HIV-1 infection of monocyte-derived macrophages reduces Fc and complement receptor expression

Defective Phagocytic Properties of HIV-Infected Macrophages: How Might They Be Implicated in the Development of Invasive Salmonella Typhimurium?

Human immunodeficiency virus type 1 (HIV-1) infects and kills T cells, profoundly damaging the host-specific immune response. The virus also integrates into memory T cells and long-lived macrophages, establishing chronic infections. HIV-1 infection impairs the functions of macrophages both in vivo and in vitro, which contributes to the development of opportunistic diseases. Non-typhoidal Salmonella enterica serovar Typhimurium has been identified as the most common cause of bacterial bloodstream infections in HIV-infected adults. In this review, we report how the functions of macrophages are impaired post HIV infection; introduce what makes invasive Salmonella Typhimurium specific for its pathogenesis; and finally, we discuss why these bacteria may be particularly adapted to the HIV-infected host.

Protective effect of vaginal application of neutralizing and nonneutralizing inhibitory antibodies against vaginal SHIV challenge in macaques

Definition of antibody (Ab) functions capable of preventing mucosal HIV transmission may be critical to both effective vaccine development and the prophylactic use of monoclonal Abs. Although direct antibody-mediated neutralization is highly effective against cell-free virus, increasing evidence suggests an important role for immunoglobulin G (IgG) Fcγ receptor (FcγR)-mediated inhibition of HIV replication. Thus, a panel of well-known neutralizing (NAbs) and nonneutralizing Abs (NoNAbs) were screened for their ability to block HIV acquisition and replication in vitro in either an independent or FcγR-dependent manner. Abs displaying the highest Fc-mediated inhibitory activity in various in vitro assays were selected, formulated for topical vaginal application in a microbicide gel, and tested for their antiviral activity against SHIVSF162P3 vaginal challenge in non-human primates (NHPs). A combination of three NAbs, 2G12, 2F5, and 4E10, fully prevented simian/human immunodeficiency virus (SHIV) vaginal transmission in 10 out of 15 treated NHPs, whereas a combination of two NoNAbs, 246-D and 4B3, although having no impact on SHIV acquisition, reduced plasma viral load. These results indicate that anti-HIV Abs with distinct neutralization and inhibitory functions differentially affect in vivo HIV acquisition and replication, by interfering with early viral replication and dissemination. Therefore, combining diverse Ab properties may potentiate the protective effects of anti-HIV-Ab-based strategies.

Effect of complement on HIV-2 plasma antiviral activity is intratype specific and potent

Human immunodeficiency virus type 2 (HIV-2)-infected individuals develop immunodeficiency with a considerable delay and transmit the virus at rates lower than HIV-1-infected persons. Conceivably, comparative studies on the immune responsiveness of HIV-1- and HIV-2-infected hosts may help to explain the differences in pathogenesis and transmission between the two types of infection. Previous studies have shown that the neutralizing antibody response is more potent and broader in HIV-2 than in HIV-1 infection. In the present study, we have examined further the function of the humoral immune response and studied the effect of complement on the antiviral activity of plasma from singly HIV-1- or HIV-2-infected individuals, as well as HIV-1/HIV-2 dually infected individuals. The neutralization and antibody-dependent complement-mediated inactivation of HIV-1 and HIV-2 isolates were tested in a plaque reduction assay using U87.CD4.CCR5 cells. The results showed that the addition of complement increased intratype antiviral activities of both HIV-1 and HIV-2 plasma samples, although the complement effect was more pronounced with HIV-2 than HIV-1 plasma. Using an area-under-the-curve (AUC)-based readout, multivariate statistical analysis confirmed that the type of HIV infection was independently associated with the magnitude of the complement effect. The analyses carried out with purified IgG indicated that the complement effect was largely exerted through the classical complement pathway involving IgG in both HIV-1 and HIV-2 infections. In summary, these findings suggest that antibody binding to HIV-2 structures facilitates the efficient use of complement and thereby may be one factor contributing to a strong antiviral activity present in HIV-2 infection.

