcinomas. The presence of Ia-like antigens in lung adenocarcinoma may not be entirely associated with malignant transformation, because normal alveolar lining cells were stained with the antibody.