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Yu X, Shang H, Jiang Y. ICAM-1 in HIV infection and underlying mechanisms. Cytokine 2019; 125:154830. [PMID: 31491723 DOI: 10.1016/j.cyto.2019.154830] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Revised: 07/29/2019] [Accepted: 08/24/2019] [Indexed: 02/07/2023]
Abstract
Intercellular adhesion molecule 1 (ICAM-1) is a glycoprotein that participates in inflammatory and immune responses. Both cell surface and soluble ICAM-1 are significantly increased during human immunodeficiency virus (HIV) infection, and ICAM-1 has important functions in promoting inflammatory responses and enhancing HIV infectivity; however, a comprehensive summary these roles has yet to be elaborated. In this review we describe the general biological characteristics of ICAM-1, its association with HIV disease progression and promotion of HIV production, mechanisms inducing upregulation of ICAM-1, and possible intervention strategies, representing important insights in the context of HIV treatment.
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Affiliation(s)
- Xiaowen Yu
- NHC Key Laboratory of AIDS Immunology (China Medical University), Department of Laboratory Medicine, The First Affiliated Hospital of China Medical University, Shenyang 110001, China; National Clinical Research Center for Laboratory Medicine, The First Affiliated Hospital of China Medical University, Shenyang 110001, China; Key Laboratory of AIDS Immunology of Liaoning Province, The First Affiliated Hospital of China Medical University, Shenyang 110001, China; Key Laboratory of AIDS Immunology, Chinese Academy of Medical Sciences, Shenyang 110001, China; Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, 79 Qingchun Street, Hangzhou 310003, China
| | - Hong Shang
- NHC Key Laboratory of AIDS Immunology (China Medical University), Department of Laboratory Medicine, The First Affiliated Hospital of China Medical University, Shenyang 110001, China; National Clinical Research Center for Laboratory Medicine, The First Affiliated Hospital of China Medical University, Shenyang 110001, China; Key Laboratory of AIDS Immunology of Liaoning Province, The First Affiliated Hospital of China Medical University, Shenyang 110001, China; Key Laboratory of AIDS Immunology, Chinese Academy of Medical Sciences, Shenyang 110001, China; Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, 79 Qingchun Street, Hangzhou 310003, China.
| | - Yongjun Jiang
- NHC Key Laboratory of AIDS Immunology (China Medical University), Department of Laboratory Medicine, The First Affiliated Hospital of China Medical University, Shenyang 110001, China; National Clinical Research Center for Laboratory Medicine, The First Affiliated Hospital of China Medical University, Shenyang 110001, China; Key Laboratory of AIDS Immunology of Liaoning Province, The First Affiliated Hospital of China Medical University, Shenyang 110001, China; Key Laboratory of AIDS Immunology, Chinese Academy of Medical Sciences, Shenyang 110001, China; Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, 79 Qingchun Street, Hangzhou 310003, China.
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LFA-1 antagonists as agents limiting human immunodeficiency virus type 1 infection and transmission and potentiating the effect of the fusion inhibitor T-20. Antimicrob Agents Chemother 2009; 53:4656-66. [PMID: 19721069 DOI: 10.1128/aac.00117-09] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Adhesion molecules are known to play major roles in the initiation and stabilization of cell-to-cell contacts during the immunological response. Human immunodeficiency virus type 1 (HIV-1) exploits those interactions to facilitate infection and propagation processes. The primary objective of the present study was to investigate the ability of antagonists specific for lymphocyte function-associated antigen 1 (LFA-1) to diminish HIV-1 infection and transmission. We demonstrate here that LFA-1 antagonists can significantly reduce HIV-1 replication in primary human cells and virus propagation by affecting cell-to-cell interactions. Moreover, the inhibition of LFA-1-mediated adhesion events also potentiates the antiviral efficacy of the peptide fusion inhibitor T-20. Altogether, our data suggest that LFA-1 antagonists represent promising antiviral agents. Antiadhesion therapy could be considered a complementary strategy targeting cellular functions essential for HIV-1 spreading and against which the combined therapy currently used displays a limited efficacy.