Role of complement in immune regulation and its exploitation by virus

Complement is activated during the early phase of viral infection and promotes destruction of virus particles as well as the initiation of inflammatory responses. Recently, complement and complement receptors have been reported to play an important role in the regulation of innate as well as adaptive immune responses during infection. The regulation of host immune responses by complement involves modulation of dendritic cell activity in addition to direct effects on T-cell function. Intriguingly, many viruses encode homologs of complement regulatory molecules or proteins that interact with complement receptors on antigen-presenting cells and lymphocytes. The evolution of viral mechanisms to alter complement function may augment pathogen persistence and limit immune-mediated tissue destruction. These observations suggest that complement may play an important role in both innate and adaptive immune responses to infection as well as virus-mediated modulation of host immunity.

Impaired complement-mediated phagocytosis by HIV type-1-infected human monocyte-derived macrophages involves a cAMP-dependent mechanism

HIV-1 infection of cells of macrophage lineage impairs a number of effector functions performed by these cells, including phagocytosis of opsonized pathogens. In this study we investigate the effects of HIV-1 on the mechanism of complement (C')-mediated phagocytosis by human monocyte-derived macrophages (MDM). Using C'-opsonized sheep red blood cells (sRBC) as targets, we demonstrate that phagocytosis is inhibited by HIV-1 infection in vitro. Inhibition is not due to downregulation of surface C' receptors (R) or altered binding of C'-opsonized targets to HIV-1-infected MDM, suggesting a postreceptor-mediated mechanism of suppression. Having shown that increased levels of intracellular cAMP in uninfected MDM inhibit phagocytosis, we demonstrate that HIV-1 infection of MDM is associated with increased intracellular cAMP. Using the adenylate cyclase inhibitors 2',5'-dideoxyadenosine and MDL-12,330A, we show that phagocytosis by HIV-1- infected MDM can be restored by inhibition of cAMP production. Defective phagocytosis by HIV-1-infected MDM did not correlate with prostaglandin secretion, and was less in uninfected MDM within the HIV-1-infected cell culture suggesting a minimal bystander effect. Inhibition required viral entry but not active viral replication, as shown by use of the antiretroviral drug lamivudine. Hence, our study suggests that HIV-1 impairs C'R-mediated phagocytosis in MDM by elevating intracellular cAMP levels, independent of prostaglandin secretion, and contributes to our understanding of how HIV-1 impairs cell-mediated immunity.

Epstein-Barr virus immunossuppression of innate immunity mediated by phagocytes

Epstein-Barr virus (EBV) is an oncogenic human herpesvirus that persistently infects approximately 90% of the world's population. Such a remarkably sustained of viral infectivity relies on EBV's ability to evade the host immune defenses. A crucial part of this anti-EBV response is mediated by cytotoxic CD8+ T lymphocytes, which maintain a life-long control over proliferating latently-infected B cells in order to prevent these from giving rise to lymphomatous diseases. On the other hand, little has been done to assess the role of phagocytes-mediated innate immunity in the pathogenesis of EBV infection. In the course of primary EBV infection, episodes of neutropenia and monocytopenia can be observed during the acute phase of infection. According to the role of those cells in the non specific and specific immunity, such a decrease in circulating phagocytes may then temporarily affect the immune defense and potentially influence the outcome of EBV infection. Recent studies have demonstrated that EBV infects both neutrophils and monocytes and modulates several of their biological functions. This review covers the current state of our knowledge relative to the role of neutrophils and monocytes in EBV pathogenesis and describes the nature of countermeasures deployed by EBV against these cells.

