Serum and effector-cell antibody-dependent cellular cytotoxicity (ADCC) activity remains high during human immunodeficiency virus (HIV) disease progression

The activity of both serum and effector cell antibody-dependent cellular cytotoxicity (ADCC) against human immunodeficiency virus (HIV-1, HIV) was assessed in HIV-infected individuals. The goal was to relate ADCC levels with the stage or progression of HIV disease. Serial serum samples, usually collected at 6-month intervals, from individuals at defined stages of HIV disease (sero-conversion, the HIV-seropositive period before AIDS, and around the time of clinical AIDS diagnosis) were tested. HIV-coated CEM tumor cells were used as targets. Effector-cell ADCC activity was evaluated using fresh peripheral blood mononuclear cells (PBMC) from HIV-infected individuals at different stages of HIV disease. Samples were obtained from male homosexual participants in the Multicenter AIDS Cohort Study (MACS). In seroconverters, ADCC-inducing HIV-specific antibodies were detected at the time that the ELISA antibody test was first positive. Within several months, serum ADCC activity stabilized in each individual. In 29 HIV-seroprevalent individuals (HIV seropositive on their first visit), serum ADCC activity remained constant regardless of whether the individual's HIV disease was stable (high stable CD4;n=9) or rapidly deteriorating (sharply declining CD4,n=10; AIDS progressors,n=10). With respect to effector-cell activity, PBMC from HIV-infected individuals with or without AIDS were capable of mediating ADCC with heterologous and usually with autologous sera. Although the level of NK cytotoxic activity and the level of antibody-armed effector cell activity have been reported to decline as disease progresses, our results support previous observations that ADCC effector-cell activity against antibody-coated targets does not decline in HIV infection. These results indicate that both serum and effector cells with ADCC activity are present in HIV-infected individuals shortly after seroconversion and are maintained throughout HIV disease. Although levels of serum and effector-cell ADCC activity do not predict whether an individual will develop AIDS, CD4 cells which express HIV antigens (either produced endogenously or adsorbed onto the surface) could serve as targets for anti-HIV-mediated ADCCin vivo. ADCC could, thereby, contribute to CD4 T-cell depletion in infected individuals. However, since serum and effector-cell ADCC levels do not seem to relate to disease stage or progression, the protective or pathogenic role that ADCC plays in HIV-disease remains unresolved.     

Deficient Antibody-Dependent Cellular Cytotoxicity against Human Immunodeficiency Virus (HIV)-Expressing Target Cells in Perinatal HIV Infection

Peripheral blood mononuclear cells (PBMC) of human immunodeficiency virus (HIV)-infected children, age-matched HIV-seronegative controls, and HIV-infected asymptomatic and symptomatic adults were compared for their ability to mediate antibody-dependent cellular cytotoxicity (ADCC) and natural killer (NK) cell-mediated cytotoxicity against target cells expressing HIV or herpes simplex virus (HSV) antigens. Target cells consisted of CD4 lymphocytes purified from PBMC of HIV-seronegative adults and incubated with the IIIB strain of HIV, HUT78 cells chronically infected with IIIB, and HSV-infected human fibroblasts. PBMC of asymptomatic HIV-infected adults were generally able to lyse CD4 cells expressing HIV antigens. Direct correlation was found between the magnitude of lysis and absolute CD4 cell counts in these individuals. In contrast to these results, PBMC from HIV-infected children were generally unable to lyse IIIB-expressing CD4 cells, regardless of the children’s clinical status, age, or absolute CD4 cell counts. Cells from HIV-seronegative adults and children did not directly lyse these target cells either but, in contrast to cells of HIV-seropositive children, were able to mediate cell lysis when serum from an HIV-seropositive adult was added. However, effector cells from these HIV-infected children were able to mediate both ADCC against HSV-infected fibroblasts and NK cell-mediated cytotoxicity against IIIB-infected HUT78 cells. Reduced ability of PBMC from vertically HIV-infected children to mediate ADCC against HIV antigen-expressing CD4 cells may contribute to rapid progression to AIDS.     

