The pathobiology of HIV infection

Splenic Transcriptional Responses in Severe Visceral Leishmaniasis: Impaired Leukocyte Chemotaxis and Cell Cycle Arrest

Structural changes in the spleen have been reported in several infectious diseases. In visceral leishmaniasis (VL), a severe parasitic disease caused by Leishmania spp., the loss of white pulp accompanies a severe clinical presentation. Hamster model reproduces aspects of human VL progression. In the early stages, a transcriptomic signature of leukocyte recruitment was associated with white pulp hyperplasia. Subsequently, impaired leukocyte chemotaxis with loss of T lymphocytes in the periarteriolar lymphoid sheath occurred. This differential gene expression was subsequently corroborated by transcriptomic profiling of spleens in severe human VL. At the latest stage, spleen disorganization was associated with increasing clinical signs of VL. White pulp disruption was accompanied by decreased DLK1 expression. The expression of CXCL13, CCR5, CCL19, CCR6, CCR7 and LTA decreased, likely regulated by CDKN2A overexpression. Our findings enlighten a pathway implying cell cycle arrest and decreased gene expression involved in spleen organization.

Co-receptor signaling in the pathogenesis of neuroHIV

The HIV co-receptors, CCR5 and CXCR4, are necessary for HIV entry into target cells, interacting with the HIV envelope protein, gp120, to initiate several signaling cascades thought to be important to the entry process. Co-receptor signaling may also promote the development of neuroHIV by contributing to both persistent neuroinflammation and indirect neurotoxicity. But despite the critical importance of CXCR4 and CCR5 signaling to HIV pathogenesis, there is only one therapeutic (the CCR5 inhibitor Maraviroc) that targets these receptors. Moreover, our understanding of co-receptor signaling in the specific context of neuroHIV is relatively poor. Research into co-receptor signaling has largely stalled in the past decade, possibly owing to the complexity of the signaling cascades and functions mediated by these receptors. Examining the many signaling pathways triggered by co-receptor activation has been challenging due to the lack of specific molecular tools targeting many of the proteins involved in these pathways and the wide array of model systems used across these experiments. Studies examining the impact of co-receptor signaling on HIV neuropathogenesis often show activation of multiple overlapping pathways by similar stimuli, leading to contradictory data on the effects of co-receptor activation. To address this, we will broadly review HIV infection and neuropathogenesis, examine different co-receptor mediated signaling pathways and functions, then discuss the HIV mediated signaling and the differences between activation induced by HIV and cognate ligands. We will assess the specific effects of co-receptor activation on neuropathogenesis, focusing on neuroinflammation. We will also explore how the use of substances of abuse, which are highly prevalent in people living with HIV, can exacerbate the neuropathogenic effects of co-receptor signaling. Finally, we will discuss the current state of therapeutics targeting co-receptors, highlighting challenges the field has faced and areas in which research into co-receptor signaling would yield the most therapeutic benefit in the context of HIV infection. This discussion will provide a comprehensive overview of what is known and what remains to be explored in regard to co-receptor signaling and HIV infection, and will emphasize the potential value of HIV co-receptors as a target for future therapeutic development.

HIV Neuropathogenesis in the Presence of a Disrupted Dopamine System

Antiretroviral therapy (ART) has transformed HIV into a chronic condition, lengthening and improving the lives of individuals living with this virus. Despite successful suppression of HIV replication, people living with HIV (PLWH) are susceptible to a growing number of comorbidities, including neuroHIV that results from infection of the central nervous system (CNS). Alterations in the dopaminergic system have long been associated with HIV infection of the CNS. Studies indicate that changes in dopamine concentrations not only alter neurotransmission, but also significantly impact the function of immune cells, contributing to neuroinflammation and neuronal dysfunction. Monocytes/macrophages, which are a major target for HIV in the CNS, are responsive to dopamine. Therefore, defining more precisely the mechanisms by which dopamine acts on these cells, and the changes in cellular function elicited by this neurotransmitter are necessary to develop therapeutic strategies to treat neuroHIV. This is especially important for vulnerable populations of PLWH with chemically altered dopamine concentrations, such as individuals with substance use disorder (SUD), or aging individuals using dopamine-altering medications. The specific neuropathologic and neurocognitive consequences of increased CNS dopamine remain unclear. This is due to the complex nature of HIV neuropathogenesis, and logistical and technical challenges that contribute to inconsistencies among cohort studies, animal models and in vitro studies, as well as lack of demographic data and access to human CNS samples and cells. This review summarizes current understanding of the impact of dopamine on HIV neuropathogenesis, and proposes new experimental approaches to examine the role of dopamine in CNS HIV infection. Graphical abstract HIV Neuropathogenesis in the Presence of a Disrupted Dopamine System. Both substance abuse disorders and the use of dopaminergic medications for age-related diseases are associated with changes in CNS dopamine concentrations and dopaminergic neurotransmission. These changes can lead to aberrant immune function, particularly in myeloid cells, which contributes to the neuroinflammation, neuropathology and dysfunctional neurotransmission observed in dopamine-rich regions in HIV+ individuals. These changes, which are seen despite the use antiretroviral therapy (ART), in turn lead to further dysregulation of the dopamine system. Thus, in individuals with elevated dopamine, the bi-directional interaction between aberrant dopaminergic neurotransmission and HIV infection creates a feedback loop contributing to HIV associated neurocognitive dysfunction and neuroHIV. However, the distinct contributions and interactions made by HIV infection, inflammatory mediators, ART, drugs of abuse, and age-related therapeutics are poorly understood. Defining more precisely the mechanisms by which these factors influence the development of neurological disease is critical to addressing the continued presence of neuroHIV in vulnerable populations, such as HIV-infected older adults or drug abusers. Due to the complexity of this system, understanding these effects will require a combination of novel experimental modalities in the context of ART. These will include more rigorous epidemiological studies, relevant animal models, and in vitro cellular and molecular mechanistic analysis.