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3
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Poloni F, Puddu P, Moretti F, Flego M, Romagnoli G, Tombesi M, Capone I, Chersi A, Felici F, Cianfriglia M. Identification of a LFA-1 region involved in the HIV-1-induced syncytia formation through phage-display technology. Eur J Immunol 2001; 31:57-63. [PMID: 11169438 DOI: 10.1002/1521-4141(200101)31:1<57::aid-immu57>3.0.co;2-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We have identified a peptide region on CD18 molecule (the beta subunit of the LFA-1 molecule) involved in syncytia formation of HIV-1-infected lymphocytes. Several phage clones mimicking an epitope of the CD18 cell-surface determinant were isolated from two 9-mer random peptide phage-displayed libraries via their binding to the CD18-specific monoclonal antibody (mAb) MHM23, which in in vitro assay inhibits syncytia formation in HIV-1-infected cells. The peptide sequences displayed on phages that blocked immunolabeling of this mAb on LFA-1-expressing cells were used to identify the epitope recognized by mAb MHM23 by sequence comparison. On the basis of this analysis, two peptides which inhibited syncytia formation in HIV-1-infected cells in vitro were synthesized, thus confirming that they mimic a CD18 domain that is involved in this phenomenon. The results here presented highlight the potential of phage-display technology for the study of biological processes at the basis of virus infection, but also suggest new approaches for the therapy of AIDS.
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Affiliation(s)
- F Poloni
- Laboratory of Immunology, Istituto Superiore di Sanità, Rome, Italy
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4
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Galea P, Vermot-Desroches C, Le Contel C, Wijdenes J, Chermann JC. Circulating cell adhesion molecules in HIV1-infected patients as indicator markers for AIDS progression. RESEARCH IN IMMUNOLOGY 1997; 148:109-17. [PMID: 9226765 DOI: 10.1016/s0923-2494(97)82482-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Cell adhesion molecules play an important role during immune responses. Circulating (c) forms of these molecules have been used as monitors of disease progression. In this study, we have investigated serum levels of ICAM1, ICAM2, ICAM3 and VCAM1 in HIV-infected patients. Our results showed that levels of cICAMs and cVCAM1 are increased during HIV infection. Among an HIV-infected population, the cICAM2 level was higher in the asymptomatic group compared to the AIDS group. In contrast, the cICAM1 level was higher in the AIDS group compared to the asymptomatic group. No difference between the two groups was observed in cICAM3 and cVCAM1 levels. A significant correlation was found between cICAM1, cICAM2 and cVCAM1 in both populations. We also showed that the cICAM1/cICAM2 ratio was correlated with the increase in the c beta 2 microglobulin level and the decrease in CD4 T-cell counts in the AIDS group. These results indicate that serum cCAM1 and cICAM2 in HIV infection could be additional markers to discriminate between asymptomatic and progressor patients.
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Affiliation(s)
- P Galea
- INSERM U322, Unité de Recherches sur les Rétrovirus et Maladies Associées, Parc Scientifique et Technologique de Luminy, Marseille, France
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5
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Ng TT, Pinching AJ, Guntermann C, Morrow WJ. Molecular immunopathogenesis of HIV infection. Genitourin Med 1996; 72:408-18. [PMID: 9038636 PMCID: PMC1195728 DOI: 10.1136/sti.72.6.408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- T T Ng
- Department of Immunology, St Bartholomew's and the Royal London School of Medicine and Dentistry, UK
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6
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Hart TK, Truneh A, Bugelski PJ. Characterization of CD4-gp120 activation intermediates during human immunodeficiency virus type 1 syncytium formation. AIDS Res Hum Retroviruses 1996; 12:1305-13. [PMID: 8891109 DOI: 10.1089/aid.1996.12.1305] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The mechanism by which cells expressing HIV envelope glycoproteins progress from binding CD4+ cells to syncytia formation is not entirely understood. The purpose of these investigations was to use physical and biochemical tools (temperature shifts, soluble CD4, protease inhibitors, and a battery of anti-CD4 monoclonal antibodies) to isolate discrete steps during syncytia formation. Previously (Fu et al., J Virol 1993;67:3818), we found that preincubation of cells stably expressing HIV-1 gp 160 (TF228.1.16) with CD4+ SupT1 cells at 16 degrees C, a temperature that is nonpermissive for syncytia formation, resulted in an increased rate of syncytia formation when the cocultures were shifted to the syncytia-permissive temperature of 37 degrees C. We have since found that syncytia formation is further enhanced by shifting the cocultures from 16 to 4 degrees C prior to incubation at 37 degrees C. Together, these data suggest that two discrete states, which we term the first and second activation intermediates (FAI and SAI), are involved in syncytia formation. We have found that acquisition of the FAI (by preincubation at 16 degree C) is sensitive to some serine protease inhibitors (PI), soluble CD4 (sCD4), shedding of gp120, and anti-CD4 monoclonal antibodies (MAb) directed toward the CDR-1/2 and CDR-3 regions of domain 1 on CD4. Expression of the FAI (formation of syncytia by shifting from 16 to 37 degrees C) remains sensitive to sCD4, shedding of gp120, and MAb directed toward CDR-1/2 but is less sensitive to MAb that bind CDR-3 and is insensitive to PI. Similarly, acquisition of the SAI (shifting cocultures from 16 to 4 degrees C), is sensitive to sCD4, shedding of gp120, and MAb directed toward CDR-1/2. In contrast, expression of the SAI (shifting cocultures from 16 to 4 to 37 degrees C) is sensitive only to MAb directed toward CDR-1/2 and cannot be blocked by sCD4, shedding of gp120, or PI. These data allow us to propose that syncytia formation, mediated by HIV-1 envelope glycoproteins, proceeds by a multistep cascade.
