Distinct reactivities of four monoclonal antibodies with human interleukin 2 receptor

Two new murine monoclonal IgG1 antibodies, H-31 and H-A26, were characterized in comparison with two previously obtained monoclonal antibodies against human interleukin 2 (IL-2) receptor (IL-2 R), anti-Tac and HIEI. In immunofluorescence assays with various human hematopoietic cells, H-31 and H-A26 antibodies both reacted with only IL-2 R-positive cells, and they precipitated IL-2 R molecules, glycoproteins with molecular weights of 60K and 53K daltons (gp60/gp53), from human T-cell leukemia virus type I (HTLV-I)-carrying MT-2 cells, as demonstrated by sequential immunoprecipitation after absorption of IL-2 R with anti-Tac. Antibody-binding competition assays showed that H-31 and anti-Tac, and H-A26 and HIEI, respectively, competed reciprocally in binding to the cells, and that anti-Tac also inhibited the binding of HIEI but not vice versa. H-31, like anti-Tac, strongly inhibited the IL-2-dependent proliferation of normal activated T-cells, absorption of IL-2 and direct binding of IL-2 to the cells, while H-A26, like HIEI, inhibited those processes only weakly. The spectra of reactivities of these antibodies with various simian cell lines derived by HTLV-I infection were different, as revealed by immunofluorescence studies. Human IL-2 R was shown to express a unique antigenic determinant, detected with HIEI, that was not detectable in IL-2 R molecules of Old and New World monkeys, and also to express determinants common to simian IL-2 R molecules. These observations indicate that H-31 and H-A26 recognize human IL-2 R molecules and that the antigenic sites on the IL-2 R molecule defined by H-31, H-A26, anti-Tac, and HIEI are different.     

Tac antigen forms disulfide-linked homodimers

Interleukin 2 (IL-2) is responsible for stimulating T-cell proliferation via interaction with specific, high-affinity membrane receptors. Although an IL-2-binding protein has been identified by virtue of its reactivity with a monoclonal antibody that competes with IL-2 for binding (anti-Tac), the complete and precise structure of functional IL-2 receptors is still unknown. To define further the composition of IL-2 receptors, both IL-2 itself and anti-Tac were used as ligands to adsorb membrane proteins for analysis by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (NaDodSO4/PAGE). A variety of experimental approaches yield results indicating that the Tac antigen, which migrates as a single protein on NaDod-SO4/PAGE under reducing conditions, is also expressed as disulfide-linked homodimers and oligomers. Examined under nonreducing conditions, both activated normal human T cells and cell lines from patients with adult T cell leukemia (HUT-102; MT-1) express Tac antigen homodimers (Mr 105,000) in addition to monomers (Mr 54,000). Formation of the disulfide bond is not a consequence of the experimental procedures used to isolate the proteins for analysis, inasmuch as identical results are obtained when the receptor proteins are iodinated and extracted in the presence of N-ethylmaleimide or prepared for electrophoresis in the absence of heat denaturation. Accordingly, these findings point to Tac antigen associating with itself preferentially. The physiologic significance of homodimer and oligomer formation, especially as it relates to the formation of high-affinity IL-2 receptors, is presently unknown.     

Nature of adult T-cell leukemia-associated membrane antigen on the surface of adult T-cell leukemia virus-carrying cells as revealed by membrane immunofluorescence

Adult T-cell leukemia-associated membrane antigen (ATLMA) expressed on the surface of living ATL virus (ATLV)-carrying cells was investigated by an indirect membrane immunofluorescence method using natural antibodies to ATLV in human sera. All the ATLV-positive cell lines tested that had cytoplasmic ATL-associated antigen (ATLA) detectable in acetone-fixed cell smears were also positive for ATLMA, but ATLMA was not detected in any ATLV-negative cell lines. The frequencies of ATLA- and ATLMA-bearing cells in seven cell lines tested were roughly parallel. The frequency of expression of both ATLMA and ATLA in cultures of MT-1 cells increased in the presence of 5-iodo-2'-deoxyuridine. All human sera having ATLA antibody had ATLMA antibody and the titers of the two were similar in most of the sera. The anti-ATLMA titers of human sera determined by using an ATLV-bound non-ATL T-cell line as antigen were also similar to the anti-ATLA titers. Absorption of anti-ATLMA-positive sera with living MT-2 cells, in which almost 100% of the cells express ATLA and ATLMA, caused parallel decreases in the anti-ATLA and anti-ATLMA titers. Analysis of the 125I-labeled surface of MT-2 cells by immunoprecipitation with anti-ATLMA-positive human serum followed by gel electrophoresis revealed that p19, p24, p28, and p46 polypeptides were specifically precipitated. These data suggest that ATLMA on the cell surface is not distinguishable from ATLA in the cytoplasm.     

