The immunopathogenesis of human immunodeficiency virus infection

Comparative biology and pathogenesis of AIDS and hepatitis B viruses: related but different

AIDS (HIV) and hepatitis B viruses are remarkably similar in their sharing of reverse transcription, in their ancestral origins and common genetic elements, and in their modes of transmission. Both are hypermutable and exist as quasispecies due primarily to errors in reverse transcription, though there is severe restriction in the replicative competence of most hepatitis B mutants. They differ in the lack of an integrase in hepatitis B virus and in their pathogenesis in the infected host. HIV survives mainly by antigenic variability, immune evasion, and impairment of immune function though viral regulatory control elements seek to restrict fatal damage to the host. Hepatitis B virus survives primarily by mutation of e antigen/core genes that directly obviates cytotoxic T cell destruction of infected liver cells, or indirectly limits destruction of infected cells through induction of anergy in the cytotoxic T cell response. Most persons infected with hepatitis B virus recover completely while recovery from HIV infection is rare if ever. Hepatitis B is highly preventable by vaccine while HIV vaccine is still seeking a meaningful immunoprophylactic target. AIDS and hepatitis B represent an extreme example, among the viruses of man, in their close similarities but distinct differences. In depth details and perspectives are presented in this review.

Long-term survivors of HIV infection

The persistent immune competence seen in a small percentage of HIV-infected individuals reflects the heterogeneity of both the virus and the host. Some HIV strains, for example, are more cytopathic than others. Host factors that promote longer survival lack "enhancing" antibodies, an appropriate balance of two crucial CD4+ cell subsets and their cytokines, and a strong CD8+ cell antiviral response.

A model for AIDS pathogenesis

The idea is put forward and analysed numerically, that within an infected person HIV evolves to increase its reproductivity within the population of CD4+ cells. A mathematical model predicts initial viremia and CD4+ cell drop after HIV infection and thereafter a slow progressive decline in the number of CD4+ cells, although for an extended period HIV is kept at a relatively low level by an active immune response. The time span T until the number of CD4+ cells falls below 20 per cent of its normal value depends on several model parameters. Assuming Gaussian distributions for these parameters, the model predicts a distribution function for T which resembles the observed distribution function for the incubation period to AIDS.

Neonatal deletion and selective expansion of mouse T cells by exposure to rabies virus nucleocapsid superantigen

The nucleocapsid (NC) of the rabies virus behaves as an exogenous superantigen (SAg) in humans. In the present report, we analyzed whether it is also a SAg in mice by studying the effect of NC on T cell receptor (TCR) V beta expression in BALB/c mice. Repeated injection of NC in newborn BALB/c mice led to a marked reduction by two- to sixfold of V beta 6 expressing CD4+ T cells in spleen and in peripheral blood. Decrease of V beta 6-expressing CD3+ mature T cells was also observed in thymus. Single NC injection in footpad resulted in a three- to sixfold expansion of V beta 6 CD4+ T cells, but not of CD8+ T cells, in the draining lymph nodes of BALB/c mice. The intensity of the stimulation was dose dependent and was maximal 3 d after the NC injection. The clonal deletion of T cells bearing a particular V beta demonstrates that NC is a SAg in mice. T cells, especially CD4+ T cells, are an essential factor in host resistance to rabies virus and also in the pathophysiology of paralysis; thus, we postulate that a rabies virus component, which stimulates T cells, such as a SAg, may increase virus immunopathogenicity. To evaluate this hypothesis, we compared the course of rabies in adult BALB/c lacking V beta 6, 7, 8.1, and 9 T cells and in normal BALB/c. Immune-related paralysis was decreased in BALB/c missing the NC target V beta T cells. Transfer of V beta 6 but not of V beta 8.1-3 T cells into recipient mice lacking V beta 6, 7, 8.1, and 9 allowed the immune-related paralysis to evolve. Taken together, these results strongly support the hypothesis that T cells expressing rabies SAg-specific V beta 6 T cells, are involved in the genesis of the immunopathology that is characteristic of paralytic rabies.

Histopathology of cerebral toxoplasmosis in human immunodeficiency virus infection: a comparison between patients with early-onset and late-onset acquired immunodeficiency syndrome

We reviewed the histological features of untreated toxoplasmosis in 18 cases with the acquired immunodeficiency syndrome (AIDS), eight of which were surgical biopsies and 10 of which were autopsy specimens. The results were compared according to the clinical status of the patient at the time the diagnosis of toxoplasmosis was made (early-onset v late-onset AIDS) and according to the source of the specimen (surgical biopsy specimen v autopsy specimen). Cerebral toxoplasmosis was the AIDS-defining illness in half of the cases (six surgical biopsy specimens and three autopsy specimens). Inflammation in these cases was moderate in 44% and severe in 56%. Fibrous capsules were found in five cases. Lymphocytes and plasma cells were more prominent than neutrophils. Cerebral toxoplasmosis developed in or was part of the terminal AIDS illness in the remaining nine cases (two surgical biopsy specimens and seven autopsy specimens). In this group inflammation was sparse in 44%, moderate in 55%, and severe in only 11%. Fibrous capsules were usually absent and neutrophils were the predominant cell type. Comparisons between surgical biopsy specimens and autopsy specimens showed moderate to severe inflammation and frequent fibrous encapsulation in all of the former specimens but only in those autopsy specimens in which toxoplasmosis was the initial manifestation of AIDS. Thus, this study demonstrates varied neuropathological patterns of untreated cerebral toxoplasmosis in patients with AIDS and correlates the inflammatory response in the brain with the clinical stage of the patient's human immunodeficiency syndrome (HIV) infection. Inflammation and fibrous encapsulation were common only in patients with early-onset AIDS in whom cerebral toxoplasmosis was the first manifestation of the illness. This study highlights important differences between the histology of this infection at surgical biopsy and at autopsy, and stresses the need to consider toxoplasma as a potential cause of encapsulated brain abscesses.