Impaired protein kinase C activation/translocation in Epstein-Barr virus-infected monocytes

Infection of human monocytes by Epstein-Barr virus (EBV) has been linked to a decrease in the production of proinflammatory mediators as well as an impairment of phagocytosis. Considering the key role of protein kinases C (PKCs) in many biological functions of monocytes, including phagocytosis, we investigated the effects of EBV on the PKC activity in infected monocytes. Our results indicate that infection of monocytes by EBV impairs both phorbol 12-myristate 13-acetate (PMA)-induced translocation of PKC isozymes alpha and beta from cytosol to membrane as well as the PKC enzymatic activity. Similarly, the subcellular distribution of the receptor for activated C kinase (RACK), an anchoring protein essential to PKC translocation, was also found to be reduced in EBV-infected monocytes. Transfection of 293T cells with an expression vector coding for the immediate-early protein ZEBRA of EBV resulted in impaired PMA-induced translocation and activity of PKC. Using co-immunoprecipitation assays, the ZEBRA protein was found to physically interact with the RACK1 protein. Thus interaction of ZEBRA with RACK likely results in the inhibition of PKC activity, which in turn affects functions of monocytes, such as phagocytosis.

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.

Infection of primary human monocytes by Epstein-Barr virus

Previous studies have reported that infection of monocytes by viruses such as cytomegalovirus and human immunodeficiency virus weakens host natural immunity. In the present study, we demonstrated the capability of Epstein-Barr virus (EBV) to infect and replicate in freshly isolated human monocytes. Using electron microscopy analysis, we observed the presence of EBV virions in the cytoplasm and nuclei of approximately 20% of monocytes. This was confirmed by Southern blot analysis of EBV genomic DNA sequences in isolated nuclei from monocytes. Infection of monocytes by EBV leads to the activation of the replicative cycle. This was supported by the detection of immediate-early lytic mRNA BZLF-1 transcripts, and by the presence of two early lytic transcripts (BALF-2, which appears to function in DNA replication, and BHRF-1, also associated with the replicative cycle). The late lytic BcLF-1 transcripts, which code for the major nucleocapsid protein, were also detected, as well as EBNA-1 transcripts. However, attempts to detect EBNA-2 transcripts have yielded negative results. Viral replication was also confirmed by the release of newly synthesized infectious viral particles in supernatants of EBV-infected monocytes. EBV-infected monocytes were found to have significantly reduced phagocytic activity, as evaluated by the quantification of ingested carboxylated fluoresceinated latex beads. Taken together, our results suggest that EBV infection of monocytes and alteration of their biological functions might represent a new mechanism to disrupt the immune response and promote viral propagation during the early stages of infection.

The effects of HIV viral load on the phagocytic activity of monocytes activated with lipopolysaccharide from oral microorganisms

A study was undertaken to determine whether viral load status in HIV+ patients has any potential effect on monocyte phagocytic function both before and after challenge of the monocytes with lipopolysaccharide (LPS) isolated from oral microorganisms. LPS of two putative periodontal pathogens Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum) was prepared. Whole blood samples in EDTA were collected from 30 HIV+ patients presenting for dental care at the University of Maryland. Control samples were prepared from appropriate uninfected individuals. Viral load was determined using quantitative RT-PCR (Amplicor, Roche Diagnostics). Phagocytic function was determined using FITC labeled Saccharomyces species in resting isolated monocytes and in cells after 24 h stimulation with 1 microgram/ml of LPS of P. gingivalis or F. nucleatum. Immunohistochemical staining was performed for complement receptor CR-1 (CD-35) on phagocyte cells. In HIV+ patients with high viral load (> 10,000 copies/ml), 13.5% of isolated resting monocytes demonstrated phagocytic activity, while 23% of the resting control monocytes from non-infected individuals showed phagocytic function. When the monocytes were stimulated with 1 microgram/ml of LPS of F. nucleatum, phagocytic activity was observed in 18.5% of monocytes in patients with high viral load, 33.5% with moderate viral load (400-10,00 copies/ml) and 51% with low viral load (<400 copies/ml), while 62% of the control monocytes demonstrated phagocytic activity. Stimulation of monocytes with LPS of P. gingivalis showed similar results. Complement receptor CD-35 showed a 50% decrease in expression in HIV+ patients with high viral load. A progressive decrease in monocyte/macrophage phagocytic function and CD-35 expression with and without oral LPS activation occurs after HIV infection and this trend appears to be accentuated in patients with high viral load. This relationship may contribute to increased susceptibility to oral opportunistic infections in advanced HIV+ patients.

