Expression and function of CCR5 and CXCR4 on human Langerhans cells and macrophages: implications for HIV primary infection.

Transmission of HIV-1 is predominantly restricted to macrophage (Mphi)-tropic strains. Langerhans cells (LCs) in mucosal epithelium, as well as macrophages located in the submucosal tissues, may be initial targets for HIV-1. This study was designed to determine whether restricted transmission of HIV-1 correlates with expression and function of HIV-1 co-receptors on LCs and macrophages. Using polyclonal rabbit IgGs specific for the HIV co-receptors cytokines CXCR4 and CCR5, we found that freshly isolated epidermal LCs (resembling resident mucosal LCs) expressed CCR5, but not CXCR, on their surfaces. In concordance with surface expression, fresh LCs fused with Mphi-tropic but not with T-tropic HIV-1 envelopes. However, fresh LCs did contain intracellular CXCR4 protein that was transported to the surface during in vitro culture. Macrophages expressed high levels of both co-receptors on their surfaces, but only CCR5 was functional in a fusion assay. These data provide several possible explanations for the selective transmission of Mphi-tropic HIV variants and for the resistance to infection conferred by the CCR5 deletion.

The role of natural killer cells and antibody-dependent cell-mediated cytotoxicity during murine cytomegalovirus infection.

Definition of the functions by which the cellular immune system contributes to control of cytomegalovirus (CMV) infection should permit determination of the specific defects which result in the increased susceptibility to infection of immunosuppressed individuals. Using a murine model, we studied the cytotoxic lymphocyte response to murine CMV infection. This response was found to be biphasic. The initial phase extended from the 3rd to the 6th d after infection, was not genetically restricted, and correlated to a rise in numbers of natural killer (NK) and antibody-dependent killer (K) cells in spleens. The NK- and K-cell responses were preceded, by 24 h, by a rise in serum interferon levels, and occurred before the time when antibody could be measured in serum by neutralization. NK and K cells appear to develop the capacity for specific recognition of CMV-infected cells and the potential to contribute to control of the acute phase of CMV infection.

Cytomegalovirus induction of tumor necrosis factor-alpha by human monocytes and mucosal macrophages.

Cytomegalovirus (CMV) is a major cause of inflammatory organ disease in immunosuppressed persons. To elucidate the mechanisms of CMV-induced inflammation, we investigated whether tumor necrosis factor-alpha (TNF-alpha) was involved in the pathogenesis of CMV colitis in patients with AIDS. In in situ hybridization experiments, TNF-alpha mRNA was shown to be abundantly present in colonic mucosa from AIDS patients with CMV colitis but not in colonic mucosa from control (AIDS and normal) subjects. The TNF-alpha transcripts, identified in macrophage-like cells containing cytomegalic inclusions, were positively associated with CMV, but not HIV-1, within the mucosa. In in vitro experiments, a patient-derived isolate of CMV, but not HIV-1Ba-L, induced human monocytes to express TNF-alpha mRNA and to release increased levels of TNF-alpha peptide following stimulation. CMV induction of TNF-alpha may play a critical role in CMV-induced inflammation and, since TNF-alpha upregulates expression of HIV-1, offers a mechanism by which CMV could serve as a co-factor for HIV-1 expression without both viruses infecting the same cell.

Common epitope in human immunodeficiency virus (HIV) I-GP41 and HLA class II elicits immunosuppressive autoantibodies capable of contributing to immune dysfunction in HIV I-infected individuals.

We previously reported the identification of highly conserved homologous regions located in the carboxy terminus of the HIV I gp41-envelope (aa 837-844), and the amino-terminal of the beta chain of all human HLA class II antigens (aa 19-25). Murine monoclonal antibodies, raised against synthetic peptides from these homologous regions, bound not only to the isolated peptides, but also to the native gp160 and class II molecules. In this study one-third of sera from HIV I-infected individuals, at different disease stages, were found to react with both the gp41 and class II-derived peptides. These sera also reacted with "native" HLA class II molecules. The potential affects of such autoantibodies on normal immune functions were examined. It was found that in the presence of class II-cross-reactive (but not control) sera, the proliferative responses of normal CD4+ T cells to tetanus toxoid and allogeneic stimuli were markedly decreased. In addition, these sera could eliminate class II-bearing cells by antibody dependent cellular cytotoxicity. Similar affects were seen with affinity-purified IgG antibodies from patients' sera. Thus, the "molecular mimicry" between HIV I and HLA class II antigens, may lead to the generation of autoantibodies in HIV I-infected individuals that may contribute to the early functional impairment of CD4+ T cell observed in many HIV I-infected individuals.

