Henry Koziel

Reduced binding and phagocytosis of Pneumocystis carinii by alveolar macrophages from persons infected with HIV-1 correlates with mannose receptor downregulation.

The macrophage mannose receptor, a pattern recognition molecule and component of innate immunity, mediates binding and phagocytosis of Pneumocystis carinii and likely represents an important clearance mechanism in the lungs of immunocompetent hosts. The purpose of this study was to examine the ability of alveolar macrophages from HIV-infected individuals to bind and phagocytose P. carinii, and to investigate the role of the macrophage mannose receptor in mediating this interaction. Compared with healthy individuals, alveolar macrophage phagocytosis of P. carinii from HIV+ persons was reduced up to 74% (P = 0.02), primarily reflecting a reduction in the number of organisms associated with each macrophage (P = 0.019). Furthermore, macrophages from HIV+ individuals demonstrated up to an 80% (P < 0.05) reduction in mannose receptor surface expression and endocytosis. Mannose receptor affinity was unaltered, and mRNA levels were modestly reduced (P < 0.05). Cells from HIV+ individuals with CD4(+) counts < 200 cells/mm3 (representing individuals at high clinical risk for P. carinii pneumonia) demonstrated the lowest levels of P. carinii phagocytosis and mannose receptor endocytosis. In vitro HIV infection of alveolar macrophages from healthy individuals reduced mannose receptor endocytosis to 53.2% (P < 0.05) and P. carinii binding and phagocytosis to 67.4% (P < 0.05) of control. Our studies suggest that HIV infection may alter innate immunity in the lungs, and that impaired alveolar macrophage mannose receptor-mediated binding and phagocytosis of P. carinii may contribute to the susceptibility of HIV-infected individuals to this opportunistic pulmonary pathogen.

MARCO is the major binding receptor for unopsonized particles and bacteria on human alveolar macrophages.

Alveolar macrophages (AMs) avidly bind and ingest inhaled environmental particles and bacteria. To identify the particle binding receptor(s) on human AMs, we used functional screening of anti-human AM hybridomas and isolated a mAb, PLK-1, which inhibits AM binding of unopsonized particles (e.g., TiO2, latex beads; 63 ± 5 and 67 ± 4% inhibition, respectively, measured by flow cytometry; n = 11) and unopsonized bacteria (∼84 and 41% inhibition of Escherichia coli and Staphylococcus aureus binding by mAb PLK-1, respectively). The PLK-1 Ag was identified as the human class A scavenger receptor (SR) MARCO (macrophage receptor with collagenous structure) by observing specific immunolabeling of COS cells transfected with human MARCO (but not SR-AI/II) cDNA and by immunoprecipitation by PLK-1 of a protein of appropriate molecular mass (∼70 kDa) from both normal human bronchoalveolar lavage cells (>90% AMs) and human MARCO-transfected COS cells. PLK-1 also specifically inhibited particle binding by COS cells, only after transfection with human MARCO cDNA. Immunostaining showed specific labeling of AMs within human lung tissue, bronchoalveolar lavage samples, as well as macrophages in other sites (e.g., lymph node and liver). Using COS transfectants with different truncated forms of MARCO, allowed epitope mapping for the PLK-1 Ab to MARCO domain V between amino acid residues 420 and 431. A panel of Abs to various SRs identified expression on AMs, but failed to inhibit TiO2 or S. aureus binding. The data support a dominant role for MARCO in the human AM defense against inhaled particles and pathogens.

Neurotrophins regulate proliferation and survival of two microglial cell lines in vitro

Microglia are thought to play a key role in the development and regeneration of the central nervous system although the mechanisms regulating their presence and activity are not fully understood. Substantial evidence suggests that members of the neurotrophin family such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 and -4 (NT-3/4) have a dramatic effect on both neurons and perineuronal cells. This study employed two murine microglial lines, BV-2 and N9, to examine the action of these neurotrophins on the mitotic activity and survival of microglia in vitro. Neurotrophins were incorporated into the media at the time of plating and cell number and levels of mitochondrial dehydrogenase activity (MTT) were determined at various time points in vitro. NGF increased cell number and MTT levels of both cell lines in a dose-dependent manner. BV-2 was more sensitive to NGF than N9. Similar responses were elicited by BDNF, although the sensitivity of each cell line was different than that found for NGF. NT-3 and NT-4 had no effect on cell proliferation. However, NT-4 had an effect on the survival of BV-2 and N9 cells. The response of these cells to neurotrophins was blocked by K252a, a tyrosine kinase inhibitor, suggesting that actions of neurotrophins were mediated by high-affinity tyrosine kinase receptors (Trk). Immunolocalization studies revealed positive Trk (pan) reactivity in the above cell lines and in primary microglia, but an absence of the low-affinity p75 neurotrophin receptor. Western blot analysis supported the above observations. These studies suggest that in addition to their neurotrophic actions, NGF and BDNF may also regulate microglial dynamics, thereby influencing the surrounding milieu during neuronal regeneration.