Histological Disorganization of Spleen Compartments and Severe Visceral Leishmaniasis

The spleen is a secondary lymphoid organ responsible for immune surveillance against blood-circulating pathogens. Absence of the spleen is associated with increased susceptibility to systemic spread and fatal infection by different pathogens. Severe forms of visceral leishmaniasis are associated with disorganization of spleen compartments where cell interactions essential for splenic immunological function take place. White pulp atrophies, secondary lymphoid follicles and marginal zones vanish, and the boundaries separating white and red pulp blur. Leukocyte populations are reduced or disappear or are replaced by plasma cells. In this paper, we review the published data on spleen disorganization in severe forms of visceral leishmaniasis and propose a histological classification to help the exchange of information among research groups.

HIV replication in CD4+ T lymphocytes in the presence and absence of follicular dendritic cells: inhibition of replication mediated by α-1-antitrypsin through altered IκBα ubiquitination

Follicular dendritic cells (FDCs) increase HIV replication and virus production in lymphocytes by increasing the activation of NF-κB in infected cells. Because α-1-antitrypsin (AAT) decreases HIV replication in PBMCs and monocytic cells and decreases NF-κB activity, we postulated that AAT might also block FDC-mediated HIV replication. Primary CD4(+) T cells were infected with HIV and cultured with FDCs or their supernatant with or without AAT, and ensuing viral RNA and p24 production were monitored. NF-κB activation in the infected cells was also assessed. Virus production was increased in the presence of FDC supernatant, but the addition of AAT at concentrations >0.5 mg/ml inhibited virus replication. AAT blocked the nuclear translocation of NF-κB p50/p65 despite an unexpected elevation in associated phosphorylated and ubiquitinated IκBα (Ub-IκBα). In the presence of AAT, degradation of cytoplasmic IκBα was dramatically inhibited compared with control cultures. AAT did not inhibit the proteasome; however, it altered the pattern of ubiquitination of IκBα. AAT decreased IκBα polyubiquitination linked through ubiquitin lysine residue 48 and increased ubiquitination linked through lysine residue 63. Moreover, lysine reside 63-linked Ub-IκBα degradation was substantially slower than lysine residue 48-linked Ub-IκBα in the presence of AAT, correlating altered ubiquitination with a prolonged IκBα t(1/2). Because AAT is naturally occurring and available clinically, examination of its use as an inhibitory agent in HIV-infected subjects may be informative and lead to the development of similar agents that inhibit HIV replication using a novel mechanism.

Cell reservoirs in lymph nodes infected with HIV-1 subtype E differ from subtype B: identification by combined in situ polymerase chain reaction and immunohistochemistry

In Thailand, the predominant HIV subtype is E, rather than subtype B as in North America and Europe. Subtype E has the ability to replicate in vitro in Langerhans cells. We hypothesized that this cell type might constitute a reservoir for the HIV virus in infected lymph nodes. We examined lymph nodes from 25 HIV-1 subtype E-infected patients to determine the immunophenotype of HIV-1-infected cells, their numbers and their distribution. The presence of HIV was detected either by in situ reverse transcriptase-polymerase chain reaction or immunoperoxidase. Cell identity was determined by double labelling using alkaline phosphatase-based immunohistochemistry. The majority of HIV-infected cells in the lymph nodes were Langerhans cells (CD1a+S100+) and Langerhans-related dendritic cells (p55+S100+). These cells were located in the paracortical areas of lymph nodes, with a few cells scattered at the edges of germinal centers, but were absent from germinal centers themselves, in contrast to the reported distribution of subtype B virus. In addition, multinucleated giant cells were significantly more common in HIV-infected nodes (64%) compared to controls (4%) (P=0.00002). In conclusion, Langerhans histiocytes and related cells are reservoirs for HIV subtype E in lymph nodes. Disrupting the pathway of infection of Langerhans cells and related cells may be a viable strategy to interfere with transmission of HIV subtype E.