Naturally processed viral peptides recognized by cytotoxic T lymphocytes on cells chronically infected by human immunodeficiency virus type 1

We have established long-term cultures of several cell lines stably and uniformly expressing human immunodeficiency virus type 1 (HIV-1) in order to (a) identify naturally processed HIV-1 peptides recognized by cytotoxic T lymphocytes (CTL) from HIV-1-seropositive individuals and (b) consider the hypothesis that naturally occurring epitope densities on HIV-infected cells may limit their lysis by CTL. Each of two A2-restricted CD8+ CTL specific for HIV-1 gag or reverse transcriptase (RT) recognized a single naturally processed HIV-1 peptide in trifluoroacetic acid (TFA) extracts of infected cells: gag 77-85 (SLYNTVATL) or RT 476-484 (ILKEPVHGV). Both processed peptides match the synthetic peptides that are optimally active in cytotoxicity assays and have the consensus motif described for A2-associated peptides. Their abundances were approximately 400 and approximately 12 molecules per infected Jurkat-A2 cell, respectively. Other synthetic HIV-1 peptides active at subnanomolar concentrations were not present in infected cells. Except for the antigen processing mutant line T2, HIV-infected HLA-A2+ cell lines were specifically lysed by both A2-restricted CTL, although infected Jurkat-A2 cells were lysed more poorly by RT-specific CTL than by gag-specific CTL, suggesting that low cell surface density of a natural peptide may limit the effectiveness of some HIV-specific CTL despite their vigorous activity against synthetic peptide-treated target cells.

Intrathecal synthesis of anti-myelin basic protein IgG in HIV-1+ patients

Human immunodeficiency virus type 1 (HIV-1)-infected individuals frequently develop a broad spectrum of neurological syndromes, classified as HIV-1-associated cognitive/motor complex. Diffuse demyelination of hemispheric white matter is a commonly observed in HIV-1 infected brain, but the events leading to myelin destruction are still obscure. Since oligodendrocyte infection by HIV-1 is not proven as yet, myelin damage in HIV-1 infection may result from indirect mechanisms such as the excessive release of myelinotoxic substances or the triggering of autoimmune responses directed to myelin constituents. To verify the latter hypothesis, we searched for elevated anti-myelin basic protein (MBP) IgG levels in the cerebrospinal fluid (CSF) and serum of 25 patients with HIV-1 infection, 12 with multiple sclerosis (MS), and 9 with non-inflammatory neurological diseases (NIND). CSF, but not serum, anti-MBP IgG levels were more frequently elevated in HIV-1+ (16/25, 64%) than in MS (3/12, 25%) or NIND (0/9) patients. By using the anti-MBP IgG index, the anti-MBP IgG antibody specificity index (ASI), and the search for anti-MBP oligoclonal IgG, we ascertained that anti-MBP IgG were produced within the CNS in 13 of 25 (52%) HIV-1+, in 6 of 12 (50%) MS, and in none of NIND patients. The incidence of increased CSF anti-MBP IgG levels was higher among HIV-1+ patients at stage II-III (4/4, 100%) or at stage IV B (7/9, 78%) than among those at stage IV C-IV D (5/12, 42%). Although our data indicate that intrathecal anti-MBP IgG may occur early during HIV-1 infection and that they are more common in patients with HIV-1-associated cognitive/motor complex, the possible demyelinating role of these antibodies remains to be demonstrated.

Quantification of human immunodeficiency virus type 1-infected mononuclear cells in peripheral blood of seropositive subjects by newly developed flow cytometry analysis of the product of an in situ PCR assay

The presence of human immunodeficiency virus type 1 (HIV-1) proviral DNA in peripheral blood mononuclear cells (PBMC) of three groups (group 1, more than 500 CD4+ T cells per microliter; group 2, between 200 and 499 CD4+ T cells per microliter; group 3, fewer than 200 CD4+ T cells per microliter) of HIV-1-infected patients, in different stages of the disease, was determined by using a newly developed flow cytometry analysis of the product of in situ PCR assay and compared with other markers of viral replication (HIV-1 p24 antigenemia and viral isolation). Results showed varied percentages of HIV-1-infected PBMC, ranging from 0.6 to 20%. Patients with more than 500 CD4+ T cells per microliter showed the lowest percentage of HIV-1-infected PBMC (2.1 +/- 1.7), compared with patients with CD4+ T-cell counts of between 200 and 499 per microliter (6.5% +/- 4.1%; P < 0.001) and patients with fewer than 200 CD4+ T cells per microliter (4.9% +/- 4.7%; P < 0.05). The difference in the percentage of HIV-1-infected PBMC between group 2 and group 3 patients may in part reflect the loss of CD4+ T lymphocytes in more advanced stages of the disease. However, the results clearly indicate a striking coincidence between the fall of the CD4+ T-cell count below 400/microliter and the sharp increase in PBMC virus loading and p24 antigenemia. Since the procedure is relatively easy to perform, it could be used to monitor the evolution of HIV-1 infection and may prove a useful adjunct in tailoring therapeutic strategies.

Clinical and immunologic evaluation of HIV-infected patients treated with dinitrochlorobenzene

BACKGROUND

Promotion of cell-mediated immunity appears to be an important goal in the control of HIV infection. Topical dinitrochlorobenzene (DNCB) stimulates systemic cell-mediated immunity via the induction of cutaneous delayed-type hypersensitivity.

OBJECTIVE

Our goal was to evaluate the clinical and immunologic effects of chronic DNCB application in a group of 24 HIV-infected patients.

METHODS

We observed the patients for a mean of 28 months (range, 14 to 44 months). Of the 24 patients, 13 continued weekly DNCB application throughout the study (the compliant group), and 11 discontinued DNCB use after a mean of 10.9 months (the noncompliant group).

