The macrophage origin of the HIV-expressing multinucleated giant cells in hyperplastic tonsils and adenoids

Mechanisms of HIV-1 cell-to-cell transfer to myeloid cells

In addition to CD4+ T lymphocytes, cells of the myeloid lineage such as macrophages, dendritic cells (DCs), and osteoclasts (OCs) are emerging as important target cells for HIV-1, as they likely participate in all steps of pathogenesis, including sexual transmission and early virus dissemination in both lymphoid and nonlymphoid tissues where they can constitute persistent virus reservoirs. At least in vitro, these myeloid cells are poorly infected by cell-free viral particles. In contrast, intercellular virus transmission through direct cell-to-cell contacts may be a predominant mode of virus propagation in vivo leading to productive infection of these myeloid target cells. HIV-1 cell-to-cell transfer between CD4+ T cells mainly through the formation of the virologic synapse, or from infected macrophages or dendritic cells to CD4+ T cell targets, have been extensively described in vitro. Recent reports demonstrate that myeloid cells can be also productively infected through virus homotypic or heterotypic cell-to-cell transfer between macrophages or from virus-donor-infected CD4+ T cells, respectively. These modes of infection of myeloid target cells lead to very efficient spreading in these poorly susceptible cell types. Thus, the goal of this review is to give an overview of the different mechanisms reported in the literature for cell-to-cell transfer and spreading of HIV-1 in myeloid cells.

Virus-Mediated Cell-Cell Fusion

Cell-cell fusion between eukaryotic cells is a general process involved in many physiological and pathological conditions, including infections by bacteria, parasites, and viruses. As obligate intracellular pathogens, viruses use intracellular machineries and pathways for efficient replication in their host target cells. Interestingly, certain viruses, and, more especially, enveloped viruses belonging to different viral families and including human pathogens, can mediate cell-cell fusion between infected cells and neighboring non-infected cells. Depending of the cellular environment and tissue organization, this virus-mediated cell-cell fusion leads to the merge of membrane and cytoplasm contents and formation of multinucleated cells, also called syncytia, that can express high amount of viral antigens in tissues and organs of infected hosts. This ability of some viruses to trigger cell-cell fusion between infected cells as virus-donor cells and surrounding non-infected target cells is mainly related to virus-encoded fusion proteins, known as viral fusogens displaying high fusogenic properties, and expressed at the cell surface of the virus-donor cells. Virus-induced cell-cell fusion is then mediated by interactions of these viral fusion proteins with surface molecules or receptors involved in virus entry and expressed on neighboring non-infected cells. Thus, the goal of this review is to give an overview of the different animal virus families, with a more special focus on human pathogens, that can trigger cell-cell fusion.

Cell-to-Cell Spreading of HIV-1 in Myeloid Target Cells Escapes SAMHD1 Restriction

We demonstrate that HIV-1 uses a common two-step cell-to-cell fusion mechanism for massive virus transfer from infected T lymphocytes and dissemination to myeloid target cells, including dendritic cells and macrophages as well as osteoclasts. This cell-to-cell infection process bypasses the restriction imposed by the SAMHD1 host cell restriction factor for HIV-1 replication, leading to the formation of highly virus-productive multinucleated giant cells as observed in vivo in lymphoid and nonlymphoid tissues of HIV-1-infected patients. Since myeloid cells are emerging as important target cells of HIV-1, these results contribute to a better understanding of the role of these myeloid cells in pathogenesis, including cell-associated virus sexual transmission, cell-to-cell virus spreading, and establishment of long-lived viral tissue reservoirs.

Dendritic cells (DCs) and macrophages as well as osteoclasts (OCs) are emerging as target cells of HIV-1 involved in virus transmission, dissemination, and establishment of persistent tissue virus reservoirs. While these myeloid cells are poorly infected by cell-free viruses because of the high expression levels of cellular restriction factors such as SAMHD1, we show here that HIV-1 uses a specific and common cell-to-cell fusion mechanism for virus transfer and dissemination from infected T lymphocytes to the target cells of the myeloid lineage, including immature DCs (iDCs), OCs, and macrophages, but not monocytes and mature DCs. The establishment of contacts with infected T cells leads to heterotypic cell fusion for the fast and massive transfer of viral material into OC and iDC targets, which subsequently triggers homotypic fusion with noninfected neighboring OCs and iDCs for virus dissemination. These two cell-to-cell fusion processes are not restricted by SAMHD1 and allow very efficient spreading of virus in myeloid cells, resulting in the formation of highly virus-productive multinucleated giant cells. These results reveal the cellular mechanism for SAMHD1-independent cell-to-cell spreading of HIV-1 in myeloid cell targets through the formation of the infected multinucleated giant cells observed in vivo in lymphoid and nonlymphoid tissues of HIV-1-infected patients.