Astrocytes and microglia differentially regulate trafficking of lymphocyte subsets across brain endothelial cells

Feline brain endothelial cells (BECs), astrocytes, and microglia were combined in different configurations in a cell culture insert system to assess the effect of different cell types on the trafficking of peripheral blood mononuclear cell (PBMC) subsets in response to feline immunodeficiency virus (FIV). The addition of astrocytes to BECs significantly increased the adherence of PBMCs. This increase in adherence was suppressed by microglia, whereas microglia alone had no effect on PBMC adherence. FIV exposure of the glial cells did not alter PBMC adherence as compared to same configurations with untreated cells. All PBMC subsets showed some level of trafficking across the endothelial cell layer. The level of trafficking of monocytes and B cells was significantly increased if astrocytes were present. The presence of microglia with the astrocytes reduced transmigration across all PBMC subsets. FIV exposure of astrocytes significantly increased the percentage of CD8 T cell transmigration from 24% to 64% of the total CD4 and CD8 numbers. The presence of microglia significantly reversed the preferential trafficking of CD8 cells in the presence of astrocytes. The results suggested that interaction between the triad of endothelial cells, astrocytes, and microglia played an important, but varying, role in the trafficking of different PBMC subsets. In general, astrocytes had a positive effect on trafficking of PBMCs, while microglia had a suppressive effect. Effects of FIV on trafficking were largely restricted to increases seen in CD8 T cells and monocytes.

Productive HIV infection of resting CD4+ T cells: role of lymphoid tissue microenvironment and effect of immunomodulating agents

The ability of resting CD4+ T cells to support HIV replication is relevant to understanding how the reservoir of HIV-1-infected resting CD4+ T cells is generated, maintained and, hopefully, how it might be reduced or eliminated. We have utilized a tonsillar histoculture system to demonstrate that HIV, particularly X4 strains, can productively infect phenotypically resting CD4+ T cells in vitro and that this event is largely dependent on the lymphoid tissue microenvironment. Highly purified CD4+ tonsillar T cells that lack expression of both cell surface and nuclear antigens characteristic of classic T cell activation produce X4 HIV-1 mRNA, p24, and infectious virus while maintaining a resting phenotype when cultured in a tonsillar tissue microenvironment; in contrast, comparable purified resting CD4+ tonsillar T cells that have been exposed to X4 HIV do not support HIV replication when cultured in the absence of a lymphoid tissue microenvironment. HIV production from phenotypically resting CD4+ T cells is dramatically inhibited by anti-proinflammatory cytokine agents or immunosuppressive cytokines, but is only modestly suppressed by an inhibitor of the cell cycle. The ability of resting CD4+ T cells to support HIV replication in the microenvironment of the lymphoid tissue has implications in the pathogenesis of HIV disease and may provide an additional avenue for therapeutic intervention.

Different localization of dendritic cell reservoirs in human immunodeficiency virus-1 subtype B versus subtype E-infected lymph nodes

The presence of p24 protein was studied in lymph nodes from human immunodeficiency virus (HIV)-positive patients affected by persistent generalized lymphadenopathy. Paraffin-embedded lymph node sections from 50 HIV-1 subtype E-infected lymph nodes from patients in Thailand and 25 HIV-1 presumably subtype B-infected lymph nodes from patients in the United States were immunostained with p24 HIV major core and capsid monoclonal antibodies using the streptavidin-biotin immunoperoxidase technique. Positivity for HIV p24 protein was detected in 20 of 22 HIV-1 subtype B infected nodes in which lymphoid follicles were present, with p24 staining demonstrating a reticular pattern within the germinal centers. Interestingly, no case from 50 clade E-infected lymph nodes containing lymphoid follicles had such a reticular pattern in the germinal centers. This difference could be explained by differential infection of subsets of dendritic cells by the two HIV-1 clades, or perhaps by different routes of initial HIV-1 transmission.