Fc receptors as targets for immunotherapy

Human membrane and soluble Fc epsilon receptors (Fc epsilon RI, Fc epsilon RII/CD23) and Fc gamma receptors (Fc gamma RI/CD64, Fc gamma RII/CD32, Fc gamma RIII/CD16) have been implicated in a number of diseases. Their functional roles such as capture and clearance of immune complexes, antibody-dependent cell cytotoxicity, or cytokine or inflammatory mediator release, make them potential targets for immuno-intervention. In the present review, we will describe how membrane and soluble human Fc epsilon R and Fc gamma R have been already used as targets/tools for immuno-interventions by using monoclonal and bispecific engineered antibodies. Some therapeutic uses of these molecules both in cancer, infectious, and auto-immune diseases are presented.

Human Immunodeficiency Virus-1 env Impairs Fcγ Receptor-Mediated Phagocytosis Via a Cyclic Adenosine Monophosphate-Dependent Mechanism

Human immunodeficiency virus (HIV)-1 expression in mononuclear phagocytes is associated with multiple functional defects, including phagocytosis. To assess Fcγ receptor (FcγR) function in cells expressing HIV-1, human promonocytic cells (U937) acutely or chronically infected with HIV-1, or stably transfected with a noninfectious reverse transcriptase (RT) defective HIV-1 provirus (Δpol), were treated with phorbol 12-myristate 13-acetate for 48 hours and tested for their ability to ingest sheep erythrocytes coated with IgG (E-IgG). HIV-1–infected or transfected U937 cells ingested 50% to 65% fewer E-IgG than controls despite normal surface expression of FcγRs. HIV-1 specifically impaired FcγR-mediated phagocytosis, as ingestion of complement-coated erythrocytes was unaffected. U937 cells transfected with an env deficient mutant of HIV-1 ingested E-IgG normally, suggesting that the expression of HIV-1 env was required for HIV-1 to inhibit FcγR-mediated phagocytosis. Expression of HIV-1 in U937 cells was associated with an increased accumulation of intracellular cyclic adenosine monophosphate (cAMP); addition of the adenylate cyclase inhibitor 2′,5′-dideoxyadenosine to these cells decreased intracellular cAMP levels to that of controls and restored FcγR-mediated phagocytosis. Addition of either interferon (IFN)-γ or an inhibitor of cAMP-dependent protein kinase A (KT 5720) to HIV-1–transfected U937 cells also restored FcγR-mediated phagocytosis. Expression of HIV-1 induces a specific defect of FcγR function in mononuclear phagocytes that correlates with increased levels of cAMP, and can be corrected by pharmacologic manipulation.

Apoptosis of CD4+ T cells induced after contact with HIV1-infected or non-infected macrophages

The hallmark of human immunodeficiency virus type 1 (HIV1) infection is the relentless destruction of CD4+ T lymphocytes. Indirect cell killing mechanisms are thought to play an outstanding role in lymphocyte depletion. One such proposed mechanism is the induction of apoptosis through cross-linking of the CD4 receptor by anti-CD4 antibodies or by the HIV1 envelope protein expressed at the surface of infected cells. Here we provide evidence that apoptosis is triggered in CD4+ lymphoblastoid cells (MT4) following cocultivation with monocyte-derived macrophages (MDMs) productively infected with the monocytotropic isolate HIV1 PAR. Blocking virus replication by AZT abrogates apoptosis of MT4 cells. Infected MDMs do not transmit virus infection to target cells. DNA nucleosomal fragmentation occurs at 46-66 h after starting cocultures. It is inhibited by the addition of neutralizing anti-gp120 monoclonal antibody (mAb), implying that the gp120/CD4 interaction triggers the apoptotic process. Cocultivating with MDMs, either infected or not, in the presence of anti-CD4 mAb Leu-3a, also leads to MT4 cell death, with DNA fragmentation being detected at 24-40 h. Leu-3a induced apoptosis does not require cross-linking of CD4 by anti-immunoglobulin, showing that MDMs provide an alternative to conventional cross-linking. Both the infected and the non-infected MDMs were found to stimulate 3H-thymidine incorporation in cocultivated MT4 cells.