Mechanisms of virus dissemination in bone marrow of HIV-1-infected humanized BLT mice

Immune progenitor cells differentiate in bone marrow (BM) and then migrate to tissues. HIV-1 infects multiple BM cell types, but virus dissemination within BM has been poorly understood. We used light microscopy and electron tomography to elucidate mechanisms of HIV-1 dissemination within BM of HIV-1–infected BM/liver/thymus (BLT) mice. Tissue clearing combined with confocal and light sheet fluorescence microscopy revealed distinct populations of HIV-1 p24-producing cells in BM early after infection, and quantification of these populations identified macrophages as the principal subset of virus-producing cells in BM over time. Electron tomography demonstrated three modes of HIV-1 dissemination in BM: (i) semi-synchronous budding from T-cell and macrophage membranes, (ii) mature virus association with virus-producing T-cell uropods contacting putative target cells, and (iii) macrophages engulfing HIV-1–producing T-cells and producing virus within enclosed intracellular compartments that fused to invaginations with access to the extracellular space. These results illustrate mechanisms by which the specialized environment of the BM can promote virus spread locally and to distant lymphoid tissues.

Inhibition of HIV-1 envelope-dependent membrane fusion by serum antilymphocyte autoantibodies is associated with low plasma viral load

The HIV-1 envelope protein (Env) mediates the membrane fusion process allowing virus entry to target cells and the efficiency to induce membrane fusion is an important determinant of HIV-1 pathogenicity. In addition to virus receptors, other adhesion/signaling molecules on infected and target cells and virus particles can enhance fusion. The presence of antilymphocyte autoantibodies (ALA) in HIV patients' serum suggests that they may contribute to the inhibition of Env-mediated membrane fusion. Here, sera from 38 HIV-1 infected treatment-naïve men and 30 healthy donors were analyzed for the presence of IgG and IgM able to bind to CD4-negative Jurkat cells. The use of CD4-negative cells precluded the binding of virus-antibody immune complexes, and allowed detection of ALA different from anti-CD4 antibodies. IgG and IgM antibodies binding to Jurkat CD4-negative cells was detected in 74% and 84% of HIV-positive sera, respectively. Then, the activity of sera on fusion of CD4⁺ with HIV Env⁺ Jurkat cells was determined before and after their adsorption on CD4-negative Jurkat cells to remove ALA. Sera inhibited fusion at variable extents, and inhibitory activity decreased in 58% of serum samples after adsorption, indicating that ALA contributed to fusion inhibition in these sera (herein called fusion inhibitory ALA). The contribution of ALA to fusion inhibition in individual sera was highly variable, with an average of 33%. IgG purified from a pool of HIV⁺ sera inhibited fusion of primary CD4 T lymphocytes with Jurkat Env⁺, and adsorption of IgG on CD4-negative Jurkat cells diminished the fusion inhibitory activity. Thus, the inhibitory activity of sera was related to IgG ALA. Our observations suggest that fusion inhibitory ALA other than anti-CD4 antibodies may contribute significantly to the inhibition of Env-mediated cell-cell fusion. Fusion inhibitory ALA, but not total ALA levels, associated with low plasma viral loads, suggesting that specific ALA may participate in virus containment by inhibiting virus-cell fusion in a significant fraction of HIV-infected patients.

Mechanisms for Cell-to-Cell Transmission of HIV-1

While HIV-1 infection of target cells with cell-free viral particles has been largely documented, intercellular transmission through direct cell-to-cell contact may be a predominant mode of propagation in host. To spread, HIV-1 infects cells of the immune system and takes advantage of their specific particularities and functions. Subversion of intercellular communication allows to improve HIV-1 replication through a multiplicity of intercellular structures and membrane protrusions, like tunneling nanotubes, filopodia, or lamellipodia-like structures involved in the formation of the virological synapse. Other features of immune cells, like the immunological synapse or the phagocytosis of infected cells are hijacked by HIV-1 and used as gateways to infect target cells. Finally, HIV-1 reuses its fusogenic capacity to provoke fusion between infected donor cells and target cells, and to form infected syncytia with high capacity of viral production and improved capacities of motility or survival. All these modes of cell-to-cell transfer are now considered as viral mechanisms to escape immune system and antiretroviral therapies, and could be involved in the establishment of persistent virus reservoirs in different host tissues.

Monocyte-lymphocyte fusion induced by the HIV-1 envelope generates functional heterokaryons with an activated monocyte-like phenotype