Peripheral blood monocytes derived from HIV+ individuals mediate antibody-dependent cellular cytotoxicity (ADCC)

Monocytes/macrophages serve a number of immunologic functions and play a major role in the host defense against infection. Abnormal functions of monocytes have been reported in AIDS and HIV+ individuals. A recent report from our laboratory demonstrated that peripheral blood monocytes (PBM) derived from AIDS patients were de novo "activated" as assessed by direct cell-mediated cytotoxicity (CMC) and secretion of cytotoxic factors and tumor necrosis factor-alpha (TNF alpha). Thus, both the direct cytotoxicity as well as the antibody-dependent cellular cytotoxicity (ADCC) exerted by the monocytes may contribute to the destruction of HIV-infected/coated cells and the immunopathogenesis of AIDS. The present study investigated the ability of HIV+ PBM to mediate ADCC against antibody-coated target cells in an 18-hr 51Cr release assay. Initial studies examined ADCC using a macrophage resistant target Raji and rabbit anti-Raji serum. The results show that the majority of PBM from HIV+ individuals mediate ADCC activity while the majority of PBM from normal healthy controls was not cytotoxic. While activation of PBM with recombinant interferon-gamma (rIFN-gamma) enhances the ADCC activity of normal PBM, treatment of HIV+ PBM with IFN-gamma resulted in significant enhancement of ADCC. Both untreated and treated PBM from HIV+ individuals had significantly higher ADCC than PBM from normal individuals. Of interest, a significant ADCC activity was found by PBM derived from two HIV- high risk individuals whether untreated or treated with rIFN-gamma. The ADCC results with RAJI target cells prompted us to investigate whether ADCC can also be obtained using HIV-infected T4+ cells. We selected a macrophage and TNF resistant T4+ CEM cell line as target for ADCC. The target was coated with inactivated HIV and pooled human anti-HIV serum was used. Studies with a few HIV+ individuals demonstrate that significant ADCC is obtained with PBM from HIV+ individuals but little or no ADCC by normal PBM and the ADCC was specific for HIV. The ADCC was also significantly enhanced by treatment of PBM with rIFN-gamma. The results of this study clearly indicate that PBM from HIV+ individuals are endowed with the capacity to mediate ADCC against HIV-infected/coated cells and thus, we postulate that PBM may play a direct role in vivo in lysis or suppression of HIV-coated/infected cells and in the pathogenesis of AIDS.     

Functional discrepancies in HIV-specific CD8+ T-lymphocyte populations are related to plasma virus load

The potent ability of current antiretroviral drug regimens to control human immunodeficiency Virus-1 (HIV-1) replication, in conjunction with the clinical practice of structured therapeutic interruptions, provides a system in which virus levels are manipulated during a persistent infection in humans. Here, we exploit this system to examine the impact of variable plasma virus load (pVL) on the functionality of HIV-specific CD8⁺ T-lymphocyte populations. Using both ELISpot methodology and intracellular cytokine staining for interferon (IFN)- to assess functional status, together with fluorochrome-labeled peptide–major histocompatibility complex (pMHC) class I tetramer analysis to detect the physical presence of CD8⁺ T lymphocytes expressing cognate T-cell receptors (TCRs), we observed that the proportion of HIV-specific CD8⁺ T lymphocytes capable of mounting an effector response to antigen challenge directly ex vivo is related to the kinetics of virus exposure. Specifically, (a) after prolonged suppression of pVL with antiretroviral therapy (ART), physical and functional measures of HIV-specific CD8⁺ T-lymphocyte frequencies approximated; and (b) the percentage of functionally responsive cells in the HIV-specific CD8⁺ T lymphocyte populations declined substantially when therapy was discontinued and pVL recrudesced in the same patients. These results corroborate and extend observations in animal models that describe nonresponsive CD8⁺ T lymphocytes in the presence of high levels of antigen load and have implications for the interpretation of quantitative data generated by methods that rely on functional readouts.for the Swiss HIV Cohort Study     

B cell activation and human immunodeficiency virus infection. V. Phenotypic and functional alterations in CD5+ and CD5− B cell subsets

