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Biomedical subjects

S M Crowe

Publications and source records attributed to S M Crowe.

At least 19 recordsLinked to original sources
PubMed1999

Does HIV cause depletion of CD4+ T cells in vivo by the induction of apoptosis?

The central pathogenic feature of AIDS is the dramatic loss of CD4+ lymphocytes. Despite more than a decade of intense research, the exact mechanism by which HIV causes this is still not understood. A major model for T cell depletion, proposed originally by Ameison and Capron in a report published in 1991, is that HIV sensitizes CD4+ T cells for activation-induced apoptosis. The apoptotic model of T cell depletion is discussed, and experiments that address the questions of whether apoptosis is restricted to infected cells or 'bystander' T cells, and whether T cell apoptosis requires participation of separate HIV-infected haematopoietic cell populations, are reviewed.

Apoptosis↗
PubMed1998

Specificity of binding of HIV-1 anti-p24 antibodies to CD4+ lymphocytes from HIV-infected subjects.

The clinical utility of a flow cytometric assay (FCA) for intracellular HIV p24 antigen was evaluated in a group of HIV-1-infected subjects. A previously described method, p24-FCA (1), was modified to minimize nonspecific staining and to include irrelevant isotype-matched control antibodies. Blood mononuclear cells from 32 HIV-1 seropositive subjects and 14 HIV-1 seronegative controls were examined. In HIV-1 seropositive individuals, the proportion of CD4+ lymphocytes that bound the p24 monoclonal and the isotype control antibodies were not different. The frequency of cells binding p24 antibodies increased with declining CD4 counts and was highest in patients with low CD4+ lymphocyte counts. Although results of p24-FCA do reflect disease progression, the high nonspecific binding of monoclonal antibodies in infected subjects obscures specific p24 binding and precludes its use as an accurate measure of infection within single cells.

Antibody Specificity↗
PubMed1998

HIV-1 selection by epidermal dendritic cells during transmission across human skin.

Macrophage tropic HIV-1 is predominant during the initial viremia after person to person transmission of HIV-1 (Zhu, T., H. Mo, N. Wang, D.S. Nam, Y. Cao, R.A. Koup, and D.D. Ho. 1993. Science. 261:1179-1181.), and this selection may occur during virus entry and carriage to the lymphoid tissue. Human skin explants were used to model HIV-1 selection that may occur at the skin or mucosal surface. Macrophage tropic, but not T cell line tropic strains of HIV-1 applied to the abraded epidermis were recovered from the cells emigrating from the skin explants. Dermis and epidermis were separated by dispase digestion after virus exposure to determine the site of viral selection within the skin. Uptake and transmission to T cells of all HIV-1 isolates was found with the dermal emigrant cells, but only macrophage tropic virus was transferred by emigrants from the epidermis exposed to HIV-1, indicating selection only within the epidermis. CD3+, CD4+ T cells were found in both the dermal and epidermal emigrant cells. After cell sorting to exclude contaminating T cells, macrophage tropic HIV-1 was found in both the dermal emigrant dendritic cells and in dendritic cells sorted from the epidermal emigrants. These observations suggest that selective infection of the immature epidermal dendritic cells represents the cellular mechanism that limits the initial viremia to HIV-1 that can use the CCR5 coreceptor.

CD4-Positive T-Lymphocytes↗
PubMed1998

Effect of GM-CSF on HIV-1 replication in monocytes/macrophages in vivo and in vitro: a review.

Cells of macrophage lineage constitute the main cellular target of Human Immunodeficiency Virus type 1 (HIV-1). Replication of HIV-1 in monocyte/macrophages is generally augmented by factors promoting their differentiation. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a key regular of the differentiation of cells of macrophage lineage. The effects of GM-CSF on HIV-1 replication in vitro are still controversial. Most of the published studies suggest that GM-CSF upregulates HIV-1 expression in both primary cultured macrophages and promonocytic cell lines. There have also been reports demonstrating that GM-CSF does not affect HIV-1 replication in cells of macrophage lineage or that GM-CSF can actually suppress HIV-1 expression. In vivo, GM-CSF administrated to HIV-positive patients at any stage of disease, without any antiretroviral therapy, appears to increase HIV-1 activity. The possible mechanism by which GM-CSF might affect HIV-1 replication in macrophages remains unclear.

Animals↗
PubMed1998

HIV-1 DNA and mRNA concentrations are similar in peripheral blood monocytes and alveolar macrophages in HIV-1-infected individuals.

