(CR3, Cd11b/CD18) Dendritic Cells Via Complement Receptor Cutting

Cutting Edge: Productive HIV-1 Infection of Dendritic Cells via Complement Receptor Type 3 (CR3, CD11b/CD18)

This information is current as Zsuzsa Bajtay, Cornelia Speth, Anna Erdei and Manfred P. of September 24, 2021. Dierich J Immunol 2004; 173:4775-4778; ; doi: 10.4049/jimmunol.173.8.4775 http://www.jimmunol.org/content/173/8/4775 Downloaded from

References This article cites 28 articles, 10 of which you can access for free at: http://www.jimmunol.org/content/173/8/4775.full#ref-list-1 http://www.jimmunol.org/ Why The JI? Submit online.

• Rapid Reviews! 30 days* from submission to initial decision

• No Triage! Every submission reviewed by practicing scientists

• Fast Publication! 4 weeks from acceptance to publication

by guest on September 24, 2021 *average

Subscription Information about subscribing to The Journal of Immunology is online at: http://jimmunol.org/subscription Permissions Submit copyright permission requests at: http://www.aai.org/About/Publications/JI/copyright.html Email Alerts Receive free email-alerts when new articles cite this article. Sign up at: http://jimmunol.org/alerts

The Journal of Immunology is published twice each month by The American Association of Immunologists, Inc., 1451 Rockville Pike, Suite 650, Rockville, MD 20852 Copyright © 2004 by The American Association of Immunologists All rights reserved. Print ISSN: 0022-1767 Online ISSN: 1550-6606. THE

JOURNAL OF IMMUNOLOGY CUTTING EDGE

Cutting Edge: Productive HIV-1 Infection of Dendritic Cells via Complement Receptor Type 3 (CR3, CD11b/CD18) Zsuzsa Bajtay,* Cornelia Speth,* Anna Erdei,† and Manfred P. Dierich1*

In the present study, we demonstrate that macrophage- as monocyte-derived DCs (MDCs) differentiated in vitro express CD11b (8). Regarding the expression of CD11c, two ma- tropic HIV-1 opsonized by complement and limited ϩ jor populations are present in the body: the CD11c myeloid amounts of anti-HIV-IgG causes up to 10-fold higher pro- Ϫ ductive infection of human monocyte-derived dendritic DCs, and the CD11c plasmacytoid DCs. CR3 and adhesion cells than HIV treated with medium or HIV opsonized by molecules are documented to facilitate viral entry into different target cells (9, 10). Ab only. Enhanced infection is completely abolished by a ϩ mAb specific for the ligand-binding site of CD11b (i.e., CD14 human monocytes can develop into MDCs in vitro Downloaded from by culturing in medium containing GM-CSF and IL-4. By day ␣-chain of complement receptor 3, receptor for iC3b), 5 in culture, the cells have the characteristics of immature DCs proving the importance of complement receptor 3 in this (imMDCs) and can be further induced to mature DCs by in- process. Inhibition of complement activation by EDTA flammatory stimulus such as LPS. Maturation rapidly induces also prevents enhanced infection, further demonstrating DCs to express costimulatory molecules, such as CD80 and

the role of complement in virus uptake and productive in- CD86, necessary for the activation of naive T cells (11). Targets http://www.jimmunol.org/ fection. Since HIV is, even in the absence of Abs, regularly of HIV during primary in vivo infection are macrophages and opsonized by complement, most probably the above-de- DCs, which are predominantly permissive for R5 viruses (12). scribed mechanism plays a role during in vivo primary imMDCs can be productively infected with R5 viruses and the infection. The Journal of Immunology, 2004, 173: virus produced by these cells is able to infect T cells. Mature 4775–4778. DCs do not produce viral particles, still they are able to transmit both R5 and X4 viruses to T cells (13). ffector functions of the complement system, one of the Our observation that complement opsonization of HIV