Identification of a glycoprotein, gp21, of adult T cell leukemia virus by monoclonal antibody

A mouse hybridoma cell line producing monoclonal antibody, F10, was established from mice hyperimmunized with cells bearing adult T cell leukemia (ATL) virus (ATLV). F10 antibody reacted with an ATLV structural polypeptide ( gp21 ) with a m.w. of 21,000 that was glycosylated on cell surfaces. The gp21 was expressed on cell surfaces of all ATL-associated antigen (ATLA)-positive human cell lines but not on ATLA-negative cell lines nor peripheral blood leukocytes stimulated with mitogens. The gp21 was also detected with anti-ATLA-positive human serum, and the binding of F10 antibody to ATLA-positive cell surfaces was significantly blocked by pretreatment with anti-ATLA-positive human sera. Double immunofluorescence staining with F10 antibody and anti-ATLA-positive human serum caused co-capping on cell surfaces, which suggests that gp21 co-exists with other ATLV antigens expressed on cell surfaces. Immunoprecipitation studies also suggested that the gp21 is a minor component of the ATLV envelope.     

New monoclonal antibodies that define multiple epitopes and a human-specific marker on the interleukin 2 receptor molecules of primates

Twelve hybridoma cell lines producing monoclonal antibodies to the human interleukin 2 (IL-2) receptor (IL-2R) molecule were prepared. These antibodies were characterized by competitive antibody-binding assay and sequential immunoprecipitation assay with four known monoclonal antibodies to the human IL-2R molecule. The twelve new monoclonal antibodies were divided among the four known antibody types, the HIEI-, H-A26-, H-31-, and anti-Tac-type, and an additional new type, the H-48-type. The H-48 antibody did not compete with any other antibodies in the competitive binding assay. The binding of 125I-IL-2 to MT-2 cells and the IL-2-dependent growth of normal activated T-cells were both strongly inhibited by all the H-31- and anti-Tac-type antibodies, and partially or slightly inhibited by HIEI- and H-A26-type antibodies, but were not inhibited by the H-48 antibody. Thus, the same type of monoclonal antibodies had a similar effect on the function of IL-2R. These results suggest that epitopes for the same type of antibodies could be single identical epitopes or epitopes closely associated with each other. On the other hand, these antibodies also reacted variously with a panel of various human and simian lymphoid cell lines immortalized with human T-cell leukemia virus type-I (HTLV-I): the H-45 antibody reacted only with the human cell lines, the H-C1 and H-44 and H-47 antibodies reacted with human and ape cell lines, and the other antibodies reacted with cell lines of humans, apes and Old and New World monkeys. These differences in the reactivity of the antibodies with the primate cell lines suggest that the antigenic structure of the IL-2R molecule changed during evolutionary divergence of the primates.     

Biosynthetic processing of human interleukin-2 receptor (Tac antigen)

Biosynthetic processing of the T-cell surface receptor for interleukin-2 was investigated in a cultured human T-cell line MT-1 by means of metabolic and cell surface radiolabeling followed by immunoprecipitation with a monoclonal anti-receptor antibody (anti-Tac) and analysis by one- and two-dimensional polyacrylamide gel electrophoresis. The nascent precursor of the receptor (Mr = about 40,000, pI = 6.2-6.5) underwent a post-translational modification giving rise to the mature receptor (IL-2R; Mr = 60,000-65,000, pI = 4.2-4.7) within 2-4 hr. The post-translational processing of IL-2R caused a 20,000-25,000 increase in apparent molecular weight and a 2.0-2.5 acidic shift in the isoelectric point. The increase in molecular weight was attributable mainly to addition of sugar residues including glucosamine and galactose, and the charge shift to the addition of sialic acids. A carboxylic ionophore monensin completely blocked the maturation of IL-2R at the mid-stage of the processing. Fatty acid attachment appeared to comprise one of the steps of the post-translational modification. Two-dimensional analyses of IL-2R biosynthesis enabled identification of the precursor of IL-2R and its intermediate forms, from which it was partially possible to estimate reactions involved in the maturation of the precursor molecule.     

