Department of Immunology/Microbiology, Rush-Presbyterian-St Luke's Medical Center, 1563 W. Congress Parkway, Chicago, IL 60612, USA
Correspondence
Gregory Spear
gspear{at}rush.edu
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ABSTRACT |
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Introduction |
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Mannose-binding lectin (MBL) is a C-type lectin, present in human serum, that acts as an effector molecule of the innate immune system (Jack et al., 2001; Petersen et al., 2001
). MBL binds to carbohydrates on microorganisms that express repetitive mannose and/or N-acetylglucosamine residues, such as Candida albicans, Salmonella typhimurium and Neisseria gonorrhoeae, resulting in opsonization and activation of the lectin complement pathway (van Emmerik et al., 1994
; Neth et al., 2000
). Several studies have shown that MBL also interacts with gp120 of HIV-1. For example, complement was activated following MBL binding to purified gp120 (Haurum et al., 1993
), recombinant MBL bound to gp120 and gp160 purified from HIV-IIIB (Ohtani et al., 1999
) and preincubation of HIV with MBL inhibited infection of a T cell line (Ezekowitz et al., 1989
). Furthermore, HIV particles lacking gp120/gp41 do not bind MBL, indicating that carbohydrates on gp120 mediate the interaction between whole virus and MBL (Saifuddin et al., 2000
). A recent study showed that MBL binds to HIV via high-mannose carbohydrates on gp120 (M. L. Hart, unpublished).
Several enzyme inhibitors are available that prevent the formation of complex and hybrid N-linked saccharides during glycoprotein processing in the endoplasmic reticulum (ER) and Golgi (reviewed in Sears & Wong, 1998). For example, castanospermine (Csp) and 1-deoxynojirimycin (dNM) inhibit
-glycosidase I and
-glycosidase II, respectively, in the ER while 1-deoxymannojirimycin (dMM) inhibits mannosidase I in the Golgi. Treatment of cells with these inhibitors results in N-linked carbohydrates that lack sialic acid but have a relatively high content of mannose residues. Many of the inhibitors have been shown to decrease the infectious titre of HIV in vitro, possibly by inhibiting the correct folding of gp160 (Gruters et al., 1987
; Jacob, 1995
; Karpas et al., 1988
; Mehta et al., 1998
; Montefiori et al., 1988
; Walker et al., 1987
). Several of these drugs have been evaluated in vivo as treatments for conditions such as diabetes, cancer metastases and viral infections including HIV infection (Jacob, 1995
).
While the high density of oligosaccharides on gp120 is thought to play a protective role by reducing the immunogenicity of gp120, it is possible that the glycans on gp120 could be used as a target in some antiviral strategies. The objective of the current study was to explore the effect of glycosylation inhibitors on the interaction between HIV and MBL, since alteration of virus carbohydrates in vivo could increase the amount of MBL-binding carbohydrates on the virus surface, resulting in more efficient clearance and/or neutralization of virus. Since one effect of these drugs is to prevent addition of sialic acid residues to gp120 as it is processed, we also tested the effect of treatment of virus with neuraminidase (NA) on binding and neutralization of HIV by MBL. Our results showed that both NA treatment and certain glycosylation inhibitors strengthen the interaction of HIV-1 with MBL and thereby enhance MBL-mediated neutralization of HIV-1.
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Methods |
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The HIV-1MN (X4) virus obtained from ARRRP (contributed by Robert Gallo) was produced in H9 cells, and primary isolates of HIV (HIVGP, HIVTH and HIVBa-L) were grown in peripheral blood mononuclear cells (PBMCs) obtained from normal healthy donors, as previously described (Takefman et al., 1998). The HIVGP (X4) and HIVTH (R5) were previously isolated in our laboratory (Takefman et al., 1998
) and HIVBa-L (R5) was obtained from the ARRRP. Phytohaemagglutinin (PHA; Sigma)-stimulated PBMCs were infected with HIV primary isolates in the presence of 30 U recombinant interleukin-2 ml-1 (obtained through the ARRRP from Maurice Gately, Hoffman LaRoche). For up to 10 days after infection, culture supernatants were harvested and tested for virus production by p24 ELISA (AIDS Vaccine Program, Frederick, MD, USA). To produce virus in the presence of inhibitors, PBMCs were infected for 7 days and were washed and cultured for an additional 48 h in the presence or absence of 1 mM Csp, dMM or dNM. Similarly, HIV-1MN-infected H9 cells were also washed and cultured for 48 h in the presence or absence of the drugs.
