Biomedical subjects

E G Engleman

Publications and source records attributed to E G Engleman.

At least 73 records · Page 4Linked to original sources

PubMed1991

Dehydroepiandrosterone enhances IL2 production and cytotoxic effector function of human T cells.

Dehydroepiandrosterone (DHEA) is the most abundant adrenal steroid hormone in humans. Although it is well established that DHEA serves as an intermediate in sex steroid synthesis, recent studies in mice suggest that DHEA may also be a physiologic regulator of IL2 secretion. To explore the effect of DHEA on the human immune system, T lymphocytes from healthy adults were exposed to DHEA followed by stimulation with mitogens or antigen. Upon activation with a variety of stimuli, T cells pretreated with 10(-8) to 10(-11) M DHEA produced significantly greater amounts of IL2 and mediated more potent cytotoxicity than T cells activated in the absence of this steroid hormone. The peak effect of DHEA was observed at 10(-9) M, the concentration of hormone present in the blood of normal adults. In contrast to its effect on murine T cells, the IL2 enhancing effect of DHEA on human lymphocytes was limited to fresh CD4+ T cells and CD4+ clones; neither fresh CD8+ cells nor CD8+ clones were directly affected by DHEA treatment, although CD8+ cells stimulated in the presence of CD4+ cells and DHEA demonstrated enhanced cytotoxicity. The enhancing effect of DHEA was also detected at the level of IL2 mRNA, suggesting that DHEA may act as a transcriptional enhancer of the IL2 gene in CD4+ T cells. These results corroborate and extend earlier studies in mice and suggest a physiologic role for DHEA in regulating the human immune response.

CD4 Antigens↗

PubMed1990

Natural killer lines and clones with apparent antigen specificity.

Fresh CD3-, CD16+ lymphocytes that adhered to selected allogeneic lymphoblastoid cell lines (LCL) were cultured with LCL in the presence of IL-2-containing medium. The resulting lines as well as clones derived from these lines expressed CD16 and/or CD56, but lacked detectable CD3 or TCR-alpha/beta or TCR-gamma/delta complexes on the cell surface. Northern blot analysis failed to detect CD3 epsilon or TCR-beta transcripts, but revealed the presence of a TCR-gamma chain transcript in one of these lines. In addition to displaying potent cytolytic activity against K562 erythroleukemia cells (a classical NK target), the vast majority of these lines and clones lysed their specific stimulator LCL to a significantly greater extent than irrelevant LCL. This selective killing was inhibited by the addition of cold stimulator LCL or K562 cells, or anti-LFA 1 mAbs, but not by irrelevant LCL or mAbs to CD3, class I or class II MHC antigens. These results indicate that some CD3- lymphocytes, phenotypically indistinguishable from NK cells, can recognize and lyse allogeneic targets in a specific manner.

Antibodies, Monoclonal↗

PubMed1990

Alloantigen-specific cytotoxic clones bearing the alpha,beta T cell antigen receptor but not CD4 or CD8 molecules.

The vast majority of circulating lymphocytes that express the alpha,beta TCR in association with CD3 also express either CD4 or CD8 molecules, which are thought to act as important accessory structures in HLA class II- and I-restricted T cell functions, respectively. In the current study alpha,beta TCR+ clones devoid of detectable CD4 or CD8 were generated by repeated stimulation of fresh CD3+,CD4-,CD8- cells with an allogeneic lymphoblastoid cell line in the presence of conditioned medium containing IL-2. Except for the absence of CD4 and CD8, which was associated with undetectable levels of CD4 and CD8 mRNA, the clones were phenotypically indistinguishable from classical CD3+,alpha,beta TCR+ cells. Furthermore, they mediated potent cytolysis of their specific stimulator line but did not kill irrelevant LCL or NK-sensitive targets. mAb to CD3 and the alpha,beta TCR inhibited cytolysis, suggesting that the clones use the TCR/CD3 complex to recognize and respond to their targets. mAbs to CD2 and CD11a also inhibited cytolysis, indicating that the clones use these accessory molecules to interact with their targets. Finally, cytolysis was inhibited by an HLA-A,B,C framework-specific mAb (W6/32) as well as a mAb (MA2.1) specific for an HLA-A2 epitope. These results demonstrate that CD3+,alpha,beta TCR+,CD4-,CD8- cytotoxic clones can be generated from the peripheral blood of healthy adults, and use their TCR/CD3 complexes to function in an HLA class I-restricted manner.