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Affiliation(s)
- T K Hart
- Department of Toxicology, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406, USA
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7
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Sandstrom PA, Pardi D, Goldsmith CS, Chengying D, Diamond AM, Folks TM. bc1-2 expression facilitates human immunodeficiency virus type-1 mediated cytopathic effects during acute spreading infections. J Virol 1996; 70:4617-22. [PMID: 8676488 PMCID: PMC190398 DOI: 10.1128/jvi.70.7.4617-4622.1996] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The cytopathic effects (CPE) resulting from the infection of CD4+ T cells by human immunodeficiency virus (HIV) have generally been characterized as single-cell killing associated with apoptosis and/or the generation of syncytia resulting from the direct cell-to-cell transmission of the virus. Little is known, however, about the cellular factors influencing host cell susceptibility to HIV-mediated CPE. Because expression of the antiapoptosis gene, bcl-2, enhances cell viability after exposure to cytotoxic agents or stimuli, the effect of bcl-2 expression on HIV infection of stably transfected T-cell clones was investigated. Unexpectedly, bcl-2 expression by these cells accelerated the kinetics of an acute spreading HIV infection, as evidenced by a rapid loss of culture viability associated with the appearance of CPE and reverse transcriptase activity in the culture supernatant. This unexpected effect of bcl-2 expression results from the arrest of syncytial apoptosis, directly facilitating the cell-to-cell transmission of HIV. In addition, bcl-2 expression is associated with enhanced HIV replication as determined by HIV type 1-specific Western blot (immunoblot) analysis. These results suggest that the inhibition of apoptosis is essential for this mode of viral transmission.
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Affiliation(s)
- P A Sandstrom
- Retrovirus Diseases Branch, Division of Viral and Rickettsial Diseases,National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA
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8
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James W, Weiss RA, Simon JH. The receptor for HIV: dissection of CD4 and studies on putative accessory factors. Curr Top Microbiol Immunol 1996; 205:137-58. [PMID: 8575194 DOI: 10.1007/978-3-642-79798-9_7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- W James
- Sir William Dunn School of Pathology, University of Oxford, UK
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9
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Okada Y, Kameoka M, Kimura T, Azuma I, Ikuta K. Stimulation of human immunodeficiency virus type 1 infected cells with superoxide enhances the chemotactic motile response of CD4+ human T cells: implication for virus transmission by cell-to-cell interaction. IMMUNOPHARMACOLOGY 1995; 31:73-84. [PMID: 8655292 DOI: 10.1016/0162-3109(95)00034-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
We previously showed that superoxide (O2-) significantly enhanced human immunodeficiency virus type 1 (HIV-1)-induced syncytia formation in co-cultured infected and uninfected human T cells. In this study, we describe a novel chemotactic response of uninfected CD4+ T cells by stimulating infected T cells with O2-. Syncytia formation was amplified only when persistently infected cells were stimulated by O2-. When the infected cells in lower well of microplate were cultured with uninfected cells in the upper well of a Boyden chamber with 8.0 microns pores, uninfected cell migration to the porous membrane was significantly amplified by stimulating infected cells with O2-. In contrast, similar functions were slight under the same assay conditions in the presence of known chemokines such as human RANTES and macrophage inflammatory protein 1 (MIP-1 alpha and beta), which all activate T lymphocytes. In addition, it is unlikely that the O2(-)-induced chemotactic response is due to soluble HIV-1 proteins from infected cells or to amplified expression levels of cell surface functional molecules such as CD4 and LFA-1 (CD11a and CD18) as well as HIV-1 Env gp120 on uninfected and/or infected cells. Thus, an unknown chemotactic factor could be generated from infected T cells by stimulation with O2- and it might contribute to viral transmission by activating cell-to-cell interactions.
