Release of Thy-1 from human and murine T-cell lines by a specific phospholipase

The murine NK2.1 antigen: a 130 kD glycoprotein dimer expressed by a natural killer cell subset of the spleen, thymus and lymph nodes

Murine natural killer (NK) cells express a few antigens not found on other leukocyte subsets. The NK1.1 antigen, that is present in only a few mouse strains, has been extensively characterized whereas our knowledge of the NK2.1 antigen, which is more commonly expressed, remains, as yet, limited. Our laboratory has previously reported the production of a mAb (4LO3311) recognizing a murine NK cell-specific molecule with a similar strain distribution as the NK2.1 antigen formerly defined with an NZB anti-BALB/c antiserum. In this study, we demonstrate by sequential immunoprecipitation that 4LO3311 represents the first NK2.1 antigen-specific mAb. This reagent was used to immunoprecipitate the NK2.1 antigen from 125I-labeled lysates of fresh NK-enriched spleen cells. SDS-PAGE analyses revealed that the NK2.1 antigen is expressed at the cell surface as a N-glycosylated disulfide-linked protein dimer with approximately 65 kD subunits. The NK2.1 antigen is likely to be anchored in the plasma membrane by a peptide moiety since its expression on NK cells was not affected by treatment with phosphatidylinositol-specific phospholipase C. In addition to be present on a splenic NK cell subset, the NK2.1 antigen is shown to be expressed by a small number of CD4-CD8-thymocytes and by a subset of CD4-CD8-IgG- lymph node cells. Finally, it is shown here that unlike the NKR-P1, the rat homologue of the murine NK1.1 antigen, neither the NK2.1 nor the NK1.1 antigen is expressed by polymorphonuclear leukocytes.

Detection of a Thy-1 precursor in human T lymphoma cell lines

In an attempt to gain insight into the biosynthesis and processing of human Thy-1, rabbit antisera (R alpha TP) were raised against a synthetic peptide (TP) of 13 amino acid residues of identical amino acid sequence to that of residues 110-122 of the putative Thy-1 precursor deduced from the cDNA sequencing. Immunoblotting assay showed that the IgG fraction of R alpha TP (R alpha TP-IgG) recognized the synthetic peptide without demonstrable cross-reactivity with isolated human brain Thy-1 and detergent-solubilized membrane proteins of human brain cells. Immunohistochemical studies showed that both R alpha TP-IgG and HB-2S-1 (a monoclonal antibody which reacts with both membrane-bound Thy-1 on viable cells and detergent-solubilized Thy-1) stained cells of two human T lymphoma cell lines (HUT-78 and HUT-102) but they did not stain cells of a human B lymphoma cell line (Raji). In contrast, in cell surface indirect immunofluorescence assay, HB-2S-1 reacted with HUT-78 and HUT-102 cells while R alpha TP-IgG did not. Taken together, these data indicate the existence of a precursor form of human Thy-1 which is processed prior to anchoring to the cell surface.

Expression of Thy-1 and effect of phosphatidylinositol-specific phospholipase C on primate and murine cell lines

BALC/c mice were immunized with isolated human brain Thy-1. The antisera at an appropriate dilution only reacted with a doublet of an apparent molecular weight (MW) around 25,000 among all the glycoproteins of brain tissue isolated by lentil lectin affinity chromatography when tested by enzyme-linked immunosorbent assay and immunoblotting. When the antisera were used to test a number of human cell lines and a marmoset T-cell line (70N2) by flow cytometry, an astrocytoma cell line (U-373), a T-lymphoblastoid cell line (MOLT-3), and two cutaneous T-lymphoma cell lines (HUT-78 and HUT-102) as well as the 70N2 cells were stained. However, a B-lymphoma cell line (Raji), a plasmacytoma cell line (HMy2), and normal peripheral blood lymphocytes were negative. When the positive cells were treated with phosphatidylinositol-specific phospholipase C, a significant decrease in both stain intensity and percentage of positive cells was demonstrated by immunofluorescence. Although Thy-1 expression in human lymphoid system is currently thought to be confined in early T- and B-lymphocyte development, our data suggest that well-differentiated T cells with mature phenotypes such as HUT-78 and HUT-102 which may be considered as tumor counterparts are also capable of expressing Thy-1, presumably after certain stimulation.