Antibodies.
Serum from an HIV-antibody-negative AB+ donor was heat-inactivated (56 °C for 50 min) as a source of normal human serum (NHS). Serum samples from five HIV-seropositive individuals were heat-inactivated and pooled in equal volumes (HIVPS). Monoclonal antibodies 2F5, 2G12 and IgG1b12 were obtained through ARRRP. 2F5 and 2G12 were contributed by Hermann Katinger (Purtscher et al., 1994; Trkola et al., 1996
), and IgG1b12 was contributed by Dennis Burton and Carlos Barbas (Barbas et al., 1992
). Polyclonal sheep anti-HIVgp120 antibody to the conserved C-terminal sequence (aa 497511) of HIV-1 gp120 (Moore et al., 1989
) was purchased from International Enzymes.
Reagents.
Csp was purchased from ICN Biomedicals and dNM, dMM and Clostridium perfringens 2
3,6,8-NA were obtained from Sigma. Endoglycosidase F1 was from Prozyme.
Mannose-binding lectin.
Recombinant vaccinia virus expressing the cDNA sequence for human MBL was used to produce recombinant MBL (rMBL) (Ma et al., 1997). Briefly, HLF cells were infected at an m.o.i. of 5 and supernatants were collected 48 h after infection. MBL was purified by passage over a mannanSepharose 4B column, as previously described (Kawasaki et al., 1983
). The resulting purified MBL was >95 % pure by Coomassie blue staining and Western blots of reducing gels. Some MBL monomers (approximately 30 kDa) were observed on non-reducing gels, but the majority of the purified material was estimated to contain multimers between 90 and 400 kDa.
Western blotting.
Virus (10 ng p24) was lysed in SDS sample buffer, separated by 7·5 % SDS-PAGE and transferred to nitrocellulose membranes. Western blotting was performed as previously described (Takefman et al., 1998) using 2·5 µg sheep anti-gp120 antibody ml-1 and horseradish peroxidase-conjugated rabbit anti-sheep immunoglobulin (Biosource). Antibody binding to gp120 was detected with an enhanced chemiluminescence detection system (Amersham) followed by exposure to X-ray film (Fuji Photo Film Co.).
Glycosidase treatment.
Virus (0·25 ml at 40 ng p24 ml-1) was treated with 1 U endoglycosidase F1 ml-1 for 24 h at 37 °C in the presence of 0·5 mM PMSF (Sigma). Virus samples were then diluted to 500 µl with veronal-buffered saline (5 mM veronal, pH 7·5, 0·145 M NaCl) containing 10 mM CaCl2 (VBS-Ca). HIVTH was treated with 0·1 U NA ml-1 (Sigma) overnight.
Binding of HIV-1 to MBL.
Ninety-six-well tissue culture plates (Costar) were coated with 100 µl 10 µg rMBL ml-1 diluted in VBS-Ca (Saifuddin et al., 2000). After overnight incubation at room temperature, wells were blocked with 3 % BSA for 1 h, washed with VBS-Ca and then incubated for 4 h with 100 µl (500 pg p24) of HIVGP, HIVTH or HIVBa-L grown in the presence or absence of glycosylation inhibitors. The plates were washed, bound virus was lysed with 0·5 % Triton X-100 and p24 was measured by ELISA.
MBL Neutralization of HIV.