Enveloped viruses induce cell-cell fusion when infected cells expressing viral envelope proteins interact with target cells, or through the contact of cell-free viral particles with adjoining target cells. CD4⁺ T lymphocytes and cells from the monocyte-macrophage lineage express receptors for HIV envelope protein. We have previously reported that lymphoid Jurkat T cells expressing the HIV-1 envelope protein (Env) can fuse with THP-1 monocytic cells, forming heterokaryons with a predominantly myeloid phenotype. This study shows that the expression of monocytic markers in heterokaryons is stable, whereas the expression of lymphoid markers is mostly lost. Like THP-1 cells, heterokaryons exhibited FcγR-dependent phagocytic activity and showed an enhanced expression of the activation marker ICAM-1 upon stimulation with PMA. In addition, heterokaryons showed morphological changes compatible with maturation, and high expression of the differentiation marker CD11b in the absence of differentiation-inducing agents. No morphological change nor increase in CD11b expression were observed when an HIV-fusion inhibitor blocked fusion, or when THP-1 cells were cocultured with Jurkat cells expressing a non-fusogenic Env protein, showing that differentiation was not induced merely by cell-cell interaction but required cell-cell fusion. Inhibition of TLR2/TLR4 signaling by a TIRAP inhibitor greatly reduced the expression of CD11b in heterokaryons. Thus, lymphocyte-monocyte heterokaryons induced by HIV-1 Env are stable and functional, and fusion prompts a phenotype characteristic of activated monocytes via intracellular TLR2/TLR4 signaling.

Hemin activation of innate cellular response blocks human immunodeficiency virus type-1-induced osteoclastogenesis

The normal skeletal developmental and homeostatic process termed osteoclastogenesis is exacerbated in numerous pathological conditions and causes excess bone loss. In cancer and HIV-1-infected patients, this disruption of homeostasis results in osteopenia and eventual osteoporesis. Counteracting the factors responsible for these metabolic disorders remains a challenge for preventing or minimizing this co-morbidity associated with these diseases. In this report, we demonstrate that a hemin-induced host protection mechanism not only suppresses HIV-1 associated osteoclastogenesis, but it also exhibits anti-osteoclastogenic activity for non-infected cells. Since the mode of action of hemin is both physiological and pharmacological through induction of heme oxygenase-1 (HO-1), an endogenous host protective response to an FDA-licensed therapeutic used to treat another disease, our study suggests an approach to developing novel, safe and effective therapeutic strategies for treating bone disorders, because hemin administration in humans has previously met required FDA safety standards.

Single-domain antibody-SH3 fusions for efficient neutralization of HIV-1 Nef functions

HIV-1 Nef is essential for AIDS pathogenesis, but this viral protein is not targeted by antiviral strategies. The functions of Nef are largely related to perturbations of intracellular trafficking and signaling pathways through leucine-based and polyproline motifs that are required for interactions with clathrin-associated adaptor protein complexes and SH3 domain-containing proteins, such as the phagocyte-specific kinase Hck. We previously described a single-domain antibody (sdAb) targeting Nef and inhibiting many, but not all, of its biological activities. We now report a further development of this anti-Nef strategy through the demonstration of the remarkable inhibitory activity of artificial Nef ligands, called Neffins, comprised of the anti-Nef sdAb fused to modified SH3 domains. The Neffins inhibited all key activities of Nef, including Nef-mediated CD4 and major histocompatibility complex class I (MHC-I) cell surface downregulation and enhancement of virus infectivity. When expressed in T lymphocytes, Neffins specifically inhibited the Nef-induced mislocalization of the Lck kinase, which contributes to the alteration of the formation of the immunological synapse. In macrophages, Neffins inhibited the Nef-induced formation of multinucleated giant cells and podosome rosettes, and it counteracted the inhibitory activity of Nef on phagocytosis. Since we show here that these effects of Nef on macrophage and T cell functions were both dependent on the leucine-based and polyproline motifs, we confirmed that Neffins disrupted interactions of Nef with both AP complexes and Hck. These results demonstrate that it is possible to inhibit all functions of Nef, both in T lymphocytes and macrophages, with a single ligand that represents an efficient tool to develop new antiviral strategies targeting Nef.

Systemic and mucosal differences in HIV burden, immune, and therapeutic responses

BACKGROUND

Mucosal tissues represent major targets for HIV transmission but differ in susceptibility and reservoir function by unknown mechanisms.

METHODS

In a cross-sectional study, HIV RNA and infectious virus were compared between oral and genital compartments and blood in HIV-infected women, in association with clinical parameters, copathogens, and putative innate and adaptive HIV inhibitors.

RESULTS

HIV RNA was detectable in 24.5% of women from all 3 compartments, whereas 45% had RNA in only 1 or 2 sites. By comparison, infectious HIV, present in blood of the majority, was rare in mucosal sites. Innate mediators, secretory leukocyte protease inhibitor and thrombospondin, were highest in mucosae. Highly active antiretroviral therapy was associated with an 80% decreased probability of shedding. Multivariate logistic regression models revealed that mucosal HIV RNA was associated with higher plasma RNA, infectious virus, and total mucosal IgA, but not IgG. There was a 37-fold increased probability of detecting RNA in both genital and oral specimens (P = 0.008; P = 0.02, respectively) among women in highest versus lowest IgA tertiles.

CONCLUSIONS

Mucosal sites exhibit distinct characteristics of infectious HIV, viral shedding, and responses to therapy, dependent upon both systemic and local factors. Of the putative innate and adaptive mucosal defense factors examined, only IgA was associated with HIV RNA shedding. However, rather than being protective, there was a striking increase in probability of detectable HIV RNA shedding in women with highest total IgA.