main components of natural immunity, include opso- causes a distinctively productive infection of DCs has not yet by guest on September 24, 2021 E nization leading to enhanced phagocytosis and lysis of been documented. In this study, we report that CR3 plays a microbes. HIV is able to activate complement both in the ab- crucial role in the productive infection of imMDCs by C3-op- sence and, even more so, in the presence of virus-specific Abs. sonized HIV. Following binding of C1q to gp41 of HIV, the classical pathway of complement activation is initiated (1), while the lectin- Materials and Methods dependent activation is initiated by the interaction of gp120 Media, Abs, cytokines and gp41 with the mannan-binding lectin (2). Covalent bind- Anti-human (hu) C3c, anti-huC3d, and anti-huIgG rabbit polyclonal Abs and ing of C3 fragments to the viral envelope allows binding of HIV FITC-conjugated goat anti-mouse Ig polyclonal Ab were obtained from Dako- to cells expressing receptors for C3b (complement receptor Cytomation (Glostrup, Denmark). Mouse mAbs used in this work were as fol- 2 lows: anti-CD4, anti-CD86, anti-CD83, anti-CD14, anti-CCR5, anti-CD11c (CR) 1, CD35), iC3b (CR3, CD11b/CD18; CR4, CD11c/ (BD Pharmingen, San Diego, CA) anti-CD18 (OKM-1); hybridoma superna- CD18), and C3d, C3dg (CR2, CD21). HIV-1 infection of hu- tants and mouse IgG1 isotype control were used at 10 ␮g/ml. mAb TMG6-5 man lymphocytes and monocytes/macrophages is greatly en- blocking anti-CD11b (14) was kindly provided by I. Ando´(Biological Research Center, Szeged, Hungary). hanced by opsonization of the virus with complement (3–5). In general, microorganisms coated with C3 fragments ac- DC cultures quire the capacity for high binding to CR1–4 (3–7). CR3 and MDCs were generated in vitro by culturing monocytes (15, 16). Briefly, PB- ␤ CR4 are members of the 2-integrin family, are expressed on MCs were obtained by the standard Ficoll-Hypaque (Pharmacia Biotech, Upp- several cell types, including phagocytic cells, and play an impor- sala, Sweden) method. Monocytes were isolated by adherence using gelatin- coated petri dishes (17). The purity of the monocyte suspension was 90–95%, tant role in phagocytosis of opsonized pathogens. It has been as judged by FACS analysis. Differentiation of monocytes into imMDCs was shown that dendritic cells (DCs) in normal human skin as well induced by culturing in RPMI 1640 medium (Invitrogen Life Technologies,

*Department of Hygiene, Microbiology and Social Medicine, Innsbruck Medical Univer- 1 Address correspondence and reprint requests to Prof. Manfred P. Dierich, Department of sity and Ludwig-Boltzman-Institute for AIDS Research, Innsbruck, Austria; and †Depart- Hygiene, Microbiology and Social Medicine, Innsbruck Medical University and Ludwig- ment of Immunology and Research Group of the Hungarian Academy of Sciences, Eo¨tvo¨s Boltzman-Institute for AIDS Research, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria. Lora´nd University, Budapest, Hungary E-mail address: [email protected] Received for publication June 8, 2004. Accepted for publication August 18, 2004. 2 Abbreviations used in this paper: CR, complement receptor; DC, dendritic cell; MDC, monocyte-derived DC; imMDC, immature MDC; hu, human; rh, recombinant human; The costs of publication of this article were defrayed in part by the payment of page charges. maMDC, mature MDC. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Grand Island, N.Y.) supplemented with 1600 U/ml recombinant human (rh) GM-CSF (Novartis, Vienna, Austria), and 1500 U/ml rhIL-4 (PromoCell, Heidelberg, Germany), 10% heat-inactivated FCS (Invitrogen Life Technolo- gies), 2 mM L-glutamine, and 50 ␮g/ml gentamicin (Sigma-Aldrich, St. Louis, MO) in 24-well tissue culture plates (Costar, Cambridge, MA). Culture medium was refreshed at days 5 and 7 and supplemented with cytokines at days 2, 5, and 7. imMDCs were CD14Ϫ, CD80ϩ, CD86ϩ, CD83Ϫ, CD11bϩ, CD11cϩ, HLA-DRϩ, CD4low, and CCR5low (12, 18). imMDCs were used for virus binding and infectious experiments on day 7 of culture. Occasionally, in vitro maturation of MDCs was induced by 100 ng/ml LPS (Sigma-Aldrich). HIV sources, p24 ELISA The M-tropic HIV-1 primary isolate 92UG037 (subtypeA/A, R5 tropism) was kindly provided by G. Stiegler (Institute of Applied Microbiology, Vienna, Austria). Virus stock was produced by PHA-activated PBMCs of healthy do- nors and maintained in RPMI 1640 supplemented with 10% FCS, 2 mM L- glutamine, 100 U/ml penicillin, and 100 ␮g/ml streptomycin. The virus was pelleted at 20,000 rpm by ultracentrifugation and stored at Ϫ80°C. For assess- ment of virus quantity, the p24 capture ELISA was used, developed at the In- stitute of Applied Microbiology in Vienna (19); it was performed as described earlier (18).

