The role of lymphoid organs in the immunopathogenesis of HIV infection.
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HIV Infections↗
Biomedical subjects
G Pantaleo
Publications and source records attributed to G Pantaleo.
Lymphoid organs function as major reservoirs for human immunodeficiency virus.
The total number of human immunodeficiency virus type 1 (HIV-1)-infected circulating CD4+ T lymphocytes is considered to be a reflection of the HIV burden at any given time during the course of HIV infection. However, the low frequency of HIV-infected circulating CD4+ T lymphocytes and the low level or absence of plasma viremia in the early stages of infection do not correlate with the progressive immune dysfunction characteristic of HIV infection. In this study, we have determined whether HIV-infected circulating CD4+ T lymphocytes are a correct reflection of the total pool of HIV-infected CD4+ T cells (i.e., HIV burden). To this end, HIV burden has been comparatively analyzed in peripheral blood and lymphoid tissues (lymph nodes, adenoids, and tonsils) from the same patients. The presence of HIV-1 DNA in mononuclear cells isolated simultaneously from peripheral blood and lymphoid tissues of the same patients was determined by polymerase chain reaction amplification. We found that the frequency of HIV-1-infected cells in unfractionated or sorted CD4+ cell populations isolated from lymphoid tissues was significantly higher (0.5-1 log10 unit) than the frequency in peripheral blood. Comparable results were obtained in five HIV seropositive patients in the early stages of disease and in one patient with AIDS. These results demonstrate that a heavy viral load does reside in the lymphoid organs, indicating that they may function as major reservoirs for HIV. In addition, the finding of a heavy viral load in the lymphoid organs of patients in the early stages of disease may explain the progressive depletion of CD4+ T lymphocytes and the immune dysfunction associated with the early stages of HIV infection.
Acquired Immunodeficiency Syndrome↗
Anti-CD2 receptor antibodies activate the HIV long terminal repeat in T lymphocytes.
The CD2 T lymphocyte glycoprotein surface molecule mediates both cell to cell adhesion and T cell activation, two processes that are involved in the spread of HIV infection. Treatment of chronically HIV-infected PBMC with anti-CD2 mAb has been shown to induce the expression of infectious virus from these cultures. In this study we investigated the mechanisms whereby anti-CD2 antibodies stimulate viral production. We demonstrate that treatment of transiently transfected T lymphocytes with anti-CD2 antibodies results in activation of the HIV long terminal repeat. Furthermore, CAT assays using mutated HIV long terminal repeat-CAT constructs and gel shift assays demonstrate that this activation is dependent on the NF-kappa B enhancer. These studies suggest that interaction of CD2 with its natural ligand, LFA-3, may play a role in regulation of HIV expression.
Antibodies, Monoclonal↗
NIH conference. Immunopathogenic mechanisms in human immunodeficiency virus (HIV) infection.
An understanding of the immunopathogenic mechanisms of infection with human immunodeficiency virus (HIV) is fundamental in developing successful approaches to designing effective therapeutic and vaccine strategies. In this regard, we have investigated the mechanisms by which HIV inserts itself into the human immune system and uses the elaborate cytokine network to its own replicative advantage. We have also shown that the burden of HIV in CD4+ T cells is directly associated with a decline in this cell population in vivo and a progression to disease. Mononuclear phagocytes may play a role in the pathogenesis of HIV infection by serving as reservoirs of the virus. Of note is the fact that monocytes in the peripheral blood of HIV-infected individuals are rarely infected in vivo, whereas infected-tissue macrophages may play a role in organ-specific HIV-related pathogenesis. The role of HIV-specific humoral and cell-mediated immunity in HIV infection is not well understood. However, fine specificity of responses against HIV have been delineated in some in-vitro systems. It is unclear why these responses, particularly HIV-specific cytolytic T-cell responses, diminish over the course of infection and are unable to contain progression of infection.
Acquired Immunodeficiency Syndrome↗
Infection of CD8+ T lymphocytes with HIV. Requirement for interaction with infected CD4+ cells and induction of infectious virus from chronically infected CD8+ cells.