Characterization of human interleukin 2 receptor (Tac antigen) in normal and leukemic T cells: co-expression of normal and aberrant receptors on Hut-102 cells

Human interleukin 2 receptors ( IL2R ) from various cell sources such as mitogen-activated normal human T cells, adult T cell leukemia (ATL)-derived cell line cells (MT-1, ATL-6, Hut-102), and a natural killer-like cell line YT cells, were studied both by one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), with a monoclonal anti- IL2R antibody (anti-Tac). In synthetic labeling with [35S]methionine, anti-Tac specifically precipitated two glycoproteins, one with m.w. of 60,000 to 65,000 and pI 4.2 to 4.7, and the other with m.w. about 40,000 and pI 6.2 to 6.5. A study of surface iodination revealed that the former component was membrane-associated mature IL2R , and a pulse-chase study showed that the latter component was a precursor for IL2R that already possessed tunicamycin-sensitive N-linked sugar side chain(s). This precursor was found to be posttranslationally processed into mature IL2R by further glycosylation within 240 min. Among the cells studied, a human T cell leukemia virus-positive leukemic cell line, Hut-102, was distinctive in that it possessed an additional membrane glycoprotein (m.w. 55,000 to 60,000, pI 4.2 to 5.0) also defined by anti-Tac. This unique glycoprotein of Hut-102 cells appeared to be an aberrant IL2R .     

Constitutive production of phagocytosis inducing factor(s) in a monocyte/macrophage lineage cell line (THP-1) by retrovirus-transformed human T cell lines

Four human T cell lines, MT-2, TCL-Kan, TCL-As 2, and TCL-Haz, established from normal leukocytes by cocultivation with adult T-cell leukemia (ATL) virus (ATLV)-producing cells, produced constitutively phagocytosis inducing factor(s) (PIF) that induced phagocytosis in a human monocytic cell line, THP-1. These cell lines expressed ATLV-associated antigens (ATLA) as well as numerous virus particles, whereas the other twelve leukocyte cell lines tested, including T cell lines, B cell lines, and non-T and non-B cell lines, did not produce detectable amounts of the factor(s) in the culture supernatants. PIF was produced in the absence of serum and was not related to either ATLV-particles or viral structural proteins. Its activity was stable at 56 C for 30 min, but labile at 80 C for 30 min and at pH 2 for 20 hr. MT-2 and TCL-Kan produced large amounts of the factor(s) in the culture supernatants but little interferon-gamma (IFN-gamma) or colony stimulating factor (CSF) activity was detected; furthermore, the activity was not neutralized by rabbit anti-IFN-gamma sera. These observations suggest that some ATLV-transformed T cell lines produce PIF that is different from IFN-gamma and CSF.     

Mapping of immunogenic regions of human T cell leukemia virus type I (HTLV-I) gp46 and gp21 envelope glycoproteins with env-encoded synthetic peptides and a monoclonal antibody to gp46

Antigenic sites on human T cell leukemia virus type I (HTLV-I) gp46 and gp21 envelope glycoproteins that are immunogenic in man were studied with envelope gene (env)-encoded synthetic peptides and a mAb to HTLV-I gp46 envelope glycoprotein. Antibodies in 78% of sera from HTLV-I seropositive subjects reacted with synthetic peptide 4A (amino acids 190 to 209) from a central region of HTLV-I gp46. Human anti-HTLV-I antibodies also bound to synthetic peptides 6 (29% of sera) and 7 (18% of sera) from a C-terminal region of gp46 (amino acids 296 to 312) and an N-terminal region of gp21 (amino acids 374 to 392), respectively. mAb 1C11 raised to affinity-purified HTLV-I gp46 reacted with gp46 external envelope glycoprotein and gp63 envelope precursor in immunoblot assay and also bound to the surface of HTLV-I+ cells lines HUT-102 and MT-2. Antibody 1C11 did not react with HTLV-II or HIV-infected cells or with a broad panel of normal human tissues or cell lines. In competitive RIA, anti-gp46 antibody 1C11 was inhibited from binding to gp46 either by antibodies from HTLV-I seropositive subjects or by HTLV-I env-encoded synthetic peptide 4A, indicating that 1C11 bound to or near a site on gp46 within amino acids 190 to 209 also recognized by antibodies from HTLV-I-seropositive individuals. When tested in syncytium inhibition assay, mAb 1C11 did not neutralize the infectivity of HTLV-I. Thus, HTLV-I infection in man is associated with a major antibody response to a region of gp46 within amino acids 190 to 209 that is on the surface of virus-infected cells.     