Pneumocystis activates human alveolar macrophage NF-kappaB signaling through mannose receptors.

ABSTRACT Alveolar macrophages (AM) represent important effector cells in the innate immune response to the AIDS-related pathogen Pneumocystis, but the early AM host defense signaling events are poorly defined. Using AM from healthy individuals, we showed in the present study that Pneumocystis organisms stimulate AM NF-κB p50 and p65 nuclear translocation in a time-dependent and multiplicity-of-infection-dependent manner as determined by electrophoretic mobility shift assay and immunofluorescence microscopy and that NF-κB nuclear translocation is associated with I-κB phosphorylation. Importantly, competitive inhibition of mannose receptor and targeted short interfering RNA-mediated gene suppression of mannose receptor mRNA and protein is associated with complete elimination of NF-κB nuclear translocation in response to Pneumocystis. Furthermore, human immunodeficiency virus (HIV) infection of AM (as a model human disease state of reduced AM mannose receptor expression and function) inhibits Pneumocystis-mediated NF-κB nuclear translocation and is associated with reduced I-κB phosphorylation and reduced interleukin-8 (IL-8) release. In contrast, NF-κB nuclear translocation and IL-8 release in response to lipopolysaccharide are intact in AM from both healthy and HIV-infected individuals, indicating that the observed impairment is not a global disturbance of the NF-κB pathway. Thus, in addition to phagocytic and endocytic effector functions, the present study identifies mannose receptors as pattern recognition receptors capable of NF-κB activation in response to infectious non-self challenge. AM mannose receptor-mediated NF-κB activation may represent an important mechanism of the host cell response to Pneumocystis, and altered NF-κB activation in the context of HIV infection may impair a critical innate immune signaling response and may contribute to pathogenesis of opportunistic lung infections.

Negative regulatory role of mannose receptors on human alveolar macrophage proinflammatory cytokine release in vitro.

Alveolar macrophages (AM) are critical components of lung innate immunity and contribute to an effective host response to Pneumocystis pneumonia. Recognition of unopsonized Pneumocystis organisms by human AM is mediated predominantly via mannose receptors and results in phagocytosis, release of reactive oxygen species, and activation of the nuclear transcription factor (NF)‐κB. However, the AM host defense genes activated by Pneumocystis have not been defined. In the present study, incubation of AM with unopsonized Pneumocystis organisms was not associated with release of interleukin (IL)‐1β, IL‐6, or tumor necrosis factor (TNF)‐α (important cytokines in the host response to Pneumocystis) and did not induce IL‐1β, IL‐6, or TNF‐α mRNA transcripts. These findings were not attributed to Pneumocystis‐induced cytopathic changes, as these same AM released IL‐8 and matrix metalloproteinase‐9 in response to Pneumocystis. NF‐κB‐mediated IL‐8 release was independent of Pneumocystis phagocytosis. The observed response was specific, as IL‐1β, IL‐6, and TNF‐α release and mRNA induction were preserved in response to lipopolysaccharide or serum‐opsonized Pneumocystis. The absence of IL‐1β, IL‐6, and TNF‐α release in response to Pneumocystis was predominately influenced by AM mannose receptors, as blocking mannose receptors or targeted mannose receptor small interfering RNA functional gene silencing resulted in TNF‐α release in response to unopsonized Pneumocystis organisms. Furthermore, ligation of AM mannose receptors by unopsonized Pneumocystis organisms reduced Toll‐like receptor 4‐mediated TNF‐α release. Taken together, these data suggest that mannose receptors on human AM may suppress select proinflammatory cytokine release and may serve to regulate the innate inflammatory responses to infectious challenge in the lungs.