Opsonization of HIV, virus capture assay Downloaded from Opsonized virus was prepared in the presence of anti-HIV IgG (purified from pooled sera of HIVϩ patients) and normal human serum as complement source (HIVIgG ϩ C) or in the presence of anti-HIV IgG alone (HIVIgG). Control samples were prepared in medium only (HIV). For opsonization, 1 ␮g/ml p24 HIV ␮ was incubated with 50 g/ml anti-HIV IgG (HIVIgG) or with anti-HIV IgG and 10-fold diluted normal human serum (HIVIgG ϩ C)for1hat37°C. In some experiments, EDTA (20 mM) was used to inhibit complement activation http://www.jimmunol.org/ FIGURE 1. Surface expression of CD11b and CD18 of imMDCs and (HIVIgG ϩ C ϩ EDTA). The opsonized virus was washed and pelleted by ultra- centrifuge; aliquots were stored at Ϫ80°C and thawed once before the experi- maMDCs at day 7. Shaded histograms represent the binding of CD11b- and ments. Opsonization was detected by a virus capture ELISA system. Prepara- CD18-specific Abs. Open histograms represent isotype-matched controls. tions containing opsonized HIV were incubated in wells coated by Abs specific Mean fluorescence intensity values are shown. The data are representative of for huIgG, or for complement fragments C3c and C3d, respectively. Captured seven independent experiments. HIV was lysed in detergent and transferred to anti-p24-coated plates. After in- cubation with anti-HIV IgG, the virus bound intensively to the anti-IgG coat. As a result of classical pathway activation of the complement system, strong C3 and low (if any) IgG deposition were detected in the HIVIgG ϩ C samples, sug-