Identifying HIV infection in diagnostic histopathology tissue samples--the role of HIV-1 p24 immunohistochemistry in identifying clinically unsuspected HIV infection: a 3-year analysis

AIMS

Because of the clinical difficulty in identifying the early stages of human immunodeficiency virus (HIV) infection, the histopathologist often has to consider the diagnosis of HIV in tissue samples from patients with no previous suspicion of HIV infection. The aim was to investigate the practicality and utility of routine HIV-1 p24 immunohistochemistry on tissue samples received at a London histopathology laboratory.

METHODS AND RESULTS

Over a 3-year period, HIV-1 p24 was evaluated immunohistochemically on 123 cases. Of these, 37 (30%) showed positive expression of p24 in lesional follicular dendritic cells (FDCs). Of these 37 cases, 11 were not clinically suspected to be HIV+ and had no prior serological evidence of HIV infection. These cases represented lymph node biopsies, tonsillar and nasopharyngeal biopsies and a parotid excision. In addition to expression on FDCs, in 22 cases (60%), p24 also highlighted mononuclear cells and macrophages. p24 was also useful in confirming the presence of HIV in lymphoid tissue in non-lymphoid organs such as the lung, anus, salivary gland and brain. Immunonegativity occurred in occasional known HIV+ cases, probably related to treatment or tissue processing.

CONCLUSIONS

This study confirms the usefulness of this technique in detecting unsuspected HIV infection in lymphoid and non-lymphoid organs on histopathological material and should be part of routine evaluation of lymph nodes and lymphoid tissue in other organs if morphological or clinical features suggest HIV infection.

Intestinal macrophages and response to microbial encroachment

Macrophages in the gastrointestinal mucosa represent the largest pool of tissue macrophages in the body. In order to maintain mucosal homeostasis, resident intestinal macrophages uniquely do not express the lipopolysaccharide (LPS) co-receptor CD14 or the IgA (CD89) and IgG (CD16, 32, and 64) receptors, yet prominently display Toll-like receptors (TLRs) 3-9. Remarkably, intestinal macrophages also do not produce proinflammatory cytokines in response to TLR ligands, likely because of extracellular matrix (stromal) transforming growth factor-β (TGF-β) dysregulation of nuclear factor (NF)-κB signal proteins and, via Smad signaling, expression of IκBα, thereby inhibiting NF-κB-mediated activities. Thus, in noninflamed mucosa, resident macrophages are inflammation anergic but retain avid scavenger and host defense function, an ideal profile for macrophages in close proximity to gut microbiota. In the event of impaired epithelial integrity during intestinal infection or inflammation, however, blood monocytes also accumulate in the lamina propria and actively pursue invading microorganisms through uptake and degradation of the organism and release of inflammatory mediators. Consequently, resident intestinal macrophages are inflammation adverse, but when the need arises, they receive assistance from newly recruited circulating monocytes.

Porcine circovirus type 2 (PCV2) induces cell proliferation, fusion, and chemokine expression in swine monocytic cells in vitro

Granulomatous lymphadenitis is one of the pathognomonic lesions in post-weaning multisystemic wasting syndrome (PMWS)-affected pigs. This unique lesion has not been reported in direct association with viral infection in pigs. The objective of the present study was to evaluate whether porcine circovirus type 2 (PCV2) alone is able to induce functional modulation in porcine monocytic cells in vitro to elucidate its possible role in the development of granulomatous inflammation. It was found that the proliferation activity of blood monocytes (Mo) and monocyte-derived macrophages (MDM) was significantly enhanced by PCV2. During monocyte-macrophage differentiation, the PCV2 antigen-containing rate and formation of multinucleated giant cells (MGC) were significantly increased in MDM when compared to those in Mo. The MDM-derived MGC displayed a significantly higher PCV2 antigen-containing rate than did the mono-nucleated MDM. Supernatants from PCV2-inoculated MDM at 24 h post-inoculation induced an increased tendency of chemotactic activity for blood Mo. At the same inoculation time period, levels of mRNA expression of the monocytic chemokines, monocyte chemoattractant protein-1 and macrophage inflammatory protein-1, also significantly increased in PCV2-inoculated MDM. The results suggest that PCV2 alone may induce cell proliferation, fusion, and chemokine expression in swine monocytic cells. Thus, PCV2 itself may play a significant role in the induction of granulomatous inflammation in PMWS-affected pigs.