OBJECTIVE: To determine the relative contribution of alveolar macrophages, peripheral blood monocytes (PBM) and peripheral blood lymphocytes (PBL) from HIV-infected individuals to HIV-1 viral load. METHODS: Alveolar macrophages were obtained by flexible bronchoscopy, and PBM and PBL by venipuncture from HIV-1-infected individuals. Alveolar macrophages and PBM were purified using immunomagnetic bead selection to deplete CD3+ and CD19+ cells from bronchoalveolar lavage and peripheral blood mononuclear cells, respectively. DNA and mRNA were extracted and gag copy number quantified using polymerase chain reaction (PCR) and reverse transcriptase PCR. The titres of infectious cell-associated HIV-1 in cells were determined by the endpoint dilution coculture technique for alveolar macrophages and PBM. RESULTS: Alveolar macrophages and PBM from HIV-1-infected subjects (n=11) contained equivalent concentrations of HIV-1 DNA and HIV-1 mRNA as determined by PCR and reverse transcriptase PCR, respectively. Antiretroviral therapy was associated with reduced viral DNA concentrations in alveolar macrophages but not in PBM. PBL had a significantly higher level of proviral DNA and mRNA than alveolar macrophages or PBM. CONCLUSIONS: Although alveolar macrophages infected in vitro are more permissive for HIV-1 replication than PBM, this difference could not be demonstrated in vivo.

Cells, Cultured↗
PubMed1998

Microsporidial disease in HIV-infected patients: a report of 42 patients and review of the literature.

Microsporidiosis is recognized as an increasingly important infection, particularly in patients with human immunodeficiency virus (HIV) infection. In this retrospective study we have reviewed the clinical features, laboratory findings and management of 42 HIV positive patients co-infected with microsporidia. All patients had spores identified in faeces stained with a modified trichome blue stain. Patients were all markedly immunosuppressed (median CD4 20 cells/microl). Common symptoms included weight loss, diarrhoea, abdominal pain, anorexia and nausea. 29 patients were diagnosed with Enterocytozoon bieneusi infection; 13 were infected with Encephalitozoon intestinalis, and disseminated disease was confirmed in 8. Albendazole therapy in patients with E. intestinalis (but not E. bieneusi) resulted in good clinical response.

Adult↗
PubMed1997

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.

CD4 Antigens↗
PubMed1997

GM-CSF and its effects on replication of HIV-1 in cells of macrophage lineage.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hemopoetic growth factor that is a member of the four-helix bundle family of cytokines and growth factors. It regulates the proliferation and differentiation of granulocytes and cells of macrophage lineage from bone marrow progenitor cells, mediating these activities through binding to its receptor. Most studies examining the effects of GM-CSF on HIV-1 replication in primary monocytes and macrophages, and in related cell lines, have demonstrated augmentation of HIV-1 expression in vitro, although some reports have been at variance with these findings. These laboratory-based observations have been confirmed in limited clinical trials. This review outlines the details of these studies and considers mechanisms by which GM-CSF may exert its effects on cells of this lineage.

Acquired Immunodeficiency Syndrome↗
PubMed1997

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.

CD18 Antigens↗
PubMed1997

Constitutive expression of p50 homodimer in freshly isolated human monocytes decreases with in vitro and in vivo differentiation: a possible mechanism influencing human immunodeficiency virus replication in monocytes and mature macrophages.

Human immunodeficiency virus type 1 (HIV-1) replicates more efficiently in vitro in differentiated macrophages than in freshly isolated monocytes. We investigated whether this may be partly explained by changes in expression of NF-kappaB with monocyte differentiation. We demonstrated that constitutive expression of NF-kappaB in primary human monocytes changed significantly with differentiation in vitro to monocyte-derived macrophages (MDMs) and differentiation in vivo to alveolar macrophages (AMs). Freshly isolated monocytes constitutively expressed high levels of transcriptionally inactive p50 homodimer which decreased with time in culture in favor of the transcriptionally active p50/p65 and p50/RelB heterodimers. As in MDMs, AMs constitutively expressed p50/p65 and p50/RelB although at lower levels. HIV infection of fresh monocytes failed to induce p50/p65 as seen in MDMs. The replacement of p50 homodimers with transcriptionally active heterodimers following time in culture may partially explain the progressive increase in susceptibility of monocytes to HIV infection during in vitro culture. The change in NF-kappaB components with monocyte differentiation in vivo may also explain the different transcriptional activities of these cell populations in HIV-infected individuals.

Cell Differentiation↗
PubMed1996

Surface CD4 is critical to in vitro HIV infection of human alveolar macrophages.