RESULTS

Two of the 13 compliant patients progressed to AIDS; none of these patients died. In contrast, AIDS developed in 5 of the 11 noncompliant patients and four of these patients died. Analysis of lymphocyte subsets revealed significant increases in natural killer cells and activated/cytotoxic CD8 T-cell subsets in the compliant group. In contrast, these cellular immune-related lymphocyte subsets decreased in the noncompliant subjects. Although CD4 T-cell levels decreased in both groups, there was a significantly greater drop in the noncompliant patients. CD8+CD38+ T cells increased significantly in both groups.

CONCLUSION

Chronic DNCB application appears to have a beneficial clinical and immunomodulatory effect in HIV-infected patients.

Feline immunodeficiency virus infection of macrophages: in vitro and in vivo inhibition by dideoxycytidine-5'-triphosphate-loaded erythrocytes

Although HIV-1 and other mammalian lentiviruses infect macrophages, they are not cytopathic. Consequently, these infected long-lived cells serve as major virus reservoirs with a key role in the propagation of the virus throughout the body as well as in the pathogenesis of AIDS. Furthermore, well-differentiated macrophages possess low abilities to phosphorylate the most common reverse transcriptase inhibitors of the nucleoside analog family. In an attempt to overcome these problems we have evaluated in vitro and in vivo in a feline immunodeficiency animal model whether it is possible to protect macrophages from FIV infection by direct administration of dideoxycytidine-5'-triphosphate (ddCTP). Because the cell membranes are impermeable to phosphorylated drugs we have encapsulated ddCTP into autologous erythrocytes. The drug-loaded erythrocyte membranes were then modified to target these carrier cells to macrophages. ddCTP-loaded erythrocytes were able to reduce FIV production by macrophages infected in vitro or obtained from naturally or experimentally infected cats. Furthermore, the administration of ddCTP-loaded erythrocytes protected the majority of peritoneal macrophages during a 7-month experimental FIV infection and reduced the percentage of circulating lymphocytes stained by an anti-p24 antibody. These results suggest that the administration of nucleoside analogs in phosphorylate form is feasible and their targeting to macrophages reduces FIV infection both in vitro and in vivo.

Intercellular adhesion molecules (ICAM)-1 ICAM-2 and ICAM-3 function as counter-receptors for lymphocyte function-associated molecule 1 in human immunodeficiency virus-mediated syncytia formation

It has been previously demonstrated that lymphocyte function-associated molecule 1 (LFA-1) plays a major role in human immunodeficiency virus (HIV)-mediated syncytia formation. In the present study we investigated the involvement of intercellular adhesion molecule-1 (ICAM-1), ICAM-2 and ICAM-3 in the process. The ability of monoclonal antibodies (mAb) directed against ICAM-1, ICAM-2 and ICAM-3 to block syncytia was analyzed either in phytohemagglutinin (PHA)-activated lymphocytes infected in vitro with primary or laboratory strains of HIV or by coculturing a T cell line stably expressing HIV envelope with PHA-activated lymphocytes. Complete inhibition of syncytia formation was observed only by the simultaneous addition to the cell cultures of all (i.e. anti-ICAM-1, anti-ICAM-2 and anti-ICAM-3) mAb. These results indicate that the interaction between LFA-1 and ICAM is a critical step in HIV-mediated syncytia formation, and that ICAM-1, ICAM-2 and ICAM-3 are the receptor molecules for the LFA-1-dependent syncytia formation.

Host defenses against respiratory infection

The respiratory tract is protected from infection by its formidable mechanical and cellular defenses, supplemented when necessary by inflammatory and immune responses. Impairments in these defenses develop as a result of underlying disease and therapeutic interventions. Specific defects in host defenses often predispose to infection with particular etiologic agents. New opportunities for the therapeutic augmentation of defenses are emerging that may be particularly helpful in the care of immunocompromised patients.

HIV-1 infection despite immediate combination antiviral therapy after infusion of contaminated white cells

We present a sixth human case in which primary human immunodeficiency virus (HIV-1) infection occurred, despite antiretroviral prophylaxis, after accidental inoculation of infected blood. In the prior five instances, variables such as large virus dose, late administration of antivirals, viral resistance to zidovudine, and pre-existent immunosuppression, may have played a role in the treatment failure. In this case, high-dosage oral zidovudine was given within minutes of the accident and replaced 2 1/2 days later with interferon alpha and dideoxyinosine (ddl). Despite aggressive treatment, HIV-1 infection was demonstrated in blood, spleen, and brain tissue at autopsy 16 days later. Of the tissues studied, detection of HIV-1 was most prominent in the spleen. Double-label immunocytochemistry confirmed the morphologic impression that while some of the infected spleen cells were CD3-positive T cells, the majority were macrophages. Thus, current single or dual (zidovudine, ddl-interferon) therapies for accidental HIV-1 inoculation may not be effective in preventing early infection. Further trials in animals appear warranted to evaluate protection by other strategies, such as passive immunity or combinations of agents that penetrate the brain and attack HIV-1 viral replication at differing sites.

Evaluation and treatment of HIV-related illnesses in the emergency department

Individuals infected with the human immunodeficiency virus (HIV) present frequently to emergency departments for treatment of complications. A working knowledge of the multisystem problems seen in HIV-infected patients is essential for the emergency physician. These problems are reviewed, with an emphasis on the respiratory, central nervous system, and gastrointestinal complications seen in patients with the acquired immune deficiency syndrome (AIDS). A practical approach is offered for management of febrile episodes and the other problems an emergency physician is likely to encounter.