In this study, we have investigated the basic requirements for HIV-1 infection of CD8+ lymphocytes in vitro. Unfractionated PBL obtained from healthy HIV-1 seronegative donors were activated with PHA and infected in vitro with HIV-1LAV. Based on immunofluorescent labeling, the vast majority of cells (85 to 97%) surviving peak virus replication belonged to the CD8+ subset and only a small percentage (0.5 to 1.5%) were CD4+. Amplification of HIV-1 proviral sequences by polymerase chain reaction performed on the sorted surviving CD8+ cells demonstrated that CD8+ cells harbored HIV-1 proviral DNA. In addition, stimulation of these HIV-1-infected, CD8(+)-sorted cells either with PHA or anti-CD2 mAb resulted in induction of virus replication, as measured by reverse transcriptase activity. Electron microscopic analysis of CD8+ cells chronically infected with HIV-1 and stimulated with PHA showed typical virions budding from, and associated with, the surface of cells immunolabeled with gold beads directed toward the CD8 molecule. Infection of CD8+ cells with HIV-1 occurred only when CD4+ cells were present in the PHA-activated lymphocyte population exposed to HIV-1 at the beginning of the culture or when sorted CD8+CD4- lymphocytes were cocultured with autologous sorted CD8-CD4+ cells that had been previously infected with HIV-1. Coculture of these cells with PHA-blasts and incubation of their supernatants with a CD4+ cell line showed that these chronically infected CD8+ cells could spread HIV-1 infection to uninfected CD4+ cells after stimulation with PHA or anti-CD2 mAb. Therefore, these results suggest that the minimal requirement for in vitro infection of CD3+CD8+CD4- lymphocytes is the presence of infected CD4+ cells and that infected CD8+ T lymphocytes can further spread the infection to CD4+ cells.
Antigens, CD↗
Human immunodeficiency virus (HIV) infection in CD4+ T lymphocytes genetically deficient in LFA-1: LFA-1 is required for HIV-mediated cell fusion but not for viral transmission.
In the present study, we demonstrated that expression of the LFA-1 molecule is necessary for cell fusion and syncytia formation in human immunodeficiency virus (HIV)-infected CD4+ T lymphocytes. In contrast, the lack of expression of LFA-1 does not influence significantly cell-to-cell transmission of HIV. In fact, LFA-1- T lymphocytes obtained from a leukocyte adhesion deficiency patient were unable to fuse and form syncytia when infected with HIV-1 or HIV-2, despite the fact that efficiency of HIV infection (i.e., virus entry, HIV spreading, and levels of virus replication) was comparable with that observed in LFA-1+ T lymphocytes. In addition, we provide evidence that LFA-1 by mediating cell fusion contributes to the depletion of HIV-infected CD4+ T lymphocytes in vitro.
Antibodies, Monoclonal↗
Dissociation between syncytia formation and HIV spreading. Suppression of syncytia formation does not necessarily reflect inhibition of HIV infection.
In this study, we have observed that a dissociation may occur in vitro between syncytia formation and HIV spreading. Efficient HIV spreading and virus replication occurred either in HIV-infected LFA-1+ lymphocytes treated with anti-LFA-1 mAb or in HIV-infected lymphocytes genetically deficient in LFA-1, despite the fact that syncytia formation was completely suppressed. Therefore, these results indicate that syncytia formation cannot be used as the sole parameter to evaluate the spread of HIV in vitro.
Antibodies, Monoclonal↗
A novel surface antigen expressed by a subset of human CD3- CD16+ natural killer cells. Role in cell activation and regulation of cytolytic function.