HIV Impairs TNF-α Mediated Macrophage Apoptotic Response to Mycobacterium tuberculosis

The factors that contribute to the exceptionally high incidence of Mycobacterium tuberculosis (MTb) disease in HIV+ persons are poorly understood. Macrophage apoptosis represents a critical innate host cell response to control MTb infection and limit disease. In the current study, virulent live or irradiated MTb (iMTbRv) induced apoptosis of differentiated human U937 macrophages in vitro, in part dependent on TNF-α. In contrast, apoptosis of differentiated HIV+ human U1 macrophages (HIV+ U937 subclone) was markedly reduced in response to iMTbRv and associated with significantly reduced TNF-α release, whereas apoptosis and TNF-α release were intact to TLR-independent stimuli. Furthermore, reduced macrophage apoptosis and TNF-α release were independent of MTb phagocytosis. Whereas surface expression of macrophage TLR2 and TLR4 was preserved, IL-1 receptor associated kinase-1 phosphorylation and NF-κB nuclear translocation were reduced in HIV+ U1 macrophages in response to iMTbRv. These findings were confirmed using clinically relevant human alveolar macrophages (AM) from healthy persons and asymptomatic HIV+ persons at clinical risk for MTb infection. Furthermore, in vitro HIV infection of AM from healthy persons reduced both TNF-α release and AM apoptosis in response to iMTbRv. These data identify an intrinsic specific defect in a critical macrophage cellular response to MTb that may contribute to disease pathogenesis in HIV+ persons.

Pneumocystis-mediated IL-8 release by macrophages requires coexpression of mannose receptors and TLR2.

Interaction with the unique fungus Pneumocystis (Pc) promotes IL‐8 release by human alveolar macrophages (AM), although the receptor(s) mediating IL‐8 release have not been identified. TLR2 recognizes fungal components and mediates release of host defense cytokines and chemokines, although whether TLR2 mediates signaling in response to Pc is not known. In the current study, Pc induced IL‐8 release by human AM, and AM pretreatment with anti‐TLR2 neutralizing antibody reduced IL‐8 release. However, in nonphagocytic human embryonic kidney (HEK)293 cells transfected with human TLR2 cDNA, incubation with Pc did not induce IL‐8 release, whereas these same cells released IL‐8 in response to the TLR2 agonist lipoteichoic acid. Targeted gene silencing of AM mannose receptors (MR; phagocytic receptors for Pc) using small interfering RNA also reduced Pc‐mediated IL‐8 release in human AM. However, HEK293 cells transfected with human MR cDNA alone did not release IL‐8 in response to Pc. In contrast, HEK293 cells cotransfected with human TLR2 and human MR cDNA released IL‐8 in response to Pc. In human AM, Pc promoted direct interaction of MR and TLR2, IL‐8 release was reduced markedly upon simultaneous blocking of TLR2 and gene silencing of MR, and IL‐8 release was dependent in part on transcription factor NF‐κB and ERK1/2 and JNK MAPKs. These studies demonstrate that Pc‐mediated IL‐8 release by human AM requires the coexpression of MR and TLR2 and further supports the concept that combinatorial interactions of macrophage innate receptors provide specificity of host defense cell responses to infectious challenge.

Cannabinoids Inhibit HIV-1 Gp120-Mediated Insults in Brain Microvascular Endothelial Cells

HIV-1 infection has significant effect on the immune system as well as on the nervous system. Breakdown of the blood-brain barrier (BBB) is frequently observed in patients with HIV-associated dementia (HAD) despite lack of productive infection of human brain microvascular endothelial cells (HBMEC). Cellular products and viral proteins secreted by HIV-1 infected cells, such as the HIV-1 Gp120 envelope glycoprotein, play important roles in BBB impairment and HIV-associated dementia development. HBMEC are a major component of the BBB. Using cocultures of HBMEC and human astrocytes as a model system for human BBB as well as in vivo model, we show for the first time that cannabinoid agonists inhibited HIV-1 Gp120-induced calcium influx mediated by substance P and significantly decreased the permeability of HBMEC as well as prevented tight junction protein down-regulation of ZO-1, claudin-5, and JAM-1 in HBMEC. Furthermore, cannabinoid agonists inhibited the transmigration of human monocytes across the BBB and blocked the BBB permeability in vivo. These results demonstrate that cannabinoid agonists are able to restore the integrity of HBMEC and the BBB following insults by HIV-1 Gp120. These studies may lead to better strategies for treatment modalities targeted to the BBB following HIV-1 infection of the brain based on cannabinoid pharmacotherapies.