The CD4 glycoprotein is the major cellular receptor for HIV. CD4 surface expression of monocytes decreases with time in culture while their susceptibility to HIV-1 increases. Our aim was to investigate whether this phenomenon occurs in macrophages that have differentiated in vivo by investigating CD4 expression and HIV-1 infection of human alveolar macrophages (AMs). Using flow cytometry to detect CD4 expression by Leu-3a labeled indirectly with fluorescein isothiocyanate or allophycocyanin, we found that CD4 was expressed at low but detectable levels, despite the high background autofluorescence well described in AMs. This finding was supported by the detection of CD4 mRNA in AMs using RT-PCR. T cell contamination of mRNA extracts of AMs was excluded by amplifying in parallel with primers to the constant region of the T cell receptor. Despite this low level of surface CD4, recombinant soluble CD4 and anti-CD4 antibody completely inhibited HIV-1 infection of AMs. We conclude that CD4, although expressed at low levels on the surface of AMs, appears to be critical to HIV-1 infection of these cells.

Acquired Immunodeficiency Syndrome↗
PubMed1996

The interaction of macrophage and non-macrophage tropic isolates of HIV-1 with thymic and tonsillar dendritic cells in vitro.

Dendritic cells isolated from thymus and tonsil were tested for susceptibility to HIV-1 strains that are tropic for macrophages or for T cell lines. DCs were purified by cell sorting and before infection expressed high levels of CD4 and HLA-DR and lacked markers for T, B, NK cells, or macrophages. Viral entry and reverse transcription was found after pulsing with strains of HIV-1 that could infect macrophages. During the first 36 h the PCR signals for gag sequences increased in DCs and macrophages. In contrast little if any viral DNA was found after pulsing macrophages or DCs with HIV-1 that was able to infect T cell lines. DCs pulsed with HIV-1 were able to transmit infection to responding T cells during an allogeneic or superantigen response. Selection for virus able to infect lymphoid DCs and other DCs expressing CD4 and its transfer to T cells during subsequent immune responses may provide a mechanism for the observed predominance of macrophage-tropic HIV-1 after in vivo transmission.

CD4 Antigens↗
PubMed1996

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.

Fluorescein-5-isothiocyanate↗
PubMed1996

Human immunodeficiency virus grown in CD4-expressing cells is associated with CD4.

Using a CD4-capture immunoassay for gp120, several strains of human immunodeficiency virus type 1 (HIV-1) grown in CD4-expressing T lymphoblastoid cells were found to contain little CD4-reactive gp120 (0.3-1.0 ng/ml) relative to virus titre (10(3.2)-10(5.0) TCID50/ml) and p24 antigen (80-1000 ng/ml). The measured CD4-reactive gp120 concentrations of HIV-1 suspensions grown in CD4-negative human neuroblastoma cells were 100- to 10,000-fold greater than those of HIV-1 grown in CD4-positive lymphoblastoid cells, even though both virus suspensions contained abundant viral gp120 as shown by immunoblot assay. It was postulated that CD4 derived from host cells might be associated with virions, concealing the binding domains of gp120. CD4 association with HIV-1 virions grown in CD4-positive cells was demonstrated directly by immunoblot assay of sucrose gradient-purified virus suspensions and by specific co-sedimentation of 125I-labelled OKT4 with virions propagated in CD4-expressing cells. CD4 coating of primary HIV-1 isolates grown in peripheral blood mononuclear cells was also observed. The biological significance of CD4 coating of HIV particles remains to be determined.

CD4 Antigens↗
PubMed1995

HIV-1 infection of human macrophages impairs phagocytosis and killing of Toxoplasma gondii.

The susceptibility of patients with AIDS to certain opportunistic infections is due to defective cell-mediated immunity. The contribution of direct infection of macrophages with HIV-1 to this defect is unknown. To address this issue, we infected normal human monocyte-derived macrophages with a monocytotropic strain of HIV-1 and examined their ability to phagocytose and kill the opportunistic pathogen, Toxoplasma gondii. Phagocytosis of heat-killed T. gondii was reduced in HIV-infected macrophages compared with mock-infected controls. Opsonization of heat-killed T. gondii increased phagocytosis by both mock- and HIV-infected macrophages, but phagocytosis in HIV-infected cultures remained lower than in controls. Internalization of live T. gondii by macrophages was unaffected by HIV infection. Intracellular replication of live T. gondii was enhanced by HIV infection, as shown in four experiments, each using monocyte-derived macrophages from a different donor. Treatment of HIV-infected macrophages with IFN-gamma decreased parasite replication but not to control levels. These findings suggest that infection of macrophages by HIV may be a contributing factor to the reactivation of T. gondii infection in patients with AIDS.

Animals↗