B cell dysregulation is a hallmark of human immunodeficiency virus infection. Since B lymphocytes comprise two distinct subpopulations, CD5⁺ and CD5^– cells, we addressed their individual phenotypic and functional behavior. Seropositive patients with both limited and advanced disease progression had an increased percentage of peripheral blood CD5⁺ B cells, compared to seronegative controls (20.1±2.1 and 22.7±5.7, respectively, vs 17.0±3.4 in controls); however, due to the lymphopenia and reduced number of circulating B cells in infected individuals, the absolute number of CD19⁺ CD5⁺ lymphocytes was actually reduced. Although HIV-specific antibodies were synthesized spontaneouslyin vitro only by CD5^– B cells, a 10-fold lower degree of spontaneous, non-HIV-specific activation was also displayed by unstimulated CD5⁺ B cells. These findings indicate that B cell dysregulation during HIV infection involves both the CD5^– and the CD5⁺ B cell compartments; moreover, in view of the putative role of CD5⁺ B cells in autoimmune phenomena and IL-10 production, these data reinforce the possibility that B cell dysfunction might be causally involved in AIDS pathogenesis.     

Antibody-dependent cellular cytotoxicity (ADCC) is directed against immunodominant epitopes of the envelope proteins of human immunodeficiency virus 1 (HIV-1).

In this study, epitopes of HIV envelope proteins that are involved in ADCC were identified. Peripheral blood mononuclear cells (PBMC) were obtained from adults with asymptomatic HIV infection or early symptoms of AIDS. These PBMC, which were reported to be "armed" in vivo with HIV-specific antibodies, were used as effector cells in 51Cr release assays. Target cells consisted of CD4 lymphocytes from healthy seronegative donors, coated with the IIIB strain of HIV-1 or with one of seven synthetic peptides. Cytotoxicity was detected against CD4 lymphocytes coated with HIV-1 IIIB or with the peptides env aa 507-518, corresponding to the carboxy-terminus of gp120, and env aa 597-611, corresponding to the region of the cysteine loop of gp41. The magnitude of target cell lysis was directly related to the quantity of peptide used. In contrast, target cells coated with the peptide gag aa 129-135, corresponding to the p17/p24 cleavage region of the gag precursor, were not killed. The same immunodominant regions which were involved in ADCC were recognized in enzyme-linked immunoabsorbent assays (ELISA) by the majority of 107 sera from HIV-infected adults. We conclude that the immunodominant epitopes located at the carboxy-terminus of gp120 and the cysteine loop of gp41 serve as recognition structure for antibodies, capable of mediating ADCC against HIV-infected cells.     

Lysis of CD4+ lymphocytes by non-HLA-restricted cytotoxic T lymphoe from HIV-infected individuals

Individuals infected with HIV have elevated numbers of total and activated CD8⁺ lymphocytes in peripheral blood. CD8⁺ lymphocytes from HIV-infected individuals have been shown to mediate non-human histocompatibility-linked antigen (HLA)-restricted suppression of viral replication, HLA-restricted killing of cells expressing HIV antigens, and killing of uninfected lymphocytes. We studied CD8⁽ T lymphocytes that lysed autologous CD4+ lymphocytes, hetcrologous CD4¹ lymphocytes from HIV-infected individuals and uninfected CD4⁺ lymphocytes. Killing in all cases required T cell receptor (TCR)-mediated recognition or triggering. However, these CD8 cytotoxic T lymphocytes (CTL) killed HLA class I mismatched CD4* lymphocytes and CD4⁴ lymphocytes treated with a MoAb against HLA-A, B and C antigens (PA2.6) which blocks HLA class I-restricted killing. HLA class H-negativc CD4* T lymphoma cells (CEM.NK^R) were also killed by anti-CD3 inhibited CTL. Stimulation of peripheral blood lymphocytes (PBL) from HIV-infected individuals, but not uninfected controls, with concanavalin A (Con A) and IL-2, induced non-HLA-restricted TCR aft¹, CD8^f CTL which lysed CD4⁺ lymphocytes. Activation ofCD4’lymphocytes increased their susceptibility to CD8^f CTL-mediated lysis. In HIV infection, a population of non-HLA-restricted CTL which lyse activated CD4⁺ lymphocytes is expanded. The expansion of CTL with unusual characteristics is interesting, because the stimulus for this expansion is unknown. CTL which recognize activated CD4⁺ cells could play a role in immune regulation and the pathogenesis of A IDS.     