Follicular dendritic cells and the persistence of HIV infectivity: the role of antibodies and Fcgamma receptors

Large quantities of HIV are found trapped on the surface of follicular dendritic cells (FDCs), and virus persists on these cells until they ultimately die. We recently found that FDCs maintain HIV infectivity for long periods in vivo and in vitro. Because FDCs trap Ags (and virus) in the form of immune complexes and are rich in FcgammaRs, we reasoned that Ab and FcgammaRs may be required for FDC-mediated maintenance of HIV infectivity. To investigate this hypothesis, HIV immune complexes were formed in vitro and incubated for increasing times with or without FDCs, after which the remaining infectious virus was determined by HIV-p24 production in rescue cultures. FDCs maintained HIV infectivity in vitro in a dose-dependent manner but required the presence of specific Ab for this activity regardless of whether laboratory-adapted or primary X4 and R5 isolates were tested. In addition, Abs against either virally or host-encoded proteins on the virion permitted FDC-mediated maintenance of HIV infectivity. We found that the addition of FDCs to HIV immune complexes at the onset of culture gave optimal maintenance of infectivity. Moreover, blocking FDC-FcgammaRs or killing the FDCs dramatically reduced their ability to preserve virus infectivity. Finally, FDCs appeared to decrease the spontaneous release of HIV-1 gp120, suggesting that FDC-virus interactions stabilize the virus particle, thus contributing to the maintenance of infectivity. Therefore, optimal maintenance of HIV infectivity requires both Ab against particle-associated determinants and FDC-FcgammaRs.

Persistence of infectious HIV on follicular dendritic cells

Follicular dendritic cells (FDCs) trap Ags and retain them in their native state for many months. Shortly after infection, HIV particles are trapped on FDCs and can be observed until the follicular network is destroyed. We sought to determine whether FDCs could maintain trapped virus in an infectious state for long periods of time. Because virus replication would replenish the HIV reservoir and thus falsely prolong recovery of infectious virus, we used a nonpermissive murine model to examine maintenance of HIV infectivity in vivo. We also examined human FDCs in vitro to determine whether they could maintain HIV infectivity. FDC-trapped virus remained infectious in vivo at all time points examined over a 9-mo period. Remarkably, as few as 100 FDCs were sufficient to transmit infection throughout the 9-mo period. Human FDCs maintained HIV infectivity for at least 25 days in vitro, whereas virus without FDCs lost infectivity after only a few days. These data indicate that HIV retained on FDCs can be long lived even in the absence of viral replication and suggest that FDCs stabilize and protect HIV, thus providing a long-term reservoir of infectious virus. These trapped stores of HIV may be replenished with replicating virus that persists even under highly active antiretroviral therapy and would likely be capable of causing infection on cessation of drug therapy.

HTLV type 1 infection in squirrel monkeys (Saimiri sciureus): a promising animal model for HTLV type 1 human infection

We show that the squirrel monkey Saimiri sciureus is susceptible to experimental infection with either syngeneic or allogeneic HTLV-1-immortalized cells. As in humans, such experimental inoculation leads to chronic infection, and HTLV-1 provirus was detected in PBMCs by PCR. Chronically infected monkeys developed high titers of antibodies against the structural proteins of the virus, as do HTLV-1-infected humans. Furthermore, in serially sacrificed squirrel monkeys infected with HTLV-1, proviral DNA was detected at primary phases of infection in PBMCs, spleens, and lymph nodes. Tax/rex mRNA was also detected by RT-PCR in the PBMCs of two monkeys at 12 days after inoculation and in the spleen and lymph nodes of the monkey sacrificed on Day 12. In this animal, scattered HTLV-1-tax/rex mRNA-positive lymphocytes were detected by in situ hybridization in frozen sections of the spleen. These results indicate that PBMCs, spleen, and lymph nodes serve as major reservoirs for HTLV-1 during the early phase of infection. To evaluate the relationship between viral expression and the immune response during infection, humoral and cytotoxic T cell responses (CTL) were studied at various times after inoculation. Antibodies to HTLV-1 were detected 3 weeks after infection and anti-p40Tax and anti-Env CTL activity was detected 2 months after infection and remained detectable thereafter. Our results indicate that the squirrel monkey provides a useful animal model for studying the pathogenesis of HTLV-1 and for evaluating new candidate vaccines.

Lymphoid organs as a major reservoir for human T-cell leukemia virus type 1 in experimentally infected squirrel monkeys (Saimiri sciureus): provirus expression, persistence, and humoral and cellular immune responses

