Human follicular dendritic cells remain uninfected and capture human immunodeficiency virus type 1 through CD54-CD11a interaction

Host Molecule Incorporation into HIV Virions, Potential Influences in HIV Pathogenesis

During the last phase of HIV viral production, nascent HIV virions acquire a fraction of the cellular lipid membrane to create the external lipid envelope, a process by which cellular proteins present on the surface of the infected cell can be incorporated along with Env trimers. Interestingly, several studies indicated that these incorporated host molecules could conserve their biological activity and consequently contribute to HIV pathogenesis either by enhancing the infectivity of HIV virions, their tissue tropism or by affecting immune cell functions. The following review will describe the main approaches used to characterize membrane bound host molecule incorporation into HIV virions, the proposed mechanisms involved, and the role of a non-exhaustive list of incorporated molecules.

Human Milk Extracellular Vesicles: A Biological System with Clinical Implications

The consumption of human milk by a breastfeeding infant is associated with positive health outcomes, including lower risk of diarrheal disease, respiratory disease, otitis media, and in later life, less risk of chronic disease. These benefits may be mediated by antibodies, glycoproteins, glycolipids, oligosaccharides, and leukocytes. More recently, human milk extracellular vesicles (hMEVs) have been identified. HMEVs contain functional cargos, i.e., miRNAs and proteins, that may transmit information from the mother to promote infant growth and development. Maternal health conditions can influence hMEV composition. This review summarizes hMEV biogenesis and functional contents, reviews the functional evidence of hMEVs in the maternal–infant health relationship, and discusses challenges and opportunities in hMEV research.

Active PD-L1 incorporation within HIV virions functionally impairs T follicular helper cells

The limited development of broadly neutralizing antibodies (BnAbs) during HIV infection is classically attributed to an inadequate B-cell help brought by functionally impaired T follicular helper (Tfh) cells. However, the determinants of Tfh-cell functional impairment and the signals contributing to this condition remain elusive. In the present study, we showed that PD-L1 is incorporated within HIV virions through an active mechanism involving p17 HIV matrix protein. We subsequently showed that in vitro produced PD-L1high but not PD-L1low HIV virions, significantly reduced Tfh-cell proliferation and IL-21 production, ultimately leading to a decreased of IgG1 secretion from GC B cells. Interestingly, Tfh-cell functions were fully restored in presence of anti-PD-L1/2 blocking mAbs treatment, demonstrating that the incorporated PD-L1 proteins were functionally active. Taken together, the present study unveils an immunovirological mechanism by which HIV specifically exploits the regulatory potential of PD-L1 to suppress the immune system during the course of HIV infection.

During HIV infection, the development of effective BnAbs remains a rare phenomenon, occurring in only 15–20% of HIV-infected individuals after years of infection. Although multiple mechanisms may be involved, recent studies have suggested that functional impairment of Tfh cells, through immune checkpoint (IC)/IC-Ligand (IC-L) interactions, may lead to a decrease in B-cell help leading to low BnAbs production. Our laboratory recently showed that PD-L1 was predominantly expressed on lymph node (LN) migratory dendritic cells located predominantly in extra-follicular areas, implying that the source of IC-L contributing to Tfh-cell functional impairment may be independent of cellular expression of IC-L. These observations prompted us to investigate the potential contribution of IC-L incorporated within HIV virion envelope to Tfh-cell functional impairment. We subsequently demonstrated that PD-L1 was incorporated into a large fraction of HIV virions in the plasma of viremic HIV-infected individuals. Interestingly, PD-L1 remains active when incorporated into HIV virions envelope and could impaired Tfh-cell proliferation, resulting in decreased IgG1 production by B cells in vitro. These findings demonstrate an unsuspected mechanism contributing to the regulation of Tfh-cell function, which may contribute to the low production of BnAbs by B cells during HIV infection.

HIV-1-Specific Chimeric Antigen Receptor T Cells Fail To Recognize and Eliminate the Follicular Dendritic Cell HIV Reservoir In Vitro

The major obstacle to a cure for HIV infection is the persistence of replication-competent viral reservoirs during antiretroviral therapy. HIV-specific chimeric antigen receptor (CAR) T cells have been developed to target latently infected CD4⁺ T cells that express virus either spontaneously or after intentional latency reversal. Whether HIV-specific CAR-T cells can recognize and eliminate the follicular dendritic cell (FDC) reservoir of HIV-bound immune complexes (ICs) is unknown. We created HIV-specific CAR-T cells using human peripheral blood mononuclear cells (PBMCs) and a CAR construct that enables the expression of CD4 (domains 1 and 2) and the carbohydrate recognition domain of mannose binding lectin (MBL) to target native HIV Env (CD4-MBL CAR). We assessed CAR-T cell cytotoxicity using a carboxyfluorescein succinimidyl ester (CFSE) release assay and evaluated CAR-T cell activation through interferon gamma (IFN-γ) production and CD107a membrane accumulation by flow cytometry. CD4-MBL CAR-T cells displayed potent lytic and functional responses to Env-expressing cell lines and HIV-infected CD4⁺ T cells but were ineffective at targeting FDC bearing HIV-ICs. CD4-MBL CAR-T cells were unresponsive to cell-free HIV or concentrated, immobilized HIV-ICs in cell-free experiments. Blocking intercellular adhesion molecule-1 (ICAM-1) inhibited the cytolytic response of CD4-MBL CAR-T cells to Env-expressing cell lines and HIV-infected CD4⁺ T cells, suggesting that factors such as adhesion molecules are necessary for the stabilization of the CAR-Env interaction to elicit a cytotoxic response. Thus, CD4-MBL CAR-T cells are unable to eliminate the FDC-associated HIV reservoir, and alternative strategies to eradicate this reservoir must be sought.IMPORTANCE Efforts to cure HIV infection have focused primarily on the elimination of latently infected CD4⁺ T cells. Few studies have addressed the unique reservoir of infectious HIV that exists on follicular dendritic cells (FDCs), persists in vivo during antiretroviral therapy, and likely contributes to viral rebound upon cessation of antiretroviral therapy. We assessed the efficacy of a novel HIV-specific chimeric antigen receptor (CAR) T cell to target both HIV-infected CD4⁺ T cells and the FDC reservoir in vitro Although CAR-T cells eliminated CD4⁺ T cells that express HIV, they did not respond to or eliminate FDC bound to HIV. These findings reveal a fundamental limitation to CAR-T cell therapy to eradicate HIV.

