A monoclonal antibody reactive with a 40-kDa molecule on fetal thymocytes and tumor cells blocks proliferation and stimulates aggregation and apoptosis

E710.2.3 is a murine thymic lymphoma cell line with an immature phenotype ( CD4(-)CD8(-)) that proliferates in response to thymocytes or PMA when cultu red at low density and proliferates spontaneously when grown at high densit y. To identify functional molecules on this cell line, we screened for mAbs that could block its proliferation. A hamster mAb, DMF10.62.3, inhibited t he spontaneous, thymocyte-induced, and PMA-stimulated proliferation of E710 .2.3 in vitro and induced these cells to undergo apoptosis. The mAb also ca used homotypic aggregation of E710.2.3, which was inhibited by cytochalasin B, trifluoperazine, a combination of sodium azide and 2-deoxyglucose, EDTA , incubation at 4 degrees C, or treatment with paraformaldehyde. The DMF10 62.3 mAb stained a number of immortalized murine and human cell lines and, where tested, blocked their proliferation and caused death to varying exten ts by apoptosis, The molecule recognized by the mAb DMF10.62.3 was expresse d on day 14 fetal thymus Thy1.2-positive cells. However, it was not detecte d on adult murine thymocytes, splenocytes, or bone marrow cells or on splen ic LPS-activated B cells or Con A-activated T cells. The Ab immunoprecipita ted a 40-kDa molecule from E710.2.3 that was not glycosylphosphatidylinosit ol linked. The data suggest that the molecule recognized by DMF62.3 is a no vel cell surface molecule that may be involved in cell proliferation and/or cell death.