gesting poor accessibility of the IgG on HIVIg ϩ C. 5, 22) we aimed to clarify whether CR3, mediating the uptake by guest on September 24, 2021 of C-coated particles by several cell types, is involved in a similar Binding of HIV to DC process of MDCs. For these experiments we used the Ab To demonstrate binding of HIV, 5 ϫ 105 imMDCs were incubated with 10 TMG6-5, which interacts with the receptor’s ligand binding ng/ml p24 HIV, HIVIgG, HIVIgG ϩ C, and HIVIgG ϩ C ϩ EDTA for1hat37°C. Then nonbound virus was removed by washing two times with warm medium. site. Fig. 1 shows that TMG6-5 binds to imMDCs and mature MDCs (maMDCs) in a similar fashion. It is also seen in Fig. 1 The cells were lysed with 1% Nonidet P-40 and the amount of p24 Ag was ϩ determined by p24 ELISA. To determine the effect of proteinase K (Sigma- that the percentage of CR3 cells is decreased in maMDCs. Aldrich) on HIV entry, the cells were held in the presence of 10 ␮g/ml enzyme before determination of p24. All data are presented as mean values Ϯ SD. Infection of MDCs with HIV-1 To determine the infectivity of HIV, 5 ϫ 105 imMDCs were incubated with 10 ng/ml p24 HIV, HIVIgG, HIVIgG ϩ C, and HIVIgG ϩ C ϩ EDTA, respectively, for 8 h, then the cells were washed two times with warm medium and placed back into culture in 24-well plates for an additional 15 days. Twenty-five percent of medium was replaced with rhIL-4 and rhGM-CSF every third day. The amount of virus produced by the cells was estimated by p24 ELISA from the supernatants every other day. Flow cytometry The expression of surface molecules of cells was determined at day 7 of culture. ϫ 4 Briefly, 5 10 cells were washed with 1% BSA-0,1% NaN3-PBS and incubated with Abs reacting with CD80, CD86, CD83, CD11b, CD11c, CD18, HLA-DR, CD14, CD4, and CCR5, followed by FITC-labeled anti-mouse IgG. As control, samples were labeled with isotype-matched control Abs. After staining, the cells were washed and fixed in PBS containing 1% Formalin and 0,1% NaN3 and analyzed by flow cytometry (FACScan; BD Biosciences, Mountain View, CA). Results Expression of CR3 during maturation of DCs FIGURE 2. Binding of nonopsonized and opsonized HIV to imMDCs. im- MDCs at day 7 were incubated with HIV, HIVIgG, HIVIgG ϩ C, and HIVIgG ϩ It has been demonstrated in earlier studies that DCs do not pos- C ϩ EDTA for1hat37°C. The concentration of p24 Ag was determined from the sess CR1 and CR2, while they express CR3 and CR4 (18, 20, cell lysates after removing nonbound viruses. The data are representative of six 21). Since opsonization is known to influence viral infection (4, independent experiments. The Journal of Immunology 4777

ments (5, 22). To test whether infection of imMDCs by HIV is influenced by opsonization, the cells were cultured with the HIV-1 primary isolate pretreated with IgG and complement. Culture supernatants were collected every other day, centri- fuged, and the concentration of free virions was estimated by p24 ELISA. As demonstrated in Fig. 3, opsonization with HIV- specific IgG and human complement caused Ͼ10-fold enhancement in HIV production by MDCs, as compared with nonopsonized HIV or HIV opsonized with specific IgG only. Virus particles treated with serum in the presence of 20 mM EDTA caused low productive infection similar to the medium- treated control. Treatment of imMDCs with CD11b-specific Ab or with proteinase K and their effect on infection by complement-opsonized HIV-1 To investigate the role of CR3 in the uptake of the opsonized FIGURE 3. Productive infection of imMDCs by opsonized HIV-1. im- virus, the cells were preincubated with mAb TMG6-5, which MDCs were infected with HIV, HIVIgG, HIVIgG ϩ C, and HIVIgG ϩ C ϩ EDTA at day 7. The amount of free virions was measured by p24 ELISA from the interacts with the ligand binding site of CD11b. As shown in Downloaded from supernatants on days as indicated. The data are representative of five indepen- Fig. 4A, the Ab reduced binding of HIVIgG ϩ C to background dent experiments. level. Also, as seen in Fig. 4B, the productive infection of MDCs tested on day 14 was almost completely abolished by the CR3- specific Ab, while the isotype-matched control Ab showed no Effect of opsonization by complement on binding of HIV-1 to imMDCs effect. To demonstrate that uptake of opsonized HIV was the

To investigate the binding of C-opsonized HIV, imMDCs key to productive infection, cells were treated with proteinase K http://www.jimmunol.org/ were incubated with HIVIgG ϩ C and for control with HIV, before p24 measurement. As shown in Fig. 4A, this enzyme HIVIgG, and HIVIgG ϩ C ϩ EDTA. After removing nonbound treatment resulted in a significant loss of HIV associated with virus, cells were lysed and the amount of p24 Ag was deter- MDCs. mined by ELISA. Fig. 2 shows that HIVIgG ϩ C binds more efficiently to imMDCs than HIVIgG. This enhancement was Discussion abolished when complement activation and opsonization were It is generally accepted that opsonization by complement en- inhibited by 20 mM EDTA. hances HIV uptake by CR-bearing cells, including MDCs. In

this study, we show that opsonization of HIV with complement by guest on September 24, 2021 Effect of opsonization of HIV by complement on infection of imMDCs (and IgG) caused a slight increase in binding to MDCs but a Infection of human monocytes and macrophages with HIV is 10-fold higher productive infection of imMDCs. This de- greatly facilitated by opsonization of the virus with C3 frag- scribes for the first time the crucial role of CR3 in this process.

