Monoclonal IgG3 (kappa) antibodies against murine Thy-1.2 antigen produced by murine hybridomas. Differences in the specificity of the antigen binding site and in the structure of the hinge region.

Two monoclonal IgG3 (kappa) antibodies against murine Thy-1.2 antigen produced by murine 1B5 and 1aG4/C5 hybridomas were partially characterized. The 1aG4/C5 antibody has slightly higher affinity for the Thy-1.2 antigen in binding tests and more efficiently kills the Thy-1.2+ thymocytes in cytotoxicity assays as compared to the 1B5 antibody. The latter, in addition, reacts significantly with the Thy-1.1 antigen (the allelic form of Thy-1 antigen expressed on the cells of the donor of the immune cells. Both monoclonal antibodies exhibit some characteristic properties of IgG3 of myeloma origin, e.g. a tendency to aggregation, high pI and interaction with protein A. Our monoclonal antibodies are sensitive to pepsin digestion, resistant to trypsin, their disulphide bonds are rapidly cleaved by sulphitolysis and reduction by dithiothreitol. They possess characteristic acidic peptides bearing the disulphide bonds between the heavy chains. These antibodies, however, differ to some extent from each other in some properties (precipitation with staphylococcal protein A, solubility, pI, electrophoretic behaviour of the light chains). They possess different heavy chain peptides bearing the interchain disulphide bonds and thus they probably differ in the hinge region. This structural difference may be associated with different sensitivity of these two antibodies to sulphitolysis and proteolysis.