The TCID50 of viruses produced in the presence or absence of inhibitors was determined by limiting dilution. Briefly, PHA-stimulated PBMCs (2x105 cells) were infected for 24 h at 37 °C with 0·1 ml of serial tenfold dilutions (1 : 10 to 1 : 100 000; three wells per dilution) of each virus in 96-well tissue culture plates (Costar). Cells were washed and resuspended in 200 µl culture medium containing IL-2 (20 U ml-1). After 7 days, culture wells were scored as positive or negative for virus growth by p24 ELISA. To assess HIV neutralization mediated by MBL, 100 TCID50 of virus grown in the presence or absence of glycosylation inhibitors was treated with 10 µg rMBL ml-1 for 2 h at 37C. Treated virus was then cultured with PHA-stimulated PBMCs for 24 h. Cells were washed and resuspended in 200 µl culture medium containing IL-2, and on day 7 supernatants were assayed for virus production by p24 ELISA.
Immunocapture of HIV.
Virus immunocapture was performed as previously described (Takefman et al., 1998). Briefly, virus was adjusted to 100 ng p24 ml-1 and incubated on ice for 1 h with NHS or HIVPS at a 1 : 10 dilution or with 50 µg 2F5, 2G12 or IgG1b12 antibody ml-1. The virusantibody mixtures were then ultracentrifuged over 20 % (w/v) sucrose in 50 mM Tris/HCl (pH 8·0) at 150 000 g for 1 h. Virus was resuspended in RPMI 1640 medium. Approximately 200 pg p24 of purified virus was incubated overnight at 4 °C with 50 µl Staphylococcus aureus cells expressing protein A (Pansorbin). Cells were then washed with PBS containing 1 % BSA and bound virus was lysed by treatment with 0·5 % Triton X-100 and p24 measured by ELISA.
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Results |
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Production of HIVTH in the presence of dMM significantly increased virus binding to MBL while binding to BSA-coated wells was not affected (Fig. 1B). Binding of virus to MBL was significantly enhanced for all three primary isolates in multiple experiments (X4 HIVGP, R5 HIVTH, P<0·0005, t-test; R5 HIVBa-L, P<0·05, t-test) when grown in the presence of dMM (Fig. 1C
). In contrast, virus binding only slightly increased when grown in the presence of dNM, while Csp treatment did not significantly increase binding (Fig. 1C
). None of the glycosylation inhibitors increased binding to BSA-coated wells (not shown). The inhibitor dMM also significantly increased the binding of HIVMN produced in H9 cells to MBL, while Csp and dNM did not (not shown).
To determine whether virus binding to MBL was mediated by high-mannose-type carbohydrates on the virus, HIVTH produced in the presence of dMM was treated with endoglycosidase F1 (eF1), an enzyme that preferentially cleaves N-linked high-mannose and hybrid oligosaccharides. MBL binding to HIVTH grown in the presence of dMM was substantially reduced when virus was treated with eF1, providing evidence that the increase in virus binding to MBL due to dMM was the result of an increase in the number of N-linked high-mannose or hybrid glycans on the virus surface (Fig. 2). Since the major difference between the structure of N-linked carbohydrates produced in the presence of either
-glucosidase and mannosidase I inhibitors is two to three terminal glucose residues, these data suggest that terminal glucose residues substantially inhibit the interaction of MBL with N-linked high-mannose glycans.
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Since one effect of these three inhibitors is to prevent addition of sialic acid to N-linked carbohydrates, we also assessed the effect of NA removal of sialic acid on MBL-mediated neutralization and binding. To confirm that NA treatment removed sialic acid from gp120, a gp120 Western blot was performed. Treatment of virus with NA removed a substantial amount of sialic acid residues from gp120, as evidenced by a change in mobility to approximately 105 kDa (Fig. 4A). NA treatment significantly increased neutralization by MBL (P<0·0005, t-test) (Fig. 4B
). The increase in MBL-mediated neutralization due to NA treatment corresponded to an approximate fourfold increase in binding of virus to MBL (Fig. 4C
). Interestingly, eF1 did not significantly decrease the amount of NA-treated virus binding to MBL, suggesting that NA exposed MBL binding sites on the virus that were not N-linked high-mannose glycans (Fig. 4C
).