Interleukin-2 enhances the depressed natural killer and cytomegalovirus-specific cytotoxic activities of lymphocytes from patients with the acquired immune deficiency syndrome.

The recently described acquired immune deficiency syndrome (AIDS) is characterized by the occurrence of severe opportunistic infections and an aggressive form of Kaposi's sarcoma. A variety of profound defects in cell-mediated immunity have been reported in association with the AIDS, including deficiencies in natural killer (NK) cell activity and cytomegalovirus (CMV)-specific cytotoxicity. In the present study, the in vitro effects of interleukin-2 (IL-2) and interferon beta (IFN Beta) on these abnormalities were examined to assess the potential use of these lymphokines in the immunotherapeutic treatment of this syndrome. The peripheral blood lymphocytes (PBL) from six male homosexuals with AIDS and an active CMV infection exhibited markedly depressed NK cell and CMV-specific cytotoxic lymphocyte responses compared with uninfected, heterosexual control subjects. Incubation of PBL with IFN Beta enhanced the NK cell activity and the CMV-specific cytotoxicity of only one of six and neither of two AIDS patients, respectively, while enhancing the NK cell activity of all six control subjects. In contrast, IL-2 dramatically enhanced both the NK cell and the CMV-specific cytotoxic lymphocyte activities of all of the patients. These results indicate that IL-2 can substantially potentiate the depressed cytotoxic effector functions of PBL from AIDS patients, while IFN Beta has little effect.

Correlation between kinetics of soluble CD4 interactions with HIV-1-Env-expressing cells and inhibition of syncytia formation: implications for mechanisms of cell fusion and therapy for AIDS.

OBJECTIVES: To study the kinetics of the interactions between soluble (s) CD4 and HIV-1-Env-expressing cells in relation to subsequent events leading to cell fusion and inhibition of syncytia formation. DESIGN: Vaccinia-HIV-1 (Env)-infected CD4- T-cells were used to study the kinetics of sCD4-gp120/41 interactions and syncytia formation (with CD4+ T-cells) under identical conditions. METHODS: sCD4 association and dissociation rates for HIV-1-Env-expressing cells, and quantification of sCD4-induced gp120 shedding was determined by a quantitative flow cytometry assay. Syncytia inhibition was measured in the continuous presence of sCD4, or after washing of HIV-1-Env-expressing cells following pre-incubation with sCD4. RESULTS: The kinetics of syncytia inhibition correlated with sCD4 binding when sCD4 was maintained during the culture. When Env-expressing cells, which had been pre-incubated with sCD4, were washed to remove unbound sCD4, no syncytia formation inhibition was observed, even following sCD4-induced shedding of greater than 50% of surface gp120 molecules. CONCLUSIONS: The lack of syncytia inhibition seen after removal of unbound sCD4, even after pre-incubation of cells under saturation and gp120 shedding conditions, indicated that sufficient numbers of fusogenic molecules remained on the sCD4-treated cells. In addition, fast dissociation of pre-bound sCD4 occurred in culture. These results are important for understanding HIV-1-Env-mediated cell fusion and AIDS therapy.

Importance of cytotoxic lymphocytes during cytomegalovirus infection in renal transplant recipients.

Thirty renal transplant recipients were studied prospectively to evaluate the relationship of cytomegalovirus-specific cytotoxic lymphocyte responses to clinical outcome during cytomegalovirus infection. Cytomegalovirus infection developed in 20 patients; of these 20, 14 had cytomegalovirus-specific cytotoxic lymphocyte responses whereas six did not. Clinical findings (fever, leukopenia, thrombocytopenia, or elevations in serum transaminase levels) were significantly more frequent among patients without responses than among patients with responses (p less than 0.001), and prolonged viremia and complications of infection including superinfection, interstitial pneumonitis, pancreatitis, and death occurred exclusively among patients without responses. Acute allograft dysfunction during infection was experienced by four patients without responses but by only one patient with response (p = 0.02), indicating that the virus-specific cytotoxic response did not result in a renal immunopathologic condition, and may have protected against virus-induced injury to the graft. In seven of nine patients with responses who shed virus, cytotoxic responses occurred within one week of detection of activation of virus shedding. Absence of cytotoxic responses correlated with prior high-dose, intravenous methylprednisolone treatment, and apparently resulted from inhibition of cytotoxic T cell precursors. Immunosuppressive treatment to inhibit graft rejection should be minimized, and methods should be developed that do not inhibit cytomegalovirus-specific cytotoxic T cell responses.

