BINDING OF NATURAL HUMAN-IGM AUTOANTIBODIES TO HUMAN TUMOR-CELL LINESAND STIMULATED NORMAL T-LYMPHOCYTES

In a recent publication we described the binding of natural IgM antibo dies derived from the human fetal B cell repertoire to the cell surfac e of some human tumor cells including colon carcinoma, small-cell lung cancer and B lymphoma lines [1]. Further analyses showed that a simil ar mole cule was bound by the respective monoclonal human antibodies o n the cell surface of polyclonally stimulated human CD3(+) T cells, bu t is absent from unstimulated MNC. Both CD4(+) and CD8(+) stimulated c ells were recognized. The molecule was found to be expressed together with lymphocyte- activation markers (4F2, CD72, CD25). The membrane an tigen expressed on both the activated T lymphocytes and tumor cells wa s characterized in a 2-D electrophoresis system: molecular weight 55-6 0 kDa, pI - approximately 6.0. Whereas the proliferation capacity of t umor cells was detected to be decreased significantly in the presence of the binding antibodies, no influence on [H-3]thymidine uptake into stimulated T cells was found, suggesting different functional conseque nces of binding the respective antigen on malignant and normal cells. An interesting finding is the enhanced expression of major histocompat ibility complex class I molecules on tumor cells incubated with human natural antibodies.