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Discussion |
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Treatment with NA also substantially increased virus neutralization and binding by MBL. Removal of sialic acid by NA has several potential effects on MBL binding, including reducing negative charge on the virus, reducing the size of the complex glycan and revealing galactose as a terminal sugar residue. However, the increase in virus neutralization by MBL was not likely to be due to a reduction of the negative charge or a decrease in the size of the glycans, since the -glucosidase inhibitors would have had these same effects on the virus but had little effect on neutralization. Furthermore, in contrast to virus produced in the presence of dMM, eF1 treatment did not reduce the amount of NA-treated virus binding to MBL. Together, these data indicate that NA treatment increased neutralization by exposing new MBL binding sites on the virus that were distinct from N-linked high-mannose carbohydrates, although it is possible that the identity of the binding sites is unclear since it is reported that MBL binds well to terminal N-acetylglucosamine, mannose, glucose and fucose residues, but binding is reduced or blocked by terminal galactose (Childs et al., 1989
). However, although sparse, some terminal N-acetylglucosamine residues are normally present on N-linked complex structures including gp120 (Malhotra et al., 1995
; Scanlan et al., 2002
), and it is possible that removing sialic acid provides better access of MBL to these residues.
While MBL is a serum protein, it reacts weakly with host high-mannose N-linked carbohydrates due to the relatively low density of these glycans and the low affinity of MBL monomers for sugars. In contrast, the multimeric nature of both native MBL and terminal MBL-binding sugar residues on microbes results in a high-avidity interaction. Also, the conformation of MBL suggests that it does not react with multiple terminal mannose residues within one N-linked high-mannose carbohydrate structure and therefore reactivity of MBL with one high-mannose carbohydrate structure is likely to be of low avidity (Weis et al., 1998). In the case of HIV gp120, there is a very high density of N-linked carbohydrates (about half being the high-mannose type), which most likely accounts for the interaction of HIV with MBL. Thus, MBL reacts strongly with HIV but does not bind to virus particles lacking gp120 (Saifuddin et al., 2000
) and we observed in the current study that treatment of HIV with eF1 substantially reduced binding of virus to MBL. While treatment with the mannosidase I inhibitor would change host-cell protein complex glycosylation to the high-mannose type and could thus contribute to MBL binding to virus, we propose that the majority of the dMM-mediated increase in binding between HIV and MBL is most likely to be due to an increase in high-mannose carbohydrates on gp120, since dMM treatment would most likely double the density of MBL binding sites on gp120. Since the complex carbohydrates on gp120 are thought to be relatively exposed, their change to the high-mannose type may have an especially large effect on MBL binding (Moore et al., 1994
; Wyatt et al., 1998
).
Two glycosylation inhibitor drugs have been tested in HIV-infected people since early studies showed that some of these inhibitors had antiviral activity in vitro (Jacob, 1995). However, both in vivo trials used
-glucosidase inhibitors. According to our studies, this alteration of carbohydrates would probably not have substantially affected the interaction of virus with MBL in vivo. Mannosidase inhibitors have been used in vivo in trials to inhibit tumour metastasis (Jacob, 1995
). Our data suggest that administration of mannosidase inhibitors during HIV infection could increase MBL-mediated antiviral effects such as neutralization, complement activation and virus clearance. These enhanced MBL effects could also change the way that virus is presented to the adaptive immune system by affecting virus uptake by antigen-presenting cells.
While the binding of MBL to virus was increased by dMM, virus binding to monoclonal antibodies 2F5 and 2G12 was also increased, although the virus interaction with pooled serum and monoclonal antibody IgG1b12 was unchanged. These results could be partially explained by studies showing that complex-type glycans have a more pronounced shielding effect on antibody binding and are located on more exposed regions of gp120 than high-mannose glycans (Back et al., 1994; Moore et al., 1994
; Wyatt et al., 1998
). Therefore, by inhibiting production of bulkier complex carbohydrates with dMM, virus is produced that binds at higher levels to some neutralizing antibodies. Alternatively, recent studies have shown that the 2G12 epitope is not only dependent on carbohydrates but also appears to be at least partially composed of mannose residues (Sanders et al., 2002
; Scanlan et al., 2002
). Therefore, it is possible that treatment with dMM increases the density of mannose residues on gp120 causing the increased binding of 2G12. Thus, alteration of carbohydrates can simultaneously affect the interaction of HIV with arms of both the innate and adaptive immune responses.