人白细胞介素2受体(IL-2R)cDNA在哺乳类细胞中表达的初步研究

按DNA-磷酸钙共沉淀法将人白细胞介素2受体(IL-2R)cDNA转染小鼠成纤维细胞L929,经RNA点渍杂交分析、荧光标记IL-2染色和抗Tac(人IL-2受体α链)特异性玫瑰花环试验,均证明转入的IL-2R cDNA在L929细胞中表达,其产物具有结合IL-2和抗Tac抗体的能力。本文还报道了T细胞白血病Jukat细胞和Molt-4等细胞系异常表达IL-2R的结果,并对此作了分析和讨论。     

Internalization of CD4 molecules in human T-cells demonstrated by immuno-electron microscopy.

Internalization of CD4 molecules on human CD4-enriched T-cells was demonstrated by immunocytochemical electron microscopy. CD4+ T-cell subclones were obtained from normal human peripheral blood, followed by one-way MLC screening and co-culturing with IL-2. Fixed and non-fixed T-cell samples were indirectly immunolabeled with mouse anti-human CD4 monoclonal antibody and goat anti-mouse IgG conjugated with peroxidase. Unfixed T-cells were immunolabeled at 4 degrees C and then re-incubated for 5-45 min at 37 degrees C. The selected CD4+ T-cell subclones showed strong CD4 binding on the cell surface after IL-2 incubation. However, fresh T-cells, monocytes, bone marrow cells and CD8+ T-cells all stained negative for CD4. The distribution of CD4 molecules on the fixed cell surface showed a homogeneous pattern. Capping and internalization of CD4-antibody-peroxidase complexes from the cell surfaces were observed follow a pathway of receptor-mediated endocytosis in unfixed T cells. Endocytotic vesicles, vacuoles of diverse sizes and shapes near the cell membrane or deep in the cell center were found to contain CD4 molecules. Negatively stained Golgi saccules were observed up to 45 min after re-incubation. These results suggest that increased CD4 molecules can be induced on the surface of normal human T-cells in vitro. Internalization and accumulation of CD4 molecules occurred in CD4-enriched T-cells with IL-2 pretreatment.     

Identification and synthesis of the epitope for a human monoclonal antibody which can neutralize human T-cell leukemia/lymphotropic virus type I

A monoclonal antibody (mAb), designated 0.5 alpha, derived from a patient with adult T-cell leukemia was found previously to neutralize the human T-cell leukemia/lymphotropic type I (HTLV-I) virus in in vitro assays and bind to the major envelope glycoprotein (gp46) of HTLV-I (Matsushita, S., Guroff, M.R., Trepel, J., Crossman, J., Mitsuya, H., and Broder, S. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 2671-2676). We have designed experiments to determine the epitope for this mAb. Using simultaneous multiple peptide synthesis, we synthesized 481 overlapping octapeptides which corresponded to the sequence of gp46. We mapped the epitope for mAb 0.5 alpha to lie between residues 186 and 195 of gp46. This result was confirmed by independently synthesizing a peptide containing this epitope which bound specifically to mAb 0.5 alpha with an approximate Ka = 4 x 10(7) M-1. In addition, the peptide inhibited mAb 0.5 alpha binding to gp46 derived from T-cells infected with HTLV-I. This epitope containing peptide may facilitate understanding HTLV-1 infection of T-cells.     

Interleukin 2 receptor blockade by anti-Tac antibody inhibits IFN-gamma induction

Anti-Tac antibody, which binds to the interleukin 2 (IL-2) receptor and thus blocks IL-2 binding to and activation of T lymphocytes, was used to investigate the role of IL-2 in interferon-gamma (IFN-gamma) production. Three T-cell mitogens (phytohemagglutinin, concanavalin A, and the pan-T monoclonal antibody OKT3) were used as IFN-gamma inducers. In each case, anti-Tac antibody clearly inhibited IFN-gamma production. This occurred even under conditions where cellular proliferation (as measured by incorporation of [3H]thymidine) was only slightly inhibited. The inhibitory effects of anti-Tac were reversed by the addition of purified IL-2. Therefore, endogenous production of IL-2 and its binding to the IL-2 receptor are needed for maximum IFN-gamma production.     

