Location of human T-cell leukemia virus (HTLV) p19 antigen on virus-producing cells

Mouse monoclonal antibody to HTLV p19 was used to locate HTLV p19 on the surface of cells and virions by immunofluorescence microscopy (IFM) and immunoelectron microscopy (IEM). When HTLV-producing cells HUT 102 (B2 clone), MT-2 and strain A were used as target cells, HTLV p19 was detected on the surface of cells and virions as spots or small sectors by both IFM and IEM. Cells infected with animal type-C retroviruses, e.g., gibbon ape leukemia virus, simian sarcoma virus, feline leukemia virus, and Gross murine leukemia virus, were completely negative for HTLVp19 expression. Other human T cells not producing HTLV, including HUT78 and HSB2-0, immature or pre-T cells (Molt-3) derived from leukemia patients, and fresh peripheral blood T cells from healthy persons, were also negative. In addition, B cells including Rob-B, IM-9, Raji, and BT-1 did not react with the monoclonal antibody to HTLV p19. In the light of the presence of HTLV p19 in the periphery of acetone-fixed HTLV-producing cells as shown by IFM, it seems most likely that HTLV p19 is an internal antigen of HTLV with part of its structure protruding out of the viral and cell membrane. The monoclonal antibody to HTLV p19 did not lyse HTLV-producing cells in the presence of complement, as expected, because the antibody is an IgG1. Antibody-dependent cell-mediated cytotoxicity was also studied by the 51Cr-release assay. No cytotoxicity was observed. Although HTLV p19 does not contribute to the destruction of malignant T cells for treatment and/or virions for prophylaxis, this protein is an important marker for diagnosis of HTLV infection. The patterns of HTLV p19 expression described above were exactly the same for American HTLV-producing HUT 102 (B2 clone), for strain A cells and for Japanese HTLV-producing MT-2 cells. These results further substantiate the close relationship of the Japanese and American HTLV isolates.