FIGURE 4. The effect of anti-CD11b mAb (TMG6-5) and proteinase K on binding of opsonized HIV and productive infection of imMDCs. A, imMDCs, pretreated with mAb TMG6-5 and, as control, with isotype-matched control Ab were incubated with HIVIgG ϩ C. The effect of proteinase K was assessed after treating the cells in the presence of 10 ␮g/ml enzyme. The amount of p24 Ag was determined by p24 ELISA. All data are presented as mean values Ϯ SD. B, To determine infectivity of imMDCs pretreated with mAb TMG6-5 and, as control, with isotype-matched control Ab were incubated with HIVIgG ϩ C, and cells were placed back into culture after washing. The amount of virus produced by the cells was estimated by p24 ELISA from the supernatants on days as indicated. The data are representative of five independent experiments. 4778 CUTTING EDGE: PRODUCTIVE HIV-1 INFECTION OF DCs VIA CR3

In contrast to CR3, DC-specific ICAM-3-grabbing noninte- 4. Legendre, C., G. Gras, R. Krzysiek, P. Galanaud, Y. Richard, and D. Dormont. 1996. Mechanisms of opsonized HIV entry in normal B lymphocytes. FEBS Lett. 381:227. grin, another important attachment receptor for HIV on DCs, 5. Thieblemont, N., N. Haeffner-Cavaillon, A. Ledur, J. L’Age-Stehr, is known to bind HIV and to operate in transmission of the H. W. Ziegler-Heitbrock, and M. D. Kazatchkine. 1993. CR1 (CD35) and CR3 ϩ (CD11b/CD18) mediate infection of human monocytes and monocytic cell lines with virus to CD4 T cells (23); however, this does not induce pro- complement-opsonized HIV independently of CD4. Clin. Exp. Immunol. 92:106. ductive infection of DCs. The key role of CR3 in efficient up- 6. Erdei, A., G. Fu¨st, and J. Gergely. 1991. The role of C3 in the immune response. take of opsonized HIV by imMDCs was proven by inhibition Immunol. Today 12:332. 7. Gordon, S. 2002. Pattern recognition receptors: doubling up for the innate immune with CD11b-specific mAbs. We also found that productive in- response. Cell 111:927. fection was strongly inhibited by anti-CD4 mAb (data not 8. Grassi, F., C. Dezutter-Dambuyant, D. McIlroy, C. Jacquet, K. Yoneda, S. Imamura, shown), suggesting that even in CR3-mediated enhancement of L. Boumsell, D. Schmitt, B. Autran, P. Debre, and A. Hosmalin. 1998. Monocyte- derived dendritic cells have a phenotype comparable to that of dermal dendritic cells productive infection CD4 plays a critical role. In other studies, and display ultrastructural granules distinct from Birbeck granules. J. Leukocyte Biol. inhibition by anti-CR3 mAb of monocyte infection (18, 22) 64:484. 9. Hildreth, J. E., and R. J. Orentas. 1989. Involvement of a leukocyte adhesion receptor and partial inhibition by CD11b-specific Abs (10) of PBMC (LFA-1) in HIV-induced syncytium formation. Science 244:1075. infection with HIV were observed. 10. Stoiber, H., I. Frank, M. Spruth, M. Schwendinger, B. Mullauer, J. M. Windisch, R. Schneider, H. Katinger, I. Ando, and M. P. Dierich. 1997. Inhibition of HIV-1 Opsonization of HIV by complement occurs in human se- infection in vitro by monoclonal antibodies to the complement receptor type 3 (CR3): rum by direct binding of C1q already in the absence of anti- an accessory role for CR3 during virus entry? Mol. Immunol. 34:855. HIV Abs (1, 2), but is much more pronounced after binding of 11. Banchereau, J., F. Briere, C. Caux, J. Davoust, S. Lebecque, Y. J. Liu, B. Pulendran, and K. Palucka. 