Quantitative determination of the organ distribution of the cell adhesion molecule cell-CAM 105 by radioimmunoassay

Abstract We have previously identified a 105,000-Da plasma membrane glycoprotein, denoted cell-CAM 105, that is involved in intercellular adhesion of reaggregating rat hepatocytes. In this communication we report on the development of a radioimmunoassay for cell-CAM 105, employing purified cell-CAM 105, specific antisera against the molecule, and formalin-fixed protein A-containing staphylococci for precipitation of the immune complexes. The assay was shown to be sensitive, specific, precise, rapid, and easy to perform. We used this radioimmunoassay in investigations of the occurrence of cell-CAM 105 in different rat organs. Cell-CAM 105 was present in a wide spectrum of organs in varying amounts. The highest concentrations were found in the gastrointestinal tract, liver, some secretory glands, vagina, kidney, and lung. In addition, cell-CAM 105 was detected in blood, where it was shown to reside mainly in the platelets. Other tissues, particularly the central nervous system and muscle tissues, were cell-CAM-negative. The results were confirmed by immunoblotting, which revealed one distinct protein component, corresponding to cell-CAM 105, in each positive organ.