Modulation of the effector function of human macrophages for Histoplasma capsulatum by HIV-1. Role of the envelope glycoprotein gp120

We have demonstrated that monocyte-derived macrophages (Mphi) from HIV+ individuals are deficient in their capacity to phagocytose Histoplasma capsulatum (Hc) yeasts, and are more permissive for the intracellular growth of Hc. To determine whether these defects in Mphi function were caused by HIV infection of the Mphi and/or by pathological events associated with HIV infection, cultured normal human Mphi were infected with the HIV-1BaL strain. Virus production, quantified by reverse transcriptase activity and p24 antigen, was evident on day 8 after infection and peaked on day 16. On days 12, 16, and 20 after infection, HIV-1-infected Mphi were deficient in their capacity to recognize and bind Hc yeasts compared with control Mphi, and also were more permissive for the intracellular growth of Hc. Culture of normal Mphi with the envelope glycoprotein gp120 inhibited phagocytosis of Hc yeasts by Mphi in a concentration-dependent manner, but did not cause more rapid intracellular growth of Hc. Normal Mphi cultured in the serum of HIV+ individuals with impaired Mphi function subsequently were deficient in their capacity to phagocytose Hc yeasts, and were more permissive for the intracellular growth of yeasts compared with Mphi cultured in normal serum. Conversely, culture of normal Mphi in the serum of HIV+ patients with normal Mphi function did not affect the interaction of Hc yeasts with Mphi. Moreover, when Mphi from HIV+ individuals that were initially defective in host defense against Hc were cultured in normal HIV- serum, normal Mphi function was demonstrated. Adsorption of gp120 from the serum of two HIV+ patients removed the capacity of the serum to cause a Mphi defect in phagocytosis of Hc, but had no effect on the capacity of the serum to cause accelerated intracellular growth. These data demonstrate that observed defects in Mphi interaction with Hc yeasts may be caused by gp120 and other, as yet unknown serum component(s) probably released into serum by HIV-infected cells.

Effects of monocyte purification and culture on integrin expression

Selective alterations in the surface expression of members of the LeuCAM (leukocyte cell adhesion molecule) family of integrins occur during in vitro culture of human monocytes. Such changes may relate in part to cellular maturation, but also to activation following purification and culture of monocytes. In this paper, we examined the effects of monocyte isolation, adherence during culture and endotoxin exposure on the expression of these molecules and the ligand for LFA-1, ICAM-1 (CD54). Expressions of CD11b, CD18 and CD54, but not CD11a or CD11c, were higher on monocytes freshly isolated by density gradient separation and plastic adherence as compared with cells labelled directly in whole blood. However, the surface expression of the LeuCAMs and CD54 on cultured monocytes was not affected by short-term adherence to plastic for 2 h, as determined by comparisons of their expression on adherence-isolated and elutriated monocytes. In contrast, prolonged adhesion of monocytes for up to 21 days in culture altered expression of CD11a without affecting that of the other LeuCAMs or CD54. Expression of CD11a decreased more rapidly on adherence-maintained cells as compared with suspension-cultured cells. Our results show that cellular manipulations required for in vitro studies of monocyte/macrophages may alter expression of the LeuCAMs.