2000. Immunobiology of dendritic cells. Annu. Rev. Immunol. Abs on the surface of HIV. Complement is also known to be 18:767. activated by HIV upon direct binding of MBL; the activation of 12. Zaitseva, M., A. Blauvelt, S. Lee, C. K. Lapham, V. Klaus-Kovtun, H. Mostowski, Downloaded from J. Manischewitz, and H. Golding. 1997. Expression and function of CCR5 and the alternative pathway in HIV-infected patients has also been CXCR4 on human Langerhans cells and macrophages: implications for HIV primary observed (24). Other studies, however, show that intact HIV infection. Nat. Med. 3:1369. activates complement only in the presence of antiviral Abs (25, 13. Granelli-Piperno, A, E. Delgado, V. Finkel, W. Paxton, and R. M. Steinman. 1998. Immature dendritic cells selectively replicate macrophagetropic (M-tropic) human 26). Sensitivity to complement-mediated lysis is influenced by immunodeficiency virus type 1, while mature cells efficiently transmit both M- and the actual composition of the viral membrane, as in vitro studies T-tropic virus to T cells. J. Virol. 72:2733. 14. Uciechowski, P., and R. E. Schmidt. 1989. White cell differentiation antigens. In http://www.jimmunol.org/ demonstrated that some primary isolates of HIV are highly re- Leukocyte Typing IV. W. Knapp, B. Do¨rken, W. R. Gilks, E. P. Rieber, R. E. Schmidt, sistant to complement-mediated lysis due to the incorporation H. Stein, and A. E. G. von dem Borne, eds. Oxford Univ. Press, Oxford, U.K., p. 543. of host cell-derived complement control proteins, including 15. Romani, N., S. Gruner, D. Brang, E. Kampgen, A. Lenz, B. Trockenbacher, G. Konwalinka, P. O. Fritsch, R. M. Steinman, and G. Schuler. 1994. Proliferating CD46, CD55, and CD59 (27, 28). dendritic cell progenitors in human blood. J. Exp. Med. 180:83. Since HIV particles in infected patients are early on coated 16. Sallusto, F., and A. Lanzavecchia. 1994. Efficient presentation of soluble antigen by cultured human dendritic cells is maintained by granulocyte/macrophage colony- with complement at the site of infection, imDCs could be the stimulating factor plus interleukin 4 and downregulated by tumor necrosis factor ␣. first target of infection. As reported by Shi et al. (29), clustering J. Exp. Med. 179:1109. of CR3 on monocytic cells recruits a Toll/IL-1R family-like sig- 17. Freundlich, B., and N. Avdalovic. 1983. Use of gelatin/plasma coated flasks for iso- lating human peripheral blood monocytes. J. Immunol. Methods 62:31. naling cascade, interacting with IL-1R-associated kinase 1 to in- 18. Kacani, L., I. Frank, M. Spruth, M. G. Schwendinger, B. Mullauer, G. M. Sprinzl, by guest on September 24, 2021 duce NF-␬B activity. HIV opsonized with C3 fragments rep- F. Steindl, and M. P. Dierich. 1998. Dendritic cells transmit human immunodeficiency virus type 1 to monocytes and monocyte-derived macrophages. J. Virol. resents a multimerized ligand. In our studies its binding most 72:6671. probably leads to clustering of CR3 and thus supports NF-␬B 19. Purtscher, M., A. Trkola, G. Gruber, A. Buchacher, R. Predl, F. Steindl, C. Tauer, signaling. This may then direct regulation of genes encoding for R. Berger, N. Barrett, and A. Jungbauer. 1994. A broadly neutralizing human monoclonal antibody against gp41 of human immunodeficiency virus type 1. AIDS Res. cytokines, chemokines, adhesion molecules, and enzymes, Hum. Retroviruses 10:1651. thereby modulating several cellular functions. 20. Hart, D. N., and J. L. McKenzie. 