Major expansion of CD8+ T cells with a predominant V beta usage during the primary immune response to HIV

A SIGNIFICANT proportion (up to 70%) of individuals experience an acute clinical syndrome of varying severity associated with primary infection with the human immunodeficiency virus (HIV). We report here studies on six individuals who showed an acute HIV syndrome which generally resolved within four weeks, concomitant with a dramatic downregulation of viraemia. To characterize the T-cell-mediated primary immune response to HIV, we used combined semiquantitative polymerase chain reaction assay and cytofluorometry to analyse the T-cell antigen receptor repertoire in sequential peripheral blood mononuclear cells from the patients. We found major oligoclonal expansions in a restricted set of variable-domain beta-chain (V beta) families. Cells expressing the expanded V beta s predominantly expressed the CD8 T-cell differentiation antigen and mediated HIV-specific cytotoxicity. Major oligoclonal expansions of these CD8+ T lymphocytes may represent an important component of the primary immune response to viral infections and may help to clarify both the immunopathogenic and the protective mechanisms of HIV infection.

Mice immunosuppressed by murine retrovirus infection (MAIDS) are susceptible to cytomegalovirus retinitis

Although various methods of immunosuppression have been used to enhance susceptibility of mice to murine cytomegalovirus (MCMV) retinitis, none reproduce the unique complexity of immune deficiency experienced by patients during the progression of AIDS. C57BL/6 mice are susceptible to a retrovirus-induced murine acquired immune deficiency syndrome (MAIDS), characterized by progressive immune dysfunction which shares many features with AIDS. We therefore evaluated the frequency and severity of MCMV retinitis in C57BL/6 mice with MAIDS. Following subretinal inoculation of MCMV, nearly 90% of mice with MAIDS developed a necrotizing retinitis 8 to 10 days postinfection, whereas retinitis was observed in only 8% of age-matched immunocompetent control mice. Histopathologic analysis of the retinitis that developed in mice with MAIDS revealed features similar to those found in AIDS-related CMV retinitis. Eyes from MAIDS animals also contained on average higher amounts of infectious virus when compared with eyes from control animals. We conclude that retrovirus-induced immunosuppression increases susceptibility of C57BL/6 mice to MCMV retinitis.

HIV vaccine development and clinical trials

The magnitude of HIV pandemic has made the development of HIV vaccines an urgent biomedical research priority. Although the biologic problems in designing a vaccine for a chronic viral infection like HIV are formidable, there has been encouraging progress. More than a dozen first generation prophylactic HIV vaccine candidates have completed phase I human trials that have established the safety and immunogenicity of these products in adults. A phase II trial of two HIV subunit envelope vaccines in adults at high risk of HIV infection is underway in the United States, and preparations for phase III efficacy trials have begun. Preliminary studies are under way to evaluate the potential application of active and passive immunization for preventing vertical transmission of HIV. Because of the higher rate of HIV transmission and a more abbreviated time course to disease, it may be more efficient to evaluate the efficacy of HIV vaccines in HIV infected pregnant women and their offspring than in adults who are exposed sexually to HIV.

Role of lymphoid organs in the pathogenesis of human immunodeficiency virus (HIV) infection

The pathogenic mechanisms of HIV disease are multifactorial and multi-phasic. The common denominator of the disease is the profound immunosuppression that occurs in the vast majority of infected patients. Studies in lymphoid tissues in HIV disease have provided considerable insight into the pathogenic processes involved from the earliest phases of infection through the advanced stages. Following primary infection, virus is disseminated throughout the body and seeds the lymphoid tissue where its replication is only incompletely suppressed and where a reservoir of virus is established. Extracellular virus is trapped within the FDC of the lymph node germinal centers and serves as a source of infection for cells which reside in or migrate through the lymph node throughout the course of infection even during the early and often prolonged asymptomatic period. Eventually, the architecture of the lymphoid tissue is destroyed, compounding the immune dysfunction that results from the depletion of CD4+ T cells. In this regard, the lymphoid tissue of LTNPs is relatively intact and viral burden and replication is considerably lower in the peripheral blood and lymph node mono-nuclear cells of LTNPs than in individuals whose disease progresses. Cytokines probably play a major role in the modulation of HIV expression in the milieu of the lymphoid tissue. Further understanding of the pathogenic mechanisms operative in the lymphoid tissues of HIV-infected individuals will have important implications in the design of therapeutic strategies involving both antiretroviral and immunomodulatory approaches.

Eosinophils and AIDS

Since early descriptions of Acquired Immune Deficiency Syndrome (AIDS) in the 1980s most of our research effort has been focused on a singular population, the CD4 cell population. Numerous investigations have been done into why there is a gradual diminution in CD4 counts; therapeutic interventions have focused on raising abnormally low CD4 levels. I suggest that another cell line, the eosinophil cell line, may also be abnormal in AIDS and hypothesize that an increase in eosinophil cell count and activation of eosinophils may also be important to AIDS.

Development of the anti-gp120 antibody response during seroconversion to human immunodeficiency virus type 1

We have studied the development of the antibody response to the surface glycoprotein gp120 of human immunodeficiency virus type 1 in three individuals who presented with primary human immunodeficiency virus type 1 infection syndrome. Serum anti-gp120 antibodies were first detected 4 to 23 days after presentation, after p24 antigen and infectious-virus titers in the peripheral blood had declined manyfold from their highest values. Whether anti-gp120 antibodies present at undetectable levels are involved in clearance of viremia remains unresolved. Among the earliest detectable anti-gp120 antibodies were those to conformationally sensitive epitopes; these antibodies were able to block the binding of gp120 monomers to soluble CD4 or to a human monoclonal antibody to a discontinuous epitope overlapping the CD4-binding site. Some of these antibodies were type specific to a degree, in that they were more effective at blocking ligand binding to autologous gp120 than to heterologous gp120. However, the appearance of these antibodies did not correlate with that of antibodies able to neutralize the autologous virus in vitro by a peripheral blood mononuclear cell-based assay. Antibodies to the V3 loop were detected at about the same time as, or slightly later than, those to the CD4-binding site. There was a weak correlation between the presence of antibodies to the V3 loop and autologous virus-neutralizing activity in two of three individuals studied. However, serum from the third individual contained V3 antibodies but lacked the ability to neutralize the autologous virus in vitro, even immediately after seroconversion. Thus, no simple, universal correlate of autologous virus-neutralizing activity in a peripheral blood mononuclear cell-based assay is apparent from in vitro assays that rely on detecting antibody interactions with monomeric gp120 or fragments thereof.