Study of viral replication in HIV-1-infected CEM T-cell subclones which are reduced in their ability to form syncytia.

The derivation of ethyl-methanesulfonate (EMS) mutagenized subclones from the CEM T-cell line has been described. These clones expressed CD4 and bound soluble gp120, however, two of the generated clones were markedly reduced in their ability to form syncytia after infection with either gp160-vaccinia vector or cell-free human immunodeficiency virus type 1 (HIV-1). Here, we asked at what stage(s) viral infection is blocked in these cells. Polymerase chain reaction (PCR) analysis revealed that at 6 and 72 h postinfection with HIV-1, cells of the syncytia-deficient clones expressed markedly reduced amounts of viral-specific DNA compared with cells of the parental line or the syncytia-positive clones. Long-term cultures revealed a marked delay in the appearance of reverse transcriptase (RT) activity in the supernatants of these subclones when compared with the parental line and viral replication did not lead to massive cell death. Syncytia formation in HIV-1-infected cultures of the syncytia-deficient subclones was enhanced by tumor necrosis factor alpha (TNF alpha) when added 24 h postinfection. In contrast, pretreatment with TNF alpha for 48 h followed by washing and infection of the cells with HIV-1 augmented syncytia formation of the syncytia-positive subclones, but not of the syncytia-negative subclones. Thus, the EMS-mutagenized subclones may provide a tool to study host cell factors required for the establishment of a productive HIV-1 infection and responsiveness to TNF alpha.

Production of a novel antigen by conjugation of HIV-1 to Brucella abortus: studies of immunogenicity, isotype analysis, T-cell dependency, and syncytia inhibition.

In the present study inactivated human immunodeficiency virus type 1 (HIV-1) was conjugated to Brucella abortus and tested for immunogenicity in normal and anti-L3T4-treated BALB/c mice. HIV-BA was more immunogenic than uncoupled HIV in normal mice, since 6-fold less virus in HIV-BA preparations elicited higher titer responses than HIV-1 alone. Furthermore, the HIV-BA antibody response reached higher levels before the HIV-1 response. Immunoblot analysis showed that most of the HIV-1 antigens were recognized by antibodies induced by either HIV-1 or HIV-BA. Isotype analysis revealed that HIV-1 induced similar levels of IgG1 and IgG2a antibodies, whereas the IgG2a responses to HIV-BA were more pronounced than the IgG1 response. These different IgG subclass patterns suggest that conjugation of HIV-1 to BA changed the immunogenic nature of HIV-1. The requirement for helper T cells was examined by immunizing mice that were depleted of CD4+ T cells by in vivo anti-L3T4 treatment. Under these conditions the IgG responses to HIV-1 were completely eliminated. Although HIV-BA antibody responses were markedly reduced in anti-L3T4-treated mice, anti-HIV-1 antibodies, mainly of the IgG2a isotype, were produced. The antibodies generated by HIV-1 and HIV-BA immunization were also tested for their ability to inhibit syncytia formed by infecting CD4 + CEM cells with gp160 vaccinia. Sera from normal mice, immunized with either HIV-1 or HIV-BA were capable of inhibiting syncytia. In contrast, following anti-L3T4 treatment, only mice immunized with HIV-BA, but not HIV-1, produced antibodies capable of inhibiting syncytia.

Treatment of cytomegalovirus retinitis with dihydroxy propoxymethyl guanine.