Interleukin-27 inhibition of HIV-1 involves an intermediate induction of type I interferon

Infection of CD4(+) chemokine coreceptor(+) targets by HIV is aided and abetted by the proficiency of HIV in eliminating or neutralizing host cell-derived defensive molecules. Among these innate protective molecules, a family of intracellular apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like (APOBEC) cytidine deaminases, is constitutively expressed but inactivated by HIV viral infectivity factor. The ability of interferon-alpha (IFN-alpha) to augment cytidine deaminases offered the possibility that the balance between virus and target cell might be altered in favor of the host. Further characterization of transcriptional profiles induced by IFN-alpha using microarrays, with the intention to identify and dissociate retroviral countermaneuvers from associated toxicities, revealed multiple molecules with suspected antiviral activity, including IL-27. To establish whether IFN-alpha toxicity might be sidestepped through the use of downstream IL-27 against HIV, we examined whether IL-27 directly regulated cytidine deaminases. Although IL-27 induces APOBECs, it does so in a delayed fashion. Dissecting the underlying regulatory events uncovered an initial IL-27-dependent induction of IFN-alpha and/or IFN-beta, which in turn, induces APOBEC3, inhibited by IFN-alpha/beta receptor blockade. In addition to macrophages, the IL-27-IFN-alpha connection is operative in CD4(+) T cells, consistent with an IFN-alpha-dependent pathway underlying host cell defense to HIV.

Replication of HIV-1 in Vivo and in Vitro

A complex relationship exists between HIV and its cellular targets. The lethal effect of HIV on circulating CD4(+) helper T lymphocytes parallels the degree of the infected individual's immunodeficiency and ultimately the transition to AIDS and death. However, as with other members of the Lentivirus family of retroviruses, the ubiquitous, mobile macrophage is also a prime target for HIV infection, and apparently, in most instances, is the initial infected cell, since most people are infected with a CCR5 chemokine-tropic virus. Unlike the lymphocyte, the macrophage is apparently a more stable viral host, capable of a long infected life as an HIV reservoir and a chronic source of infectious virus. Published in vitro studies have indicated that whereas lymphocytes replicate HIV solely on their plasma membrane, macrophages have been envisaged to predominantly replicate HIV within cytoplasmic vacuoles, and thus have been likened to a "Trojan horse," when it comes to the immune system. Recent studies have revealed an ingenious way by which the cultured monocyte-derived macrophage (MDM) replicates HIV and releases it into the medium. The key macrophage organelle appears to be what is alternatively referred to as the "late endosome" (LE) or the "multivesicular body" (MVB), which have a short and a long history, respectively. Proof of the association is that chemically, LE/MVB and their vesicles possess several pathopneumonic membrane markers (e.g., CD63) that are found on released HIV particles. The hypothesis is that HIV usurps this vesicle-forming mechanism and employs it for its own replication. Release of the intravacuolar virus from the cell is hypothesized to occur by a process referred to as exocytosis, resulting from the fusion of virus-laden LE/MVB with the plasma membrane of the macrophage. Interestingly, LE/MVB are also involved in the infection stage of MDM by HIV. Close review of the literature reveals that along with the Golgi, which contributes to the formation of LE/MVB, the MVB was first identified as a site of HIV replication by macrophages many years ago, but the full implication of this observation was not appreciated at the time. As in many other areas of HIV research, what has been totally lacking is an in vivo confirmation of the in vitro phenomenon. Herein, the ultrastructure of HIV interaction with cells in vitro and in vivo is explored. It is shown that while HIV is regularly found in LE/MVB in vitro, it is infrequently the case in vivo. Therefore, the results challenge the "Trojan horse" concept.

Multinucleated giant cells in HIV-associated benign lymphoepithelial cyst-like lesions of the parotid gland on FNAC

Benign lymphoepithelial cyst-like lesion (BLEL), a previously rare lesion of the parotid gland consisting of marked lymphoid hyperplasia with accompanying squamous-lined cysts, has been described in patients with the acquired immune deficiency syndrome (AIDS) or AIDS risk factors. Histologically, these cysts are lined by a squamous or cuboidal epithelium. The lumen contains a pale homogenous material with foamy macrophages and lymphocytes with the cyst wall having germinal centers and a dense infiltrate of lymphoid cells. On FNAC, the aspirates are mostly cystic with the presence of reactive lymphoid tissue, numerous histiocytes, and metaplastic cell clusters. Multinucleated giant cells (MGCs) are also rarely seen in such lesions. We report a case of HIV-associated BLEL with numerous large sized multinucleated giant cells.