Differential isotype expression and binding properties of T cell-reactive antibodies in human immunodeficiency virus (HIV) infection

Isotype and binding characteristics of T cell-reactive antilymphocyte antibodies (ALA) were investigated in 287 human immunodeficiency virus (HIV)⁺ sera from patients with CDC II to IVC clinical disease. Using purified soluble T-lymphoblast (CEM cell line) membranes and an ELISA method, 29 HIV⁺ sera showed significant reactions with this substrate and a selective expression of IgG-ALA was detected in 7 HIV⁺ sera. Subsequent microcytotoxicity assays, utilizing peripheral T lymphocytes and CEM cells as targets, demonstrated no significant cytotoxic capability in such sera, whereas 12 of 17 HIV⁺ serum samples with IgM-ALA ELISA reactivities showed a significant degree of killing in the Terasaki test. Further experiments of saturation of CD4 molecules on CEM extract by OKT4 monoclonal antibody (MoAb) induced a high inhibition of IgG-ALA binding to the T-cell membranes in only two IgG-ALA⁺ sera (No. 93, CDC III; No. 179, CDC II stage). Conversely, treatment of CEM membrane lysate with Leu3a MoAb, specific for the gp120 reactive domain of the HIV receptor, failed to prevent membrane binding in all seven of the IgG-ALA⁺ sera. Following the adsorption of serum 93 on a T-cell membrane antigen affinity column, SDS-PAGE analysis demonstrated that the predominant ALA material reacting with T-cell membranes was IgG with no detectable traces of IgM. These data provide evidence that ALA in HIV⁺ patients may be simultaneously or selectively expressed as IgG and/or IgM with different properties. While IgM-ALA show predominant cytotoxic activity, IgG-ALA may include anti-CD4 molecules. However, IgG binding to the C-terminal domain of native HIV receptor appears to occur at a lower rate than IgM-ALA in HIV infection.     

Histone deacetylase inhibitor chidamide promotes reactivation of latent human immunodeficiency virus by introducing histone acetylation

Highly active antiretroviral therapy can reduce the human immunodeficiency virus (HIV) viral load in the plasma to undetectable levels. However, because of the presence of latent HIV reservoirs, it is difficult to completely eradicate HIV in infected patients. Our objective was to assess the potency of chidamide, a novel histone deacetylase inhibitor recently approved for cancer treatment by the China Food and Drug Administration, to reactivate latent HIV‐1 via histone acetylation. Viral reactivities of chidamide were accessed in 2 latent HIV pseudotype virus cell reporter systems (J‐Lat Tat‐green fluorescent protein clone A72 and TZM‐bl), a latently infected full‐length HIV virus cell system (U1/HIV), and resting CD4⁺ T cells from 9 HIV‐infected patients under highly active antiretroviral therapy with undetectable viral load. Chidamide was able to increase HIV expression in each cell line, as evidenced by green fluorescent protein, luciferase activity, and p24, as well as to reactivate latent HIV‐1 in primary CD4⁺ T cells of HIV‐infected patients. Histone acetylation adjacent to the HIV promoter in A72 cells was determined by chromatin immunoprecipitation. Chidamide was able to increase histone H3 and H4 acetylation at the HIV promoter. In brief, chidamide induced the reactivation of latent HIV in pseudotype virus reporter cells, latently infected cells, and primary CD4⁺ T cells, making this compound an attractive option for future clinical trials.     

Role of CD4+ Cytotoxic T Lymphocytes in the Control of Viral Diseases and Cancer

Our knowledge on the physiological role of CD4⁺ T lymphocytes has improved in the last decade: available data convincingly demonstrate that, besides the ‘helper’ activity, CD4⁺ T cells may be also endowed with lytic properties. The cytotoxic function of these effector cells has a relevant role in the control of pathogenic infections and in mediating antitumor immune responses. On these bases, several immunotherapeutic approaches exploiting the cytotoxic properties of CD4⁺ T cells are under investigation. This review summarizes available data supporting the functional and therapeutic relevance of cytotoxic CD4⁺ T cells, with a particular focus on Epstein-Barr virus (EBV)-related disorders.     