The Incorporation of Host Proteins into the External HIV-1 Envelope

The incorporation of biologically active host proteins into HIV-1 is a well-established phenomenon, particularly due to the budding mechanism of viral egress in which viruses acquire their external lipid membrane directly from the host cell. While this mechanism might seemingly imply that host protein incorporation is a passive uptake of all cellular antigens associated with the plasma membrane at the site of budding, this is not the case. Herein, we review the evidence indicating that host protein incorporation can be a selective and conserved process. We discuss how HIV-1 virions displaying host proteins on their surface can exhibit a myriad of altered phenotypes, with notable impacts on infectivity, homing, neutralization, and pathogenesis. This review describes the canonical and emerging methods to detect host protein incorporation, highlights the well-established host proteins that have been identified on HIV-1 virions, and reflects on the role of these incorporated proteins in viral pathogenesis and therapeutic targeting. Despite many advances in HIV treatment and prevention, there remains a global effort to develop increasingly effective anti-HIV therapies. Given the broad range of biologically active host proteins acquired on the surface of HIV-1, additional studies on the mechanisms and impacts of these incorporated host proteins may inform the development of novel treatments and vaccine designs.

Immunophenotyping of Sheep Paraffin-Embedded Peripheral Lymph Nodes

Sheep are not only a major livestock species globally, they are also an important large animal model for biomedical research and have contributed to our understanding of the ontogeny and architecture of the mammalian immune system. In this study, we applied immunohistochemistry and multicolor immunofluorescence in fixed and paraffin-embedded lymph nodes to phenotype the key populations of antigen presenting cells, lymphocytes, and stromal cells that orchestrate the host adaptive immune response. We used an extensive panel of antibodies directed against markers associated with dendritic cells (MHC class II, CD83, and CD208), macrophages (CD11b, CD163, and CD169), stromal cells (CNA.42, S100, and CD83), and lymphocytes (CD3, Pax5, CD4, CD8). Using different methods of tissue fixation and antigen retrieval, we provide a detailed immunophenotyping of sheep lymph nodes including the identification of potential subpopulations of antigen presenting cells and stromal cells. By characterizing cells expressing combinations of these markers in the context of their morphology and location within the lymph node architecture, we provide valuable new tools to investigate the structure, activation, and regulation of the sheep immune system in health and disease.

Exosomes from breast milk inhibit HIV-1 infection of dendritic cells and subsequent viral transfer to CD4+ T cells

OBJECTIVE

To investigate whether exosomes derived from human breast milk or plasma confer protection against HIV-1 infection of monocyte-derived dendritic cells (MDDCs) and subsequent viral transfer to CD4 T cells.

DESIGN

MDDCs were generated and milk and plasma-derived exosomes were isolated from healthy donors. To determine the capacity of exosomes to inhibit HIV-1 infection, MDDCs were preincubated with exosomes before exposure to HIV-1BaL. To investigate transfer of HIV-1 from MDDCs to CD4 T cells, MDDCs preincubated with exosomes and HIV-1BaL were cocultured with allogeneic CD4 T cells. To explore receptors used by MDDCs for binding of exosomes, blocking experiments were performed.

METHODS

Productive HIV-1 infection was analysed in MDDCs and CD4 T cells by determining p24 expression by flow cytometry. Confocal microscopy and flow cytometry was used to investigate uptake of fluorescently labelled exosomes by MDDCs.

RESULTS

Milk exosomes, but not plasma exosomes, bind MDDCs via DC-SIGN inhibiting HIV-1 infection of MDDCs and subsequent viral transfer to CD4 T cells.

CONCLUSION

We propose that milk exosomes act as a novel protective factor against vertical transmission of HIV-1 by competing with HIV-1 for binding to DC-SIGN on MDDCs.

Role of Follicular Dendritic Cells in the Early HIV-1 Infection:In vitroModel without Specific Antibody

About 90% of HIV-1 RNA in the lymph nodes is reported to localize in follicular dendritic cellsnetwork (FDC-NW) as early as several days after infection and as much as that in the late stage. But the mechanism remains to be fully understood. To elucidate the role of follicular dendritic cells (FDC) in the early stage of HIV-1 infection, FDC-like cell strains (FDCLC) were established and they were characterized in the co-culture system with T cells for their effect on HIV-1 trapping and replication in p24 immunoassay, immunohistochemistry as well as confocal and electronmicroscopy. Established FDCLC were positive for CNA-42, S-100alpha and intercellular desmosome-like junctions. L-SIGN and DC-SIGN were also detected in FDCLC. Alu-HIV-1 PCR analysis showed no HIV-1 integration in FDCLC. FDCLC trapped HIV-1 and transferred them to uninfected MOLT-4 T cells (MOLT-4) efficiently in the absence of specific antibody. FDCLC also accelerated HIV-1 replication in HIV-1-pre-exposed MOLT-4. These unique FDCLC effects were explained, at least partly, by the fact that FDCLC up-regulated CD4 expression in MOLT-4 and helped T cells escape from apoptosis in the co-culture. These data suggest that FDC/FDCLC engage not only in trapping but also in active expansion of HIV-1 in the absence of specific antibody.

Analysis of humoral immune responses in rhesus macaques vaccinated with attenuated SIVmac239Deltanef and challenged with pathogenic SIVmac251

BACKGROUND

To determine the correlation between protection and humoral immune response against simian immunodeficiency virus (SIVmac251), 11 macaques were immunized with live-attenuated SIVmac239Deltanef either intravenously or via the tonsils and exposed to SIVmac251 after either 6 or 15 months along with unvaccinated controls.

RESULTS

Independent of the route of vaccine application, viremia was significantly reduced in vaccinees compared with controls 2 weeks post-challenge. Concomitantly, viremia correlated inversely with SIV-specific IgG, complement-mediated lysis and neutralizing antibodies and these parameters seemed to contribute to reduced viremia. During chronic infection, six monkeys controlled viremia in the circulation (two or fewer infectious units per 10(6) PBMCs) and showed no signs of trapping in lymphatic tissues (Appendix S1).

