Distribution and functional analysis of a 120- to 130-kDa T-cell surface antigen

A monoclonal antibody (mAb), SPV-L14, was raised that detected a human T-cell surface antigen with a molecular weight (MW) of 120 kDa on resting and phytohemagglutinin-activated peripheral blood T lymphocytes (PBL). An additional band with a MW of 130 kDa could be precipitated with variable intensities from thymocytes, neoplastic T cells, and CD4+- or CD8+ T-cell clones. Based on their reactivity with SPV-L14 and a mAb directed against CD3, four subpopulations of CD2+ lymphocytes could be detected and their existence was confirmed at the clonal level. The majority (95%) of the CD3+ cells were SPV-L14+, whereas 5% were CD3+, SPV-L14-. Among cloned cell lines CD3-,SPV-L14- and CD3-,SPV-L14+ cells were found to exist. The CD3-,SPV-L14- and CD3-,SPV-L14+ clones were shown to have NK cell activity, indicating that the 120- to 130-kDa antigen is expressed heterogeneously on CD3- NK cell clones. In addition, neoplastic T cells representing these four subpopulations were shown to exist. Although the tissue distribution and the MW of the SPV-L14 target antigen strongly suggest that SPV-L14 reacts with an epitope on CD6, the SPV-L14 mAb did not react with resting or activated B cells or with malignant B cells. Blocking studies showed that SPV-L14 inhibited the proliferative response of PBL, induced by anti-CD3 mAb, but that SPV-L14 did not affect the proliferation induced by phytohemagglutinin. These results suggest that the 120- to 130-kDa MW antigen is associated with T-cell proliferation, depending on the mode of activation.