Th1 versus Th2 responses in AIDS

During the past two years, a simple theory that seeks to explain what causes the progression of HIV-infected individuals to AIDS has been gaining support. The theory holds that HIV-infected people switch from a T-helper type 1 (Th1) to a T-helper type 2 (Th2) state as the disease progresses. However the experimental data do not support the concept that a Th1/Th2 switch occurs in the majority of HIV-infected subjects, although it is conceivable that HIV-infected individuals who mount sustained and chronic Th2-type responses, as a result of allergic disorders and helminthic infestations, may undergo more active HIV replication and therefore progress faster to full-blown disease.

Gene therapy for human immunodeficiency virus infection: genetic antiviral strategies and targets for intervention

Gene therapeutic strategies for the treatment of human immunodeficiency virus type 1 (HIV-1) infection have received increased attention due to lack of chemotherapeutic drugs or vaccines that show long-term efficacy in vivo. An emerging group, referred to here as "genetic antivirals," is reviewed. Genetic antivirals are defined as DNA or RNA elements that are transferred into cells and affect their intracellular targets either directly, or after expression as RNA or proteins. They include antisense oligonucleotides, ribozymes, RNA decoys, transdominant mutants, toxins, and immunogens. They offer the possibility to target simultaneously multiple sites in the HIV genome, thereby minimizing the production of resistant viruses. We review the molecular mechanisms of genetic antivirals, their HIV molecular targets, and discuss issues concerning their application as anti-HIV agents.

Keynote address: variations in the natural history of HIV infection

In general, the natural history of HIV infection as revealed by prospective cohort studies such as the Multicenter AIDS Cohort Study (MACS) is consistent with our current understanding of the immunopathogenesis of HIV disease. Although the limitations of CD4+ T cell counts as a predictor of response to therapy are now recognized, enumeration of these cells remains an important predictor of outcome. Additional information regarding prognosis can be obtained using other immunological and virological information. Analysis of data from cohort studies has revealed varying patterns of CD4+ lymphocyte count decline associated with differing evidence of immune activation, specific antibody responses, CD8+ T cell responses, and level of viral burden. Of interest, some asymptomatic HIV-infected persons appear to show immune stability in the absence of therapeutic interventions. In addition, the combination of antiretroviral therapy and prophylaxis for Pneumocystis carinii pneumonia (but apparently not prophylaxis for fungal or Mycobacterium avium-intracellulare infections) has prolonged survival in patients with AIDS.

Indirect mechanisms of HIV pathogenesis: how does HIV kill T cells?

Although twelve years have passed since the identification of HIV as the cause of AIDS, we do not yet know how HIV kills its target, the CD4+ T cell, nor how this killing cripples the immune system. Prominent theories include direct killing of infected CD4+ T cells by the action or accumulation of cytopathic viral DNA, transcripts or proteins, or by virus-specific cytotoxic T lymphocytes, and indirect killing of uninfected CD4+ T cells (and other immune cells) by autoimmune mechanisms, cytokines, superantigens, or apoptosis. In the past year, studies have provided tantalizing clues as to why infected cells may not die and how these infected cells kill innocent bystander cells.

Tracking HIV during disease progression

Several recent advances have been made in the delineation of the multiple pathogenic mechanisms involved in the progression of HIV disease. Included among these are the virological and immunological events associated with primary infection and the delineation of the role of lymphoid organs.

Ability of HIV to promote a TH1 to TH0 shift and to replicate preferentially in TH2 and TH0 cells

Both interferon gamma (IFN-gamma) produced by T helper 1 (TH1) lymphocytes and interleukin-4 (IL-4) produced by TH2 lymphocytes were reduced in either bulk circulating mononuclear cells or mitogen-induced CD4+ T cell clones from the peripheral blood of individuals infected with human immunodeficiency virus (HIV). There was a preferential reduction in clones producing IL-4 and IL-5 in the advanced phases of infection. However, enhanced proportions of CD4+ T cell clones producing both TH1-type and TH2-type cytokines (TH0 clones) were generated from either skin-infiltrating T cells that had been activated in vivo or peripheral blood T cells stimulated by antigen in vitro when cells were isolated from HIV-infected individuals. All TH2 and most TH0 clones supported viral replication, although viral replication was not detected in any of the TH1 clones infected in vitro with HIV. These results suggest that HIV (i) does not induce a definite TH1 to TH2 switch, but can favor a shift to the TH0 phenotype in response to recall antigens, and (ii) preferentially replicates in CD4+ T cells producing TH2-type cytokines (TH2 and TH0).

Lack of evidence for the dichotomy of TH1 and TH2 predominance in HIV-infected individuals

A switch from a T helper 1 (TH1) cytokine phenotype to a TH2 phenotype has been proposed as a critical element in the progression of human immunodeficiency virus (HIV) disease. Here, constitutive cytokine expression was analyzed in unfractionated and sorted cell populations isolated from peripheral blood and lymph nodes of HIV-infected individuals at different stages of disease. Expression of interleukin-2 (IL-2) and IL-4 was barely detectable (or undetectable) regardless of the stage of disease. CD8+ cells expressed large amounts of interferon gamma and IL-10, and the levels of these cytokines remained stably high throughout the course of infection. Furthermore, similar patterns of cytokine expression were observed after stimulation in vitro of purified CD4+ T cell populations obtained from HIV-infected individuals at different stages of disease. These results indicate that a switch from the TH1 to the TH2 cytokine phenotype does not occur during the progression of HIV disease.