Hyperplastic lymphoid tissue in HIV/AIDS: an electron microscopic study

The purpose of this study was to characterize the ultrastructure of lymphoid tissue from HIV/AIDS patients and to evaluate it as a reservoir and source of HIV. HIV has been demonstrated in lymph nodes and tonsils and adenoids, by immunohistochemistry (IHC), in situ hybridization (ISH), and transmission electron microscopy (TEM), to be associated with germinal center (GC) follicular dendritic cells (FDC). The presence of HIV in the larger gastrointestinal tract-associated lymphoid tissue (GALT) has been much less studied. Whether FDC themselves are productively infected by HIV in any of the lymphoid sites is controversial. Lymph nodes, tonsils, and gastrointestinal biopsies were fixed in neutral buffered glutaraldehyde and prepared for TEM. Mature HIV particles were abundant in GC of hyperplastic lymph nodes, tonsils, and the GALT. They were enmeshed within an electron-dense matrix associated with an all-encompassing branching FDC network of processes. HIV particles were seen budding from both FDC and lymphocytes. The greatest numbers of particles were seen in hyperplastic lymphoid tissue from untreated individuals and in lymph nodes co-infected with opportunistic organisms, such as Mycobacterium avium complex. In addition to HIV, unidentifiable "particles" of varying sizes, possibly including other viruses, were regularly seen in association with FDC. Ultrastructural study graphically demonstrated the abundance of HIV particles associated with the complex FDC network of hyperplastic lymph nodes, tonsils, and GALT. HIV was shown to productively infect FDC, as well as lymphocytes.

HIV expression in surgical specimens

We determined the HIV-1 RNA and Gag p24 protein expression in gastrointestinal tract-associated lymphoid tissue (GALT), deep lymph nodes (LNs), and inflammatory lesions, acquired during surgery on HIV-infected patients. Surgically excised gastrointestinal tract specimens, LNs, and cervices removed from HIV-1-infected patients for various clinical conditions were studied by immunohistochemistry (IHC) for Gag p24 HIV protein and in situ hybridization (ISH) for HIV-specific RNA. Fragments of some specimens were also submitted in glutaraldehyde for TEM analysis. Germinal centers (GC) in the GALT had at least as much HIV RNA and p24 protein deposited on their follicular dendritic cell (FDC) networks as did GC in LNs draining or associated with areas of inflammation or ulceration. The level of viral expression in the deep LNs, e.g., mesenteric and retroperitoneal, was at least equivalent to that seen in superficial LNs, i.e., inguinal, axillary, and cervical, and tonsils and adenoids. HIV expressing T and B lymphocytes and macrophages were seen in GALT and LNs. Virus-expressing mononuclear cells (MNC) were also seen in inflammatory lesions such as gastrointestinal ulcers and acute appendicitis. Abundant virus was seen in the cervix of patients with and without cancer and in LNs of patients with metastatic cancer. Individual and clusters of mature HIV particles were identified by TEM in LN GC and in GALT. Gastrointestinal tract lymphoid tissue, inflammatory lesions, and deep LNs showed levels of HIV RNA and Gag p24 protein expression in the range seen in superficial LNs.

Regulation of the tonsil cytokine milieu favors HIV susceptibility

Mucosal associated lymphoid tissues are major targets of HIV during early infection and disease progression but can also provide a viral safe haven during highly active antiretroviral therapy. Among these tissues, the tonsils remain enigmatic regarding their status as primary and/or secondary sites of retroviral infection. To dissect the mechanisms underlying susceptibility to HIV in this compartment, isolated tonsil cells were studied for phenotypic and functional characteristics, which may account for their permissiveness to infection. For this, tonsil cells and PBMC were infected in parallel with HIV, and viral replication was monitored by p24 ELISA. Our results demonstrate that unstimulated tonsil cells were more readily infected than PBMC with HIV. Phenotypic characterization of the tonsil cells revealed heterogeneous lymphoid populations but with increased expression of early activation markers and the viral co-receptor CXCR4, relative to PBMC, all of which may contribute to viral susceptibility. Furthermore, the cytokine microenvironment appeared to be key in facilitating HIV infection and tonsil-secreted products enhanced HIV infection in PBMC. Of the cytokines detected in the tonsil supernatants, TH2 cytokines, particularly IL-4, promoted HIV infection and replication. Interestingly, this TH2 profile appeared to dominate, even in the presence of the TH1 cytokine IFNgamma and the anti-viral factor IFNalpha, likely due to the enhanced expression of suppressor of cytokine signaling (SOCS) proteins, which may disengage IFN signaling. These and other local environmental factors may render tonsil cells increasingly susceptible to HIV infection.

Coreceptor usage of primary HIV type 1 isolates obtained from different lymph node subsets

Biological characteristics of virus quantitatively rescued from different cell types present in lymph nodes of HIV-1-infected individuals in various stages of their disease were determined, not including patients with AIDS defining illness. Viruses were obtained by cocultivation with donor monocyte-derived macrophages and T-lymphocytes and their biological phenotype compared to viruses obtained from the peripheral blood mononuclear cells of the same patient. The biological phenotype was determined on established cell lines (U937-2, CEM, and MT-2) and on the U87.CD4 coreceptor indicator cell lines and variable region 3 (V3) of the envelope was subjected to direct sequencing. All isolates obtained from lymph node subsets used CCR5 as coreceptor. Furthermore, these viruses were also sensitive to inhibition by beta-chemokines as analyzed for viruses of one patient. All 12 V3 regions showed a unique sequence indicating compartmentalization within each patient. The biological phenotype of CCR5-dependent (R5) HIV-1 isolates obtained from PBMC resembles the phenotype of viruses isolated from different lymph node cell subsets.