CONCLUSIONS

As no significant differences were observed throughout the study, with respect to the humoral immune response and viremia control, between the two vaccinated cohorts, mucosal immunization strategies are recommended due to more simplified application.

Antiretroviral effect of lovastatin on HIV-1-infected individuals without highly active antiretroviral therapy (The LIVE study): a phase-II randomized clinical trial

Background

Highly active antiretroviral therapy produces a significant decrease in HIV-1 replication and allows an increase in the CD4 T-cell count, leading to a decrease in the incidence of opportunistic infections and mortality. However, the cost, side effects and complexity of antiretroviral regimens have underscored the immediate need for additional therapeutic approaches. Statins exert pleiotropic effects through a variety of mechanisms, among which there are several immunoregulatory effects, related and unrelated to their cholesterol-lowering activity that can be useful to control HIV-1 infection.

Methods/design

Randomized, double-blinded, placebo controlled, single-center, phase-II clinical trial. One hundred and ten chronically HIV-1-infected patients, older than 18 years and naïve for antirretroviral therapy (i.e., without prior or current management with antiretroviral drugs) will be enrolled at the outpatient services from the most important centres for health insurance care in Medellin-Colombia. The interventions will be lovastatin (40 mg/day, orally, for 12 months; 55 patients) or placebo (55 patients). Our primary aim will be to determine the effect of lovastatin on viral replication. The secondary aim will be to determine the effect of lovastatin on CD4+ T-cell count in peripheral blood. As tertiary aims we will explore differences in CD8+ T-cell count, expression of activation markers (CD38 and HLA-DR) on CD4 and CD8 T cells, cholesterol metabolism, LFA-1/ICAM-1 function, Rho GTPases function and clinical evolution between treated and not treated HIV-1-infected individuals.

Discussion

Preliminary descriptive studies have suggested that statins (lovastatin) may have anti HIV-1 activity and that their administration is safe, with the potential effect of controlling HIV-1 replication in chronically infected individuals who had not received antiretroviral medications. Considering that there is limited clinical data available on this topic, all these findings warrant further evaluation to determine if long-term administration of statins may benefit the virological and immunological evolution in HIV-1-infected individuals before the use of antiretroviral therapy is required.

Trial registration

Registration number NCT00721305.

HIV-1 upregulates intercellular adhesion molecule-1 gene expression in lymphoid tissue of patients with chronic HIV-1 infection

OBJECTIVES

Intercellular adhesion molecule (ICAM)-1 is an adhesion molecule that plays an important role in the transmission of HIV-1 to CD4+ target cells and in the decrease of these cells in lymphoid tissue (LT). Our main objective was to study ICAM-1 expression in LT from HIV-1-infected persons and to correlate this expression with LT viral load and the immunoarchitecture alteration before and after highly active antiretroviral therapy (HAART).

METHODS

Tonsillar LT samples from 16 patients with chronic asymptomatic HIV-1 infection were studied before initiating treatment and after 12 months of HAART. ICAM-1 protein expression was studied by immunohistochemistry in all cases, and ICAM-1 messenger RNA (mRNA) was quantified from frozen tissue in 6 patients using quantitative real-time polymerase chain reaction (PCR). LT viral load was determined by PCR. The LT immunoarchitecture, p24 immunoexpression, and CD4+ cell count were assessed from tissue sections.

RESULTS

Before initiating HAART, there was high immunohistochemical ICAM-1 expression in follicular dendritic and endothelial cells and high ICAM-1 mRNA quantification. These findings correlated with a high LT viral load, strong p24 expression, and an effacement of LT immunoarchitecture with a low number of CD4+ cells. After HAART, there was a significant decrease of immunohistochemical and gene ICAM-1 expression. These results correlated with a significant decrease of LT viral load and p24 immunoexpression, a recovery of LT architecture, and a significant increase of CD4+ cells.

CONCLUSIONS

HIV-1 upregulates ICAM-1 expression in LT. This finding is associated with a marked effacement of LT architecture. HAART produces downregulation of ICAM-1 expression and recovery of LT architecture by reducing LT viral load significantly.

Complement-HIV interactions during all steps of viral pathogenesis

Upon crossing the endothelial barrier of the host, HIV initiates immediate responses of the immunity system. Among its components, the complement system is one of the first the first elements, which are activated to affect HIV propagation. Complement participates not only in the early phase of the immune response, but its effects can be observed continuously and also concern the induction and modification of the adaptive immune response. Here we discuss the role of complement in early and late stages of HIV pathogenesis and review the escape mechanisms, which protect HIV from destruction by the complement system.

Human immunodeficiency virus type 1 replication in dendritic cell-T-cell cocultures is increased upon incorporation of host LFA-1 due to higher levels of virus production in immature dendritic cells

Dendritic cells (DCs) act as a portal for invasion by human immunodeficiency virus type-1 (HIV-1). Here, we investigated whether virion-incorporated host cell membrane proteins can affect virus replication in DC-T-cell cocultures. Using isogenic viruses either devoid of or bearing host-derived leukocyte function-associated antigen 1 (LFA-1), we showed that HIV-1 production is augmented when LFA-1-bearing virions are used compared to that for viral entities lacking this adhesion molecule. This phenomenon was observed in immature monocyte-derived DCs (IM-MDDCs) only and not in DCs displaying a mature phenotype. The increase is not due to higher virus production in responder CD4(+) T cells but rather is linked with a more important productive infection of IM-MDDCs. We provided evidence that virus-associated host LFA-1 molecules do not affect a late event in the HIV-1 life cycle but rather exert an effect on an early step in virus replication. We demonstrated that the enhancement of productive infection of IM-MDDCs that is conferred by virus-anchored host LFA-1 involves the protein kinase A (PKA) and PKC signal transduction pathways. The biological significance of this phenomenon was established by performing experiments with virus stocks produced in primary human cells and anti-LFA-1 antibodies. Together, our results indicate that the association between some virus-bound host proteins and their natural cognate ligands can modulate de novo HIV-1 production by IM-MDDCs. Therefore, the additional interactions between virus-bound host cell membrane constituents and counter receptors on the surfaces of DCs can influence HIV-1 replication in IM-MDDC-T-cell cocultures.

