We prepared a monoclonal antibody (MAb), Lt-4, which recognizes a tax protein expressed in HTLV-I-infected cells. Indirect immunofluorescence staining showed that the antigen recognized by Lt-4 MAb located mainly in the nuclei of HTLV-I-infected T cell lines such as HUT102, TCL-As2, MT-1 and MT-2, and also weakly in the cytoplasm of MT-2 cell line. Lt-4 MAb did not react with two HTLV-I-uninfected T cell lines tested and fresh and PHA-activated peripheral blood lymphocytes (PBL) of several normal donors. Furthermore, Lt-4 MAb stained the nuclei of HeLa cells infected with a recombinant vaccinia virus encoding the tax but not with a wild type vaccinia virus. In Western blot (WB) and radioimmunoprecipitation analyses, Lt-4 MAb detected a 40 kDa molecule (p40) in HUT102 and TCL-As2 cells, and p40 and p68 in MT-2 cells. These results show that Lt-4 MAb is highly specific for the tax protein.

Three distinct monoclonal antibodies (MAbs) specific for human T-cell leukemia virus type-I (HTLV-I) core proteins with molecular weights of 24 kDa (p24), p19 or p15 were produced, characterized and compared. These antibodies were named NOR-1 (anti-p24, IgG2a), GIN-7 (anti-p19, IgG2b) and FR-45 (anti-p15, IgG2a). Immunofluorescence assay showed that they reacted specifically with methanol-fixed cells of virus-bearing cell lines, and that only GIN-7 bound, albeit weakly, to the surface of a small percentage of viable cells. Like natural antibodies to HTLV-I in human serum, GIN-7 stained the fixed cells brightly and diffusely, and gave more intense fluorescence than NOR-1 and FR-45, which stained restricted areas of the cells. NOR-1, GIN-7 and FR-45 specifically precipitated core proteins p24, p19 and p15, respectively, from a lysate of HTLV-IMT-2 labelled with 35S-cysteine. NOR-1 precipitated p53, p36, and p24, GIN-7 precipitated p53, p32, p28 and p19, and FR-45 precipitated p53, p36, and p15 from a lysate of 35S-cysteine-labelled MT-2 cells. GIN-7 also precipitated p32, p28 and p19 from a lysate of MT-2 cells, labelled by surface iodination, but NOR-1 and FR-45 did not detect any proteins in this lysate. GIN-7 also detected p28 in 3H-glucosamine-labelled MT-2 cells. Antibody binding competition assay showed that the sera of ATL patients significantly interfered with the binding of NOR-1 and GIN-7 but not with that of FR-45, to antigens of disrupted virus of MT-2 cells. This complete set of MAbs against the HTLV-I gag gene products is useful for biological and functional studies of the HTLV-I core proteins.

Sixteen monoclonal antibodies (MAbs) against TA34 antigen found on the surface of human T-cell leukemia virus type-I (HTLV-I) infected cells were prepared. These MAbs and one previously prepared anti-TA34 MAb (TAG34) recognized 34-kDa peptide not only in HTLV-I-infected cells, but also in cells infected with simian T-cell leukemia virus (STLV-I), which is analogous in antigenicity and gene structure to HTLV-I. Radioimmuno-precipitation (RIP) tests with the MAbs showed that TA34 antigen had at least 3 overlapping epitope groups. The antigenicities of the TA34 antigens of HTLV-I-infected cells derived from various primates were investigated by immunofluorescence staining using 9 anti-TA34 MAbs. Cells from humans, apes and Old World monkeys reacted with all these antibodies, whereas cells from New World monkeys were stained by most of the antibodies, but little if at all by the remaining 2 (5A8 and TAG34). Similar results were obtained with various primate cells infected with STLV-I. All 17 MAbs used recognized a 22-kDa peptide in HTLV-I-infected cells cultured in the presence of tunicamycin. When incubated with 1% 2-mercaptoethanol at pH 7.2 at 37 degrees C, TA34 antigen lost its reactivity with TAG34, suggesting that the antigen has an intramolecular S-S bond. Twenty sera of adult T-cell leukemia (ATL) patients did not react with TA34 antigen in RIP tests.