Demonstration of a direct inhibitory effect of cyclosporine on normal human T-cells with two novel models of T-cell activation as probes

Two novel models of activation of human peripheral blood quiescent T-cells (T-cells) were utilized herein as probes to analyze the mechanisms and to locate the site of action of cyclosporine (CsA) in the T-cell activation pathway. Highly purified T-cells were activated, independently of accessory cells, with either crosslinked anti-CD2 + anti-CD3 monoclonal antibodies (mAbs) or with sn-1,2-dioctanoylglycerol (DAG) and ionomycin. CsA inhibited the expression of 55-kDa interleukin-2 receptors (IL-2R) and T-cell proliferation in these accessory cell-independent models of T-cell activation. Recombinant IL-2, over a wide range of concentrations that included different binding affinities of cellular receptors for IL-2, did not completely reverse CsA-associated inhibition of IL-2R expression and/or proliferation. In additional experiments, designed to examine early activation related events, CsA did not interfere with the increase in intracellular free calcium concentration initiated with anti-CD2, anti-CD3, anti-CD2 + anti-CD3 mAbs or with ionomycin. DAG-induced and PKC-activation-dependent down-regulation of cell surface expression of CD3 antigens was similarly unaffected by CsA. Our findings unambiguously indicate that CsA has a direct inhibitory effect on T-cells. Moreover, CsA's cellular site of action is distal to calcium mobilization and PKC activation but proximal to IL-2R expression and IL-2-dependent DNA synthesis in normal human T-cells.     

Interleukin 2 receptors are expressed by alveolar macrophages during pulmonary sarcoidosis and are inducible by lymphokine treatment of normal human lung macrophages, blood monocytes, and monocyte cell lines

Expression of receptors for IL 2 was believed initially to be restricted to T cells after their activation by IL 1 and antigen. However, recently IL 2 receptors (IL 2R) were demonstrated on activated B cells by using an anti-IL 2R monoclonal antibody (anti-Tac). In this study, we examined the capacity of cultured human alveolar macrophages, blood monocytes, and myelomonocytic (HL-60) or monoblast (U937) cell lines to bind three different anti-IL 2R monoclonal antibodies before or after stimulation with the monocyte-activating agents IFN-gamma, LPS, phorbol ester, or lymphokine-containing conditioned medium. For each of the four cell populations examined, resting unstimulated cells bound little or no anti-IL 2R antibody, as shown independently by quantitative cell binding assay and by immunoperoxidase labeling. By contrast, incubation with recombinant IFN-gamma, conditioned medium, or to a lesser extent, native or recombinant IL 2 itself, resulted in a significant enhancement of anti-IL 2 receptor monoclonal antibody binding by all four populations, whereas LPS, PMA, or IL 1 had no effect. In addition, membrane binding of anti-Tac antibody, similar to that seen after stimulation of normal lung macrophages with IFN-gamma, was detected by using macrophages obtained by bronchoalveolar lavage of five patients with active pulmonary sarcoidosis. These findings are consistent with the expression of a functional IL 2R on activated cells of the monocyte lineage, since anti-Tac binding to IFN-gamma-treated HL-60 cells was inhibited by addition of excess IL-2; specific binding of anti-IL 2 monoclonal antibodies was detected in the presence of exogenous IL 2; and a 50 to 55 kD molecule was immunoprecipitated from both activated lung macrophages and T lymphoblasts by using anti-Tac antibody. We conclude that human mononuclear phagocytes can be induced by lymphokines to express IL 2R, and that such IL 2R+ macrophages can be detected in vivo during inflammation.     

Internalization of CD4 molecules in human T-cells demonstrated by immuno-electron microscopy

Summary Internalization of CD4 molecules on human CD4-enriched T-cells was demonstrated by immunocytochemical electron microscopy. CD4⁺ T-cell subclones were obtained from normal human peripheral blood, followed by one-way MLC screening and co-culturing with IL-2. Fixed and non-fixed T-cell samples were indirectly immunolabeled with mouse anti-human CD4 monoclonal antibody and goat anti-mouse IgG conjugated with peroxidase. Unfixed T-cells were immunolabeled at 4° C and then re-incubated for 5–45 min at 37° C. The selected CD4⁺ T-cell subclones showed strong CD4 binding on the cell surface after IL-2 incubation. However, fresh T-cells, monocytes, bone marrow cells and CD8⁺ T-cells all stained negative for CD4. The distribution of CD4 molecules on the fixed cell surface showed a homogeneous pattern. Capping and internalization of CD4-antibody-peroxidase complexes from the cell surfaces were observed follow a pathway of receptor-mediated endocytosis in unfixed T cells. Endocytotic vesicles, vacuoles of diverse sizes and shapes near the cell membrane or deep in the cell center were found to contain CD4 molecules. Negatively stained Golgi saccules were observed up to 45 min after re-incubation. These results suggest that increased CD4 molecules can be induced on the surface of normal human T-cells in vitro. Internalization and accumulation of CD4 molecules occurred in CD4-enriched T-cells with IL-2 pretreatment.     