Antigens, CD↗

PubMed1990

Intracellular processing of the gp160 HIV-1 envelope precursor. Endoproteolytic cleavage occurs in a cis or medial compartment of the Golgi complex.

The intracellular processing of the gp160 HIV-1 envelope precursor was characterized in acutely infected CD4+ T cells. Our data show that gp160 undergoes endoproteolytic cleavage by a nonacid dependent protease(s) in the rough endoplasmic reticulum-Golgi complex, within cis or medial cisternae, and is not transported to the cell surface. Two-dimensional electrophoretic pulse-chase analysis indicates that it takes greater than 2 h for gp160 to be transported from the rough endoplasmic reticulum to the site of action of sialyltransferases in the trans Golgi. Evidence is presented that gp160 is subject to mannose trimming in the Golgi complex, which is inhibited by 1-deoxymannojirimycin (a specific Golgi alpha-mannosidase I inhibitor). Preliminary data also suggest that gp120 is post-translationally modified by sialylated O-linked oligosaccharides.

Cell Line↗

PubMed1990

Differences in surface phenotype and mechanism of action between alloantigen-specific CD8+ cytotoxic and suppressor T cell clones.

We have previously demonstrated that fresh CD8+ T cells proliferate in response to autologous, alloantigen-primed CD4+ T cells, and differentiate into Ts cells, which inhibit the response of fresh T cells to the primary allogeneic stimulator cell but not irrelevant stimulators. Although such Ts do not have discernible cytolytic activity, like classical cytotoxic T cells (Tc) they express CD3 and CD8 on their surface and function in a class I MHC-restricted manner. Our study was an attempt to compare the surface phenotype and mechanism of action of Ts and Tc clones derived from the same individual. Ts clones were generated from donor JK by repeated stimulation of CD8+ T cells with an autologous CD4+ T inducer line specific for an allogeneic lymphoblastoid cell line (LCL). These clones were noncytolytic for either the inducer line or the allogeneic stimulator LCL. Tc clones, generated by direct stimulation of JK CD8+ T cells with the same allogeneic LCL, mediated potent, alloantigen-specific cytolysis. All Tc clones were alpha, beta TCR+, CD3+, CD4-, CD8+, CD11b-, and CD28+. Ts clones were also alpha, beta TCR+, CD3+, and CD8+, but in contrast to Tc clones, Ts clones were CD11b+ and CD28-. When added to MLR both Ts and Tc clones inhibited the response of fresh JK CD4+ T cells to the original but not irrelevant allogeneic LCL. However, Ts inhibited the response of only those CD4+ T cells that shared class I)MHC determinants with the Ts donor, whereas Tc inhibited the response of CD4+ T cells from all responders, regardless of HLA type. Pretreatment of Ts clones with mAb to CD2, CD3, or CD8 blocked suppression, whereas similar pretreatment of Tc clones blocked cytotoxicity in 4-h 51Cr release assays but had no effect on Tc-mediated suppression of the MLR. These results suggest that both Ts and Tc clones can inhibit the MLR but they do so through different mechanisms. Moreover, the maintenance of distinct surface phenotypes on these long term clones suggests that Ts may be a distinct sublineage of CD8+ T cells rather than a variant of CD8+ Tc.

Antigen-Antibody Reactions↗

PubMed1990

Abnormal T suppressor cell function in juvenile rheumatoid arthritis.

