Opsonization of HIV with complement enhances infection of dendritic cells and viral transfer to CD4 T cells in a CR3 and DC-SIGN-dependent manner

In the present study, we demonstrated that opsonization of primary HIV-1 with human complement enhances infection of immature monocyte-derived dendritic cells (iDC) and transmission in trans of HIV to autologous CD4(+) T lymphocytes. Infection of iDC by opsonized primary R5- and X4-tropic HIV was increased 3- to 5-fold as compared with infection by the corresponding unopsonized HIV. Enhancement of infection was dependent on CR3 as demonstrated by inhibition induced by blocking Abs. The interaction of HIV with CCR5 and CXCR4 on iDC was affected by opsonization. Indeed, stromal-derived factor-1 was more efficient in inhibiting infection of iDC with opsonized R5-tropic HIV-1(BaL) (45%) than with heat-inactivated complement opsonized virus and similarly RANTES inhibited more efficiently infection of iDC with opsonized X4-tropic HIV-1(NDK) (42%) than with heat-inactivated complement opsonized virus. We also showed that attachment of complement-opsonized virus to DC-specific ICAM-grabbing nonintegrin (DC-SIGN) molecule on iDC and HeLa DC-SIGN(+) CR3(-) cells was 46% and 50% higher compared with heat-inactivated complement opsonized virus, respectively. Hence, Abs to DC-SIGN suppressed up to 80% and 60% the binding of opsonized virus to HeLa cells and iDC, respectively. Furthermore, Abs to DC-SIGN inhibited up to 70% of the infection of iDC and up to 65% of infection in trans of autologous lymphocytes with opsonized virus. These results further demonstrated the role of DC-SIGN in complement opsonized virus uptake and infection. Thus, the virus uses complement to its advantage to facilitate early steps leading to infection following mucosal transmission of HIV.     

Soluble CD16 inhibits CR3 (CD11b/CD18)-mediated infection of monocytes/macrophages by opsonized primary R5 HIV-1

We demonstrate that soluble CD16 (sCD16; soluble Fc gamma RIII), a natural ligand of CR3, inhibits the infection of monocytes by primary R5 HIV-1 strain opsonized with serum of seronegative individuals. Inhibition of monocyte infection by sCD16 was similar to that observed with anti-CR3 mAbs, indicating that opsonized HIV may use a CR3-dependent pathway for entry in monocytic cells. Cultured human monocytes express both CR3 (CD11b/CD18) and CCR5 receptors. RANTES, the natural ligand of CCR5, inhibited infection of monocytes with unopsonized HIV particles and partially that of monocytes infected with HIV particles opsonized with complement-derived fragments. Although HIV-infected monocytes from homozygous CCR5 Delta 32/Delta 32 (CCR5(-/-)) individuals produce low levels of p24, cells infected with opsonized particles produced higher levels of p24 than cells infected with unopsonized particles. Our results thus suggest that CR3 may represent an alternative coreceptor to CCR5 of opsonized primary R5 virus entry into monocytes/macrophages. We also observed that the concentration of sCD16 is greatly decreased in sera of HIV-infected patients with low lymphocyte CD4(+) counts. Taken together, our findings suggest that sCD16, present in plasma, may play an important role in controlling HIV-1 spread.     

Factor I-mediated processing of complement fragments on HIV immune complexes targets HIV to CR2-expressing B cells and facilitates B cell-mediated transmission of opsonized HIV to T cells

Our study demonstrates that binding of complement-opsonized HIV to complement receptor type 1 on human erythrocytes (E) via C3b fragments is followed by a rapid normal human serum-mediated detachment of HIV from E. The release was dependent on the presence of factor I indicating a conversion of C3b fragments to iC3b and C3d on the viral surface. This in turn resulted in an efficient binding of opsonized HIV to CR2-expressing B cells, thus facilitating B cell-mediated transmission of HIV to T cells. These data provide a new dynamic view of complement opsonization of HIV, suggesting that association of virus with E might be a transient phenomenon and the factor I-mediated processing of C3b to iC3b and C3d on HIV targets the virus to complement receptor type 2-expressing cells. Thus, factor I in concert with CR1 on E and factor H in serum due to their cofactor activity are likely to be important contributors for the generation of C3d-opsonized infectious HIV reservoirs on follicular dendritic cells and/or B cells in HIV-infected individuals.     