Immunogenicity of Salmonella vector vaccines expressing SBR of Streptococcus mutans under the control of a T7-nirB (dual) promoter system

The purpose of the present study was to determine if a Salmonella vector expressing the cloned saliva-binding region (SBR) of Streptococcus mutans or SBR linked to the A2 and B subunits of cholera toxin (CTA2/B) under the control of both the T7 and nirB promoters (T7-nirB dual promoter) was more effective in inducing mucosal and systemic anti-SBR antibody responses than Salmonella clones expressing the same antigens but under the control of either the nirB or T7 promoter. Mice were immunized by the intranasal route on days 0, 18 and 320 with Salmonella enterica serovar Typhimurium strain BRD 509 containing one of six plasmids encoding SBR or SBR-CTA2/B under the control of the T7-nirB, T7, or nirB promoter. Serum, saliva and vaginal wash samples were collected throughout the experiment and assessed for antibody activity by ELISA. Evidence is provided that Salmonella clones expressing SBR or SBR-CAT2/B under the control of either the T7 or T7-nirB promoter induced a high and persistent mucosal and systemic anti-SBR antibody response. All Salmonella clones induced good anti-SBR responses following the boost on day 320.

Expression of HIV receptors, alternate receptors and co-receptors on tonsillar epithelium: implications for HIV binding and primary oral infection

Background

Primary HIV infection can develop from exposure to HIV in the oral cavity. In previous studies, we have documented rapid and extensive binding of HIV virions in seminal plasma to intact mucosal surfaces of the palatine tonsil and also found that virions readily penetrated beneath the tissue surfaces. As one approach to understand the molecular interactions that support HIV virion binding to human mucosal surfaces, we have examined the distribution of the primary HIV receptor CD4, the alternate HIV receptors heparan sulfate proteoglycan (HS) and galactosyl ceramide (GalCer) and the co-receptors CXCR4 and CCR5 in palatine tonsil.

Results

Only HS was widely expressed on the surface of stratified squamous epithelium. In contrast, HS, GalCer, CXCR4 and CCR5 were all expressed on the reticulated epithelium lining the tonsillar crypts. We have observed extensive variability, both across tissue sections from any tonsil and between tonsils, in the distribution of epithelial cells expressing either CXCR4 or CCR5 in the basal and suprabasal layers of stratified epithelium. The general expression patterns of CXCR4, CCR5 and HS were similar in palatine tonsil from children and adults (age range 3–20). We have also noted the presence of small clusters of lymphocytes, including CD4⁺ T cells within stratified epithelium and located precisely at the mucosal surfaces. CD4⁺ T cells in these locations would be immediately accessible to HIV virions.

Conclusion

In total, the likelihood of oral HIV transmission will be determined by macro and micro tissue architecture, cell surface expression patterns of key molecules that may bind HIV and the specific properties of the infectious inoculum.

Statins Could Be Used to Control Replication of Some Viruses, Including HIV-1

Statins are mainly known for their plasma cholesterol-lowering properties and are widely used for the prevention of cardiovascular diseases. They however also exert pleiotropic effects through a variety of mechanisms, among which several immunosuppressive effects that are unrelated to their cholesterol-lowering activity. Interestingly, there has been recent evidence of antiviral effects, including preliminary studies on the efficacy of statins against HIV-1. This paper more particularly focuses on the specific inhibition of the binding of leukocyte function-associated antigen-1 (LFA-1) to intercellular adhesion molecule (ICAM-1) by statins, independently of the inhibition of HMGCoA reductase. Targeting the statin-binding site within LFA-1 or regulating LFA-1 affinity by inhibiting prenylation of the small GTPases could prove useful to treat inflammatory, autoimmune diseases and possibly viral infections, including HIV-1.

Complement dependent trapping of infectious HIV in human lymphoid tissues

OBJECTIVES

HIV-1 bound extracellularly to follicular dendritic cells (FDC) in germinal centers (GC) of lymphoid tissues (LT) represents the largest viral reservoir in HIV-infected individuals; however there is no direct evidence as to whether HIV trapped in human GC remains infectious. In the GC, complement receptors and Fc gamma receptors have been suggested to participate in trapping of HIV; therefore, the relative contribution of complement- and Fc gamma receptors in binding HIV on LT was investigated and the infectivity of this virus was tested.

DESIGN

As it is difficult to isolate FDC without contaminations of productively infected cells, HIV was detached from LT of HIV positive individuals using antibodies blocking complement- and Fc gamma receptors. Isolated virus was tested in an infectivity assay.

METHODS

HIV detached from LT was quantified by HIV p24 ELISA, PCR and in an in vitro infectivity assay. Presence and accessibility of viral envelope proteins, complement factors and immunoglobulins on the surface of detached viral particles were evaluated through viral capture by respective antibodies.

RESULTS

Although both C3d-fragments and IgG molecules were identified on the surface of HIV detached from LT, trapping of HIV was mediated solely by CR2-C3d interactions, whereas contribution of Fc gamma receptors was not detectable. Infectivity assays with HIV stripped from LT of HIV positive individuals revealed that in four out of ten patients HIV particles were infectious.

CONCLUSIONS

These findings indicate that in the GC infectious virus is trapped on CR2-expressing FDC (or B cells). Reduction of this pool of HIV could be a therapeutic goal.

HIV and human complement: inefficient virolysis and effective adherence

Both, HIV envelope proteins gp120 and gp41 can directly activate complement system, even in the absence of HIV-specific antibodies. During the budding process HIV acquires host membrane-associated molecules among these complement regulatory proteins (CRPs). The presence of CRPs on the viral surface rescues HIV from complement-mediated virolysis. The inefficient virolysis results in the deposition of complement-fragments on the viral surface allowing interactions of HIV with complement receptor expressing cells. In this review, the interaction of HIV with the complement system and the consequences of complement opsonisation on virus infection will be discussed.

