Two murine monoclonal antibodies (MAbs) 5G8 and 2H6 were generated by fusing spleen cells obtained from mice immunized with human fetal tissue extract (14 weeks, Nonidet P-40 membrane fraction) from the early first trimester, followed by a booster injection of a lung cancer cell line. The MAb 5G8 recognized antigens with a molecular weight of 90, 50, 20 kDa, was neuraminidase-resistant and showed cross-reactivity with both carcinoembryonic antigen and non-specific cross-reacting antigen. The MAb 2H6 reacted with a sialomucin whose molecular weight was more than 1000 kDa and was different from previously known tumor associated-marker antigens. The distribution of the MAb-recognizing antigens in various tissues was investigated immunohistochemically. In malignant epithelial tumors of the lung, acinar adenocarcinoma and bronchioloalveolar carcinoma were positive for both MAbs; papillary adenocarcinoma, squamous cell carcinoma, and adenoid cystic carcinoma were positive only for MAb 5G8; solid carcinoma with mucin formation, small cell carcinoma, and large cell carcinoma were positive only for MAb 2H6. The combination of the two MAbs covered almost all histological types of lung carcinomas (23 of 24 cases) except carcinoid tumors. MAbs 5G8 and 2H6 reacted also with a restricted number of adenocarcinomas of the other organs. MAb 5G8 did not react with normal fetal or adult tissues, except for metaplastic gastric mucosa, acinar cells of the breast and leucocytes, whereas MAb 2H6 reacted with the surface epithelium of the stomach and colon, the Brunner gland of the duodenum and uterine cervix as well as the epithelium of the fetal digestive tract. Thus, MAb 2H6 which recognized oncofetal sialomucin, played a complementary role to MAb 5G8 as a CEA-related MAb in the immunohistochemical diagnosis of lung carcinomas.

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