The purpose of this study was to analyze T suppressor cell function in juvenile rheumatoid arthritis (JRA). JRA is a chronic inflammatory childhood disease of unknown etiology that is characterized by arthritis and immunoregulatory abnormalities. T suppressor cell precursors (CD8+, CD28-) were purified from the peripheral blood of 24 JRA patients, using a combination of monoclonal antibodies. These cells were treated with histamine or concanavalin A, agents that are known to induce suppressor activity. They were also tested for their ability to inhibit the proliferative response of autologous T cells to phytohemagglutinin. In some experiments, the accumulation of intracellular cAMP following histamine treatment was also measured. Twelve of 13 patients with clinically active JRA showed abnormal histamine-inducible T suppressor cell function, characterized by the failure of CD8+, CD28- T cells to mediate any detectable suppression. The failure of these cells to accumulate intracellular cAMP after histamine treatment was observed in 5 of 5 patients tested who had active disease. In contrast, 11 of 11 patients with clinically inactive JRA, 5 of 5 patients with cystic fibrosis, and 9 of 9 pediatric control subjects had normal histamine- and concanavalin A-inducible T suppressor cell function, and a normal cAMP response to histamine. These results suggest that patients with clinically active JRA have a reversible defect in T suppressor cell function that is associated with a failure of T suppressor cell precursors to accumulate intracellular cAMP following their exposure to selected immune stimuli.

Adolescent↗

PubMed1990

Impaired immunity in AIDS. The mechanisms responsible and their potential reversal by antiviral therapy.

The inability of CD4+ T cells of HIV-1-infected patients to mount an effective immune response is widely believed to explain the increased susceptibility of these patients to opportunistic infections. Although the full explanation for T-cell dysfunction in HIV-1 infection is not yet understood, at least two fundamentally distinct mechanisms are thought to contribute: depletion of CD4+ T cells and qualitative CD4+ T-cell dysfunction independent of T-cell depletion. Many HIV-1-infected patients manifest reduced T-cell responses to recall antigens prior to measurable CD4+ T-cell depletion, and among the proposed explanations for this phenomenon are gp120-mediated interference with T-cell activation by way of inhibition of CD4-class II major histocompatibility complex (MHC) determinant interactions, gp41-mediated inhibition of protein kinase C-dependent T-cell activation, formation of gp41 cross-reactive antibodies that react with MHC class II determinants, transforming growth factor-beta (TGF-beta)-mediated immunosuppression, and decreased functions of antigen-presenting and antigen-processing cells (macrophages and bone marrow-derived dendritic cells). Despite their detection in most HIV-1-infected patients, these qualitative T-cell defects do not herald the onset of life-threatening disease. The appearance of severe clinical manifestations of AIDS, particularly opportunistic infections, occurs primarily in patients whose CD4+ T-cell count is significantly reduced. Depletion of CD4+ T cells may be a direct consequence of HIV-1 infection that occurs as a result of syncytia formation, autoantibody-mediated cytolysis, gp120-specific antibody-dependent cytolysis, and/or gp120-specific T-cell mediated cytolysis. The thymus is severely affected in patients with late-stage disease, and although there is no proof that the failure of the thymus to regenerate new T cells contributes to T-cell depletion in patients with AIDS, the likelihood seems high that this is the case. Indeed, if prolonged suppression of HIV-1 replication can be achieved with newer anti-HIV drugs or combinations of drugs, reconstitution of a normal immune system seems likely, provided that the capacity to regenerate T cells has not been irrevocably lost as a consequence of viral infection. In summary, available evidence indicates that HIV-1 uses a complex array of mechanisms to disrupt T-cell mediated immunity, but because most of these involve a direct role for HIV-1 proteins, such mechanisms are likely to be reversible if suppression of HIV-1 replication can be achieved.

Acquired Immunodeficiency Syndrome↗

PubMed1990

Identification of an immunostimulating protein from Mycobacterium leprae.