Complement mediates the binding of HIV to erythrocytes

A fraction of HIV is associated with erythrocytes even when the virus becomes undetectable in plasma under antiretroviral therapy. The aim of the present work was to further characterize this association in vitro. We developed an in vitro model to study the factors involved in the adherence of HIV-1 to erythrocytes. Radiolabeled HIV-1 (HIV) and preformed HIV-1/anti-HIV immune complexes (HIV-IC) were opsonized in various human sera, purified using sucrose density gradient ultracentrifugation, and incubated with human erythrocytes. We observed that, when opsonized in normal human serum, not only HIV-IC, but also HIV, bound to erythrocytes, although the adherence of HIV was lower than that of HIV-IC. The adherence was abolished when the complement system was blocked, but was maintained in hypogammaglobulinemic sera. Complement-deficient sera indicated that both pathways of complement were important for optimal adherence. No adherence was seen in C1q-deficient serum, and the adherence of HIV was reduced when the alternative pathway was blocked using anti-factor D Abs. The adherence could be inhibited by an mAb against complement receptor 1. At supraphysiological concentrations, purified C1q mediated the binding of a small fraction of HIV and HIV-IC to erythrocytes. In conclusion, HIV-IC bound to erythrocytes as other types of IC do when exposed to complement. Of particular interest was that HIV alone bound also to erythrocytes in a complement/complement receptor 1-dependent manner. Thus, erythrocytes may not only deliver HIV-IC to organs susceptible to infection, but free HIV as well. This may play a crucial role in the progression of the primary infection.     

Opsonization of HIV-1 by semen complement enhances infection of human epithelial cells

In the present study we demonstrate that both X4- and R5-tropic HIV-1 strains are able to infect the human epithelial cell line HT-29. Infection was enhanced 2-fold when HIV was added to semen before contact with the cell cultures. The enhancing effect of semen was complement dependent, as evidenced by blockage of generation of C3a/C3a(desArg) in semen by heat or EDTA treatment of semen and suppression of semen-dependent enhancement with mAbs directed to complement receptor type 3 (CD11b/CD18) and soluble CD16. Infection of HT-29 cells was assessed by the release of p24 Ag in cultures and semiquantitative PCR of the HIV-1 pol gene. Inhibition of infection of HT-29 by stromal cell-derived factor 1 was decreased in the case of semen-opsonized X4- and R5-tropic virus compared with unopsonized virus. In contrast, inhibition of infection by RANTES was increased for opsonized X4-tropic HIV-1 compared with unopsonized virus. Taken together these observations indicate that activation of complement in semen may play an enhancing role in mucosal transmission of HIV-1 by facilitating infection of epithelial cells and/or enhancing infection of complement receptor-expressing target cells in the mucosa.     

Contribution of complement component C3 and complement receptor type 3 to carbohydrate-dependent uptake of oligomannose-coated liposomes by peritoneal macrophages

Peritoneal macrophages (PEMs) preferentially and rapidly take up oligomannose-coated liposomes (OMLs) and subsequently mature to induce a Th-1 immune response following administration of OMLs into the peritoneal cavity. Here, we examine the contributions of complement component C3 and complement receptor type 3 (CR3) to carbohydrate-dependent uptake of OMLs by PEMs. Effective uptake of OMLs into PEMs in vitro was observed only in the presence of peritoneal fluid (PF), and OMLs incubated with PF were incorporated by PEMs in vitro in the absence of PF. These phenomena were inhibited by methyl-alpha-mannoside, N-acetylglucosamine or EDTA, but not by galactose. Pull-down analysis followed by peptide mass fingerprinting of PF-treated OMLs indicated that the OMLs were opsonized with complement fragment iC3b. In vivo uptake of OMLs by PEMs was inhibited by intraperitoneal injection of an antibody against CR3, a receptor for iC3b, and OML uptake by PEMs in the peritoneal cavity was not observed in C3-deficient mice. Thus, our results indicate that OMLs are opsonized with iC3b in a mannose-dependent manner in the peritoneal cavity and then incorporated into PEMs via CR3.     