The importance of virus-associated host ICAM-1 in human immunodeficiency virus type 1 dissemination depends on the cellular context

The primary objective of this study was to define whether the nature of virion-bound host cell membrane proteins influenced the process of human immunodeficiency virus 1 (HIV-1) capture and transmission. We pulsed cells of monocytoid lineage (established and primary) and CD4-negative epithelial cells transiently expressing DC-SIGN or LFA-1 with isogenic HIV-1 particles either devoid or bearing host-derived ICAM-1 or ICAM-3 before incubation with an indicator cell line. To our surprise, the ICAM-1/LFA-1 association was a more efficient transmission factor than the combined gp120/DC-SIGN and ICAM-3/DC-SIGN interactions. The involvement of the association between virus-bound ICAM-1 and its natural ligand LFA-1 in virus binding and carriage was confirmed when using more physiological cellular targets, i.e., human lymphoid tissues cultured ex vivo. However, the contribution of virus-anchored host ICAM-1 to the process of retention and transmission of HIV-1 could not be confirmed when using primary human cells of macrophage/dendritic lineage as transmitter cells and autologous CD4+ T lymphocytes as targets. Altogether these data underscore the complexity of factors participating in virus-cell contact and efficient dissemination of HIV-1 to target cells.

T cell dynamics in HIV-1 infection

In the absence of antiretroviral treatment, HIV-1 establishes a chronic, progressive infection of the human immune system that invariably, over the course of years, leads to its destruction and fatal immunodeficiency. Paradoxically, while viral replication is extensive throughout the course of infection, deterioration of conventional measures of immunity is slow, including the characteristic loss of CD4(+) T cells that is thought to play a key role in the development of immunodeficiency. This conundrum suggests that CD4(+) T cell-directed viral cytopathicity alone cannot explain the course of disease. Indeed, recent advances now indicate that HIV-1 pathogenesis is likely to result from a complex interplay between the virus and the immune system, particularly the mechanisms responsible for T cell homeostasis and regeneration. We review these data and present a model of HIV-1 pathogenesis in which the protracted loss of CD4(+) T cells results from early viral destruction of selected memory T cell populations, followed by a combination of profound increases in overall memory T cell turnover, damage to the thymus and other lymphoid tissues, and physiological limitations in peripheral CD4(+) T cell renewal.

Role of complement in the control of HIV dynamics and pathogenesis

In all ex vivo preparations of HIV tested so far, C3 fragments and, after seroconversion, antibodies were detected on the viral surface. This indicates that HIV survives complement-mediated lysis. The virus has adopted different protection mechanisms to keep complement activation under the threshold necessary to induce virolysis. Among them are complement regulatory proteins that remain functionally active on the surface of HIV and turn down the complement cascade and serum proteins with complement regulatory activities. Therefore, opsonized virions accumulate in HIV-infected individuals, and subsequently adhere to complement receptor (CR) expressing cells. Among them are B cells, which bind opsonized virus. Such bound virus is efficiently transferred to autologous T cells, which subsequently are infected. Other cells interacting via CR with opsonized HIV are follicular dendritic cells (FDC). As shown by ex vivo experiments, up to 80% of virus is bound to follicular dendritic cells through C3-CR interactions. In the brain, HIV is not only interacting with complement proteins, but is able to induce their expression. Thus, interaction of HIV with the complement system is a main mechanism for pathogenesis to AIDS, since retention of (complement-resistant) opsonized viral particles on cell surfaces via CRs occurs in different compartments in HIV-infected individuals, thereby promoting transmission of virus to other permissive cells.

Potential roles of cellular proteins in HIV-1

Human immunodeficiency virus type-1 particles contain host proteins, both on their surface and interior. This review summarises the cellular proteins found in these virions and covers some of their potential roles in the viral life cycle and pathogenesis. For most proteins studied, their role and function are either unknown or in the hypothesis stage. This reflects the relatively recent emphasis given to these proteins by the HIV-1 field as well as the incomplete understanding of their function in the cell. The study of cellular proteins in HIV-1 promises to help us better understand the interaction of this virus with the cell, the immune system, and the whole human host as well as to shed light on the nature of AIDS and suggest more targets for therapeutic intervention. Finally, many of the cell systems themselves are still poorly understood. The extensive study of HIV-1 has already brought increased attention to the fields of immunology and vaccine science and, in the same way, might assist our understanding of the cellular pathways themselves.

PrP(CWD) lymphoid cell targets in early and advanced chronic wasting disease of mule deer

Up to 15% of free-ranging mule deer in northeastern Colorado and southeastern Wyoming, USA, are afflicted with a prion disease, or transmissible spongiform encephalopathy (TSE), known as chronic wasting disease (CWD). CWD is similar to a subset of TSEs including scrapie and variant Creutzfeldt-Jakob disease in which the abnormal prion protein isoform, PrP(CWD), accumulates in lymphoid tissue. Experimental scrapie studies have indicated that this early lymphoid phase is an important constituent of prion replication interposed between mucosal entry and central nervous system accumulation. To identify the lymphoid target cells associated with PrP(CWD), we used triple-label immunofluorescence and high-resolution confocal microscopy on tonsils from naturally infected deer in advanced disease. We detected PrP(CWD) primarily extracellularly in association with follicular dendritic and B cell membranes as determined by frequent co-localization with antibodies against membrane bound immunoglobulin and CD21. There was minimal co-localization with cytoplasmic labels for follicular dendritic cells (FDC). This finding could indicate FDC capture of PrP(CWD), potentially in association with immunoglobulin or complement, or PrP(C) conversion on FDC. In addition, scattered tingible body macrophages in the germinal centre contained coarse intracytoplasmic aggregates of PrP(CWD), reflecting either phagocytosis of PrP(CWD) on FDC processes, apoptotic FDC or B cells, or actual PrP(CWD) replication within tingible body macrophages. To compare lymphoid cell targets in early and advanced disease, we also examined: (i) PrP(CWD) distribution in lymphoid cells of fawns within 3 months of oral CWD exposure and (ii) tonsil biopsies from preclinical deer with naturally acquired CWD. These studies revealed that the early lymphoid cellular distribution of PrP(CWD) was similar to that in advanced disease, i.e. in a pattern suggesting FDC association. We conclude that in deer, PrP(CWD) accumulates primarily extracellularly and associated with FDCs and possibly B cells - a finding which raises questions as to the cells responsible for pathological prion production.

