Carcinoma autoantigens T and Tn and their cleavage products interact with Gal/GalNAc-specific receptors on rat Kupffer cells and hepatocytes

Abstract

We studied interactions of isolated Thomsen-Friedenreich (T)- and Tn-specific glycoproteins with the Gal/GalNAc-specific receptors on rat Kupffer cells and compared them to those with rat hepatocytes. Immunoreactive T and Tn are specific pancarcinoma epitopes. Electron microscopy of gold-labelled T and Tn antigens revealed their specific binding to Kupffer cells, followed by their uptake via the coated pit/vesicle pathway of receptor-mediated endocytosis. Preincubation of Kupffer cells with GalNAc and GalNAc-BSA, but not GlcNAc or GlcNAc-BSA specifically inhibited binding of the T and Tn glycoproteins. Desialylated, isologous erythrocytes (T RBC) are known to bind to the Gal/GalNAc receptors of rat Kupffer cells and hepatocytes. This attachment was specifically inhibited by T and Tn in a concentration-dependent manner: 50% T RBC-Kupffer cell contacts were inhibited at 8.5.10(-6) mM T and 8.5.10(-5) mM Tn antigen concentrations, respectively. The corresponding figures for hepatocytes were 6.10(-6) mM T and 1.2.10(-6) mM Tn antigen. Amino-terminal cleavage products of the T glycoprotein, possessing clusters terminating in non-reducing Gal/GalNAc, inhibited T RBC binding to Kupffer cells and hepatocytes usually at 10(-2) to 10(-5) mM concentrations, whereas GalNAc, galactose and galactose glycosides inhibited at millimolar concentrations. Galactose-unrelated carbohydrates were inactive at concentrations greater than or equal to 50 mM.