Antibodies against CD4+ lymphocytes in plasma of HIV-infected patients are related to CD4 cell depletion in vivo

The role of autoimmune phenomena in the pathogenesis of AIDS is not well understood. Antibodies against CD4+ lymphocytes are frequently detectable in HIV-infected patients. However, the relevance of these antibodies is unknown. In this study anti-CD4 cell antibodies in plasma of HIV-infected patients were compared to patients' CD4 cell count. Lymphocytes of a healthy donor were incubated with plasma of patients and controls. Antibodies against CD4+ lymphocytes were detected using anti-human Ig antibodies and monoclonal anti-CD4 antibodies simultaneously. The degree of staining was visualized by flow cytometry. The experiments revealed that 60% of HIV-infected patients harbored anti-CD4 cell antibodies in their plasma. Anti-CD4 cell antibodies were not detectable in plasma of healthy controls. Patients with anti-CD4 cell antibodies in their plasma presented with significantly lower numbers of circulating CD4+ lymphocytes (P = 0.025). The degree of antibody reactivity was negatively correlated to patients' CD4 cell counts (P = 0.02). In conclusion there is evidence for an association between plasma anti-CD4 cell antibodies and CD4 cell depletion. Whether this association represents an epiphenomenon or a pathogenetic relevant pathway needs to be investigated in further studies.

Serum and cerebrospinal fluid levels of soluble intercellular adhesion molecule 1 (sICAM-1) in patients with HIV-1 associated neurological diseases

We measured levels of soluble intercellular adhesion molecule 1 (sICAM-1) in paired serum and CSF samples of 110 HIV-1-positive patients with and without neurological symptoms and 40 HIV-negative non-immune neurological controls, and in sera of 26 asymptomatic HIV-1-positive patients. Serum sICAM-1 levels in asymptomatic HIV-1-positive patients were significantly increased in comparison to HIV-negative controls. Moreover, they were significantly higher in HIV-1-positive patients with AIDS-defining diseases than in the asymptomatic HIV-1-positive group. In subgroups of patients with neurological disease, the highest serum values were found in HIV encephalopathy. CSF levels of sICAM-1 were elevated only in HIV-1-positive patients with neurological disease mainly due to passive diffusion through a defective blood-brain barrier. An sICAM-1 index was calculated as a measure for intrathecal production of sICAM-1 but showed no significant differences between patients with and without neurological involvement. However, increased levels of the sICAM-1 index were found in some patients with opportunistic CNS infection of bacterial or fungal origin. Serum and CSF levels of sICAM-1 correlated with neopterin levels, a marker of interferon-gamma-mediated macrophage activation and CSF sICAM-1 levels were inversely correlated to numbers of CD4+ T cells. Elevated serum sICAM-1 levels already in asymptomatic HIV-1-positive individuals add to the evidence for an early immune activation in HIV infection. With the further increase of serum and CSF s-ICAM-1 in patients with AIDS-defining diseases sICAM-1 could serve as a new surrogate marker similar to neopterin.

Normal and abnormal consequences of apoptosis in the human heart. From postnatal morphogenesis to paroxysmal arrhythmias

Apoptosis and necrosis are two distinctly different forms of cell death, and both occur in the human heart. In contrast to necrosis, apoptosis is not associated with inflammation for two reasons. First, the apoptotic cell does not swell or rupture before it is engulfed by either a macrophage or even a neighboring like cell. Second, the phagocytosis occurs with unusual rapidity. Apoptosis, also thought of as cell suicide, is a tidy way of removing cells no longer useful, in essence a form of selective deletion. These features make apoptosis a valuable component of morphogenesis, mediation of hormonal and immunologic responses, and the homeostatic balance between hypertrophy and atrophy or involution. In the human heart apoptosis has been found in the sinus node of patients with the long QT syndrome. It most likely participates in the important postnatal morphogenesis of the sinus node, AV node, and His bundle. Apoptosis may also participate in the genesis and pathophysiology of cardiomyopathy, paroxysmal arrhythmias, or conduction disturbances (some of which may be responsible for sudden death), focal fibromuscular dysplasia of small coronary arteries, hereditary medial degeneration of the tunica media of coronary arteries, and arrhythmogenic right ventricular dysplasia. The possible role apoptosis in numerous other changes in the human heart, among them the pathogenesis of atherosclerosis and mechanisms of aging in the myocardium, merits future investigation.

Combined intra- and extracellular immunization against human immunodeficiency virus type 1 infection with a human anti-gp120 antibody

In this study, a human CD4+ T lymphocyte line was transduced to secrete Fab fragments of a broadly neutralizing human monoclonal antibody F105 that reacts with the CD4-binding site of human immunodeficiency virus type 1 (HIV-1) envelope protein. In the transduced cells infected with HIV-1, the nascent Fab fragments bind intracellularly to the HIV-1 envelope protein and inhibit HIV-1 production. The secreted Fab fragments are able to neutralize cell-free HIV-1. In addition, the nascent Fab fragments can inhibit HIV-1 production by binding intracellularly to envelope mutants that escape neutralization by extracellular F105 antibody. The combined intra- and extracellular binding activities of the expressed Fab fragments result in the efficient blocking of cytopathic syncytium formation and infectious virus production. Thus, these antibody-producing T lymphocytes are not only resistant to HIV-1 infection but also can protect surrounding lymphocytes by secreting neutralizing antibodies. This novel strategy of combining intracellular and extracellular immunization may be useful for gene therapy of AIDS and other diseases.