A study by Means & Desrosiers (2000) assessed the effect of glycosidases and glycosylation inhibitors on neutralization of simian immunodeficiency virus (SIV) by pooled sera from infected macaques. Treatment of two SIV strains with NA decreased neutralization sensitivity while other glycosidases did not have a consistent effect on sensitivity. Treatment of virus-producing cells with either the mannosidase inhibitor swainsonine or DANA, an inhibitor of sialic acid, also slightly decreased neutralization sensitivity. These results suggest that removal of sialic acid somehow increases the resistance of virus to antibody neutralization by the pooled sera, a somewhat unexpected result given that the bulk of complex glycans is thought to shield the envelope protein from antibody binding (Wyatt et al., 1998
). The effect of NA and swainsonine in the SIV system are also interesting in light of our results with MBL neutralization of HIV, since we found that NA treatment of virus or dMM treatment of virus-producing cells increased MBL-mediated neutralization.
This is the first study to assess MBL-mediated effects on HIV after treatment of virus-producing cells with N-linked glycosylation inhibitors or treatment of virus with NA. The results show that, by altering the glycosylation of the envelope protein of HIV with dMM or NA, neutralization by and binding of MBL is increased. It is not known whether dMM or related compounds offer a realistic prospect of therapy for those infected with HIV, but this study suggests that further exploration of this possibility is warranted. Important issues to be considered before therapies are attempted include whether effective in vivo drug concentrations can be achieved and the resultant side effects. No clinical trials of dMM have yet been reported. A trial in HIV-infected people with the -glucosidase inhibitor N-butyl-deoxynojirimycin resulted in significant side effects including diarrhoea, flatulence, leukopenia and neutropenia (Tierney et al., 1995
) and the concentration achieved in serum was slightly lower than the antiviral concentration predicted in vitro. Many of the glycosylation inhibitor drugs cause similar side effects (Jacob, 1995
). N-nonyl-deoxynojirimycin, another
-glucosidase inhibitor, was shown to substantially reduce viraemia in hepadnavirus-infected woodchuck (Block et al., 1998
). Also, the
-mannosidase I inhibitor swainsonine was given to cancer patients over 5 days and serum levels of the drug were achieved that were much higher than the 50 % in vitro inhibitory concentrations (Baptista et al., 1994
). The above studies suggest that, while inhibitory concentrations of some of the glycosylation inhibitors could be achieved in vivo for treatments of short duration, long-term treatment with these types of drug, which is likely to be needed in the case of HIV-infected people, may be difficult due to their toxicity.
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ACKNOWLEDGEMENTS |
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REFERENCES |
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Baptista, J. A., Goss, P., Nghiem, M., Krepinsky, J. J., Baker, M. & Dennis, J. W. (1994). Measuring swainsonine in serum of cancer patients: phase I clinical trial. Clin Chem 40, 426430.