CD46 (membrane cofactor protein) acts as a human epithelial cell receptor for internalization of opsonized uropathogenic Escherichia coli

Escherichia coli is a common urinary pathogen whose uptake into epithelial cells is mediated by attachment through type 1 fimbriae. In this study, we show by using using human urinary tract epithelial cells that maximal internalization of E. coli is achieved only when bacteria are opsonized with complement. The concentrations of complement proteins in the urine rise sufficiently during infection to allow bacterial opsonization. The complement regulatory protein, CD46 (membrane cofactor protein), acts in cohort with fimbrial adhesion to promote the uptake of pathogenic E. coli. This uptake is inhibited by RNA interference to lower the expression of CD46 and by soluble CD46 that will competitively inhibit opsonized bacteria binding to cell surface CD46. We propose that efficient internalization of uropathogenic E. coli by the human urinary tract depends on cooperation between fimbrial-mediated adhesion and C3 receptor (CD46)-ligand interaction. Complement receptor-ligand interaction could pose a new target for interrupting the cycle of reinfection due to intracellular bacteria.     

Requirement of leukocytic cell adhesion molecules (CD11a-c/CD18) in the enhanced NK lysis of iC3b-opsonized targets

Treatment of Raji or Daudi cells with human serum under conditions which allow the alternative pathway of C activation results in their C3-opsonization and enhanced sensitivity to NK-mediated lysis. The effector lymphocytes have low buoyant density, carry CD16 and HNK1 markers as well as the CD11a-c/CD18 leukocytic cell adhesion molecules. One of these molecules, made up of CD11b-CD18 (alpha- and beta-chains), is also the receptor for iC3b. We studied the role of the cell adhesion molecules in the NK effect on targets with and without C3-fragments. We focused on the E/T interaction of opsonized cells in the presence of anti CD18 mAb. mAb directed to the CD11a molecule caused 0 to 30% inhibition of the lysis of both non-opsonized and opsonized cells whereas the mAb antibody directed to the CD11c molecule had no effect. Reagents reactive with the iC3b binding site of CD11b (alpha-chain of the CR3) molecule did not alter the lysis of non-opsonized targets whereas they abrogated the C3-mediated increment of the Nk effect on opsonized cells. Two mAb preparations, 60.3 and IB4, directed to the CD18 chain shared by the three cell adhesion molecules abrogated in a dose-dependent way the lysis of both non-opsonized and opsonized targets. The 60.3 mAb inhibited the iC3b binding site of CR3 (despite its localization on the alpha-chain) and in accordance it inhibited the binding of lymphocytes to the opsonized target also. The IB4 did not affect this site and in accordance it inhibited only partially the binding of effectors to the C3 fragment carrying Raji, nevertheless it inhibited their lysis. This result indicates that the iC3b-CR3 bridge is insufficient for triggering the lysis in absence of the contact through the adhesion molecules.     

Fine Tuning Inflammation at the Front Door: Macrophage Complement Receptor 3-mediates Phagocytosis and Immune Suppression for Francisella tularensis

Complement receptor 3 (CR3, CD11b/CD18) is a major macrophage phagocytic receptor. The biochemical pathways through which CR3 regulates immunologic responses have not been fully characterized. Francisella tularensis is a remarkably infectious, facultative intracellular pathogen of macrophages that causes tularemia. Early evasion of the host immune response contributes to the virulence of F. tularensis and CR3 is an important receptor for its phagocytosis. Here we confirm that efficient attachment and uptake of the highly virulent Type A F. tularensis spp. tularensis strain Schu S4 by human monocyte-derived macrophages (hMDMs) requires complement C3 opsonization and CR3. However, despite a>40-fold increase in uptake following C3 opsonization, Schu S4 induces limited pro-inflammatory cytokine production compared with non-opsonized Schu S4 and the low virulent F. novicida. This suggests that engagement of CR3 by opsonized Schu S4 contributes specifically to the immune suppression during and shortly following phagocytosis which we demonstrate by CD11b siRNA knockdown in hMDMs. This immune suppression is concomitant with early inhibition of ERK1/2, p38 MAPK and NF-κB activation. Furthermore, TLR2 siRNA knockdown shows that pro-inflammatory cytokine production and MAPK activation in response to non-opsonized Schu S4 depends on TLR2 signaling providing evidence that CR3-TLR2 crosstalk mediates immune suppression for opsonized Schu S4. Deletion of the CD11b cytoplasmic tail reverses the CR3-mediated decrease in ERK and p38 activation during opsonized Schu-S4 infection. The CR3-mediated signaling pathway involved in this immune suppression includes Lyn kinase and Akt activation, and increased MKP-1, which limits TLR2-mediated pro-inflammatory responses. These data indicate that while the highly virulent F. tularensis uses CR3 for efficient uptake, optimal engagement of this receptor down-regulates TLR2-dependent pro-inflammatory responses by inhibiting MAPK activation through outside-in signaling. CR3-linked immune suppression is an important mechanism involved in the pathogenesis of F. tularensis infection.     