The aim of this study was to investigate the distribution of human T-cell leukemia virus type 1 (HTLV-1) in various organs of serially sacrificed squirrel monkeys (Saimiri sciureus) in order to localize the reservoir of the virus and to evaluate the relationship between viral expression and the humoral or cellular immune response during infection. Six squirrel monkeys infected with HTLV-1 were sacrificed 6, 12, and 35 days and 3, 6, and 26 months after inoculation, and 20 organs and tissues were collected from each animal. PCR and reverse transcription-PCR (RT-PCR) were performed with gag and tax primers. Proviral DNA was detected by PCR in peripheral blood mononuclear cells (PBMCs) of monkeys sacrificed 6 days after inoculation and in PBMCs, spleens, and lymph nodes of monkeys sacrificed 12 and 35 days and 3, 6, and 26 months after inoculation. Furthermore, tax/rex mRNA was detected by RT-PCR in the PBMCs of two monkeys 8 to 12 days after inoculation and in the spleens and lymph nodes of the monkey sacrificed on day 12. In this animal, scattered HTLV-1 tax/rex mRNA-positive lymphocytes were detected by in situ hybridization in frozen sections of the spleen, around the germinal centers and close to the arterial capillaries. Anti-HTLV-1 cell-mediated immunity was evaluated at various times after inoculation. Anti-p40(Tax) and anti-Env cytolytic T-cell responses were detected 2 months after infection and remained detectable thereafter. When Tax peptides were used, this response appeared to be directed against various Tax epitopes. Our results indicate that squirrel monkeys represent a promising animal model for studying the early events of HTLV-1 infection and for evaluating candidate vaccines against HTLV-1.

Organ-specific immune responses associated with infectious disease

The immune response to infection can vary markedly in different organs of the same animal. In some organs, the infection can resolve with subsequent immunity to re-infection, whereas in other organs, pathogens can persist. Here, Christian Engwerda and Paul Kaye highlight the importance of defining organ-specific immune mechanisms for developing strategies that deal effectively with infectious diseases and their associated pathologies.

Multilocular thymic cysts in children with human immunodeficiency virus infection: clinical and pathologic aspects

BACKGROUND

Children with human immunodeficiency virus (HIV) infection have an increased susceptibility to severe and unusual infections, malignancies, and disorders characterized by abnormal lymphoproliferation (e.g., lymphoid interstitial pneumonitis). We report a novel disease entity associated with pediatric HIV infection that is characterized by massive enlargement of the thymus as a result of lymphoid hyperplasia and multicystic changes.

METHODS

Eight patients with HIV infection and cystic enlargement of the thymus are subject of this report. The status of their HIV disease and its clinical and radiologic manifestations at the time of diagnosis of the mediastinal mass are described. Tissue specimens were obtained from six patients and examined by microscopy and immunohistochemistry. The specimens were also evaluated for the evidence of HIV and Epstein-Barr virus by in situ hybridization.

RESULTS

Patients were between 2.1 and 12.1 years of age, with CD4+ cell counts between 102 and 733 cells/mm3. In all eight cases an anterior mediastinal mass was discovered incidentally on radiography of the chest, and computed tomography of the chest revealed a multicystic appearance. Histologic examination demonstrated distortion of the thymic architecture by focal cystic changes, lymphoid follicular hyperplasia, diffuse plasmacytosis, and multinucleated giant cells. In situ hybridization revealed HIV particles on the surface of follicular dendritic cells. Further, results of in situ hybridization for EBV were positive in lymphoid cells from biopsy samples of four patients. The patients were followed between 8 months and 4.8 years. In five patients the mass either decreased in size or resolved completely.

CONCLUSIONS

We describe a series of children with HIV infection and multilocular thymic cysts. We hypothesize that aberrant immunoregulation in these HIV-infected children leads to follicular hyperplasia and multicystic changes in the thymus, causing massive enlargement. EBV infection might also contribute to the pathogenesis of this process. Because none of our patients had symptoms from the mass, and there was no evidence of malignancy in the examined biopsy samples, it seems prudent to manage such children with careful follow-up examinations.

Role of dendritic and follicular dendritic cells in HIV infection and pathogenesis

Dendritic cells (DCs) and follicular dendritic cells (FDCs) play important roles in HIV-mediated pathogenesis. Recent studies have defined new DC subsets and shown that DCs in lymphoid mucosa can both harbor virus and stimulate its spread into CD4(+) T cells. FDCs harbor unspliced HIV mRNA and immune complexed virus, but not actively infectious virus, yet these cells are a key regulated reservoir of virions.

The RGD-containing domain of exogenous HIV-1 Tat inhibits the engulfment of apoptotic bodies by dendritic cells

OBJECTIVE

HIV-1 Tat can be released by infected cells and exert various extracellular functions on bystander cells, possibly contributing to immunodeficiency. In order to investigate whether exogenous Tat can affect antigen presentation, the effects of synthetic Tat on the function of dendritic cells displaying antigen presenting cell phenotype were studied.

DESIGN

Cultured dendritic cells were challenged with apoptotic bodies and monitored for cell engulfment and free intracellular calcium ([Ca2+]i) increase. The effect of synthetic HIV-1 Tat and its RGD-containing domain (peptide 65-80) or basic domain (peptide 46-60) on both functions was investigated.