The GL183 mAb was obtained by immunizing BALB/c mice with the E57 clone (CD7+CD2+CD3-CD16+CD56+) derived from human peripheral blood NK cells. In human peripheral blood, GL183-reactive cells ranged between 2 and 12% (mean 6.5%) in 10 different donors. Double fluorescence and FACS analysis showed that GL183+ cells were consistently included in the CD56+ or CD16+ cell populations. Moreover, since only a fraction of CD56+ or CD16+ cells (approximately 40%) coexpressed GL183 surface antigen, reactivity with GL183 mAb appears to define two subsets within the CD3- lymphocyte population expressing NK cell markers. Although, the majority of GL183+ cells were CD3-, approximately 1% expressed CD3 surface antigens. As shown by clonal analysis, these infrequent CD3+GL183+ cells coexpressed CD56 and CD16 antigens. Cloning of CD3-GL183+ or CD3-GL183- cell populations under limiting dilution conditions yielded clonal progenies that maintained their original surface phenotype. Therefore, expression or lack of expression of GL183 surface antigens represents a stable phenotypic property of a subset of human CD3- NK cells. Immunoprecipitation experiments and two-dimensional PAGE analysis indicated that GL183-reactive molecules were represented in different clones either by a single 58-kD chain or, more frequently, by two chains of approximately 55 and approximately 58 kD, respectively. Analysis of GL183+ or GL183- NK clones for their ability to lyse human (IGROV I) or murine (P815) tumor target cells indicated that GL183- clones were, on average, fivefold more efficient in inducing target cell lysis. GL183+ and GL183- clones produced comparable levels of TNF-alpha in response to PHA plus PMA or anti-CD16 mAb plus PMA. Importantly, production of TNF-alpha was also induced by stimulation of GL183+ clones with GL183 mAb plus PMA. These data indicated that GL183 antigen could mediate cell triggering. This concept was confirmed by the analysis of Ca2+ mobilization, as GL183 mAb induced (in GL183+ clones) increments of [Ca2+]i comparable with those induced by PHA. Moreover, GL183 mAb, or its F(ab')2 fragments, strongly enhanced the cytolytic activity of GL183+ clones against a panel of human tumor target cells, including U937, Raji, IGROV I, M14, and A549. In contrast, GL183 mAb, but not the F(ab')2 fragments, sharply inhibited the cytolytic activity of the same clones against P815, M12, and P3U1 murine target cells. In this case, the effect of GL183 mAb (inhibition) was opposite that of PHA or of stimulatory anti-CD2 or anti-CD16 mAbs, which consistently enhanced the target cell lysis.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Defective clonogenic potential of CD8+ T lymphocytes in patients with AIDS. Expansion in vivo of a nonclonogenic CD3+CD8+DR+CD25- T cell population.
This study examines the potential mechanism(s) responsible for the defective clonability of CD8+ T lymphocytes in patients with AIDS. By the combined use of one- and two-color fluorescence cytofluorometry we have shown an increase in the number of circulating DR+ cells due to the expression of DR on a relatively large proportion of T lymphocytes (one-third of CD3+ cells), the majority of them belonging to the CD8+ subset. In addition, the majority of CD8+DR+ cells in AIDS patients did not express CD25 Ag (the receptor for IL-2), a surface marker generally expressed on normal activated T lymphocytes. Sorted CD8+DR+ and CD8+DR- cell populations were analyzed comparatively for their ability to proliferate in response to different stimuli, including anti-CD3, anti-CD2, alone or in combination with anti-CD28 mAb and mitogens such as PHA, alone or in combination with PMA. We have demonstrated that CD8+DR+ cells were severely defective in their proliferative response to triggering via these major pathways of T cell activation even when an exogenous source of IL-2 or IL-4 was added to the microcultures 24 h after initiating the cultures. In contrast, CD8+DR- cells showed a significant proliferation in response to the different stimuli and the proliferative response was strongly enhanced by the addition of IL-2 or IL-4. At the end of the stimulation period CD8+DR+ and CD8+DR- proliferating populations were analyzed for CD25 Ag expression. Only 1 to 10% of CD8+DR+ cells expressed CD25 antigen compared with 40 to 50% of CD8+DR- cells. The proliferative defect of CD8+DR+ cells was further confirmed in experiments performed at the clonal level. The analysis of the frequency of proliferating T lymphocyte-precursors in both CD8+DR+ and CD8+DR- subsets showed that the defective clonogenic potential of CD8+ cells in AIDS patients could be in large part ascribed to CD8+DR+ cells. Five percent of CD8+DR+ cells showed a clonogenic potential compared to the 25% of CD8+DR- cells. Finally, we analyzed the surface expression of VLA-2 Ag, a marker of a chronic state of T cell activation, on circulating T lymphocytes. We have shown that a large proportion of CD3+DR+CD25- cells (50 to 80% in the different patients with AIDS analyzed) expressed VLA-2 Ag.(ABSTRACT TRUNCATED AT 400 WORDS)
Acquired Immunodeficiency Syndrome↗
CD8+ T lymphocytes of patients with AIDS maintain normal broad cytolytic function despite the loss of human immunodeficiency virus-specific cytotoxicity.