Disturbed immunoregulatory properties of the neuropeptide substance P on lymphocyte proliferation in HIV infection

The neuropeptide substance P (SP) is known to increase cell-mediated immune responses in animal models and healthy subjects. Several studies have suggested an involvement of neuropeptides in the immunopathogenesis of some diseases. The study of the immunomodulatory effects of neuropeptides, namely SP, may represent a model for the analysis of immunoregulatory defects in HIV infection at the level of the interaction between the immune and nervous systems, both of which are known to be affected by the virus. In the present study, we investigate the possibility of a disturbance in the immunomodulatory properties of SP in HIV infection by analysing the effects of SP (10(-10)-10(-6) M) on the lymphocyte proliferative responses to concanavalin A (Con A) and phytohaemagglutinin (PHA) assessed by 3H-thymidine incorporation in peripheral blood lymphocytes from 34 HIV-infected patients (16 asymptomatic (ASY)/persistent generalized lymphadenopathy (PGL); 18 ARC/AIDS) and in 37 healthy subjects. In ASY/PGL HIV-infected patients, SP 10(-7) M was identified as the concentration inducing the maximal increase in the lymphocyte responses to Con A and PHA, similarly to what was observed in healthy subjects. In ARC/AIDS patients, SP appeared to inhibit the mitogenic responses, particularly those induced by Con A, in contrast to the effects found either in healthy subjects or in ASY/PGL patients. These results suggest the existence of an alteration in the in vitro immunomodulatory properties of SP in ARC/AIDS patients compared with healthy subjects and ASY/PGL patients. In conclusion, the unexpected finding of an inhibitory effect of SP on lymphocyte proliferation from ARC/AIDS patients justifies further investigation of the neuropeptide-dependent immunoregulatory systems in HIV infection.

Transfer of HIV-1 to human tonsillar stromal cells following cocultivation with infected lymphocytes

The susceptibility of normal human tonsillar stromal cells (HTSCs) to infection by HIV-1 was assessed using transmission electron microscopy (TEM), immunocytochemistry, and HIV-1-specific PCR analyses. Our results demonstrate that HTSCs are efficiently infected following cocultivation with the HIV-1-infected lymphoblastoid cell line GY1. Infected stromal cells contain intracellular viral particles present as free virus or associated with phagocytic vesicles. These particles express the HIV-1-specific p24 antigen as assessed by immunocytochemical analyses using an HIV-specific anti-p24 monoclonal antibody. Moreover, PCR analysis of genomic DNA isolated from particle-bearing tonsillar stromal cells identified HIV-1-specific sequences not present in either uninfected stromal cells or parental GY1 uninfected cells. The mechanism by which HIV-1 infects HTSCs does not appear to be CD4 mediated, as none of the human tonsillar stromal cell lines express CD4 as assessed by flow cytometry, immunohistochemistry, and PCR analysis. Taken together, these results demonstrate that human tonsillar stromal cells can be infected by HIV-1, and that subsequent to infection the viral genome is reverse transcribed, and integrated into the stromal cell DNA. The infection of HTSCs may contribute to HIV-1-mediated pathogenesis indirectly as a viral reservoir or directly by structural and functional modification of the lymphoid microenvironment.

Imbalance between oxidants and antioxidants in the lungs of HIV-seropositive individuals

Following the initial infection with HIV, there is evidence of immune dysfunction despite an apparent normal clinical state. In the context that the lung is a major site affected by opportunistic infection, and that some components of the immune system are activated during early HIV infection, we hypothesized that there may be activation of alveolar macrophages (AM), a key component of the pulmonary host defense system. Compared to cells from normal individuals, AM of asymptomatic HIV-seropositive (HIV+) individuals (CDC-stage II) spontaneously released significantly more superoxide anion (O2-.) (P < 0.002). The O2-. release by AM of HIV-infected individuals was comparable to the spontaneous O2-.-release by AM of cigarette smokers (P > 0.6), a condition often associated with chronic damage of respiratory tissues. The destructive effects of oxidants are normally suppressed by antioxidant defense systems. Evaluation of the concentrations of glutathione, a major component of the pulmonary antioxidant protective screen, demonstrated that the HIV+ state is also characterized by a significant glutathione deficiency in lung epithelial lining fluid (P < 0.001) and in venous plasma (P < 0.001). This suggests that the alveolar structures of HIV+ individuals are continuously exposed to increased amounts of toxic oxygen radicals without adequate protection, i.e. the reactive oxygen metabolites may cause sufficient tissue damage culminating in interstitial lung disease. Further, since many immune functions are susceptible to injury by extracellular oxidants, the consequences of an unsuppressed oxidant burden in the lung may amplify the extent of local immunocompromise. In addition, since glutathione plays an important role in modulating lymphocyte activation and effector functions independent of its antioxidant activity, the systemic glutathione deficiency may contribute to the progressive global immune dysfunction that characterizes HIV infection.

Radiotherapy of primary central nervous system lymphoma in patients with and without human immunodeficiency virus. Ten years of treatment experience at the University of California San Francisco

BACKGROUND

Classic human immunodeficiency virus (HIV) negative primary central nervous system lymphoma (PCNSL) is a relatively uncommon occurrence, whereas the incidence of HIV positive PCNSL has increased dramatically during the past 5 years. Between 2% and 6% of all patients with acquired immune deficiency syndrome (AIDS) will have PCNSL develop clinically, and as many as 11% will have PCNSL found at autopsy. In the United States, some of the earliest and most extensive experience with HIV positive PCNSL has occurred in San Francisco. This article reports on PCNSL in patients with and without HIV.

METHODS

Using our diagnosis-based computer retrieval system, we identified all patients treated with radiotherapy for PCNSL between January 1982 and January 1992 and reviewed their medical records. Population characteristics, risk factors and length of survival (LOS), were analyzed. Statistical methodology included the Cox proportional hazards model and Kaplan-Meier survival curves.

RESULTS

Fifty-six patients were identified with PCNSL, of which 41 were HIV positive and 15 were HIV negative. There was a fourfold increase in the total number of PCNSL cases during the time period 1987-1991 as compared with the preceding 5 years; these cases primarily were in the HIV positive group. The average Karnofsky performance score (KPS) in the HIV positive group was 50, whereas in the HIV negative group, the KPS was 35. However, the median LOS in the HIV positive group was 3 months, whereas in the HIV negative group it was 20 months. Within each group, there was a statistically significant correlation between KPS and LOS.