Despite the recent identification of a number of Mycobacterium leprae proteins, the major immunogenic determinants of this organism remain obscure. We isolated from M. leprae a potent immunostimulatory preparation, designated the MLP fraction, which contains a major protein of 35 kilodaltons (kDa). This protein was precipitated by monoclonal antibody ML03-A1, which recognizes a 35-kDa protein of M. leprae, and by sera obtained from patients with lepromatous leprosy. Neither sera from healthy controls nor sera from patients with pulmonary tuberculosis recognized the 35-kDa protein, and only one of four serum samples from patients with borderline tuberculoid leprosy reacted with this protein. The MLP fraction stimulated T-cell proliferation in patients with leprosy whose T cells proliferate in response to whole M. leprae cells. Apparently, the T-cell epitope associated with MLP is also expressed on M. tuberculosis and M. bovis BCG, since patients with pulmonary tuberculosis and BCG-vaccinated individuals demonstrated significant responses to the MLP fraction. The 35-kDa M. leprae protein, purified to homogeneity in the laboratory of P. J. Brennan, stimulated T-cell proliferative responses in all MLP-responsive subjects. These findings suggest that the 35-kDa protein present in MLP is an immunostimulatory component of M. leprae. In addition to serving as a useful probe for study of the T-cell anergy associated with lepromatous disease, this protein may ultimately be useful as a component of a vaccine designed to provide protection against infection with M. leprae.

Adjuvants, Immunologic↗

PubMed1990

Effective vaccination of mice against leprosy bacilli with subunits of Mycobacterium leprae.

Model vaccines against leprosy bacilli have consisted of nonvirulent, live, attenuated Mycobacterium bovis BCG and irradiated, heat-killed, or autoclaved intact M. leprae. We report that immunization with various cell wall fractions of M. leprae, progressively depleted of lipids, carbohydrates, and soluble proteins, as well as a partially purified protein(s) derived from a pellet fraction of sonicated M. leprae, conferred significant protection against subsequent infection with live leprosy bacilli. Moreover, lymphocytes from regional lymph nodes and spleens of mice immunized with these M. leprae-derived subunits responded by proliferation when stimulated with M. leprae in vitro. Our results provide the first evidence that vaccination with M. leprae-derived fractions protects mice against leprosy bacilli.

Animals↗

PubMed1990

Anti-DNA antibody production by CD5+ and CD5- B cells of patients with systemic lupus erythematosus.

Although the presence of anti-DNA antibody is a hallmark of systemic lupus erythematosus (SLE), neither the subsets of B cells that secrete anti-DNA antibody nor the stimuli responsible for the induction of anti-DNA secretion is known. In particular, the role of CD5+ B cells in human SLE, a distinct subpopulation of antibody-secreting cells shown previously to be a source of anti-DNA antibody in murine models of SLE, is unknown. To approach these questions, we developed a sensitive enzyme-linked immunospot (ELIspot) assay to measure spontaneous secretion of antibody to single-stranded (ss) DNA, double-stranded (ds) DNA, tetanus toxoid, and polyclonal immunoglobulin (Ig) by purified CD5+ and CD5- B cells of 15 SLE patients and 15 healthy control subjects. The B cells of only 1 of 15 healthy subjects secreted a significant level of anti-ssDNA antibody, and none secreted anti-dsDNA. By contrast, in the majority of SLE patients both CD5+ and CD5- B cells secreted IgG and/or IgM anti-ssDNA as well as anti-dsDNA antibody. Further analysis of the anti-ssDNA response revealed that the level of IgG and IgM anti-DNA antibody secretion by CD5- B cells correlated closely with the level of polyclonal Ig production by the same subpopulation (r = 0.81 and 0.70, respectively). In contrast, production of anti-DNA by CD5+ B cells occurred independently of polyclonal Ig production by both CD5+ and CD5- B cell subpopulations. These results suggest that in human SLE there exist two anti-DNA antibody-producing B cell subpopulations with distinct induction mechanisms: one (CD5+), which independently secretes anti-DNA, and another (CD5-), which produces anti-DNA as an apparent consequence of polyclonal B cell activation.

Adult↗

PubMed1990

Granulocyte-macrophage colony-stimulating factor promotes differentiation and survival of human peripheral blood dendritic cells in vitro.