In this study, we have investigated the potential mechanisms responsible for the loss of human immunodeficiency virus type 1 (HIV-1)-specific cytolytic activity in the advanced stages of HIV-1 infection. We have demonstrated that HIV-1-specific cytotoxic T lymphocytes are predominantly contained within the CD8+DR+ subset. Furthermore, we have shown by a redirected killing assay that there is a dichotomy between HIV-1-specific cytolytic activity and broad cytolytic potential since the cytolytic machinery of CD8+DR+ cells is still functioning even in patients with AIDS who have lost their HIV-1-specific cytolytic activity. In addition, by comparative analysis of these two types of cytolytic activity over time we have demonstrated a progressive loss of HIV-1-specific cytolytic activity in the advanced stages of the disease, whereas the cytolytic potential remained unchanged regardless of the clinical stage. As previously shown in patients with AIDS, even in asymptomatic HIV-1-seropositive patients, CD8+DR+ cells from the same patient, compared to CD8+DR- lymphocytes, showed a substantial reduction in their ability to proliferate in vitro in response to different stimuli, such as mitogens (phytohemagglutinin and phorbol 12-myristate 13-acetate) and monoclonal antibodies directed against CD3, CD2, and CD28 molecules, and displayed a defective clonogenic potential. Thus, on the basis of these results we propose that the loss of HIV-1-specific cytolytic activity in HIV-1-infected individuals may result at least in part from a progressive decrease in the pool of HIV-1-specific cytotoxic T lymphocytes belonging to the CD8+DR+ subset whose ability to expand has been impaired.
Acquired Immunodeficiency Syndrome↗
Comparison of phorbol-12-myristate-13-acetate and dioctanoyl-sn-glycerol in the activation of EL4/6.1 thymoma cells.
The present study compared the role of two protein kinase C (PK-C) activating agents, the phorbol ester phorbol-12-acetate-13-myristate (PMA) and the membrane-permeating diacylglycerol dioctanoyl-sn-glycerol (DiC8) in the activation of EL4/6.1 thymoma cells. These cells have been shown to express interleukin-2 receptors (IL-2R) upon stimulation with optimal amounts of PMA (10 ng/ml); also, suboptimal amounts of PMA (1 ng/ml) synergized with the Ca2+ ionophore ionomycin and recombinant interleukin-1 (rIL-1) (Lowenthal et al., 1986). Comparing PMA and DiC8 led to the following results: PMA at 10 ng/ml induced IL-2R; in contrast, DiC8 (30-3 micrograms/ml) alone was unable to induce IL-2R, although it did synergize with ionomycin (0.5 micrograms/ml) and rIL-1. Bihourly additions of DiC8 did not change this pattern. The addition of DiC8 together with rIL-2 also resulted in no IL-2R expression. Furthermore, DiC8 (10 micrograms/ml) effectively translocated PK-C. Therefore, the differences observed between PMA and DiC8 do not seem to be due to differences in metabolism or to an inability to translocate PK-C. Analysis of messenger (m) RNA produced in stimulated EL4/6.1 cells revealed that DiC8 was also unable to induce mRNA for IL-2R. Our data suggest that PMA, especially at "optimal" concentrations, might have effects that cannot be mimicked by diacylglycerol. Furthermore, it seems that the deficient activity of diacylglycerols can be compensated for by a Ca2+ ionophore and, depending on the cellular system, by further signals such as IL-1.