CONCLUSIONS

Patients with HIV and PCNSL have a much shorter median LOS than do patients with PCNSL but without HIV; however, the outcome for both groups is dismal. Randomized clinical trials are needed to determine which patients with HIV might benefit from more aggressive therapy and to determine the optimal choice and dosages of chemoradiation therapy for patients with PCNSL without HIV.

Unique lentivirus--host interactions: SIVsmmPBj14 infection of macaques

The most virulent primate lentivirus identified to date, the simian virus SIVsmmPBj14 (SIV-PBj14), is unique not only because it causes acute disease and death within days instead of months or years, but also because of its replicative and cellular activation properties. The acute disease syndrome has many features in common with primary HIV-1 disease, but differences in the respective outcomes of these two acute lentiviral infections appear to be linked to the rapidity with which SIV-PBj14 replicates and the high titers of virus that subsequently accumulate in lymphoid tissues. The most prominent pathologic feature of SIV-PBj14 is extensive lymphoid hyperplasia of T-cell zones, especially in the gut-associated lymphoid tissue. These expanded T-cell zones contain a high proportion of lymphoblasts, activated macrophages and syncytial cells, which are positively correlated with high numbers of SIV antigen-positive cells. Replication of the virus to high titers, accompanied by extensive cellular activation and proliferation, leading to high levels of cytokines, such as interleukin-6 and tumor necrosis factor-alpha, are consistent with acute inflammatory disease. The pathogenesis of SIV-PBj14 also appears to correlate most directly with some of its unique biologic properties, such as the ability to replicate in resting peripheral blood mononuclear cells, to activate lymphocytes, and to induce lymphocyte proliferation. Biologically and molecularly cloned viruses derived from SIV-PBj14 and isolates obtained from macaque PBj at earlier times, are being used to identify viral determinants that influence biologic and pathogenic properties of SIV-PBj14. Further characterization of this virus should provide new insights into lentivirus-cell interactions and their contributions to disease.

Intracellular antibodies as a new class of therapeutic molecules for gene therapy

Intracellularly expressed antibodies, referred to as "intrabodies" can be designed to bind and inactivate target molecules inside cells. In our previous study, mammalian cells were transduced to produce an anti-gp120 single-chain intrabody sFv105 to inactivate human immunodeficiency virus type-1 (HIV-1) infection. Here, an inducible expression vector was constructed in which the sFv105 intrabody, which reacts with the CD4-binding site of HIV-1 gp120, is under the control of the HIV-1 long terminal repeat (LTR)/promoter. The sFv105 intrabody is inducibly expressed after HIV-1 infection or in the presence of Tat protein and is retained intracellularly. A human CD4+ lymphocyte line transformed with the expression vector exhibits resistance to the virus-mediated syncytium formation and a decreased ability to support HIV-1 production. Surface gp120 expression is markedly reduced and surface CD4 is restored to normal following HIV-1 infection in the transformed lymphocytes. Cell-surface phenotype, replication rate, morphology, and response to mitogenic stimulation of the transformed cells are also normal. Thus, intrabodies are a new class of active molecules that may be useful for the gene therapy of acquired immunodeficiency virus (AIDS) and other diseases.

An alternative view of the Th1/Th2 switch hypothesis in HIV infection

A theory that seeks to explain what induces the relentless progression of HIV-infected subjects to AIDS has received considerable attention. This theory holds that HIV infection results in a Th1/Th2 switch. However, analysis of constitutive cytokine mRNA expression in lymphoid tissues from HIV-infected individuals did not confirm an in vivo Th1/Th2 switch. Moreover, data available at the level of in vitro-stimulated peripheral blood mononuclear cells or cloned T cells do not provide clear evidence for a definite switch to the Th2 responses in any HIV-infected subject and in any phase of HIV infection. At most, currently available data on the profile of cytokines released in response to in vitro stimulation suggest a Th1-to-Th0 shift in a proportion of memory CD4+ T cells. On the other hand, experiments of in vitro infection with HIV of already established CD4+ T cell clones indicated that Th2 and Th0 cells support HIV replication better than Th1 cells, suggesting that early destruction of Th2 cells by direct or indirect HIV-mediated cell killing may occur. Finally, in some HIV-infected individuals with low CD4+ T cell counts, a prevalence of CD8+ T cells producing type 2 cytokines was found in both peripheral blood and skin. Thus, although the induction of a general Th2 state in HIV infection is not proven, enhanced production of type 2 cytokines may occur in a proportion of HIV-infected individuals and play some role in the pathogenesis of the disease.

The nature of the autoimmune antibody repertoire in human immunodeficiency virus type 1 infection

Human immunodeficiency virus type 1 (HIV-1) seropositive donors typically have high serum antibody titers to a range of autoantigens, and the corresponding autoantibodies have been suggested to be of importance in the pathogenesis of HIV-1 infection. We have prepared 38 IgG human monoclonal autoantibodies from asymptomatic HIV-1 seropositive donors with elevated serum titers to autoantigens by construction of Fab combinatorial libraries on the surface of phage and affinity selection using a range of autoantigens, including double-stranded DNA, major histocompatibility complex class II, CD14, epidermal growth factor receptor, and ganglioside GD2. The autoantibodies are shown to be of moderate affinity and exhibit marked cross-reactivity with a range of antigens. This contrasts with the specific high-affinity antibodies selected (i) against infectious agents using the same libraries and (ii) against one of the autoantigens using a library from a donor with established autoimmune disease. The results lend no support to the presence of specific autoantibodies in HIV-1 infection and instead suggest attention should be focused on the pathological significance of high serum levels of antibodies capable of interacting with multiple molecular species.