Dependence of regulatory volume decrease on transient receptor potential vanilloid 4 (TRPV4) expression in human corneal epithelial cells

TRPV4 is a non-selective cation channel with moderate calcium permeability, which is activated by exposure to hypotonicity. Such a stress induces regulatory volume decrease (RVD) behavior in human corneal epithelial cells (HCEC). We hypothesize that TRPV4 channel mediates RVD in HCEC. Immunohistochemistry revealed centrally and superficially concentrated TRPV4 localization in the corneal tissue. Immunocytochemical and fluorescence activated cell sorter (FACS) analyses identified TRPV4 membrane surface and cytosolic expression. RT-PCR and Western blot analyses identified TRPV4 gene and protein expression in HCEC, respectively. In addition, 4alpha-PDD or a 50% hypotonic medium induced up to threefold transient intracellular Ca2+ ([Ca2+]i) increases. Following TRPV4 siRNA HCEC transfection, its protein expression level declined by 64%, which abrogated these [Ca2+]i transients. Similarly, exposure to either ruthenium red or Ca(2+)-free Ringers solution also eliminated this response. In these transfected cells, RVD declined by 51% whereas in the non-transfected counterpart, ruthenium red and Ca(2+)-free solution inhibited RVD by 54 and 64%, respectively. In contrast, capsazepine, a TRPV1 antagonist, failed to suppress [Ca2+]i transients and RVD. TRPV4 activation contributes to RVD since declines in TRPV4 expression and activity are associated with suppression of this response. In conclusion, there is TRPV4 functional expression in HCEC.

The Influence of Diagnostic Bronchoscopy on Clinical Outcomes Comparing Adult Autologous and Allogeneic Bone Marrow Transplant Patients

STUDY OBJECTIVES To review our experience with diagnostic bronchoscopy in the evaluation of pulmonary infiltrates in adult hematopoietic stem cell transplantation (HSCT) recipients in the era of Pneumocystis prophylaxis and cytomegalovirus antigen testing. The study focused on diagnostic yields and the influence of bronchoscopic findings on pharmacologic therapy and mortality, comparing allogeneic (allo) HSCT patients to autologous (auto) HSCT patients. DESIGN Case series review. SETTING Tertiary care academic urban medical centers. PATIENTS All adult allo-HSCT and auto-HSCT patients undergoing bronchoscopy for the evaluation of pulmonary infiltrates from January 1997 to September 2001. MEASUREMENTS AND RESULTS The review identified 169 bronchoscopies that had been performed on HSCT patients, representing 12.5% of all HSCT patients (allo-HSCT patients, 125 bronchoscopies; auto-HSCT patients, 44 bronchoscopies). Bronchoscopy was requested more often in allo-HSCT patients (18.7%) compared to auto-HSCT patients (6.6%). Findings at bronchoscopy provided a specific diagnosis more frequently in allo-HSCT patients (50%) compared to auto-HSCT patients (34%). For both allo-HSCT and auto-HSCT patients, most diagnoses were obtained by BAL alone, whereas transbronchial biopsy (TBBx) provided additional specific information in < 10% of cases. For select patients (n = 27), surgical lung biopsy following bronchoscopy provided unique diagnoses in 47 to 50% of cases. Information from bronchoscopy influenced clinical decisions more often in allo-HSCT patients (50%) than in auto-HSCT patients (36%), and allowed for the discontinuation or addition of antimicrobial, corticosteroid, or antineoplastic agents to treatment. Complications from bronchoscopy occurred in 9% of all HSCT patients (n = 15), and were associated with higher in-hospital mortality rates in allo-HSCT patients (82%; n = 9) compared to auto-HSCT patients (50%; n = 2). The overall in-hospital mortality rates for allo-HSCT and auto-HSCT patients having bronchoscopy was similar (38% vs 27%, respectively; p = 0.25), and establishing a specific diagnosis by bronchoscopy did not improve the in-hospital mortality rate for allo-HSCT or auto-HSCT patients. CONCLUSIONS Bronchoscopy may provide clinically useful information in the evaluation of adult allo-HSCT and auto-HSCT recipients with pulmonary infiltrates. The results of testing BAL fluid samples alone suggested an etiology in most cases, whereas the findings of TBBx provided unique diagnoses infrequently. Further studies are warranted to improve the utility of diagnostic bronchoscopy in the evaluation of HSCT patients.