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Affiliation(s)
- Y Okada
- Institute of Immunological Science, Hokkaido University, Sapporo, Japan
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Srinivas RV, Su T, Trimble LA, Lieberman J, Ardman B. Enhanced susceptibility to human immunodeficiency virus infection in CD4+ T lymphocytes genetically deficient in CD43. AIDS Res Hum Retroviruses 1995; 11:1015-21. [PMID: 8554898 DOI: 10.1089/aid.1995.11.1015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
CD43 is a cell surface sialoglycoprotein expressed by most cells of hematopoietic origin, including all T lymphocytes. Elimination of CD43 expression by gene targeting in the CEM T cell line results in its increased homotypic adhesion and binding to HIV-1 gp120. Here we report that the CD43-negative CEM cells show increased susceptibility to HIV-1 infection and increased viral replication compared with the parental CD43+ CEM cell line. Increased HIV-1 replication also was observed in CEM cells with diminished CD43 expression secondary to functional inactivation of a single CD43 allele. The CD43- CEM cells were more susceptible to HIV-1-induced cytopathicity than their CD43+ counterparts. HIV-1 replication also was increased in the CD43- CEM cells after transfection with the infectious HIV molecular clone pNL4-3. These data suggest that factors that diminish CD43 expression on T lymphocytes may enhance their susceptibility to HIV-1 infection.
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Affiliation(s)
- R V Srinivas
- Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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Stefano KA, Collman R, Kolson D, Hoxie J, Nathanson N, Gonzalez-Scarano F. Replication of a macrophage-tropic strain of human immunodeficiency virus type 1 (HIV-1) in a hybrid cell line, CEMx174, suggests that cellular accessory molecules are required for HIV-1 entry. J Virol 1993; 67:6707-15. [PMID: 8411372 PMCID: PMC238110 DOI: 10.1128/jvi.67.11.6707-6715.1993] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
To investigate the mechanism underlying one aspect of the cellular tropism of human immunodeficiency virus type 1 (HIV-1), we used a macrophage-tropic isolate, 89.6, and screened its ability to infect a number of continuous cell lines. HIV-1 (89.6) was able to replicate robustly in a T-cell/B-cell hybrid line, CEMx174, while it replicated modestly or not at all in either of its parents, one of which is the CD4-positive line CEM.3. Analysis by transfection of a molecular clone, a virus uptake assay, and polymerase chain reaction all provided strong evidence that the block to HIV-1(89.6) replication in the CEM.3 line lies at the level of cellular entry. These results were complemented by preparing a CD4-expressing derivative of the B-cell parent, 721.174, and demonstrating that it is permissive for productive HIV-1(89.6) replication. Given these experimental findings, we speculate that there exist cellular accessory factors which facilitate virus entry and infection in CD4-positive cells. Furthermore, these cellular accessory factors may be quite virus strain specific, since not all macrophage-tropic strains of HIV-1 were able to replicate in the CEMx174 hybrid cell line. This experimental model provides a system for the identification of one or more of these putative cellular accessory factors.
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Affiliation(s)
- K A Stefano
- Department of Neurology, University of Pennsylvania Medical Center, Philadelphia 19104
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12
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Clapham P, McKnight A, Simmons G, Weiss R. Is CD4 sufficient for HIV entry? Cell surface molecules involved in HIV infection. Philos Trans R Soc Lond B Biol Sci 1993; 342:67-73. [PMID: 7904349 DOI: 10.1098/rstb.1993.0137] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
HIV-1, HIV-2 and SIV each bind to CD4 as the first step in virus entry. However, alternative receptors may also be used. HIV-1 binds to glycolipids with terminal galactosylceramide residues on neural cells; opsonized virus binds to Fc receptors; HIV-2 can infect certain CD4-negative cells. Further receptors may also play a role in CD4-mediated infection, including cell adhesion molecules and possibly cell surface proteinases. After binding to CD4, immunodeficiency viruses require secondary molecules to effect fusion between the virus envelope and the cell membrane; these accessory requirements differ between HIV-1, HIV-2 and SIV.
