Phorbol diester induces expression of Tac antigen on human acute T lymphocytic leukemic cells

In general, the human acute T lymphocytic leukemias are composed of malignant expansions of immature T cells lacking membrane receptors for T cell growth factor (TCGF, interleukin 2) and significant immunoregulatory activity. We investigated whether cultured acute lymphocytic leukemic T cell lines can be induced to differentiate and express the Tac antigen, a cell surface protein that contains a TCGF-binding site, after exposure to phorbol 12-myristate 13-acetate (PMA) and/or phytohemagglutinin (PHA). Reactivity of anti-Tac with induced leukemic T cells was studied by three techniques, including: 1) flow microfluorometry; 2) specific binding of [3H]anti-Tac; and 3) receptor immunoprecipitation with anti-Tac and analysis by SDS-PAGE. After exposure to PMA with or without PHA, both JURKAT and HSB-2 acute lymphocytic leukemic T cells displayed Tac antigen within 6 to 8 hr. Induction of receptor expression was blocked by actinomycin D, suggesting a requirement for new mRNA transcription. Induced JURKAT cells contained approximately 7000 Tac molecules per cell, and the binding of anti-Tac to these cells was blocked in a dose-related manner by purified TCGF but not by insulin or purified recombinant interferon-alpha. SDS-PAGE analysis of anti-Tac immunoprecipitates demonstrated that receptors present on induced JURKAT cells were 2000 to 3000 daltons smaller than those present on PHA-activated normal lymphoblasts or induced HSB-2 cells. Induction of JURKAT cells with both PHA and PMA resulted in marked secretion of TCGF as well as the appearance of Tac antigen. After activation of these cells with PMA alone, Tac antigen was similarly expressed, but the level of TCGF synthesis was less than 1% of that obtained after dual induction with PHA and PMA. These data indicate that the signals required for TCGF synthesis and Tac expression are not identical, and furthermore that induction of Tac antigen and TCGF is not obligately linked in these cells.

Cyclosporin A inhibits T-cell growth factor gene expression at the level of mRNA transcription

Cyclosporin A (CsA) is a potent immunosuppressive agent, now gaining wide application in human organ transplantation. The immunosuppressive activity of CsA is at least in part due to inhibition of lymphokine production by activated T lymphocytes. Specifically, inhibition of T-cell growth factor (TCGF; also designated interleukin 2) production appears to be an important pathway by which CsA impairs T-cell function. To define further both the specificity of CsA and the level at which it interferes with lymphokine gene expression, we have studied its effects on TCGF mRNA accumulation as well as TCGF gene transcription. These studies were performed with a cloned human leukemic T-cell line (Jurkat, subclone 32), which can be induced with phytohemagglutinin and phorbol 12-myristate 13-acetate to produce large amounts of TCGF. In these cells, high levels of TCGF mRNA were present in induced but not in uninduced Jurkat cells as judged by hybridization to a cloned human TCGF cDNA probe. CsA completely inhibited induced TCGF mRNA accumulation at concentrations of 0.3-1.0 microgram/ml, whereas low levels of appropriately sized TCGF mRNA were present at 0.01 microgram/ml. In nuclear transcription experiments, CsA inhibited the synthesis of TCGF transcripts in a dose-dependent manner with complete inhibition at a concentration of 1 microgram/ml. In contrast, CsA did not inhibit the expression of two other inducible genes, TCGF receptor and HT-3. Further, HLA gene expression was also less affected than TCGF in CsA-treated cells. These data suggest a relatively selective action of CsA on TCGF gene transcription.

Phorbol diester induces expression of Tac antigen on human acute T lymphocytic leukemic cells

In general, the human acute T lymphocytic leukemias are composed of malignant expansions of immature T cells lacking membrane receptors for T cell growth factor (TCGF, interleukin 2) and significant immunoregulatory activity. We investigated whether cultured acute lymphocytic leukemic T cell lines can be induced to differentiate and express the Tac antigen, a cell surface protein that contains a TCGF-binding site, after exposure to phorbol 12-myristate 13-acetate (PMA) and/or phytohemagglutinin (PHA). Reactivity of anti-Tac with induced leukemic T cells was studied by three techniques, including: 1) flow microfluorometry; 2) specific binding of [3H]anti-Tac; and 3) receptor immunoprecipitation with anti-Tac and analysis by SDS-PAGE. After exposure to PMA with or without PHA, both JURKAT and HSB-2 acute lymphocytic leukemic T cells displayed Tac antigen within 6 to 8 hr. Induction of receptor expression was blocked by actinomycin D, suggesting a requirement for new mRNA transcription. Induced JURKAT cells contained approximately 7000 Tac molecules per cell, and the binding of anti-Tac to these cells was blocked in a dose-related manner by purified TCGF but not by insulin or purified recombinant interferon-alpha. SDS-PAGE analysis of anti-Tac immunoprecipitates demonstrated that receptors present on induced JURKAT cells were 2000 to 3000 daltons smaller than those present on PHA-activated normal lymphoblasts or induced HSB-2 cells. Induction of JURKAT cells with both PHA and PMA resulted in marked secretion of TCGF as well as the appearance of Tac antigen. After activation of these cells with PMA alone, Tac antigen was similarly expressed, but the level of TCGF synthesis was less than 1% of that obtained after dual induction with PHA and PMA. These data indicate that the signals required for TCGF synthesis and Tac expression are not identical, and furthermore that induction of Tac antigen and TCGF is not obligately linked in these cells.

