Immunological screening of a glycoprotein antigen expressed by Zajdela ascites hepatoma cells on normal rat tissues and tumour cells

Abstract

Expression of the glycoprotein MII2 antigen originally identified in Zajdela ascites hepatoma cells was investigated in several normal rat tissues and in more or less differentiated tumours using biochemical and immunological approaches. SDS-polyacrylamide gel electrophoresis followed by fluorography or immunoblotting with an antiserum raised against the purified MII2 antigen revealed that this antigen was absent from normal liver cells. ELISA assays, indirect immunofluorescence and immunoprecipitation experiments using the same antiserum showed that this glycoprotein was not expressed in various normal tissues such as liver, spleen, lung, pancreas, intestine and stomach, but it was unexpectedly detected in kidney and thymic tissues. However, the molecular weight of the antigens immunoprecipitated from kidney and thymus was lower than the one of MII2 (Mr of 60,000 versus 110,000-160,000 for purified MII2). No staining was observed in embryonic rat liver at 10 and 20 days of development. Moreover, this antigen was present on the surface of Morris hepatoma 7777, another rapidly proliferating and poorly differentiated hepatocellular carcinoma. In contrast, this antigen was not detected on the surface of in vitro Zajdela hepatoma cells (ZHC) or of partially differentiated hepatomas (Faza) which have recovered some hepatic functions. In addition, the MII2 antigen was found on the human non-hepatic HT-29 tumour cell line, under its undifferentiated form (HT-29 G+ subline). The possible relationships between the expression of this antigen and both the malignant transformation process and the differentiation process are discussed.