1988. Isolation and characterization of human tonsil dendritic cells. J. Exp. Med. 168:157. Although the precise mechanism through which comple- 21. Stingl, G., E. C. Wolff-Schreiner, W. J. Pichler, F. Gschnait, W. Knapp, and ment coating of HIV leads to a 30% increase in HIV binding to K. Wolff. 1977. Epidermal Langerhans cells bear Fc and C3 receptors. Nature CR3 on imMDCs but to a 10-fold increase in virus production 268:245. 22. Bouhlal, H., J. Galon, M. D. Kazatchkine, W. H. Fridman, C. Sautes-Fridman, and remains unclear. The following hypothesis may be offered: N. Haeffner Cavaillon. 2001. Soluble CD16 inhibits CR3 (CD11b/CD18)-mediated Binding of complement-coated HIV to CR3 may induce spe- infection of monocytes/macrophages by opsonized primary R5 HIV-1. J. Immunol. 166:3377. cific signaling cascades and direct HIV to compartments in 23. Geijtenbeek, T. B., S. J. van Vliet, A. Engering, B. A. ’t Hart, and Y. van Kooyk. 2004. DCs which are favorable for productive infection. Both aspects Self- and nonself-recognition by C-type lectins on dendritic cells. Annu. Rev. Immu- are subjects of future research. nol. 22:33. 24. Yefenof, E., T. Magyarlaki, E. M. Fenyo, B. Wahren, and E. Klein. 1994. Alternative complement pathway activation by CD4ϩ T cells of HIV infected individuals: a possible role in AIDS pathogenesis. Int. Immunol. 6:1361. Acknowledgments 25. June, R. A., S. Z. Schade, M. J. Bankowski, M. Kuhns, A. McNamara, T. F. Lint, We thank C. Larcher for helpful discussion and the Austrian Research Fond A. L. Landay, and G. T. Spear. 1991. Complement and antibody mediate enhance- (FWF, P15379, and P15375), the state of Tyrol, and the Ludwig-Boltzmann ment of HIV infection by increasing virus binding and provirus formation. AIDS Society for support. 5:269. 26. Sullivan, B. L., E. J. Knopoff, M. Saifuddin, D. M. Takefman, M. N. Saarloos, B. E. Sha, and G. T. Spear. 1996. Susceptibility of HIV-1 plasma virus to comple- References ment-mediated lysis: evidence for a role in clearance of virus in vivo. J. Immunol. 1. Ebenbichler, C. F., N. M. Thielens, R. Vornhagen, P. Marschang, G. J. Arlaud, and 157:1791. M. P. Dierich. 1991. Human immunodeficiency virus type 1 activates the classical 27. Stoiber, H., C. Speth, and M. P. Dierich. 2003. Role of complement in the control of pathway of complement by direct C1 binding through specific sites in the transmem- HIV dynamics and pathogenesis. Vaccine 21(Suppl. 2):77. Review. brane glycoprotein gp41. J. Exp. Med. 174:1417. 28. Montefiori, D. C., R. J. Cornell, J. Y. Zhou, J. T. Zhou, V. M. Hirsch, and 2. Dierich, M. P., C. F. Ebenbichler, P. Marschang, G. Fust, N. M. Thielens, and P. R. Johnson. 1994. Complement control proteins, CD46, CD55, and CD59, as G. J. Arlaud. 1993. HIV and human complement: mechanisms of interaction and common surface constituents of human and simian immunodeficiency viruses and biological implication. Immunol. Today 14:435. possible targets for vaccine protection. Virology 205:82. 3. Delibrias, C. C, M. D. Kazatchkine, and E. Fischer. 1993. Evidence for the role of 29. Shi, C., X. Zhang, Z. Chen, M. K. Robinson, and D. I. Simon. 2001. Leukocyte CR1 (CD35), in addition to CR2 (CD21), in facilitating infection of human T cells integrin Mac-1 recruits Toll/interleukin-1 receptor superfamily signaling intermedi- with opsonized HIV. Scand. J. Immunol. 38:183. ates to modulate NF-␬B activity. Circ. Res. 89:859.