Biosynthesis and compartmentalization of rat-intestinal vitamin-D-dependent calcium-binding protein

We have purified the primary translation product of rat intestinal vitamin-D-dependent calcium-binding protein mRNA from wheat germ and ascites cell-free systems. We show that calcium-binding protein is neither synthesized as a larger percursor nor likely to be exported from the intestinal epithelium. Our conclusions are based on the following observations. (1) The primary translation product, NH2-terminally labeled with formyl[35S]methionine, comigrates with the mature cytoplasmic protein during electrophoresis through denaturing gels. (2) It does not possess a cleavable signal peptide sequence or internal signal equivalent as judged by co- and post-translational cleavage assays in vitro. (3) The NH2 terminus of the cell-free product is acetylated. (4) Comparison of the NH2-terminal amino acid sequences of the primary translation product and cyanogen bromide peptides obtained from the blocked, purified cytoplasmic protein. The kinetics of calcium-binding protein mRNA accumulation and decay in rachitic intestinal epithelium after primary and secondary stimulation with 1,25-dihydroxycholecalciferol (calcitriol) were studied using the cell-free translation system. The results are reminiscent of other steroid-hormone-inducible systems. Both the rate of mRNA accumulation and the peak response were greater after secondary stimulation.

Characterization of the human receptor for T-cell growth factor

Anti-Tac monoclonal antibody has been identified as a putative antibody against the receptor for T-cell growth factor (TCGF). We now show that: (i) TCGF blocks 85% of 3H-labeled anti-Tac binding to phytohemagglutinin-activated lymphoblasts and (ii) both anti-Tac and anti-TCGF immunoprecipitate a protein band that appears to represent TCGF crosslinked to its receptor on HUT-102B2 cells. In HUT-102B2 cells, the TCGF receptor is a Mr 50,000 glycoprotein with internal disulfide bond(s) and a pI of 5.5-6.0, and it represents approximately equal to 0.05% of total cellular de novo protein synthesis. It contains a peptide of Mr 33,000 that is processed to a mature form that includes N-linked and O-linked sugars and sialic acid.

Blockade of the interleukin-2 receptor by anti-Tac antibody: inhibition of human lymphocyte activation

We have previously shown that monoclonal anti-Tac antibody inhibits the proliferation of interleukin-2 (IL-2) dependent human continuous T cell lines. Further, we have shown that anti-Tac specifically blocks greater than 95% of the binding of radiolabeled II-2 to a continuous T cell line. In view of these data, we suggested that anti-Tac antibody may bind to and block the human T cell receptor for IL-2. We now report the effects of anti-Tac on the activation of human peripheral blood T lymphocytes. We find that anti-Tac: 1) blocks T cell proliferation induced by soluble antigens (80-90%), autologous antigens (90%) and alloantigens (75-90%); 2) partially inhibits T cell proliferation induced by mitogenic lectins, including Concanavalin A (50-88%), pokeweed mitogen (40-87%), and phytohemagglutinin (20-80%); 3) abrogates (greater than 95%) the generation of cytolytic T lymphocytes in allogeneic cell cocultures, but does not inhibit killing by cytolytic T lymphocytes once formed; 4) and inhibits T cell dependent pokeweed mitogen activated B cell immunoglobulin production (78-95%). We further demonstrate that anti-Tac inhibition of proliferation is not secondary to diminished production of IL-2. Finally, in antigen induced T cell proliferative assays, we demonstrate that the addition of highly purified IL-2 reverses the inhibitory effects of anti-Tac. These data are consistent with the hypothesis that anti-Tac recognizes the human IL-2 receptor and illustrate ways in which this antibody can be used to modulate the human immune response.

Blockade of the interleukin-2 receptor by anti-Tac antibody: inhibition of human lymphocyte activation