Effects of HIV-1 on the surface expression of LFA-1 on cultured monocytes

CD11a, the alpha chain of LFA-1, which is a member of the LeuCAM family of integrins, has been implicated in the formation of HIV-induced syncytia and may contribute to the depletion of CD4-positive lymphocytes seen in patients with HIV infection. In this study, we examined the effects of HIV-1 infection on the expression of CD11a on cultured monocyte-derived macrophages (MDMs). Monocytes isolated from peripheral blood and maintained in suspension culture were infected in vitro with a monocytotropic variant of HIV-1 (Ba-L). Surface expression of CD11a, measured by indirect immunofluorescence and flow cytometry, was significantly higher on HIV-infected cells than on mock-infected cells from the same donor. Upregulation of CD11a expression was unaffected by the HIV reverse transcriptase inhibitor, zidovudine, indicating that it did not depend on reverse transcription. A step before reverse transcription, such as viral binding, appears sufficient to trigger an increase in CD11a expression. This hypothesis is supported by our findings of soluble recombinant CD4 inhibition of HIV-induced CD11a upregulation. It is possible that induction of a cytokine network by HIV underlies this effect, given our findings that exposure of uninfected MDMs to granulocyte-macrophage colony-stimulating factor (GM-CSF) specifically increased CD11a expression and that HIV-infected MDMs secreted more GM-CSF than mock-infected cells.

HIV-1-infected monocytes and monocyte-derived macrophages are impaired in their ability to produce superoxide radicals

Monocytes and monocyte-derived macrophages play a key role in immune defense against pathogenic organisms. Superoxide anion production is a key mechanism by which phagocytes kill pathogens. We sought to determine whether human immunodeficiency virus-infected monocytes and monocyte-derived macrophages are compromised in their ability to produce the superoxide anion following stimulation with phorbol myristate acetate (PMA) or after cross-linking the type I Fc receptor for IgG (Fc gamma RI). Fc gamma RI was cross-linked by the binding of monoclonal antibody 197, which reacts with an epitope of Fc gamma RI via its Fc region. Monocytes and monocyte-derived macrophages obtained from seronegative donors were infected in vitro with human immunodeficiency virus-1JR-FL and used in effector assays that measured superoxide anion production by the reduction of nitroblue tetrazolium. Reduced nitroblue tetrazolium was measured spectrophotometrically and by microscopy in which the percentage of cells containing intracellular deposits of the dye was assessed. By spectrophotometric measurement, we found that human immunodeficiency virus-infected monocytes and monocyte-derived macrophages produced less superoxide anion following either phorbol myristate acetate stimulation or Fc gamma RI cross-linking than uninfected cells from the same donor. Using microscopy we saw no difference in the percentage of infected and uninfected macrophages containing intracellular deposits of nitroblue tetrazolium suggesting that human immunodeficiency virus-infected macrophages produce less superoxide anion on a per cell basis than uninfected macrophages. Activation of human immunodeficiency virus-infected monocytes with interferon-gamma for 72 h prior to stimulation with phorbol myristate acetate or monoclonal antibody 197 increased their ability to reduce nitroblue tetrazolium. These findings suggest that impairment in the production of reactive oxygen intermediates may, in some cases, contribute to the pathogenesis of human immunodeficiency virus infection and the acquired immunodeficiency syndrome.

Impairment of phagosome-lysosome fusion in HIV-1-infected macrophages

Phagosome-lysosome fusion is critical for intracellular killing of most organisms and is inhibited by some viruses, notably influenza. We explored the effects of infection in vitro with HIV-1 (IIIB or Ada-M) on phagosome-lysosome fusion in blood monocyte-derived macrophages. After 8 days of infection, fusion was assessed from the fluorescence change occurring up to 2 h after labeling the lysosome compartment with acridine orange and loading of phagosomes with opsonized yeast. Compared with mock-infected control macrophages, the proportion of cells showing fusion after infection was reduced from a mean of 70% to a mean of 47% (p = 0.0001). Inhibition was seen with heat-killed HIV-1 IIIB but not virus-free filtrate. It was mimicked by recombinant gp 120 and blocked by soluble CD4 or antibody to CD4 but not by a neutralizing antibody to the V3 loop of gp 120. The inhibitory effect was seen 8 days after the original, transient exposure to gp 120. These results suggest that a lasting abnormality of phagosome-lysosome fusion results from interaction between gp 120 and CD4, contributing, perhaps, to the increased susceptibility to opportunistic infections of people infected with HIV.