METHODS

Dendritic cells were obtained by culture of monocytes with granulocyte-macrophage colony-stimulating factor. Apoptosis was induced in Jurkat cells by sub-lethal irradiation. Engulfment of radiolabelled apoptotic bodies by dendritic cells was obtained by a 45 min co-incubation at 37 degrees C. Non-ingested apoptotic bodies were removed and cell-associated radioactivity evaluated in a gamma-counter after cell lysis. Single cell analysis of calcium fluxes was performed by video-microscopy and ratio-imaging, after cell staining with the fluorescent calcium chelator FURA-2.

RESULTS

Apoptotic bodies were engulfed by dendritic cells: this process was accompanied by [Ca2+]i rise. Synthetic HIV-1 Tat inhibited both apoptotic body engulfment and [Ca2+]i increase. The same inhibition was obtained with the RGD-containing domain (peptide 65-80), but not with the basic domain (peptide 46-60) of Tat, suggesting the involvement of an integrin. This integrin is likely to be alpha v beta 3, since RGD-containing peptides from vitronectin, but not from fibronectin, inhibited apoptotic body engulfment. Furthermore, both HIV-1 Tat and its 65-80 peptide blocked [Ca2+]i increase due to beta 3-integrin cross-linking.

CONCLUSIONS

Our results support a role for HIV-1 Tat in decreasing the function of dendritic cells, possibly impairing antigen presentation.

Follicular dendritic cells (FDC) in retroviral infection: host/pathogen perspectives

Follicular dendritic cells (FDC) are found in the follicles of virtually all secondary lymphoid tissues. In health, these cells trap and retain antigens (Ag) in the form of immune complexes and preserve them for months in their native conformation. FDC thus serve as a long-term repository of extracellular Ag important for induction and maintenance of memory responses. In retroviral infection, FDC trap and retain large numbers of retroviral particles with profound effects on FDC. FDC-trapped retrovirus induces follicular hyperplasia, and conventional Ag trapped prior to infection are lost and new Ag cannot be trapped. Concomitantly, antibody-forming cells (AFC) specific for Ag lost from FDC decrease followed by loss of specific serum antibody (Ab). Eventually, FDC die and follicular lysis occurs. From the pathogen perspective, binding to FDC is remarkably beneficial, bringing together virus and activated target cells that are highly susceptible to infection. Furthermore, FDC permit HIV to infect surrounding cells even in the presence of a vast excess of neutralizing Ab. Preliminary data suggest that FDC maintain virus infectivity-even when the virus cannot replicate. Thus retrovirus infection monopolizes FDC networks, thereby transforming the FDC Ag repository into a highly infectious retroviral reservoir.

Spectrum of morphologic changes of lymph nodes in HIV infection

Cervical lymph nodes biopsies from 31 HIV positive patients (with or without AIDS) were studied by histologic methods and immunohistochemistry (StreptABC staining of paraffin sections) to identify cellular and extracellular matrix components. The results were the following: (1) the biopsies were included in the stages of follicular hyperplasia without fragmentation FH-FF (4 cases); follicular hyperplasia with follicular fragmentation FH + FF (16 cases); follicular involution FI (6 cases) and diffuse pattern DP (5 cases); (2) the most important alteration was the germinal centers disruption due to follicle lysis, which began in the light zone; (3) there was coincidence between intrafollicular hemorrhages and segmental hyaline mycroangiopathy; (4) during the progression of the disease occurred; (a) an increase in the number of mast cells, CD68+ and Mac 387+ macrophages; (b) a diffuse augment of collagen III, elastic fibers, laminin, fibronectin and proteoglycans; (c) maintenance of Factor VIII-related antigens in the vascular endothelial cells, with decrease in the expression of Ulex-Europeus I lectin. Follicular hyperplasia (FH - FF or FH + FF) was the most common histologic pattern recognized in the lymph nodes of patients without AIDS and follicular involution and difuse pattern were seen in those who had AIDS. The results indicate that the lymph node biopsies may provide important information about the evolutive stage of the disease and its prognosis.

Influence of chemical allograft preservation procedures on the human immunodeficiency virus

Since chemically preserved allogenic transplants have an established place in reconstructive procedures, the possibility of transferring the human immunodeficiency virus (HIV) with these transplants has been intensively discussed. In this study the authors obtained brain and spleen samples from six HIV-infected cadavers and preserved them with Merthiolate, Cialit, and formaldehyde. After preservation, the tissues were examined for proviral HIV-1 DNA (gag, pol, env) using the polymerase chain reaction. Proviral sequences were clearly demonstrated after the preservation procedure. The results of this study indicate that HIV remains in tissues that have been treated with Merthiolate, formaldehyde, or Cialit. Further investigations are necessary to determine if the virus is in an inactivated or activated form. It can be concluded that, because of the possible transmission of HIV by chemically preserved homografts, serologic screening of donors should be mandatory.