Animals↗
Stimulation of antibody response in the gastrointestinal mucosa of immunodeficient mice by oral treatment with bacterial antigens. An immunoperoxidase study.
The immunodeficient (nude) mice were chosen as a model to verify the in vivo stimulating activity of bacterial antigens on the humoral immune response. By using an immunoperoxidase technique, the Ig+ cell content in the gastro-intestinal mucosa of mice was evaluated after oral treatment with a mixture of bacterial antigen fractions (trade name Colopten). Treatment for 15 days was able to induce a significant increase in the proportions of Ig+ cells in both the jejunum and ileum. In contrast, the number of Ig+ cells was significantly increased after 30 days of treatment throughout the gastro-intestinal tract. Based on the staining intensity, a semiquantitative evaluation of the Ig content of the cells was made. Strongly stained Ig+ cells were localized into the gastro-intestinal mucosa during treatment and appeared to be the prominent lymphoid cell population in the small bowel after prolonged administration of Colopten. The morphological analysis of tissues showed that after treatment Ig+ cells tended to be collected within the mucosa rather than being isolated as in untreated animals. Therefore, these results demonstrate that oral administration of Colopten was able to elicit a local humoral immune response in an animal model for severe immunodeficiency.
Animals↗
Surface molecules involved in the activation and regulation of T or natural killer lymphocytes in humans.
The surface molecules that mediate activation of different subsets of T or NK cells have been reviewed. A suitable approach to the study of different lymphocyte activation pathways is provided by mAbs specific for these molecules. MAbs directed to the CD3 surface molecules mediate a polyclonal T-cell activation, whereas mAbs to "clonotypic" structures of TCR only trigger cells bearing the corresponding clonotypic determinant (thus mimicking the effect of antigen/MHC). MAbs directed to appropriate epitopes of CD2 molecules or to CD28 molecules mediate polyclonal T-cell activation, leading to triggering of the functional program of the cell (i.e. proliferation, lymphokine production or activation of the cytolytic machinery). Interaction of specific mAbs with CD3/TCR molecules leads to surface modulation of these molecules which lasts for 48-72 h. During this interval the cell is refractory to any further activation stimulus. No such refractoriness occurs following mAb-induced modulation of CD2 or CD28 surface molecules. The mechanisms by which CD3/TCR modulation results in the inactivation of T-cell function appears to involve the early metabolic steps of T-cell activation, as neither Ca++ mobilization nor IP3 formation could be further induced by any stimulus. The surface molecules and mechanisms involved in the activation of TCR gamma/delta cells are similar to those of TCR alpha/beta + cells. TCR gamma/delta molecules are heterogeneous in size and charge mobility. MAbs directed to one or another form of TCR gamma/delta trigger the functional program of the cell (primarily cytolytic function). However, a receptor form composed of a heavy form (55 kD) of the gamma chain appears to be relatively inefficient in signal transduction upon binding with anti-TCR mAbs. Evidence has also been provided that TCR gamma/delta + cells are capable of (allo)antigen responses and that polymorphic determinants of class I can be recognized (specific lysis of P815 cells transfected with HLA-A24 allele). Although the mechanisms and the surface receptor molecules involved in (CD3-, CD16+) NK cell activation are still poorly understood, several surface molecules have been identified that mediate NK-cell triggering. These include CD2 and CD16 and the novel GL183 molecule which is selectively expressed by a fraction of NK cells and thus identifies a well-defined NK subsets. Under appropriate conditions, mAbs to CD16 or GL183 mediate an inhibitory effect on the NK cell activation. These data suggest that also NK cells are characterized by surface molecules capable of initiating distinct pathways of cell activation and that, similarly to T lymphocytes, mechanisms exist which regulate NK cell function.
Antibodies, Monoclonal↗
A monoclonal antibody specific for a common determinant of the human T cell receptor gamma/delta directly activates CD3+WT31- lymphocytes to express their functional program(s).