Differential transmission of human immunodeficiency virus type 1 by distinct subsets of effector dendritic cells

Dendritic cells (DC) support human immunodeficiency virus type 1 (HIV-1) transmission by capture of the virus particle in the mucosa and subsequent transport to the draining lymph node, where HIV-1 is presented to CD4(+) Th cells. Virus transmission involves a high-affinity interaction between the DC-specific surface molecule DC-SIGN and the viral envelope glycoprotein gp120 and subsequent internalization of the virus, which remains infectious. The mechanism of viral transmission from DC to T cells is currently unknown. Sentinel immature DC (iDC) develop into Th1-promoting effector DC1 or Th2-promoting DC2, depending on the activation signals. We studied the ability of these effector DC subsets to support HIV-1 transmission in vitro. Compared with iDC, virus transmission is greatly upregulated for the DC1 subset, whereas DC2 cells are inactive. Increased transmission by DC1 correlates with increased expression of ICAM-1, and blocking studies confirm that ICAM-1 expression on DC is important for HIV transmission. The ICAM-1-LFA-1 interaction is known to be important for immunological cross talk between DC and T cells, and our results indicate that this cell-cell contact is exploited by HIV-1 for efficient transmission.

Retention of antigen on follicular dendritic cells and B lymphocytes through complement-mediated multivalent ligand-receptor interactions: theory and application to HIV treatment

In HIV-infected patients, large quantities of HIV are associated with follicular dendritic cells (FDCs) in lymphoid tissue. During antiretroviral therapy, most of this virus disappears after six months of treatment, suggesting that FDC-associated virus has little influence on the eventual outcome of long-term therapy. However, a recent theoretical study using a stochastic model for the interaction of HIV with FDCs indicated that some virus may be retained on FDCs for years, where it can potentially reignite infection if treatment is interrupted. In that study, an approximate expression was used to estimate the time an individual virion remains on FDCs during therapy. Here, we determine the conditions under which this approximation is valid, and we develop expressions for the time a virion spends in any bound state and for the effect of rebinding on retention. We find that rebinding, which is influenced by diffusion, may play a major role in retention of HIV on FDCs. We also consider the possibility that HIV is retained on B cells during therapy, which like FDCs also interact with HIV. We find that virus associated with B cells is unlikely to persist during therapy.

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.

Presence of host ICAM-1 in laboratory and clinical strains of human immunodeficiency virus type 1 increases virus infectivity and CD4(+)-T-cell depletion in human lymphoid tissue, a major site of replication in vivo

Human immunodeficiency virus type 1 (HIV-1) incorporates several host proteins. Earlier studies have indicated that such foreign constituents can modulate the virus life cycle, although the potential roles that these proteins might play in the viral pathology in vivo remain unclear. In an attempt to shed light on this issue, we first exposed explants of human lymphoid tissue to isogenic viruses except for the presence or absence of host-derived ICAM-1. Incorporation of ICAM-1 alone increased HIV-1 infectivity for human tonsillar tissue cultured ex vivo. This observation was made for viruses bearing distinct coreceptor utilization profiles. Conversion of LFA-1 to a high-affinity-high-avidity state for ICAM-1 further augmented the susceptibility of human tonsillar histocultures to infection by ICAM-1-bearing virions. A more massive depletion of CD4(+) T lymphocytes was seen with X4 ICAM-1/POS viruses than with isogenic ICAM-1/NEG virions. Exposure of X4 and R5 primary isolates of HIV-1 to a blocking anti-ICAM-1 antibody resulted in a decrease of virus infection. Finally, X4 and R5 virions derived from a natural human lymphoid tissue microenvironment incorporated high levels of ICAM-1. Altogether, these results indicate that the incorporation of host ICAM-1 can significantly modulate the biology of HIV-1 in a cellular milieu recognized as the major site of replication in vivo and suggest that host proteins found in HIV-1 particles may participate in the pathogenesis of this disease.

Regulation of primary HIV-1 isolate replication in dendritic cells

The potential role of dendritic cells (DC) in the immunopathology of human immunodeficiency virus 1 (HIV-1) disease remains controversial. This study examines replication of a panel of HIV-1 strains (both laboratory adapted and primary) within DC, in the context of the well-established monocyte-DC and monocyte-macrophage transition. Viral replication was assessed by p24 ELISA assay. All strains of HIV-1 tested replicated in DC. Only CCR5-tropic virus replicated in macrophages. Lipopolysaccharide (LPS) induced DC maturation (as reflected in altered cell phenotype) and at the same time diminished the ability of DC to support HIV-1 replication. In contrast the presence of activated T cells, which had been fixed to prevent them acting as a site for viral replication, enhanced the ability of the DC to support viral replication, as has been reported previously for macrophages. Thus cells that are DC by phenotype, but are not activated, act as the optimum reservoir for HIV-1 replication. If this form of DC is present in peripheral tissues, this will be permissive for amplification of the in vivo viral load at sites where there are few responder cells available, and hence contribute to the persistent immunopathology.

HIV gp120 receptors on human dendritic cells

Dendritic cells (DCs) are important targets for human immunodeficiency virus (HIV) because of their roles during transmission and also maintenance of immune competence. Furthermore, DCs are a key cell in the development of HIV vaccines. In both these settings the mechanism of binding of the HIV envelope protein gp120 to DCs is of importance. Recently a single C-type lectin receptor (CLR), DC-SIGN, has been reported to be the predominant receptor on monocyte-derived DCs (MDDCs) rather than CD4. In this study a novel biotinylated gp120 assay was used to determine whether CLR or CD4 were predominant receptors on MDDCs and ex vivo blood DCs. CLR bound more than 80% of gp120 on MDDCs, with residual binding attributable to CD4, reconfirming that CLRs were the major receptors for gp120 on MDDCs. However, in contrast to recent reports, gp120 binding to at least 3 CLRs was observed: DC-SIGN, mannose receptor, and unidentified trypsin resistant CLR(s). In marked contrast, freshly isolated and cultured CD11c(+ve) and CD11c(-ve) blood DCs only bound gp120 via CD4. In view of these marked differences between MDDCs and blood DCs, HIV capture by DCs and transfer mechanisms to T cells as well as potential antigenic processing pathways will need to be determined for each DC phenotype.