Interest in human dendritic cells (DC) has been heightened recently by the discovery that this cell type is a primary target of the human immunodeficiency virus, the causative agent of AIDS. DC are bone marrow-derived cells with an extraordinarily potent ability to promote the immunological activity of T lymphocytes. Unfortunately, since DC constitute less than 0.5% of peripheral blood mononuclear cells and die within a few days of their isolation, they are not readily accessible to study. We report here that granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine with well-recognized effects on granulocyte and macrophage maturation, profoundly affects the morphology and viability of DC isolated from peripheral blood. GM-CSF not only promotes DC survival but also induces DC differentiation to mobile, reversibly adherent cells with long-branched projections. DC cultured in GM-CSF survive for up to 6 wk and retain their ability to stimulate the proliferation of T cells in allogeneic and autologous mixed leukocyte reactions.

Cell Differentiation↗

PubMed1989

Heterogeneous distribution and transmembrane signaling properties of lymphocyte function-associated antigen (LFA-1) in human lymphocyte subsets.

The role of LFA-1, a member of the integrin supergene family, in intercellular adhesion, including lymphocyte-endothelial cell (EC) binding, has been established. We now demonstrate that differences in LFA-1 cell surface density are responsible for the variable adhesion efficiency of lymphocyte subsets to EC. Electrophoretic analysis revealed multiple glycosylated isoforms of both alpha and beta subunits, largely as a result of different degrees of sialylation, with variable expression among different lymphocyte subsets. Neuraminidase digestion before EC adhesion increased the binding efficiency of all lymphocyte subsets, although the relative increase in each subset was proportional to the initial LFA-1 sialic acid content. LFA-1 cross-linking resulted in phosphoinositide hydrolysis and a rise in [Ca2+]i when using anti-alpha but not anti-beta subunit antibodies. These findings indicate that the density of LFA-1 on lymphocyte subsets controls their adhesive properties, and that the LFA-1 alpha subunit has transmembrane signaling properties that may result in activation events after interaction with its natural ligands.

Adult↗

PubMed1989

Natural killer (NK)-like cytotoxic activity of allospecific T cell receptor-gamma,delta+ T cell clones. Distinct receptor-ligand interactions mediate NK-like and allospecific cytotoxicity.

We recently generated a series of human alloantigen-specific, CD3+,TCR-gamma,delta+ clones by stimulating CD3+,CD4-,CD8- T cells from normal individuals with allogeneic lymphoblastoid cell lines (LCL). As reported previously, these clones display cytotoxic activity against their specific stimulators but not against irrelevant LCL. Further studies of these and other TCR-gamma,delta+ clones, described in this report, indicate that most but not all of these clones express the NK cell associated marker, NKH-1 or Leu-19, and kill NK-sensitive targets such as the K562 and Molt 4 lines, but not an irrelevant LCL or NK-resistant line, Raji. TCR-gamma,delta+ clones which lacked expression of Leu-19 lysed their allospecific targets but had no detectable NK activity. The allospecific cytotoxicity of Leu-19+ and Leu-19- clones was inhibited by mAb to CD3 or the TCR delta-chain. In contrast, the NK-like activity of the Leu-19+ clones was enhanced by these antibodies over a wide range of antibody concentration. Although mAb to LFA-1 markedly inhibited both the allospecific and NK-like activity of these clones, an HLA class I framework specific mAb (W6/32) had no effect on NK-like cytolysis but did inhibit allospecific killing, suggesting that the target structures on the surface of allospecific and NK-sensitive cells are distinct. The receptors utilized by the TCR-gamma,delta+ clones to recognize NK-sensitive and allospecific targets are also distinct, since killing of NK-sensitive targets was blocked by the presence of cold (unlabeled) NK-sensitive cells but not by cold allospecific targets, whereas allospecific cytolysis was inhibited by cold allospecific targets but not by NK-sensitive cells. We conclude that some CD3+,TCR-gamma,delta+ clones exhibit NK-like as well as allospecific killing and that these two activities are mediated by distinct receptor-ligand interactions.

Adult↗

PubMed1989

Identification of protein intermediates in the processing of the p55 HIV-1 gag precursor in cells infected with recombinant vaccinia virus.