Immunohistochemical characterisation of PCV2 associate lesions in lymphoid and non-lymphoid tissues of pigs with natural postweaning multisystemic wasting syndrome (PMWS)

The lymphoid, renal, pulmonary, and hepatic lesions of naturally occurring postweaning multisystemic wasting syndrome (PMWS) affected pigs have been studied by means of immunohistology. Ten conventionally reared pigs showing acute clinical signs of PMWS were selected from a farm on which animal were seronegative to porcine reproductive and respiratory virus and to Aujeszky's disease virus. All pigs were positive in tests for porcine circovirus type 2 by ISH and IHC. Monoclonal and polyclonal antibodies to CD3, CD79alpha, CD45RA (3C3/9), lysozyme, SLA-II-DQ (BL2H5), and MAC387 were used to characterise cells in PMWS lesions. The most relevant changes were reduction or loss of B and T lymphocytes, increased numbers of macrophages, and partial loss and redistribution of antigen presenting cells throughout lymphoid tissues compared to uninfected controls. The characteristics of lymphoid lesions in the present study strongly suggest an immunosuppressive effect of PMWS in affected pigs.

Potential regulatory function of human dendritic cells expressing indoleamine 2,3-dioxygenase

Antigen-presenting cells (APCs) can induce tolerance or immunity. We describe a subset of human APCs that express indoleamine 2,3-dioxygenase (IDO) and inhibit T cell proliferation in vitro. IDO-positive APCs constituted a discrete subset identified by coexpression of the cell-surface markers CD123 and CCR6. In the dendritic cell (DC) lineage, IDO-mediated suppressor activity was present in fully mature as well as immature CD123+ DCs. IDO+ DCs could also be readily detected in vivo, which suggests that these cells may represent a regulatory subset of APCs in humans.

The maturation of dendritic cells results in postintegration inhibition of HIV-1 replication

Maturation of dendritic cells (DC) is known to result in decreased capacity to produce HIV due to postentry block of its replicative cycle. In this study, we compared the early phases of this cycle in immature DC (iDC) and mature DC (mDC) generated from monocytes cultured with GM-CSF and IL-4, trimeric CD40 ligand (DC(CD40LT)), or monocyte-conditioned medium (DC(MCM)) being added or not from day 5. Culture day 8 cells exposed to X4 HIV-1(LAI) or R5 HIV-1(Ba-L) were analyzed by semiquantitative R-U5 PCR, which detects total HIV DNA. CXC chemokine receptor 4(low) (CXCR4(low)) CCR5(+) iDC harbored similar viral DNA amounts when exposed to either strain. HIV-1(LAI) entered more efficiently into DC(CD40LT) or DC(MCM) with up-regulated CXCR4. CCR5(low) DC(CD40LT) still allowed entry of HIV-1(Ba-L), whereas CCR5(-) DC(MCM) displayed reduced permissivity to this virus. Comparing amounts of late (long terminal repeat (LTR)-gag PCR) and total (R-U5 PCR) viral DNA products showed that HIV-1(Ba-L) reverse transcription was more efficient than that of HIV-1(LAI), but was not affected by DC maturation. Southern blot detection of linear, circular, and integrated HIV DNA showed that maturation affected neither HIV-1 nuclear import nor integration. When assessing virus transcription by exposing iDC to pNL4-3.GFP or pNL4-3.Luc viruses pseudotyped with the G protein of vesicular stomatitis virus (VSV-G), followed by culture with or without CD40LT or MCM, GFP and luciferase activities decreased by 60-75% in mDC vs iDC. Thus, reduced HIV replication in mDC is primarily due to a postintegration block occurring mainly at the transcriptional level. We could not relate this block to altered expression and nuclear localization of NF-kappa B proteins and SP1 and SP3 transcription factors.

HIV-associated multinucleated giant cells in lymphoid tissue of the Waldeyer's ring: a detailed study