AIDS: a disease of impaired Th-cell renewal?

Individuals who are infected with human immunodeficiency virus (HIV) and develop AIDS are characterized by the progressive loss of T helper (Th) cells, together with an increase in virus load. Despite a remarkable similarity to humans, and their susceptibility to persistent HIV-1 infection, chimpanzees have a relative resistance to the development of AIDS. Here, Jonathan Heeney proposes that the critical underlying event perpetuating the progression to AIDS is the impairment of the immunological microenvironment necessary for competent, antigen-specific, Th-cell renewal. Survival is dependent on the host's ability to preserve the immunological infrastructure sufficiently in order to maintain the capacity for renewal of a balanced, competent Th-cell population.

Follicular dendritic cells and human immunodeficiency virus infectivity

Large amounts of human immunodeficiency virus (HIV) localize on follicular dendritic cells (FDC) in the follicles of secondary lymphoid tissues following viral infection. During clinical latency, active viral infection occurs primarily at these sites. As HIV on FDC is in the form of immune complexes, some of which may be formed with neutralizing antibody, we investigated whether HIV on FDC is infectious. We report here that HIV on FDC is highly infectious. Furthermore, FDC can convert neutralized HIV into an infectious form even in the presence of a vast excess of neutralizing antibody. Thus FDC may provide a mechanism whereby HIV infection can continue in the presence of neutralizing antibody.

Immunosuppression by a noncytolytic virus via T cell mediated immunopathology. Implication for AIDS

HIV is basically a non- or poorly cytocidal virus. Therefore, HIV infections in humans represent an apparent perversity in the balance between the host immune system and infectious agent: This noncytopathic virus infects macrophages, antigen presenting cells, helper T cells and other host cells which are then destroyed by the CD8+ T cell immune response. Thus, HIV infects some of the key cells involved in immune reactions and therefore induces the immune system to destroy itself and thereby enables the virus to persist. Accordingly, immunosuppression is not a cause of HIV cytopathogenicity but a consequence of conventional T cell mediated immunopathology that destroys macrophages antigen presenting cells, T helper cells and facilitates infection by trivial intracellular parasites which eventually cause fatal disease. This immunopathological view of AIDS is testable and, if correct, impinges on rationales for AIDS prevention and treatment.

Variable course of primary simian immunodeficiency virus infection in lymph nodes: relation to disease progression

To investigate the dynamics of spread of simian immunodeficiency virus (SIV) in the lymphoid organs, we sequentially analyzed the viral burden in lymph nodes (LN) of eight rhesus macaques inoculated intravenously with a high or low dose of the pathogenic SIVmac 251 isolate. For each animal, four axillary or inguinal LN were collected during the first weeks of infection and a fifth LN was taken 6 or 8 months later to estimate disease progression. Measurement of SIV RNA by in situ hybridization showed that all of the macaques studied had a phase of acute viral replication in LN between 7 and 14 days postinoculation which paralleled that observed in the blood. In a second phase, productive infection was controlled and viral particles were trapped in the germinal centers that developed in LN. While the peaks of productive infection were similar for the eight animals, marked differences in the numbers of productively infected cells that persisted in LN after primary infection were seen. Differences were less pronounced in the blood, where productive infection was efficiently controlled in all cases. The persistence of productively infected cells in LN after primary infection was found to be associated with more rapid disease progression, as measured by the decrease of the T4/T8 ratio and the occurrence of clinical signs. However, the persistence of a significant level of viral particles in germinal centers was observed even in animals that remained healthy over a 1- to 2-year observation period. This study indicates that the course of primary SIV infection in LN is variable, and it suggests that the initial capacity of the host to control productive infection in LN may determine the rate of disease progression.

Follicular dendritic cells in non-Hodgkin's lymphomas

Follicular dendritic cells (FDC) are restricted to the B-cell regions of secondary lymphoid tissue and to non-Hodgkin's lymphomas derived from the follicular center or the mantle zone. With their cytoplasmic ramifications they form a dense network which contains the B-lymphocytes. In situ, FDC are only detectable at the ultrastructural level or when stained with anti FDC-reagents. On the surface of their dendritic extensions they express transferrin receptors (CD71), the B-cell epitope CD20, class II antigens, the myelomonocytic molecule CD14, the glycoprotein gp50 (CD40), and several receptors for components of the complement system (CD11b, CD21, CD35). Subsequent to an antigen challenge, FDC trap and retain immune-complexes for a long period of time. In vitro FDC and neoplastic lymphocytes spontaneously form small cellular aggregates. This adhesion is mediated by the LFA-1-alpha/beta = ICAM-1, the VLA-4 = VCAM-1, and the ICAM-1 = C3bi- receptor ligand pathways on B-cells and on FDC, respectively. The loss of LFA-1- alpha/beta and ICAM-1 molecules may enable neoplastic lymphocytes to detach from FDC. The monoclonal B-cells now invade new compartments. In vitro, FDC have the capacity to activate resting B-cells and to save them from dying by apoptosis. Signals involved in this activation include cell-surface immunoglobulin and CD40. Immunocytochemistry and autoradiography with single cell suspensions of neoplastic B cells suggest that FDC also provide signals leading to the continued stimulation of lymphoma lymphocytes. During the early stage of HIV infection lymph nodes show an immense follicular hyperplasia, with a massive increase of the dendritic network of FDC. In the later stage of the disease, the continuous involution of the germinal centers is associated with a progressive destruction of FDC.