We have used a recombinant vaccinia virus (VV) which expresses high levels of human immunodeficiency virus-1 (HIV-1) gag proteins to analyze the processing pathway of the gag p55 precursor. HIV-1 gag proteins were isolated from [3H]leucine-labeled VV:gag-infected H9 T lymphocytes by immunoprecipitation with either anti-p24, anti-p17, or anti-p6 antibodies. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that processing of the p55 precursor involves three major intermediates (p41a, p41b, and p39). The p41a and p39 proteins contain the p17 and p24 protein segments, and the p41b is comprised of p24 and p15 segments. On two-dimensional gels, each intermediate as well as the mature p24 and p17 proteins migrated as distinct species. [3H]Myristic acid labeling of the HIV-1 gag proteins revealed that in addition to p55 and p17, the p41a and p39 intermediates, but not p41b, are myristylated, confirming that myristylation occurs at the NH2 terminus before cleavage of the p55 precursor protein. We conclude that the myristylated HIV-1 gag p55 precursor is initially cleaved at random either at the p17/p24 junction or at two sites between p24 and p15 proteins, resulting in three intermediates (p41a, p41b, and p39) which are subsequently cleaved to yield mature gag proteins.

Antigens, Viral↗

PubMed1989

Differences in surface phenotype between cytolytic and non-cytolytic CD4+ T cells. MHC class II-specific cytotoxic T lymphocytes lack Leu 8 antigen and express CD2 in high density.

A number of cell surface molecules are differentially expressed on functionally distinct subsets of CD4+ T cells. However, to date CD4+ T cells capable of becoming CTL have not been shown to be phenotypically distinct from other CD4+ T cells, and in the current study we examined the ability of Leu 8+ and Leu 8- CD4+ subpopulations to become cytotoxic effectors after their stimulation with allogeneic lymphoblastoid cell lines. Although CD4+, Leu 8+ cells proliferated more vigorously than CD4+, Leu 8- cells in primary cultures stimulated with allogeneic LCL, the CD4+, Leu 8- population was the major source of cytotoxic effectors, killing targets with specificity for their class II MHC alloantigens. In most subjects, CD4+ precursors of CTL were distinguished not only by their lack of Leu 8 expression but also by their relatively high density of CD2, LFA-1, and LFA-3, molecules known to mediate non-specific cell-to-cell adhesion and postulated to be markers of immunologic memory. The absence of Leu 8 does not appear to be a reliable memory cell marker, however, because Leu 8+ as well as Leu 8-, CD4+ cells from PPD skin test positive subjects responded to the recall Ag, PPD. During 3 mo of continuous culture with allogeneic stimulators, Leu 8- cells retained their cytolytic activity and remained unreactive with anti-Leu 8 mAb, whereas Leu 8+ cells remained non-cytolytic and reactive with anti-Leu 8, suggesting that under the conditions used the Leu 8 phenotype is relatively stable. PHA or anti-CD3 mAb enhanced non-specific killing by alloantigen-stimulated CD4+,Leu 8- lines but failed to unmask any cytolytic potential in CD4+,Leu 8+ lines. We conclude that MHC class II-specific cytolytic CD4+ T cells can be distinguished from non-cytolytic CD4+ cells on the basis of their surface phenotype, and that most CD4+ CTL are contained within the Leu 8- subpopulation.

Animals↗

PubMed1989

Evidence for involvement of the gamma, delta T cell antigen receptor in cytotoxicity mediated by human alloantigen-specific T cell clones.

