A new autoreactive monoclonal antibody specific for the Thy-1 antigen.

The present study describes the development of a new IgM monoclonal autoantibody reactive with the Thy-1 antigen. The C16-31 monoclonal antibody (mAb) was considered as autoreactive because it reacted with thymus cells of both the C3H and BALB/c strains, which were involved in the development of the antibody. The antibody was reactive with thymus cells in both immunofluorescent and cytotoxic tests. It also showed a weak immunofluorescent reactivity with peripheral T-lymphocytes. The identification of the specificity detected by the C16-31 mAb as the Thy-1 antigen was based on the following criteria: C16-31 mAB displayed a preferential reactivity with Thy-1.2 bearing thymus cells, rather than with Thy-1.1 bearing thymus cells. The tissue distribution of the antigen detected by the C16-31 antibody by direct tests and by direct tests and by adsorption experiments was in accordance with that characteristic for Thy-1. It was high on brain tissue and on thymus cells, and considerably lower on peripheral T-lymphocytes. Coating of thymocytes with C16-31 antibody blocked their reactivity with other monoclonal Thy-1 antibodies. Conversely, coating of thymus cells with rabbit anti-brain serum (RABR) inhibited the binding of C16-31. The C16-31 mAb differed from the Thy-1 autoantibodies described previously in its relatively strong reactivity with brain tissue and its considerably weaker reactivity with peripheral T-lymphocytes. Moreover, C16-31 mAb showed a preferential allospecificity for Thy-1.2, only in its reactivity with thymocytes. In contrast, it reacted equally well with brain tissue from either Thy-1.2 or Thy-1.1 mice.