Quantifying phagocytosis of Mycobacterium avium complex by human monocytes in whole blood

Studies of phagocytic efficiency in cells of the macrophage lineage have assumed additional importance since the discovery that HIV infection of these cells impairs their immune function. A rapid method has been developed for measuring phagocytosis of the opportunistic pathogen Mycobacterium avium complex by human monocytes. Fluoresceinated M. avium complex (F-MAC) was incubated with whole blood at 37 degrees C and the fluorescence of extracellular F-MAC was quenched using a vital blue stain. Monocytes were then stained with a monoclonal antibody (mAb) to human CD14 conjugated to phycoerythrin (PE) red cells were lysed, and the percentage of monocytes which had phagocytosed F-MAC was measured by flow cytometry. The results were reproducible in samples of blood taken from individual donors over a period of 1 or 2 weeks, and optimum F-MAC concentrations and an optimum incubation time were determined by experiment. This method has the advantages of requiring only a small volume of blood, not necessitating manipulation of cells before testing, and using a phagocytic target relevant to the pathogenesis of HIV infection.

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

There are a number of machanisms by which HIV-infected macrophages contribute to the pathogenesis of the Acquired Immunodeficiency Syndrome (AIDS). Macrophage-tropic strains of HIV are present at the time of infection, and persist throughout the course of infection, despite the emergence of T cell tropic quasispecies. As HIV causes chronic infection of macrophages with only minimal cytopathology, these cells can provide an important viral reservoir in HIV-infected persons. Macrophages are more susceptible to HIV infection than freshly isolated monocytes. HIV-infected macrophages can contribute to CD4 T lymphocyte depletion through a gp120-CD4 dependent fusion process with uninfected CD4-expressing T cells. Increasing data support the role of HIV-infected macrophages and microglia in the pathogenesis of HIV-related encephalopathy and AIDS-related dementia through the production of neurotoxins. HIV infection of macrophages in vitro results in impairment of many aspects of their function. Reduced phagocytic capacity for certain opportunistic pathogens, including Toxoplasma gondii and Candida albicans, may be responsible for reactivation of these pathogens in persons with advanced HIV infection, although the mechanisms underlying reactivation of infections and susceptibility to disease from new infections are likely to be multifactorial. Our studies showing defective phagocytosis and killing provide additional information that contribute to our understanding of the pathogenesis of AIDS. Studies of in vitro efficacy of potential antiretroviral therapies should be performed in both primary lymphocyte and monocyte cultures, given the importance of both of these cell populations to HIV pathogenesis and their differing biology.

The kinetics of surface expression of CD11/CD18 integrins and CD54 on monocytes and macrophages

Cells of the macrophage lineage mediate extremely important normal functions of the immune system. Such functions are in part related to interactions between cell-bound LeuCAMs and their ligands. MoAb staining and flow cytometric analysis were used to follow changes in surface expression of LeuCAMs and the LFA-1 ligand CD54 during maturation of peripheral blood monocytes (BM) in vitro. Surface expression of these molecules increased on BM following isolation, the greatest increase being in CD54 and CD11c. Following an initial increase, there was a reduction in CD11a expression after 2 weeks in culture, this being greater on adherent compared with suspension-maintained cells. Expression of CD11b remained high throughout the culture period. LeuCAM and CD54 expression was further compared on freshly isolated alveolar macrophages (AM) and BM paired donors. A reciprocal relationship was observed between CD11c and CD11b on AM and BM, in that BM expressed higher levels of CD11b than CD11c, whilst the converse was true for AM. CD54 expression was also higher on AM than on BM, whilst there was no significant difference in expression of CD11a on these cells. These data suggest that consistent changes occur in the surface expression of the LeuCAMs and CD54 as monocytes mature into macrophages, which may reflect the specific functions of these cells.