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Concanavalin A-induced proliferation of spleen cells of C57B1/6 mice was inhibited by syngeneic normal bone marrow cells. Elimination of Ag-Eb-positive cells by panning was shown to result in markedly reduced inhibitory activity of bone marrow cells. To evaluate the role of Ag-Eb in natural suppressor activity, bone marrow cells were preincubated with different dilutions of MAE-15 monoclonal antibody and then added to spleen cells. The inhibitory effect of bone marrow cells decreased with the increasing concentration of the monoclonal antibody in a dose-dependent manner and nearly disappeared at a concentration of MAE-15 of 150 m micrograms/ml and 300 m micrograms/ml. In control experiments, bone marrow cells were preincubated with antibodies non-reactive with Ag-Eb under the same conditions. It is concluded that the decrease of natural suppressor activity after incubation of bone marrow cells with MAE-15 monoclonal antibody is specific for anti-Ag-Eb antibodies.

Murine monoclonal antibodies to human small cell lung cancer (SCLC) have been developed and partially characterized. Primary hybridoma clones were screened in the indirect immunofluorescence assay (IFA) on alive H417 cells. Then five clones (IgG1, IgG2a, IgG3 and IgM) non-reactive with normal human bone marrow cells and positively reactive with SCLC tumors were selected. The H417.3 antibody is directed against 47-50kD surface antigens of H417 cells. The antibodies are supposed to be applied for the immunodetection of SCLC metastases to bone marrow and immunotoxin preparations.