Selective alterations in immunoregulatory lymphocyte subsets in early HIV (human T-lymphotropic virus type III/lymphadenopathy-associated virus) infection

In order to characterize the effects of HIV (human T-lymphotropic virus type III/lymphadenopathy-associated virus) on the immune system, Leu8^– and Leu8⁺ subsets of CD4 and CD8 cells were studied in seropositive homosexually active men without acquired immune deficiency syndrome (AIDS). Controls included both heterosexual men and HIV-seronegative homosexually active men. The decrease in CD4 levels, observed in HIV-seropositive men who were asymptomatic, as well as in those who had persistent generalized lymphadenopathy or constitutional symptoms of HIV infection, occurred proportionally in both the Leu8^– and the Leu8⁺ CD4 subsets. This observation, that HIV infection does not selectively diminish either subset of CD4 cells, indicates that the selective loss of T cell-mediated functions which accompanies the development of AIDS is not related to preferential loss of the Leu8⁺ CD4 subset. Among CD8 cells, however, HIV infection resulted in a threefold elevation in the number of Leu8^– CD8 cells, while the number of Leu8⁺ CD8 cells remained constant. The increase in Leu8^– CD8 cells was present in recent seroconverters, persistently seropositive men, and patients with AIDS. We propose that the increase in Leu8^– CD8 cells represents an HIV-specific cytotoxic T-cell response. These cells may operate by killing infected CD4 cells, thereby partially controlling viral infection while simultaneously contributing to the destruction of the immune system.     

Impairment in T-lymphocyte responses during early infection with the human immunodeficiency virus

Uncertainty has existed as to whether a T-cell deficiency exists in human immunodeficiency virus (HIV) infection different from that inherent in the reduced T-cell numbers characteristic of the disease. Heretofore, methods for measuring T-cell responses in patients have been carried out with systems requiring monocytes as accessory cells. In the presence of high concentrations of interleukin-2, however, highly purified T cells respond in a monocyte-independent fashion to antibody reactive with the CD3 component of the antigen receptor complex Ti/CD3. Highly purified T cells of HIV-infected patients responded subnormally in this anti-CD3/IL-2 system, even in the case of patients who were asymptomatic or had only lymphadenopathy. The defective T-cell responses occurred over a wide range of concentrations of the anti-CD3. Neither poor IL-2 receptor function as reflected by responses to limiting dilutions of IL-2 nor IL-1 receptor function as defined by incremental proliferation when IL-1 is added accounted for this defect, which also correlated poorly with T4 and T8 numbers. These results suggested that the T-cell abnormality was closely related to Ti/CD3 function, was not specifically or restrictively associated with T4 cells, and was not due to defective IL-2- or IL-1-receptor functions. The amount of HIV RNA in 10⁵ T lymphocytes from the patients amounted to less than that found in one cell of a standard HIV infected laboratory cell line (CEM), using slot-blot hybridization. Thus the T-cell deficiency we have observed was not likely to be due directly to cell killing by HIV resident in the T4 cells. Other factors may be important in inducing the immunodeficiency, some of which are discussed.     

Impaired natural killer cell‐induced antibody‐dependent cell‐mediated cytotoxicity is associated with human immunodeficiency virus‐1 disease progression

This study evaluates the correlation between natural killer (NK) cell function and human immunodeficiency virus (HIV)-1 disease progression in 133 untreated HIV-1 positive Chinese subjects, including 41 former plasma donors (FPDs) and 92 men who have sex with men, and 35 HIV-negative controls. Flow cytometry was used to determine the abundance of NK cell subsets, the expression levels of receptor species, human leucocyte antigen (HLA) genotyping and the antibody-dependent cell-mediated cytotoxicity (ADCC) responses of NK cells. We observed a decreased expression of CD56^dimCD16⁺ NK cell subsets and an increased expression of CD56⁻CD16⁺ with HIV-1 infection. As well, the expression of activating and inhibitory receptors increased significantly in NK cells, but CD16 receptor levels and the NKG2A/NKG2C ratio were down-regulated with HIV-1 infection. ADCC responses were higher in elite controllers than in all other groups, and were correlated inversely with HIV-1 viral load but correlated positively with CD4 count only in FPDs. Furthermore, individuals infected for < 1 year have lower ADCC responses than those infected for > 1 year. We also observed a negative association between ADCC responses and viral load in those who carry the HLA-A*30/B*13/Cw*06 haplotype. The positive correlation between CD16 expression and ADCC responses and a negative correlation trend between CD158a and ADCC responses were also observed (P = 0·058). Our results showed that the ADCC response is associated with patients'' disease status, receptor expression levels, infection time and specific HLA alleles, which indicates that ADCC may offer protective effects against HIV-1 infection.     