Attachment of human immunodeficiency virus-1 (HIV-1) particles bearing host-encoded B7-2 proteins leads to nuclear factor-kappa B- and nuclear factor of activated T cells-dependent activation of HIV-1 long terminal repeat transcription

Previous studies have shown that human immunodeficiency virus type-1 (HIV-1) can incorporate several surface proteins of host origin. Recent findings indicate that host-encoded cell surface constituents retain their functionality when found embedded into the viral envelope. The primary objective of the current study was to define whether interaction between some specific virion-bound host proteins with their natural cognate ligands present on target cells could mediate intracellular signaling cascade(s). For this purpose, we have generated a whole series of isogenic virus stocks (NL4-3 backbone) bearing or not bearing on their surface foreign CD28, CD54 (ICAM-1), CD80 (B7-1) or CD86 (B7-2) proteins. Our results indicate that incubation of human T lymphoid cells with virions bearing host-derived B7-2 proteins and anti-CD3 antibody can potently activate HIV-1 long terminal repeat-driven gene expression. This up-regulating effect necessitates the involvement of nuclear factor-kappa B (NF-kappa B) and nuclear factor of activated T cells (NFAT) as revealed by the use of vectors coding for dominant negative versions of both transcription factors (i.e. I kappa B alpha S32A/36A and dnNFAT) and band shift assays. The increase of NF-kappa B activity was abolished when infection with B7-2-bearing HIV-1 particles was performed in the presence of the fusion protein CTLA-4 Ig suggesting that the interaction between virally embedded B7-2 and CD28 on the target cell is responsible for the observed NF-kappa B induction. The findings presented here provide the first demonstration that host-encoded proteins acquired by HIV-1 can mediate signal transduction events.

Residual Cell-Associated Unspliced HIV-1 Rna in Peripheral Blood of Patients on Potent Antiretroviral Therapy Represents Intracellular Transcripts

Unspliced HIV-RNA (HIV-UsRNA) associated with peripheral blood mononuclear cells (PBMCs) persists in patients on potent antiretroviral therapy even in the absence of detectable plasma HIV-RNA. To further characterize such residual HIV-RNA, cell-associated virion-encapsidated HIV and intracellular unspliced HIV-RNA were differentiated and monitored using a novel highly sensitive method. In addition, expression of HIV-mRNA encoding tat and rev was assessed. PBMCs of patients with unsuppressed plasma viraemia harboured an extracellular fraction of HIV-UsRNA, which correlated highly with intracellular HIV-RNA levels. Thus, extracellular PBMC-associated HIV-RNA may, to a significant extent, reflect nascent virions attached to productively infected cells. Upon treatment with potent antiretroviral therapy resulting in plasma viraemia <50 copies/ml, expression of cell-associated viral particles was hardly discernible in PBMCs but transcription of unspliced HIV-RNA persisted. Given the virtual absence of rev-mRNA, translation of residual HIV-UsRNA was probably precluded by retention of these transcripts in the nucleus. As shown by limiting dilution analysis, HIV-1 infected cells with such a repressed viral transcription pattern were observed at high frequencies in PBMC from untreated patients.

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.

Impact of TNFalpha, LTalpha, Fc gammaRII and complement receptor on HIV-1 trapping in lymphoid tissue from HIV-infected patients

OBJECTIVES

To investigate HIV trapping mechanisms in patients with acute infection and in asymptomatic individuals prior to and during antiretroviral therapy. To determine the role of complement receptor (CR), Fc gamma receptor II (Fc gammaRII), tumour necrosis factor alpha (TNFalpha), and lymphotoxin alpha (LTalpha) expression in HIV trapping efficiency.

METHODS

Lymphoid tissues from three acutely HIV-infected patients and six asymptomatic, chronically HIV-infected patients collected prior to and during antiretroviral therapy were compared with lymphoid tissues from six HIV-seronegative subjects. HIV, TNFalpha and LTalpha RNA expression was detected and quantified by fluorescence in situ hybridization. CR, Fc gammaRII and HIV p24 antigen were detected and quantified by fluorescence immunohistochemistry.

RESULTS

The amount of trapped HIV did not differ significantly between patients with acute HIV infection and asymptomatic individuals, and was independent of the presence of CR or Fc gammaRII expression. However, in patients with acute infection, the amount of trapped virus was correlated inversely with the number of HIV-infected cells (P = 0.0092) and with the size of the light zone (P = 0.037). In these patients, the number of TNFalpha-expressing cells was correlated inversely with the amount of trapped virus (P = 0.014) and positively correlated with the size of the light zone in germinal centers (P = 0.041). No correlations were observed between TNFalpha or LTalpha expression and Fc gammaRII or CR expression.

CONCLUSION

This report provides the first evidence that in humans TNFalpha is involved in the development of lymphoid follicles, HIV trapping, and, consequently, in early host immune responses. A model is proposed for early events in patients during acute HIV infection.

Highly active antiretroviral therapy results in HIV type 1 suppression in lymph nodes, increased pools of naive T cells, decreased pools of activated T cells, and diminished frequencies of peripheral activated HIV type 1-specific CD8+ T cells

This study examines sequential lymph nodes from 13 drug-naive patients before and after 24 weeks of highly active antiretroviral therapy (HAART). A multipronged approach was used to study changes in HIV-1 RNA in each paired lymph node in relation to tissue architecture and frequency of naive T cells. After 24 weeks, all patients showed significant suppression of plasma viral load and 12 of 13 showed concordant viral suppression in the lymph node (p = 0.001). Using in situ hybridization and quantitative image analysis, we showed that HIV-1 RNA was reduced to below detectable levels (two copies per cell) in follicular dendritic cell (FDC) and mononuclear cell pools. Independent immunohistochemical analysis of lymph node sections revealed that 5 of 13 patients displayed increased FDC networks and 6 of 13 showed no change and all patients showed increases in tissue-resident CD4+ cells. All lymph node biopsies at 24 weeks showed increased proportions of CD4+ and CD8+ cells coexpressing the naive markers CD45RA and CD62L when compared with baseline values. Significant correlations existed between viral load suppression and loss of activated CD8+ T cells after 24 weeks in both lymph node and blood, which was mirrored by significantly lowered frequencies of activated peripheral Gag peptide/MHC tetramer+ CD8+ cells. Overall, these data show that a potent and successful treatment strategy that significantly suppresses and removes FDC-resident HIV-1 results in improvements in lymphoid architecture and by so doing provides the structures available for increased numbers of naive cells to interact with cognate antigen. In addition, our article shows that suppression of HIV-1 replication results in diminished frequencies of peripherally activated antigen-specific CD8+ cells.