Hyperplastic lymphoid tissues of the Waldeyer's ring in human immunodeficiency virus (HIV)-infected patients may occasionally contain multinucleated giant cells (MGCs). These cells, which are unrelated to any opportunistic infection, previously have been demonstrated to harbor significant amounts of HIV. Studies undertaken to characterize these MGCs have generated conflicting results: some reports suggested a macrophage origin, whereas others supported a dendritic cell lineage. This study was performed to determine the occurrence of MGCs in a series of adenoid/tonsil specimens from HIV-seropositive patients showing no histological evidence of opportunistic infection in order to further characterize the phenotype of these cells and to investigate the role of a viral infection in their pathogenesis. Adenoid/tonsil tissue specimens from 21 HIV-seropositive patients with no documented opportunistic infection were scrutinized for the presence of MGCs and evaluated immunohistochemically on paraffin sections by antibodies directed against various macrophage and DC antigens. These antigens included CD68, the macrophage marker 3A5, major histocompatibility complex Class II, S-100 protein, CD1a, and CD83. Additional immunostainings directed at CD21 and CD35 as well as at the HIV-associated p24 antigen were also performed. Finally, the presence of Epstein-Barr virus and human herpesvirus 8 viral sequences was investigated by in situ hybridization and by polymerase chain reaction analysis, respectively. MGCs were found in 14 patients (66.7%), regardless of gender, age, method of viral transmission, CD4 cell count, viral load, or ethnic group. These cells were mostly localized at the lymphoepithelium layer of the tonsillar crypts and, to a lesser extent, in the interfollicular areas of the underlying lymphoid tissue, which consistently exhibited features of follicular hyperplasia. Phenotypically, MGCs were found to be CD68+, 3A5+, major histocompatibility complex Class II+, S-100 protein+/-, CD1a-, CD21-, CD35-, and CD83-. Although the HIV-associated p24 protein was consistently present in the cytoplasm of these cells, no sign of Epstein-Barr virus or human herpesvirus 8 infection could be demonstrated. Consequently, our study didn't show any conclusive evidence to support that MGCs in hyperplastic lymphoid tissues of the Waldeyer's ring from HIV-seropositive patients originated from dendritic cells. The definite nature of these cells has yet to be elucidated, but it is plausible that they simply represent activated macrophages that are infected with HIV present in the oropharyngeal secretions during the circulation of their precursor through the lymphoepithelium area of adenoids and tonsils.

Normalization of immune activation in lymphoid tissue following highly active antiretroviral therapy

Although significant progress has been made in understanding immune reconstitution in peripheral blood following highly active antiretroviral therapy (HAART), less is known about immune changes in lymphoid tissue. Here, the expression of cytokine proteins (interferon gamma [IFN-gamma], interleukin [IL]-2, IL-4, IL-10, IL-1alpha, and IL-1beta) and surface antigens (CD4, CD8, CD1a, CD68) as well as cellular proviral HIV-1 DNA were determined in sequential tonsil biopsies before and at 4, 12, and 48 to 56 weeks posttherapy by quantitative in situ image analysis and fluorescent in situ 5;-nuclease assay (FISNA). Despite plasma virus suppression, a fraction of tonsil cells harbored pro-viral DNA for up to 1 year. A fourfold to eightfold increase in CD8+ T cells in tissue compared with seronegative controls and an increased frequency of CD1a+ dendritic cells prior to HAART reached control levels at week 56. The frequency of IFN-gamma expressing cells was 10-to 15-fold higher than controls before therapy and was comparable with findings in seronegative controls by week 56. Elevated baseline expression of IL-1alpha and IL-1beta was reduced by week 4 but IL-1alpha levels remained elevated in 1 of 3 patients at week 56. These findings suggest that with effective viral suppression the immune system in tissue may return to a more resting state.

Lymph node architecture preceding and following 6 months of potent antiviral therapy: follicular hyperplasia persists in parallel with p24 antigen restoration after involution and CD4 cell depletion in an AIDS patient

OBJECTIVES

To evaluate changes in architecture, viral RNA, and viral protein over 6 months in lymph nodes from retroviral-naïve HIV-infected persons before and after commencing highly active antiretroviral therapy (HAART).

METHODS

Nine antiretroviral-naïve HIV-infected persons had lymph nodes excised at baseline and at 2 and 6-8 months after beginning a four-drug combination regimen containing zidovudine, lamivudine, nevirapine, and indinavir. Two patients had AIDS. Lymph nodes were examined by immunohistochemical staining for Gag p24 HIV, CD3, CD21, CD20, HAM 56, and Ki67 antigens and by in-situ hybridization (ISH) for HIV RNA and H3-histone RNA.

RESULTS

Eight of nine baseline lymph nodes showed follicular hyperplasia and germinal center and paracortical mononuclear cell activation. At 2 months, the lymph nodes from seven patients, including the AIDS patients, showed more follicular hyperplasia and activation than their baseline specimens but with decreased mononuclear cell activation. By 6 months, seven lymph nodes were less hyperplastic and activated than their corresponding 2 month specimens. Combined ISH/immunohistochemical staining of baseline lymph nodes revealed productively infected T (CD3) and B (CD20) cells and macrophages (HAM56+). HIV RNA-positive mononuclear cells were infrequent at 2 months, and rare at 6 months. HIV RNA was still associated with follicular dendritic cells (FDC) at 2 months, but not at 6 months. HIV p24-positive antigen in germinal centers persisted through all 6, and the one 8 month specimens. The baseline lymph nodes from one of the AIDS patients was involuted and T cell depleted, whereas the follow-up lymph nodes were hyperplastic with normal T cell levels.

CONCLUSION

Follicular hyperplasia and cell activation, possibly caused by persistent viral protein in germinal centers, may help explain why HIV viremia rebounds so rapidly after the interruption of HAART. Restoration of architecture may follow the treatment of patients with AIDS who initially had involuted and CD4 cell-depleted lymph nodes.