An inhibitor of cytotoxic functions produced by CD8+CD57+ T lymphocytes from patients suffering from AIDS and immunosuppressed bone marrow recipients

An inhibitor of the cytotoxic functions (ICF) mediated by human immunodeficiency virus (HIV)- or HLA-specific cytotoxic T lymphocytes, natural killer and lymphokine-activated killer (LAK) cells is secreted by CD8⁺CD57^? T lymphocytes, a subset expanded during infection with HIV and after bone marrow transplantation. We previously showed an apparent molecular mass of 20–30 kDa for this soluble glycosylated concanavalin A-binding inhibitor which is distinct from known cytokines. Here, we report a characterization of the mechanism of action of this CD8⁺CD57⁺ ICF. We show that the ICF-induced inhibition of LAK cell cytolytic activity is transient, with a spontaneous recovery of cytolytic potential after 18 h. When testing interactions of ICF with a large set of cytokines we found that the ICF-mediated inhibition of cytotoxic functions is antagonized by two cytokines: recombinant interleukin (rIL)-4 and recombinant interferon (rIFN)-γ. Finally, we show that ICF acts at the level of cytolytic effector cells, where it induces a significant increase of cyclic AMP (cAMP) level. In contrast, no modification of either cell surface antigen expression or of target/effector cell conjugate formation could be evidenced. Addition of rIL-4 and rIFN-γ reverses such an increase of cAMP levels and in parallel restores the cytolytic activity. Altogether, these data demonstrate that the glycoprotein ICF produced by CD8⁺CD57⁺ cells (1) inhibits cell-mediated cytotoxicity by sensitizing cytolytic effector cells to the cAMP pathway, and (2) is part of a cytokine network controlling cell-mediated cytotoxic functions.     

Characterisation of simian immunodeficiency virus-infected cells in pigtail macaques

Defining which cells become infected with simian immunodeficiency virus (SIV) in vivo should assist in unravelling the pathogenesis of human immunodeficiency virus (HIV)/SIV infection. HIV/SIV infection of CD4⁺ T cells resulted in down-regulation of CD3 and CD4 surface molecules in vitro, however this phenomenon is poorly characterised in vivo. Intracellular SIV p27 was studied by flow cytometry in serial blood samples and lymph node samples during acute infection of 17 SIVmac-infected pigtail macaques. Two weeks after infection, a mean of 56±6.8% the p27⁺ cells were lymphocytes negative for surface CD4 and CD3, and indeed the highest proportion of SIV infected cells were found in the small subset of CD3^LoCD4⁻CD8⁻ lymphocytes, indicating that infection has lead to down-regulation of these markers in vivo. Furthermore, the relative amount of SIV p27 within lymphocytes (based of mean fluorescence intensity) was higher in CD3^LoCD4⁻ and CD3⁻ infected cells than in CD3⁺ or CD4⁺ p27⁺ populations, consistent with greater viral production in CD4⁺ T cells down-regulating CD3 and CD4 molecules. The CD3⁻CD4⁻ infected cells expressed T cell markers CD2 and CD5 and were negative for monocyte, NK and B cell markers. The majority of infected cells were CD28⁺CD95⁺ central memory T cells. Surprisingly, p27⁺ blood lymphocytes were mostly negative for activation markers CD25 and CD69, but most of the infected lymph nodes cells were activated. Our results characterise productively-infected macaque lymphocytes in vivo. The high proportion of SIV-infected lymphocytes that are CD3⁻CD4⁻ has important implications for the in vivo study of pathogenesis of SIV/HIV infections.     

Biological significance of the antibody response to HIV antigens expressed on the cell surface

Summary Human antibodies to HIV antigens expressed on the surface of infected cells may inhibit cell fusion with uninfected CD 4-positive cells and mediate killing of the infected cells by effector cells bearing the Fc receptor.Sequential sera from ten HIV-antibody seroconverted men, of which five progressed to ARC or AIDS (CDC stage IV) during the follow-up period of two years, were tested for the ability to inhibit CD 4-dependent cell fusion, (CFI) and to mediate antibody-dependent cellular cytotoxicity (ADCC).Nine patients developed HIV-specific ADCC and seven CFI-antibodies using the HIV strain HTLV-IIIB as target antigen. These antibodies appeared approximately at the same time 2–12 months after primary infection, defined as antibody seroconversion or antigenaemia. ADCC antibodies were detectable at higher titers as compared to CFI-antibodies. All sera of asymptomatic individuals (CDC stage II and III) were CFI antibody positive and had a higher mean ADCC titer as compared to sera from patients progressing to AIDS or ARC.ADCC and CFI antibodies coincided in some cases in the complete absence of core antibodies. Because the relationship between ADCC and CFI was not exclusive it is concluded that distinct domains of the HIV envelope induce natural antibodies mediating ADCC and CFI.     