Eight patients with cytomegalovirus retinitis in one or both eyes were treated with 9-(1,3 dihydroxy 2-propoxymethyl) guanine. Of the 14 eyes with retinitis, eight demonstrated more than 90% resolution, four had partial improvement, one failed to respond, and one could not be evaluated. Two of the eight patients had chemotherapy-induced immunosuppression and had ocular remissions for at least several months. The remaining six patients had AIDS or probable AIDS and relapsed in five weeks or less after discontinuation of therapy. Dihydroxy propoxymethyl guanine appears to be effective biologically in treating human cytomegalovirus retinitis without the development of unacceptable side effects but a single course of therapy is not capable of eradicating the virus.

Antivirus antibody-dependent cell-mediated cytotoxicity during murine cytomegalovirus infection.

BALB/c mice infected with murine cytomegalovirus were studied to determine whether antibody-dependent cell-mediated cytotoxicity contributes to the immune control of this infection. Antibody-dependent killer cells from uninfected mice were used as effector cells to assay for antibody in sera of infected mice. Secondary immune sera were found to contain both cytomegalovirus-specific and autoreactive antibodies. After primary infection only cytomegalovirus-specific antibodies were found. These were detected by antibody-dependent cell-mediated cytotoxicity within 8 to 10 days after onset of infection, but usually not until day 21, by a neutralizing antibody assay. Antibody titers were about 10-fold higher by antibody-dependent cell-mediated cytotoxicity than by neutralization. The results indicate that cellular immunity to cytomegalovirus infection includes an antibody-dependent cell-mediated cytotoxicity response which is likely to be highly efficient and may contribute significantly to control of both acute and later stages of infection.

Genetically determined resistance to lethal murine cytomegalovirus infection is mediated by interferon-dependent and -independent restriction of virus replication.

Susceptibility of 4-week-old mice of different strains to lethal murine cytomegalovirus (MCMV) infection was studied. Strains homozygous for H-2k and C57BL strains were resistant to greater than or equal to 10(5.5) PFU. B10.BR mice congenic for C57BL background genes and H-2k were about 10-fold more resistant than either C3H/HeN or C57BL strains. BALB/c mice (H-2d) were susceptible (50% lethal dose, 10(5.05) PFU). This susceptibility was dominant over resistance associated with H-2k but not that associated with C57BL background genes. The dominant susceptibility trait segregated in backcross mice as if carried by a single gene. Virus replication in spleen cells in vivo correlated with susceptibility to lethal infection. A similar trend was found in tests of salivary glands. Replication of MCMV in vitro in cultures of adherent spleen cells and primary mouse embryo cells correlated with replication in vivo. Neutralization of interferon (IFN) in cultures of adherent spleen cells reversed H-2k-linked restriction of viral replication but had minor effects on cells of other strains. Natural killer cell responses to infection were often higher in more resistant strains, but B10.BR mice developed minimal natural killer cell responses. Specific antibody and cytotoxic T cell responses in B10.BR mice were similar or lower than in other strains. Thus, resistance to lethal MCMV infection was not immunologically mediated, was dependent on and reflected by the capacity of cells from a given mouse strain to support replication in vivo and in vitro, and was IFN dependent and recessive if linked to H-2k but IFN independent when associated with C57BL background genes.

Role of cytotoxic T lymphocytes in murine cytomegalovirus infection.

Cell-mediated immunity is important in host control of CMV infection. A chromium release microcytoxicity assay was used to evaluate the role of cytotoxic T lymphocytes (CTL) in murine CMV infection. Within a few days after intranasal inoculation virus was detected in cultures of buffy-coat, spleens, anterior cervical lymph nodes and salivary glands. CTL were first detected on day 5 post-infection in spleen and peripheral blood, and on day 6 in anterior cervical nodes. The course of the CTL response approximated to that of virus titres during the acute phase of infection in the spleen and blood. The findings indicate that CTL are distributed to infected tissues and appear to be important during the acute, viraemic phase of infection.

The effect of mycoplasmas on replication and plaquing ability of Herpes simplex virus.

M. arginini, an arginine utilizer, can decrease the yield of Herpes simplex virus, type 1 grown in Vero cells. M. arginini can also cause a reduction in number and size of plaques produced by HSV. The reduction in titer and plaque size produced in M. arginini-infected cells can be reversed by supplementing medium with additional arginine. A. laidlawii, a nonarginine utilizing mycoplasma, had no effect on the growth of HSV.

Involvement of natural killer cells in the pathogenesis of murine cytomegalovirus interstitial pneumonitis and the immune response to infection.