Barbas, C. F., III Bjorling, E., Chiodi, F. & 8 others. (1992). Recombinant human Fab fragments neutralize human type 1 immunodeficiency virus in vitro. Proc Natl Acad Sci U S A 89, 93399343.[Abstract]
Block, T. M., Lu, X., Mehta, A. S. & 7 other authors (1998). Treatment of chronic hepadnavirus infection in a woodchuck animal model with an inhibitor of protein folding and trafficking. Nat Med 4, 610614.[Medline]
Childs, R. A., Drickamer, K., Kawasaki, T., Thiel, S., Mizuochi, T. & Feizi, T. (1989). Neoglycolipids as probes of oligosaccharide recognition by recombinant and natural mannose-binding proteins of the rat and man. Biochem J 262, 131138.[Medline]
Dedera, D., Vander Heyden, N. & Ratner, L. (1990). Attenuation of HIV-1 infectivity by an inhibitor of oligosaccharide processing. AIDS Res Hum Retrov 6, 785794.[Medline]
Ezekowitz, R. A., Kuhlman, M., Groopman, J. E. & Byrn, R. A. (1989). A human serum mannose-binding protein inhibits in vitro infection by the human immunodeficiency virus. J Exp Med 169, 185196.[Abstract]
Gruters, R. A., Neefjes, J. J., Tersmette, M., de Goede, R. E., Tulp, A., Huisman, H. G., Miedema, F. & Ploegh, H. L. (1987). Interference with HIV-induced syncytium formation and viral infectivity by inhibitors of trimming glucosidase. Nature 330, 7477.[CrossRef][Medline]
Haurum, J. S., Thiel, S., Jones, I. M., Fischer, P. B., Laursen, S. B. & Jensenius, J. C. (1993). Complement activation upon binding of mannan-binding protein to HIV envelope glycoproteins. AIDS 7, 13071313.[Medline]
Jack, D. L., Klein, N. J. & Turner, M. W. (2001). Mannose-binding lectin: targeting the microbial world for complement attack and opsonophagocytosis. Immunol Rev 180, 8699.[CrossRef][Medline]
Jacob, G. S. (1995). Glycosylation inhibitors in biology and medicine. Curr Opin Struct Biol 5, 605611.[CrossRef][Medline]
Karpas, A., Fleet, G. W., Dwek, R. A., Petursson, S., Namgoong, S. K., Ramsden, N. G., Jacob, G. S. & Rademacher, T. W. (1988). Aminosugar derivatives as potential anti-human immunodeficiency virus agents. Proc Natl Acad Sci U S A 85, 92299233.[Abstract]
Kawasaki, N., Kawasaki, T. & Yamashina, I. (1983). Isolation and characterization of a mannan-binding protein from human serum. J Biochem 94, 937947.[Abstract]
Leonard, C. K., Spellman, M. W., Riddle, L., Harris, R. J., Thomas, J. N. & Gregory, T. J. (1990). Assignment of intrachain disulfide bonds and characterization of potential glycosylation sites of the type 1 recombinant human immunodeficiency virus envelope glycoprotein (gp120) expressed in Chinese hamster ovary cells. J Biol Chem 265, 1037310382.
Ma, Y., Shida, H. & Kawasaki, T. (1997). Functional expression of human mannan-binding proteins (MBPs) in human hepatoma cell lines infected by recombinant vaccinia virus: post-translational modification, molecular assembly, and differentiation of serum and liver MBP. J Biochem 122, 810818.[Abstract]
Malhotra, R., Wormald, M. R., Rudd, P. M., Fischer, P. B., Dwek, R. A. & Sim, R. B. (1995). Glycosylation changes of IgG associated with rheumatoid arthritis can activate complement via the mannose-binding protein. Nat Med 1, 237243.[Medline]
Means, R. E. & Desrosiers, R. C. (2000). Resistance of native, oligomeric envelope on simian immunodeficiency virus to digestion by glycosidases. J Virol 74, 1118111190.
Mehta, A., Zitzmann, N., Rudd, P. M., Block, T. M. & Dwek, R. A. (1998). Alpha-glucosidase inhibitors as potential broad based anti-viral agents. FEBS Lett 430, 1722.[CrossRef][Medline]
Montefiori, D. C., Robinson, W. E., Jr. & Mitchell, W. M. (1988). Role of protein N-glycosylation in pathogenesis of human immunodeficiency virus type 1. Proc Natl Acad Sci U S A 85, 92489252.[Abstract]
Moore, J. P., Wallace, L. A., Follett, E. A. & McKeating, J. A. (1989). An enzyme-linked immunosorbent assay for antibodies to the envelope glycoproteins of divergent strains of HIV-1. AIDS 3, 155163.[Medline]
Moore, J. P., Sattentau, Q. J., Wyatt, R. & Sodroski, J. (1994). Probing the structure of the human immunodeficiency virus surface glycoprotein gp120 with a panel of monoclonal antibodies. J Virol 68, 469484.[Abstract]
Muster, T., Steindl, F., Purtscher, M., Trkola, A., Klima, A., Himmler, G., Ruker, F. & Katinger, H. (1993). A conserved neutralizing epitope on gp41 of human immunodeficiency virus type 1. J Virol 67, 66426647.[Abstract]
Neth, O., Jack, D. L., Dodds, A. W., Holzel, H., Klein, N. J. & Turner, M. W. (2000). Mannose-binding lectin binds to a range of clinically relevant microorganisms and promotes complement deposition. Infect Immun 68, 688693.