Double-negative (CD4- CD8-) T cells with an alpha/beta T cell receptor. Non-MHC-restricted cytolytic activity and lymphokine production

T cell lines with a novel phenotype (CD3+ TCR-alpha/beta+ CD4- CD8-) were developed from the peripheral blood of a patient with a combined immunodeficiency and tissue injury resembling graft-vs-host disease. One of these IL-2-dependent T cell lines demonstrated non-MHC-restricted cytolytic function against tumor targets, syngeneic and allogeneic fibroblasts, and PHA blasts from allogeneic donors. The other cell line only became cytotoxic in the presence of lectin or anti-CD3 antibody. The two cell lines also differed in their expression of the T-200 gene products CD45RO (gp180) and CD45RA (gp220). Both cell lines produced tumor necrosis factor-alpha and -beta and IFN-gamma activity when activated with mitogens or PMA and IL-1. The in vitro functions of these T-cell lines suggest a potential role for alpha/beta double-negative T lymphocytes in tissue injury resembling graft-vs-host disease.     

Prostaglandin E2 inhibits human T-cell proliferation after crosslinking of the CD3-Ti complex by directly affecting T cells at an early step of the activation process

We have studied the effects of prostaglandin E2 (PGE2) on in vitro human T-cell activation induced by crosslinking of the CD3-Ti complex with the monoclonal anti-CD3 antibodies OKT3 and UCHT-1. PGE2 (greater than or equal to 3 X 10(-9) M) when added simultaneously with anti-CD3 to cultures of peripheral blood mononuclear cells (PBMC), significantly suppressed, in a dose-dependent way, T-cell proliferation (P less than 0.002). However, when T cells were first preactivated with OKT3 for 3 days, subsequent proliferation driven by recombinant interleukin 2 (IL-2) was not inhibited by addition of PGE2. This indicates that PGE2 affects the activation step resulting from crosslinking of CD3-Ti, but not the IL-2-driven proliferative phase. Other manifestations of T-cell activation were therefore examined. Both IL-2 production and the expression of receptors for IL-2 (as detected with the anti-Tac monoclonal antibody) were inhibited by PGE2. The addition of purified interleukin 1 (IL-1) or recombinant IL-2 to the cultures did not reverse the inhibiting effect of PGE2 on IL-2-receptor expression. PGE2, added at the time of culture initiation, also inhibited T-cell proliferation in cultures which were supplemented with exogenous IL-1 or IL-2. Proof for a direct effect of PGE2 on T cells was obtained in experiments in which monocyte-depleted T cells were stimulated, in the presence of IL-1, with solid-phase-bound anti-CD3 antibody. Proliferation of T cells in this system is accessory cell independent and still was strongly inhibited by PGE2. Finally, preincubation of PBMC with PGE2 (3 X 10(-6) M) for 48 hr did not result in the generation of suppressor cells for anti-CD3-induced T-cell proliferation or for IL-2 production. Our results demonstrate that PGE2 has a direct inhibitory effect on an early step of T-cell activation, resulting in decreased IL-2 production, decreased IL-2-receptor expression, decreased responsiveness to exogenous IL-2, and decreased proliferation. However, PGE2 does not affect IL-2-driven proliferation of activated T cells. The inhibitory effect on T-cell activation is not mediated through suppressor T cells, nor through inhibition of accessory cell function.     

Molecular cloning of two CD7 (T-cell leukemia antigen) cDNAs by a COS cell expression system.

The human CD7 antigen (gp40) is a cell surface glycoprotein found on thymocytes and mature T-cells. It is one of the earliest antigens to appear on cells of the T-lymphocyte lineage, and the most reliable clinical marker of T-cell acute lymphocytic leukemia. This report describes the isolation and nucleotide sequence of a full length CD7 cDNA, and of a cDNA for an unusual intron-bearing precursor. The DNA sequence of the clone predicts a highly glycosylated membrane protein with homology to members of the immunoglobulin superfamily, and no relationship to known oncogenes. Over-expression of CD7 RNA was observed in only one T-cell tumor line, and genomic DNA rearrangement was not observed in any lines. Prompted by a recent suggestion that CD7 plays a role in IgM binding, COS cells expressing CD7 were tested and found not to bind IgM or IgM immune complexes.