mAb 104, a new monoclonal antibody, recognizes the B7 antigen that is expressed on activated B cells and HTLV-1-transformed T cells.

A new monoclonal antibody (mAb) of the IgG1 subclass, mAb 104, has been obtained after immunization of mice with the Burkitt lymphoma cell line Jijoye. It only weakly binds to a small proportion of non-activated normal B cells and binds to a larger proportion of in vitro-activated normal B cells. All tested Epstein-Barr virus (EBV)-transformed B-cell lines, Burkitt lymphoma cell lines and freshly isolated follicular B-lymphoma cell preparations strongly bound mAb 104. mAb 104 did not bind to peripheral monocytes or tested myelomonocytic cell lines, or to resting and activated normal T cells, T-cell lines and T-cell clones. However, the recognized antigen is expressed on HTLV-1-infected T-cell lines and HTLV-1-transformed T-cell clones. mAb 104 immunoprecipitates, from Jijoyce cell lysates, a single polypeptide with an apparent MW of 45,000-60,000 and an isoelectric point of 5.6. Competition studies with the anti-B7 antibody (Freedman et al., 1987) demonstrated that mAb 104 and the anti-B7 block each others' binding. Furthermore, mAb 104 binds to transfected COS cells (Freedman et al., 1989) expressing the B7 antigen. Thus mAb 104 and and anti-B7 define the same antigen. The restricted distribution of the 104/B7 antigen to activated B cells and HTLV-1-transformed T cells may make it a useful marker for the study of pathological states linked to lymphocyte activation and for the functional study of B-cell subpopulations.