In an attempt to select mAbs specific for human TCR-gamma/delta, a polyclonal CD3+ 4-8-WT31- (TCR-gamma/delta+) cell line (MV1) was used for mice immunization. An mAb, termed BB3, reacted with MV1 cells but not with a large panel of CD3+ WT31+ (TCR-alpha/beta+) cell populations or clones. In addition, BB3 mAb reacted with the majority of CD3+ WT31- clones derived from six different donors. Double-color fluorescence experiments and FACS analysis showed that BB3+ cells were restricted to the CD3+ fraction of peripheral blood lymphocytes; in addition, in several donors the percentages (0.5-8% of total PBL) of BB3+ cells paralleled those of CD3+ WT31- cells. Surface molecules recognized by BB3 were susceptible to antibody-induced modulation; in addition, cell treatment with either BB3 or anti-CD3 mAb caused the simultaneous downregulation of the two molecules. That BB3 molecules are physically linked to CD3 antigen was further supported by immunoprecipitation experiments. Thus, under conditions that preserve the TCR-CD3 association, both BB3 and anti-CD3 mAb precipitated from 125I-labeled MV1 cells the same set of molecules. These consisted in the 18-28-kD CD3 molecules and in three bands of approximately 44, 42, and 38 kD under reducing conditions. When cell lysis was performed in 1% NP-40, the molecules immunoprecipitated by BB3 mAb were represented by an 80-kD band under nonreducing conditions, which resolved, under reducing conditions, in the three 44-, 42-, and 38-kD bands. Similar disulphide-linked forms of the TCR molecules were revealed in all of the other eight CD3+ WT31- BB3+ clones analyzed. Analysis of TCR molecules by electrophoresis (NEPHGE) showed that BB3 or anti-CD3 precipitated a 44-kD molecule displaying a basic PI (approximately 7.5) and two more acidic proteins (PI approximately 6) with a mol mass of 42 and 38 kD. Studies aimed to define whether stimuli directly acting on TCR-gamma/delta could induce CD3+ WT31- cell activation revealed that (a) In the presence of PMA, soluble BB3 mAb induced IL-2 production by MV1 cell line and by three other CD3+ WT31- BB3+ clones analyzed. (b) BB3 mAb-producing hybridoma used as triggering target, was efficiently lysed by CD3+ WT31- BB3+ effector cells (but not by CD3+ WT31+ BB3- conventional CTL). (c) Soluble BB3 mAb induced CD3+ WT31- BB3+ effector cells to lyse the Fc receptor-positive P815 target cells. (d) BB3-TCR-gamma/delta interaction on CD3+ WT31- BB3+ cells induced a rapid increase of [Ca2+]i levels, similar to that observed in response to anti-CD3 mAbs.
Animals↗
Human cytolytic cell clones lacking surface expression of T cell receptor alpha/beta or gamma/delta. Evidence that surface structures other than CD3 or CD2 molecules are required for signal transduction.
We have analyzed the transmembrane signaling operating in human cytolytic lymphocytes lacking surface expression of the CD3/TCR complex. Peripheral blood lymphocytes were fractionated into CD3+ and CD3- on the FACS and cloned under limiting conditions in the presence of PHA and IL-2. Approximately 90% CD3+ and 10% CD3- cells underwent clonal expansion. Clones obtained from the CD3- fraction belonged to two main phenotypic groups: CD2+ CD7+ and CD2- CD7+. Several clones were expanded and analyzed for surface phenotype and function. All of the five clones selected for detailed analysis did not express CD4, CD8, and CD28 antigens and did not release IL-2, whereas they displayed cytolytic activity against NK-sensitive, NK-resistant, and fresh tumor target cells. After stimulation with anti-CD2 mAbs or PHA a rapid increase in [Ca2+]i was detected in CD3- CD2+ CD7+ clones. This increment was caused by the release of Ca2+ from intracellular stores and by the influx from the extracellular compartment. Signaling in response to PHA did not appear to be dependent upon surface expression of CD2 molecules since antibody-induced modulation of CD2 did not prevent PHA-induced signal transduction. Similarly, in CD3- CD2- CD7+ clones [Ca2+]i increments and inositol phosphate formation occurred after stimulation with PHA. These data indicate that the functional PHA-binding structures, expressed in both groups of CD3- clones, are distinct from CD3/TCR complex and CD2 molecules.