Detection of antibodies which mediate human immunodeficiency virus-specific cellular cytotoxicity (ADCC) in vitro

A method to detect antibodies which mediate antibody-dependent cellular cytotoxicity (ADCC) against HIV-infected target cells was developed. Normal lymphocytes were used as effector cells and different HIV-infected cell lines as target cells. The level of ADCC varied depending on both the effector cell function and the target cell susceptibility. For evaluation of HIV-specific ADCC, the effector function was simultaneously tested against a standard antigen (beta 2 microglobulin), expressed both on infected and uninfected target cells. The HIV-infected monocytoid cell line U937, clone 2, was found to be the most useful target cell in the present system. The detection of antibodies which induce HIV-specific ADCC killing will permit clinical and experimental analysis of the possible importance of such antibodies in protection against HIV-associated disease symptoms.     

Human Immunodeficiency Virus Type 1 Replication,Immune Activation, and Circulating CytotoxicT Cells Against Uninfected CD4+ T Cells

Cytotoxic T lymphocytes (CTL) that kill uninfected activated CD4⁺ T cells can be induced in vitro by stimulating CD8⁺ T cells with activated autologous CD4⁺ T cells. Similar CTL have been detected in circulating T cells from human immunodeficiency virus type 1 (HIV)-infected individuals. To define the in vivo correlates of this CTL activity, we studied plasma -2 microglobulin and HIV RNA levels, T-lymphocyte subset counts, and expression of CD28 on CD8⁺ T cells concurrently with circulating CTL activity against uninfected CD4⁺ T cells in 75 HIV-infected individuals at different stages of disease progression. Mean values of each parameter were compared in subsets of this group of 75 segregated on the basis of this CTL activity. The group with CTL against uninfected activated CD4⁺ T lymphocytes had more CD8⁺ T cells, a higher percentage of CD28^– CD8⁺ T cells, and higher plasma levels of HIV RNA and -2 microglobulin. CTL against uninfected activated CD4⁺ T cells were predominantly CD28^– and in HIV-infected individuals were associated with immunological or virological evidence of progressive disease. In HIV infection, circulating CTL activity against uninfected activated CD4⁺ T lymphocytes is associated with immune activation, CD8⁺ T cell expansion, accumulation of CD28^– CD8⁺ T cells, and inadequate suppression of HIV replication.     

Fas (CD95) expression on CD4+ T cells from HIV-infected patients increases with disease progression

Active T cell suicide (apoptosis) is supposed to be involved in the CD4⁺ T cell depletion in the course of HIV infection. We investigated the expression of the apoptosis-related antigen Fas on CD4⁺ T cells from 25 HIV-positive individuals (CDC I-III) and 8 HIV-negative controls by two-colour flowcytometry. In addition, we evaluated: total CD4 count, HIV p24 antigen concentration in serum after immune complex dissociation, and clinical course of infection in HIV-positive individuals. We found a significant increase in mean Fas expression on CD4⁺ T cells from HIV-positive individuals compared to HIV-negative individuals (85.84±14.92% vs. 64.28±7.59%, P<0.001). Within the HIV-positive group the increase in Fas expression was correlated with the decline in CD4 count (r=–0.76, P<0.001), p24 antigen concentration in serum after immune complex dissociation (r=0.67, P<0.001), and CDC stage (r=0.73, P<0.001). The upregulation of Fas antigen on CD4 cells is associated with CD4 depletion and other virological and clinical marker of disease progression in HIV infection.Abbreviations AIDS Acquired immunodeficiency syndrome - CDC Center of disease control - CTL Cytotoxic T lymphocyte - FasL Fas ligand - HIV Human immunodeficiency virus - MFI Mean fluorescence intensity