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Affiliation(s)
- P Clapham
- Chester Beatty Laboratories, Institute of Cancer Research, London, U.K
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13
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Diegel ML, Moran PA, Gilliland LK, Damle NK, Hayden MS, Zarling JM, Ledbetter JA. Regulation of HIV production by blood mononuclear cells from HIV-infected donors: II. HIV-1 production depends on T cell-monocyte interaction. AIDS Res Hum Retroviruses 1993; 9:465-73. [PMID: 8100439 DOI: 10.1089/aid.1993.9.465] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Cell-cell interactions induced between T cells and monocytes by certain soluble anti-CD3 monoclonal antibodies (MAbs) were previously shown to be required for high-level production of HIV-1 by peripheral blood mononuclear cells (PBMCs) from infected donors. Staphylococcal enterotoxin or superantigen (SAg) is another mitogen inducing monocytes-T cell interactions that exhibit potent induction of HIV-1 production. Antibodies to several adhesion molecules were used to test the requirements for T cell- and monocyte-associated adhesion molecules in HIV-1 production following activation with anti-CD3 or SAg. Blocking of either CD2-LFA-3, or CD18-ICAM-1, inhibited anti-CD3- or SAg-induced HIV-1 production by more than 90% without inhibiting CD4+ T cell proliferation. Inhibition of HIV production was observed when either the T cell or monocyte coreceptor was bound by MAbs to these adhesion molecules. Blocking of CD28-B7 interactions by soluble CTLA-4 fusion protein, a CD28 homolog, inhibited both HIV-1 production and CD4+ T cell proliferation. Fc binding was not required for HIV-1 inhibition by MAbs to CD2 and CD18, because Fab or F(ab')2 fragments of these MAbs inhibited HIV-1 production by more than 80%. A chimeric single-chain MAb to CD2 was produced, containing heavy and light chain variable regions from MAb 35.1 to CD2 linked to the constant regions of human IgG1 (CD2 SFv-Ig). This humanized CD2 SFv-Ig inhibited HIV-1 production by 30% to > 98%. These results thus indicate that simultaneous engagement of multiple adhesion pathways between T cells and monocytes are required for HIV production by patients PBMCs and may have implications for therapy of HIV infections.
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Affiliation(s)
- M L Diegel
- Bristol-Myers Squibb Pharmaceutical Research Institute, Seattle, WA 98121
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Thieblemont N, Haeffner-Cavaillon N, Ledur A, L'Age-Stehr J, Ziegler-Heitbrock HW, Kazatchkine MD. CR1 (CD35) and CR3 (CD11b/CD18) mediate infection of human monocytes and monocytic cell lines with complement-opsonized HIV independently of CD4. Clin Exp Immunol 1993; 92:106-13. [PMID: 7682158 PMCID: PMC1554886 DOI: 10.1111/j.1365-2249.1993.tb05955.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Peripheral blood and tissue mononuclear phagocytes serve as major viral reservoirs in HIV-infected individuals. We investigated the role of complement receptors CR1 (CD35) and CR3 (CD11b/CD18) in mediating productive infection with complement-opsonized HIV-1 and HIV-2 of cultured normal human peripheral blood monocytes, the promonocytic cell line THP-1, the monocytic cell line Mono Mac 6 and the glial cell line U251-MG. Cells were infected with the HTLV-IIIB strain of HIV-1 or the LAV-2 strain of HIV-2 that had been preopsonized with fresh human normal HIV seronegative serum. Productive infection was assessed by syncytia formation, the MTT cytotoxicity assay and/or release of p24 antigen in culture supernatants. Using suboptimal amounts of virus to infect the cells, we observed a higher and earlier productive infection of the cells with complement-opsonized HIV than with unopsonized virus. The enhancing effect of complement was totally suppressed by blocking CR1 or CR3 function with F(ab)'2 fragments of anti-receptor MoAbs; while blocking of the LFA-1 antigen had no effect. The infection of monocytic cells with complement-opsonized virus occurred independently of CD4 since it was not inhibited by F(ab)'2 fragments of a MoAb against the gp120 binding site of CD4 and since infection also occurred with Mono Mac 6 and U251-MG cells, which lack expression of the CD4 antigen and of CD4 mRNA. These observations suggest that complement may mediate productive infection of cells of the monocytic lineage with 'lymphocytotropic' HIV strains independently of CD4.
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