Antibodies, Monoclonal↗
Stimulation and proliferation of CD4+ peripheral blood T lymphocytes induced by an anti-CD4 monoclonal antibody.
There is experimental evidence that the CD4 molecule participates in the antigen-driven activation of T cells expressing this surface glycoprotein. Whether CD4, a member of the immunoglobulin supergene family, acts as a ligand-binding molecule and/or is directly involved in the activation pathway has yet to be established. In this study, we show that human CD4+ lymphocytes can be activated by exposure to the anti-CD4 monoclonal antibody (mAb) B66. Normal peripheral blood CD4+ cells were induced to proliferate and to synthesize interleukin 2 (IL 2) by the antibody. The specificity of the antibody stimulatory activity was tested by using IL 2-producing clones bearing either CD4 or CD8 on their surface. IL 2 production was induced by mAb B66 in CD4+, but not CD8+, clones, whereas both types of clones responded to stimulation by the anti-CD3 mAb Leu-4. Despite its unique stimulatory activity, mAb B66 shared with other anti-CD4 antibodies the ability to inhibit the specific cytolytic activity of CD4+ effector cells. These results clearly indicate that cross-linking of surface CD4 molecules with appropriate antibodies can fully activate CD4+ lymphocytes. Whether the natural ligand for CD4 can trigger this activation pathway remains to be defined.
Antibodies, Monoclonal↗
Group-specific, major histocompatibility complex class I-restricted cytotoxic responses to human immunodeficiency virus 1 (HIV-1) envelope proteins by cloned peripheral blood T cells from an HIV-1-infected individual.
Freshly separated unfractionated peripheral blood mononuclear cells (PBMC) and cloned cell lines from a healthy human immunodeficiency virus 1 (HIV-1)-seropositive individual were examined for cytotoxic responses to HIV proteins expressed by recombinant vaccinia viruses. It was found that freshly isolated PBMC recognize variant envelope proteins of HIV-1 but not a more distantly related envelope protein derived from the simian immunodeficiency virus (SIVmac). Although the effector cells were predominantly CD8+, both MHC-matched and -unmatched target cells were lysed. Cytotoxic T lymphocyte (CTL) clones were found to lyse cells expressing HIV-1 envelope or reverse transcriptase. In contrast to the cytotoxic response detected with PBMC, the cloned CTLs were major histocompatibility complex (MHC) class I restricted. Our finding that a cloned CTL line lysed cells expressing highly divergent HIV envelopes strongly suggested that a conserved epitope was recognized. Identification of these shared epitopes may assist in designing a vaccine for HIV-1 that could stimulate MHC-restricted cytotoxic responses.
Acquired Immunodeficiency Syndrome↗
Analysis of signal transducing mechanisms in CD3+ CD4- CD8- cells expressing the putative T cell receptor gamma gene product.
The signal transducing mechanisms, involved in the activation of CD3+ WT31- cells bearing the putative products of T cell receptor gamma genes, have been investigated. After stimulation with phytohemagglutinin or with monoclonal antibodies directed against CD2 or CD3 surface molecules, a rapid increase in free cytoplasmic Ca2+ concentration rise was detected in one representative CD3+ WT31- clone and in PEER cell line. Experiments performed in the presence of the Ca2+ chelator EGTA indicated that the free cytoplasmic Ca2+ concentration rise was consequent to an early release of Ca2+ from internal stores, followed by a sustained Ca2+ influx from the extracellular compartment. Moreover, increased levels of inositol-3-phosphate (the putative mobilizer of Ca2+ from the intracellular stores) were observed after stimulation, thus suggesting that activation of this cell subset occurs via the classical inositol-lipid metabolic pathway.
Antibodies, Monoclonal↗