Ohtani, K., Suzuki, Y., Eda, S. & 7 other authors (1999). High-level and effective production of human mannan-binding lectin (MBL) in Chinese hamster ovary (CHO) cells. J Immunol Methods 222, 135144.[CrossRef][Medline]
Petersen, S. V., Thiel, S. & Jensenius, J. C. (2001). The mannan-binding lectin pathway of complement activation: biology and disease association. Mol Immunol 38, 133149.[CrossRef][Medline]
Purtscher, M., Trkola, A., Gruber, G., Buchacher, A., Predl, R., Steindl, F., Tauer, C., Berger, R., Barrett, N., Jungbauer, A. and others (1994). A broadly neutralizing human monoclonal antibody against gp41 of human immunodeficiency virus type 1. AIDS Res Hum Retroviruses 10, 16511658.[Medline]
Saifuddin, M., Hart, M. L., Gewurz, H., Zhang, Y. & Spear, G. T. (2000). Interaction of mannose-binding lectin with primary isolates of human immunodeficiency virus type 1. J Gen Virol 81, 949955.
Sanders, R. W., Venturi, M., Schiffner, L., Kalyanaraman, R., Katinger, H., Lloyd, K. O., Kwong, P. D. & Moore, J. P. (2002). The mannose-dependent epitope for neutralizing antibody 2G12 on human immunodeficiency virus type 1 glycoprotein gp120. J Virol 76, 72937305.
Scanlan, C. N., Pantophlet, R., Wormald, M. R. & 7 other authors (2002). The broadly neutralizing anti-human immunodeficiency virus type 1 antibody 2G12 recognizes a cluster of 1
2 mannose residues on the outer face of gp120. J Virol 76, 73067321.
Sears, P. & Wong, C. H. (1998). Enzyme action in glycoprotein synthesis. Cell Mol Life Sci 54, 223252.[CrossRef][Medline]
Takefman, D. M., Sullivan, B. L., Sha, B. E. & Spear, G. T. (1998). Mechanisms of resistance of HIV-1 primary isolates to complement-mediated lysis. Virology 246, 370378.[CrossRef][Medline]
Tierney, M., Pottage, J., Kessler, H. & other authors (1995). The tolerability and pharmacokinetics of N-butyl-deoxynojirimycin in patients with advanced HIV disease (ACTG 100). The AIDS Clinical Trials Group (ACTG) of the National Institute of Allergy and infectious Diseases. J Acquir Immune Defic Syndr Hum Retrovirol 10, 549553.[Medline]
Trkola, A., Purtscher, M., Muster, T. & 7 other authors (1996). Human monoclonal antibody 2G12 defines a distinctive neutralization epitope on the gp120 glycoprotein of human immunodeficiency virus type 1. J Virol 70, 11001108.[Abstract]
van Emmerik, L. C., Kuijper, E. J., Fijen, C. A., Dankert, J. & Thiel, S. (1994). Binding of mannan-binding protein to various bacterial pathogens of meningitis. Clin Exp Immunol 97, 411416.[Medline]
Walker, B. D., Kowalski, M., Goh, W. C., Kozarsky, K., Krieger, M., Rosen, C., Rohrschneider, L., Haseltine, W. A. & Sodroski, J. (1987). Inhibition of human immunodeficiency virus syncytium formation and virus replication by castanospermine. Proc Natl Acad Sci U S A 84, 81208124.[Abstract]
Weis, W. I., Taylor, M. E. & Drickamer, K. (1998). The C-type lectin superfamily in the immune system. Immunol Rev 163, 1934.[Medline]
Wyatt, R., Kwong, P. D., Desjardins, E., Sweet, R. W., Robinson, J., Hendrickson, W. A. & Sodroski, J. G. (1998). The antigenic structure of the HIV gp120 envelope glycoprotein. Nature 393, 705711.[CrossRef][Medline]
Received 29 July 2002;
accepted 10 October 2002.