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.

If it ain't fixed, don't break it

Value-judgements about the need for more 'goal-directed' or 'basic' scientific research beg the question of how the publicly funded scientific enterprise works. An efficient management would start to put things right.

T-cell-mediated immunopathology versus direct cytolysis by virus: implications for HIV and AIDS

It has been much debated as to whether CD4+ T-cell depletion and the pathogenesis of AIDS is the result of direct cytolytic effects of human immunodeficiency virus (HIV), T-cell apoptosis by nonspecific activation, dysregulation of cytokine production, or autoimmunity. In this context, Rolf Zinkernagel and Hans Hengartner discuss data from model infections with non-cytopathic viruses. They suggest that HIV may cause immunosuppression, not by direct cytolytic effects, but rather by a conventional virus-specific cytotoxic T-cell-mediated immunopathology.

Detection of intracellular HIV in lymphocytes by flow cytometry

Various permeabilization procedures and defined gating techniques were tested in order to optimize existing flow cytometric assays and devise a specific assay for the direct detection of intracellular HIV-1 antigens in clinical blood specimens. In our optimal procedure, blood lysed with Orthomune Lysing Reagent was fixed with 3.7% formaldehyde for 10 min at room temperature and then permeabilized with 0.2% Tween 20 for 15 min at room temperature. Cells from whole blood were labeled with either FITC-anti-p18 or FITC-anti-p24 monoclonal antibodies and PE-anti-Leu M9 (CD33) in order to exclude monocytes and granulocytes from the lymphocyte gate. The assay demonstrated that mean percentages of HIV p24 antigen positive cells were increased in patients with advanced disease. The assay in its present form is useful for monitoring disease progression and for monitoring the effects of antiviral therapy in individuals, but it is not currently sensitive enough to detect consistently the low levels of HIV infected peripheral blood cells in asymptomatic individuals.

Immunobiological aspects of HIV treatment

Recent information on the efficacy of anti-retroviral therapy and vaccination strategies has been disappointing as well as confusing. The recently announced Concorde study suggested that there is no advantage to early treatment of asymptomatic HIV infection with azidothymidine alone, even though the levels of CD4+ cells in the treated group were consistently higher than in the untreated group. This will lead to increasing attention being paid to the mechanisms whereby HIV causes AIDS, which have sadly been sidelined in the rush to produce classically based therapies and vaccines. Over the last year many different theories on how HIV kills CD4+ cells and leads to AIDS have been discussed and tentatively explored.

Infection of dendritic cells with HIV1: virus load regulates stimulation and suppression of T-cell activity

Patients with HIV infection show two major types of immunological effects. The first is hyperactivity of both T and B lymphocytes which may be in response to HIV antigens themselves, and the second is a loss in T-cell activity in response to other antigens. Dendritic cells (DC) show a higher rate of infection with HIV than other peripheral blood cells in vitro and in vivo. The effects of HIV infection of DC in vitro on their stimulating capacity for T cells were, therefore, examined. We compared the development of the capacity to stimulate primary proliferative responses to virus in autologous lymphocytes with their potency in stimulating allogeneic cells in the mixed leukocyte reaction (MLR). Small numbers of uninfected DC caused little or no stimulation of autologous lymphocytes, but stimulated high MLR. The level of HIV infection in in vitro infected DC preparations was dependent on the time of infection and the titre of the input virus. DC exposed to low doses of HIV (e.g., 10(3) TCID/10(6) cells) for up to 4 days or to a higher dose (e.g. 10(5) TCID/10(6) cells) for 1 day caused significant primary proliferation in autologous T cells and, under these conditions, capacity to stimulate allogeneic MLR remained intact. However, DC exposed to increasing doses of HIV or infected for a longer period showed reduced capacity to stimulate allogeneic lymphocytes and then a loss of stimulation of autologous cells. This provides evidence suggesting that both stimulatory and inhibitory effects of HIV infection can be produced through infection of DC.