Detachment of human immunodeficiency virus type 1 from germinal centers by blocking complement receptor type 2

After the transition from the acute to the chronic phase of human immunodeficiency virus (HIV) infection, complement mediates long-term storage of virions in germinal centers (GC) of lymphoid tissue. The contribution of particular complement receptors (CRs) to virus trapping in GC was studied on tonsillar specimens from HIV-infected individuals. CR2 (CD21) was identified as the main binding site for HIV in GC. Monoclonal antibodies (MAb) blocking the CR2-C3d interaction were shown to detach 62 to 77% of HIV type 1 from tonsillar cells of an individual in the presymptomatic stage. Although they did so at a lower efficiency, these antibodies were able to remove HIV from tonsillar cells of patients under highly active antiretroviral therapy, suggesting that the C3d-CR2 interaction remains a primary entrapment mechanism in treated patients as well. In contrast, removal of HIV was not observed with MAb blocking CR1 or CR3. Thus, targeting CR2 may facilitate new approaches toward a reduction of residual virus in GC.

CD4-Negative cells bind human immunodeficiency virus type 1 and efficiently transfer virus to T cells

The ability of human immunodeficiency virus strain MN (HIV(MN)), a T-cell line-adapted strain of HIV, and X4 and R5 primary isolates to bind to various cell types was investigated. In general, HIV(MN) bound to cells at higher levels than did the primary isolates. Virus bound to both CD4-positive (CD4(+)) and CD4-negative (CD4(-)) cells, including neutrophils, Raji cells, tonsil mononuclear cells, erythrocytes, platelets, and peripheral blood mononuclear cells (PBMC), although virus bound at significantly higher levels to PBMC. However, there was no difference in the amount of HIV that bound to CD4-enriched or CD4-depleted PBMC. Virus bound to CD4(-) cells was up to 17 times more infectious for T cells in cocultures than was the same amount of cell-free virus. Virus bound to nucleated cells was significantly more infectious than virus bound to erythrocytes or platelets. The enhanced infection of T cells by virus bound to CD4(-) cells was not due to stimulatory signals provided by CD4(-) cells or infection of CD4(-) cells. However, anti-CD18 antibody substantially reduced the enhanced virus replication in T cells, suggesting that virus that bound to the surface of CD4(-) cells is efficiently passed to CD4(+) T cells during cell-cell adhesion. These studies show that HIV binds at relatively high levels to CD4(-) cells and, once bound, is highly infectious for T cells. This suggests that virus binding to the surface of CD4(-) cells is an important route for infection of T cells in vivo.

Anti-CD4-binding domain antibodies complexed with HIV type 1 glycoprotein 120 inhibit CD4+ T cell-proliferative responses to glycoprotein 120

HIV-specific CD4+ helper T cell responses, particularly to the envelope glycoproteins, are usually weak or absent in the majority of HIV-seropositive individuals. Since antibodies, by their capacity to alter antigen uptake and processing, are known to have modulatory effects on CD4+ T cell responses, we investigated the effect of antibodies produced by HIV-infected individuals on the CD4+ T cell response to HIV-1 gp120. Proliferative responses of gp120-specific CD4+ T cells were inhibited in the presence of either serum immunoglobulin from HIV-infected individuals or human monoclonal antibodies specific for the CD4-binding domain (CD4bd) of gp120. Human monoclonal antibodies to other gp120 epitopes did not have the same effect. The anti-CD4bd antibodies complexed with gp120 suppressed T cell lines specific for varying gp120 epitopes but did not affect T cell proliferation to non-HIV antigens. Moreover, inhibition by the anti-CD4bd/gp120 complexes was observed regardless of the types of antigen-presenting cells used to stimulate the T cells. These results indicate that the presence of anti-CD4bd antibodies complexed with gp120 can strongly suppress CD4+ helper T responses to gp120.

Treatment-induced decline of human immunodeficiency virus-1 p24 and HIV-1 RNA in lymphoid tissue of patients with early human immunodeficiency virus-1 infection

We report detailed quantitative analysis of human immunodeficiency virus-1 (HIV-1) p24 and HIV-1 RNA in tonsil biopsies from 13 patients with early, asymptomatic HIV infection before and during combination antiretroviral therapy. Using fluorescent microscopy in conjunction with reverse transcriptase-polymerase chain reaction of frozen tissue sections, we show that plasma and tissue viral loads decreased by approximately 3 logs during the 1-year treatment period, with good correlation between the HIV-1 p24 and HIV-1 RNA response in tissue. The decrease of tissue viral load was delayed compared to plasma viral load, possibly explained by the observation that the amount of follicular dendritic cell-associated virus correlated best with the area under the curve of plasma HIV-1 RNA throughout the last 12 weeks. Before and during treatment, the relative proportions of HIV-1 on follicular dendritic cells and within mononuclear cells remained constant, suggesting similar decay characteristics in these two lymphoid tissue compartments. However, viral p24 or RNA remained almost always detectable in tissue despite full suppression of HIV-1 RNA in plasma, and increased even after short-term rebounds in plasma viral load. Thus, full and sustained suppression of viral replication was required to efficiently decrease viral load in lymphoid tissue, but complete abolition of residual viral replication was not achieved.

Immune complexes containing human immunodeficiency virus type 1 primary isolates bind to lymphoid tissue B lymphocytes and are infectious for T lymphocytes

This study investigated the interaction of tonsil B lymphocytes with immune complexes containing human immunodeficiency virus (HIV IC) primary isolates and the infectivity of the B cell-bound HIV IC. Treatment of virus with a source of antibody and complement increased HIV IC binding to B cells by 5.6-fold. Most of the HIV IC that bound to B cells were not internalized but remained on the cell surface and were gradually released over 72 h. Cell-bound HIV IC were highly infectious for T cells while virus released by cultured B cells was only slightly infectious. Removal of HIV IC from the B-cell surface by protease treatment reduced the infection of T cells to near-background levels, indicating that infectious virus remained on the B-cell surface. These studies show that B lymphocytes can carry and transfer infectious HIV IC to T cells and thus suggest a novel mode of infection of T cells in lymphoid tissue that could be important for pathogenesis during HIV infection.