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

In a recent publication we described the binding of natural IgM antibodies derived from the human fetal B cell repertoire to the cell surface of some human tumor cells including colon carcinoma, small-cell lung cancer and B lymphoma lines [1]. Further analyses showed that a similar mole cule was bound by the respective monoclonal human antibodies on the cell surface of polyclonally stimulated human CD3(+) T cells, but is absent from unstimulated MNC. Both CD4(+) and CD8(+) stimulated cells were recognized. The molecule was found to be expressed together with lymphocyte- activation markers (4F2, CD72, CD25). The membrane antigen expressed on both the activated T lymphocytes and tumor cells was characterized in a 2-D electrophoresis system: molecular weight 55-60 kDa, pI - approximately 6.0. Whereas the proliferation capacity of tumor 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 consequences of binding the respective antigen on malignant and normal cells. An interesting finding is the enhanced expression of major histocompatibility complex class I molecules on tumor cells incubated with human natural antibodies.