The vast majority of mature T cells express the alpha, beta TCR and use this receptor to recognize Ag in association with MHC determinants. Recent reports indicate that a small subpopulation of CD3+ T cells does not express alpha, beta TCR and lacks CD4 and CD8 molecules, but expresses another TCR heterodimer designated gamma, delta. To date, however, there are very few examples of gamma, delta TCR-bearing T cells which have Ag-specific functions and the precise role of the gamma, delta TCR remains unknown. In an attempt to explore the function of the gamma, delta TCR in man, we generated a panel of CD3+, CD4-, CD8- T cell clones from cultures of normal T cells stimulated with allogeneic lymphoblastoid cell line (LCL). All of the clones stained with mAb to gamma, delta TCR determinants, and Northern blot analysis of total cellular RNA revealed mature gamma- and delta-chain transcripts and immature beta-chain transcript. The clones displayed cytolytic activity against their specific stimulating LCL, but not irrelevant LCL, and killing was inhibited by a mAb to HLA class I (HLA-A,B,C) determinants, suggesting that these cells recognized class I MHC antigenic determinants on specific stimulator/target cells. Cytolysis by these clones was markedly inhibited by low concentrations (0.00001 to 0.001 microgram/ml) of mAb to CD3 or TCR delta-chain, but high concentrations (0.1 to 20 micrograms/ml) of the same antibodies enhanced cytotoxicity. When absorbed to plastic tissue culture wells, anti-CD3 mAb stimulated the clones to proliferate. These results indicate that alloantigen specific, gamma, delta TCR+, CD4-, CD8- T cell clones can be reproducibly generated in vitro, and that the gamma, delta TCR plays a direct role in the specific recognition and cytolysis displayed by these clones.

Adult↗

PubMed1989

Evidence that T cell activation is required for HIV-1 entry in CD4+ lymphocytes.

The relationship of T cell activation to HIV entry and generation of viral DNA intermediates was studied in freshly isolated CD4+ T lymphocytes. Unstimulated cells exposed to infectious virus for up to 48 h did not synthesize any detectable unintegrated HIV DNA duplex forms or integrated genomic provirus. However, activation of these cells with either PHA or OKT3 (anti-CD3) mAb before viral exposure resulted in the generation of unintegrated HIV DNA after 6 h and integrated copies after 24 h. Cell-to-cell fusion studies showed significantly attenuated fusion between freshly isolated resting T cells and T cells constitutively expressing high levels of HIV envelope glycoprotein (HXB/gpt) compared with T cells first stimulated with either PHA or OKT3 mAb. The baseline fusion observed with resting T cells is believed to be a consequence of allogeneic stimulation by the HXB/gpt cell line. These results provide evidence that HIV entry and HIV envelope-dependent cell-to-cell fusion require T cell activation.

Antigens, Differentiation, T-Lymphocyte↗

PubMed1989

Antigen-specific suppressor T lymphocytes in man.

The cellular signals that lead to activation of suppressor T cells (Ts) as opposed to cytotoxic T cells (CTL) are unknown. This review describes an in vitro suppressor-induction system developed by us to characterize interactions among various T cells leading to the development of antigen-specific suppression. In this system, antigen-specific CD4+ inducer T cells are first activated with antigen-presenting cells (APC). Antigen-primed CD4+ inducer blasts are then cultured with fresh autologous CD8+ T cells in the absence of the priming antigen. CD8+ T cells isolated from this culture suppress the proliferative response of autologous CD4+ T cells to the priming antigen only. The activated CD8+ Ts lyse neither APC nor antigen-primed CD4+ inducer T cells and can be distinguished from their CD8+CD28+ CTL counterpart by their lack of expression of the CD28 molecule. Furthermore, the ability to induce CD8+ Ts is restricted to antigen-primed CD4+CD29+CD45R-p80+ (Leu8+) T cells. Antibody-mediated inhibition experiments suggest the involvement of CD3/TCR and class I MHC molecules on the surface of CD4+ inducer T cells and the CD2, CD3/TCR, CD8, and CD11a/CD18 molecules on the surface of CD8+ Ts during both the induction and the effector phase of Ts function. Furthermore, compatibility at the class I MHC genes between CD8+ Ts and CD4+ antigen-reactive T cells is required for effective suppression of CD4+ T cells. Together, these results suggest that human antigen-specific CD8+ Ts employ the TCR complex to recognize TCR and class I MHC molecules on the surface of autologous CD4+ inducer T cells during the induction and effector phases of Ts function, and the apparent antigen specificity of suppression reflects specificity for antigen receptors on CD4+ antigen-reactive T cells. This may be a common mechanism by which antigen-specific suppression is accomplished.

Antigens↗