The significance of the natural killer (NK) cell response to murine cytomegalovirus (MCMV) infection was evaluated in C3H/HeN mice. This strain was selected for study after preliminary demonstration that the NK cell response, occurring between 3 and 6 days post-infection was relatively high in comparison to other mouse strains studied. A dose-response effect of hydrocortisone treatment on suppression of this response was found. A dose of hydrocortisone, given subcutaneously on two successive days, which was found to markedly inhibit the NK cell response, had no effect on development of serum interferon or antibody levels, or spleen cytotoxic T cell activity under the conditions studied. Suppression of the NK cell response by this treatment, however, was accompanied by enhanced spleen and pulmonary virus replication in vivo and increased susceptibility of mice to lethal infection. MCMV interstitial pneumonitis was characterized histologically and lung lymphocytes studied at 4 days post-infection were found to have increased NK cell activity. Treatment of mice with hydrocortisone was found to inhibit development of gross and histological evidence of pneumonitis. These findings indicate that NK cells are involved in the pathogenesis of MCMV interstitial pneumonitis and may function early in infection to restrict the extent of virus replication.

Synergistic effect of ganciclovir and foscarnet on cytomegalovirus replication in vitro.

Ganciclovir and foscarnet possess substantial activity against cytomegalovirus. Both exhibit dose-limiting toxicity, which reduces their clinical usefulness. We demonstrated synergistic inhibition of cytomegalovirus replication in vitro by ganciclovir and foscarnet. Reduced-dose combination therapy may provide a means to treat patients with cytomegalovirus infection while reducing drug toxicity.

Adenovirus colitis in the acquired immunodeficiency syndrome.

Adenovirus was identified in colonic tissue by transmission electron microscopy or culture in 5 of 67 (7.4%) homosexual men seropositive for human immunodeficiency virus (51 with the acquired immunodeficiency syndrome) with diarrhea. Colonoscopy showed the mucosa to be normal in 3 cases and mildly inflamed in 2. Light microscopy showed foci of mucosal necrosis that contained chronic inflammatory cells and degenerating and necrotic epithelial cells with amphophilic nuclear inclusions. By transmission electron microscopy, hexagonal viral particles characteristic of adenovirus were identified within the inclusions. Only 1 patient was concomitantly infected by a second potential enteric pathogen. It was concluded that adenovirus, an uncommon enteric pathogen in immunocompetent adults, causes intestinal pathology and may be associated with diarrheal illness in persons with the acquired immunodeficiency syndrome.

Fusion of human B cell lines with HIV-1 envelope-expressing T cells is enhanced by antigen-specific Ig receptors. Possible mechanism for elimination of gp120-specific B cells in vivo.

The possible contribution of Ag-specific Ig receptors on B cells to syncytium formation with HIV-1 envelope (env)-expressing cells was examined. A unique model system was designed that used anti-TNP/TNP interactions between a panel of TNP-specific human B cell lines and TNP-haptenated HIV-1 env-expressing T cells. The prototype B cell line 1:13 (CD4dull) produced few syncytia with vaccinia gp120/41-infected CD4- T cell effectors. However, TNP-haptenation of the HIV-1 env-expressing cells resulted in a five- to 10-fold increase in syncytium formation. The "enhanced" syncytia were blocked by OKT4A mAb, soluble CD4, anti-TNP serum, and TNP-BSA, suggesting a role for both CD4 and Ig receptors. In contrast, the number of syncytia formed between CD4+ CEM T cells and TNP-haptenated effectors was reduced by 30 to 40%, compared with the unhaptenated effectors, suggesting that a fraction of the TNP haptens bound close to the CD4 binding regions on the gp120 envelope, which was confirmed by other experiments. The possibility that B cells specific for the CD4 binding site on HIV-1 gp120 may be involved in syncytium formation with HIV-1 env-expressing cells was tested by screening a panel of five hybrid B cell lines from HIV-1-seropositive individuals. One of these lines produced anti-gp120 antibodies, which bound near the CD4 binding site, and also formed syncytia with HIV-1 env-expressing cells. This study suggests that, in addition to CD4 receptors, certain B cell Ig receptors that bind to gp120 may induce conformational changes leading to cell fusion and their elimination.