We have previously shown that monoclonal anti-Tac antibody inhibits the proliferation of interleukin-2 (IL-2) dependent human continuous T cell lines. Further, we have shown that anti-Tac specifically blocks greater than 95% of the binding of radiolabeled II-2 to a continuous T cell line. In view of these data, we suggested that anti-Tac antibody may bind to and block the human T cell receptor for IL-2. We now report the effects of anti-Tac on the activation of human peripheral blood T lymphocytes. We find that anti-Tac: 1) blocks T cell proliferation induced by soluble antigens (80-90%), autologous antigens (90%) and alloantigens (75-90%); 2) partially inhibits T cell proliferation induced by mitogenic lectins, including Concanavalin A (50-88%), pokeweed mitogen (40-87%), and phytohemagglutinin (20-80%); 3) abrogates (greater than 95%) the generation of cytolytic T lymphocytes in allogeneic cell cocultures, but does not inhibit killing by cytolytic T lymphocytes once formed; 4) and inhibits T cell dependent pokeweed mitogen activated B cell immunoglobulin production (78-95%). We further demonstrate that anti-Tac inhibition of proliferation is not secondary to diminished production of IL-2. Finally, in antigen induced T cell proliferative assays, we demonstrate that the addition of highly purified IL-2 reverses the inhibitory effects of anti-Tac. These data are consistent with the hypothesis that anti-Tac recognizes the human IL-2 receptor and illustrate ways in which this antibody can be used to modulate the human immune response.

Rearrangement and expression of immunoglobulin genes and expression of Tac antigen in hairy cell leukemia

The origin and exact stage of differentiation of the neoplastic cells that comprise hairy cell leukemia have remained uncertain. As Ig heavy and light chain genes must both undergo a DNA rearrangement during B-cell development but rarely do so within other hematopoietic lineages, we examined these genes in this leukemia. The neoplastic cells of all eight cases demonstrated rearranged heavy and light chain genes and, in two cases examined, contained the corresponding mRNA for heavy and light chain Ig. Consistent with this B-cell genotype, all cases displayed cell surface HLA-DR and B-cell-associated antigens. Unexpectedly, all cases demonstrated cell surface Tac antigen, which previously had been restricted predominantly to select T-cell malignancies and activated T cells. Prior studies suggested that the anti-Tac monoclonal antibody recognized a peptide associated with the binding of interleukin 2 (T-cell growth factor) in such T cells. Immunoprecipitation with anti-Tac and NaDodSO4/polyacrylamide gel electrophoresis revealed an antigen on leukemic hairy cells with a Mr of 53,000-57,000, identical in size to the receptor on activated T cells. This apparent biphenotypic status might reflect a transformation-associated expression of the Tac antigen in this leukemia. Alternatively, hairy cell leukemia may be a malignancy of a unique stage of normal B-cell differentiation in which the Tac antigen is expressed.

Polymorphonuclear neutrophils express the common acute lymphoblastic leukemia antigen

Monoclonal antibodies J5, VIL-A1, and BA-3, known to react with the common acute lymphoblastic leukemia antigen (CALLA) were found to specifically stain normal human polymorphonuclear neutrophils (PMN). The antigen detected on PMN had a molecular weight (95,000-110,000 mol wt) close to that of CALLA (95,000-100,000 mol wt) and thus these surface membrane antigens are likely related, if not identical. The fluorescent staining intensity of PMN is comparable to that of CALLA-positive leukemic cells and the presence of PMN in patient samples could potentially produce false-positive results in diagnosis.

Characterization of a soluble suppressor of human B cell function produced by a continuous human suppressor T cell line. II. Evidence for suppression through a direct action of CTC-SISS-B on human B cells

CTC-SISS-B is an antigen-nonspecific suppressive lymphokine elaborated by an interleukin 2-dependent suppressor T cell line that produces noncytotoxic inhibition of human B cell but not T cell function. Like SISS-B, a soluble suppressive lymphokine present in the supernatants of Con A-activated peripheral blood T cell cultures, CTC-SISS-B is of 60,000 to 90,000 m.w., and its action is blocked by the simple sugar L-rhamnose. CTC-SISS-B inhibits human B cell Ig production and proliferation through a direct interaction with human B cells rather than through indirect effects on immunoregulatory T cells or monocytes. CTC-SISS-B suppression occurs through inhibition of an early event(s) in B cell activation since proliferation and Ig production by established human B cell lines are not inhibited by this lymphokine. Despite sharing many biochemical and biologic properties, CTC-SISS-B and gamma-interferon appear to be distinct mediators.

Characterization of a soluble suppressor of human B cell function produced by a continuous human suppressor T cell line. II. Evidence for suppression through a direct action of CTC-SISS-B on human B cells

CTC-SISS-B is an antigen-nonspecific suppressive lymphokine elaborated by an interleukin 2-dependent suppressor T cell line that produces noncytotoxic inhibition of human B cell but not T cell function. Like SISS-B, a soluble suppressive lymphokine present in the supernatants of Con A-activated peripheral blood T cell cultures, CTC-SISS-B is of 60,000 to 90,000 m.w., and its action is blocked by the simple sugar L-rhamnose. CTC-SISS-B inhibits human B cell Ig production and proliferation through a direct interaction with human B cells rather than through indirect effects on immunoregulatory T cells or monocytes. CTC-SISS-B suppression occurs through inhibition of an early event(s) in B cell activation since proliferation and Ig production by established human B cell lines are not inhibited by this lymphokine. Despite sharing many biochemical and biologic properties, CTC-SISS-B and gamma-interferon appear to be distinct mediators.