Enhancement of the function of neutrophil type-1 and type-3 complement receptors by human leukocyte inhibitory factor (LIF)

The lymphokine leukocyte inhibitory factor (LIF) has previously been documented to enhance several neutrophil (PMN) functions, including stimulated chemotaxis and superoxide generation, phagocytosis and adherence of opsonized targets, and antibody-dependent cellular cytotoxicity. The present studies were designed to investigate the effects of LIF on PMN function mediated by the complement components C3b and C3bi. LIF induced a dose-dependent increase in superoxide production generated by opsonized zymosan (up to 97.1 +/- 31.4% at 16 U LIF/ml; P less than 0.01). While neither control nor LIF-treated PMN were capable of inducing phagocytosis of either C3b- or C3bi-opsonized sheep erythrocytes (E) directly, exposure to LIF caused a significant (P less than 0.05) increase in their adherence to E (137.4 and 59.4%, respectively). Specificity for complement receptor function was confirmed by the ability of anti-CR1 antibody to block adherence of LIF-treated PMN to EAC3b (77.0% inhibition) and anti-CR3 antibody to block adherence to EAC3bi (70.2% inhibition). Increased C3b and C3bi function may have been due, at least in part, to increased expression of their respective surface membrane receptors. Thus, using indirect immunofluorescence, LIF induced a 38.2% increase in fluorescence of the anti-CR1 antibody and a 96.1% increase in anti-CR3 binding. These studies describe an additional mechanism through which LIF may have an important pro-inflammatory role in vivo.     

Hematin promotes complement alternative pathway-mediated deposition of C3 activation fragments on human erythrocytes: potential implications for the pathogenesis of anemia in malaria

Childhood malaria caused by Plasmodium falciparum is often characterized by severe anemia at low parasite burdens; the mechanism(s) responsible for this pathology remain to be defined. We have reported, based on clinical observations and in vitro models, that complement control proteins on erythrocytes such as CR1, the immune adherence receptor specific for C3b, may be reduced in childhood malaria, suggesting a possible role for complement in erythrocyte destruction. Intravascular lysis of iE by P. falciparum leads to release of erythrocyte breakdown products such as hemoglobin and hematin, which have inflammatory properties. In the present article, we demonstrate that in serum and in anticoagulated whole blood, moderate concentrations of hematin activate the alternative pathway of complement and promote deposition of C3 activation and breakdown products on erythrocytes. The degree of C3 fragment deposition is directly correlated with erythrocyte CR1 levels, and erythrocytes opsonized with large amounts of C3dg form rosettes with Raji cells, which express CR2, the C3dg receptor which is expressed on several types of B cells in the spleen. Thus, the reaction mediated by hematin promotes opsonization and possible clearance of the youngest (highest CR1) erythrocytes. A mAb specific for C3b, previously demonstrated to inhibit the alternative pathway of complement, completely blocks the C3 fragment deposition reaction. Use of this mAb in nonhuman primate models of malaria may provide insight into mechanisms of erythrocyte destruction and thus aid in the development of targeted therapies based on inhibiting the alternative pathway of complement.     

Two sides of a cellular coin: CD4(+)CD3- cells regulate memory responses and lymph-node organization

We propose that CD4(+)CD3(-) cells have two functions: a well-established role in organizing lymphoid tissue during development, and a newly discovered role in supporting T-cell help for B cells both during affinity maturation in germinal centres and for memory antibody responses. As CD4(+)CD3(-) cells express the HIV co-receptors CD4 and CXC-chemokine receptor 4, we think that infection of these cells by HIV, and their subsequent destruction by the host immune system, could help to explain the loss of memory antibody responses and the destruction of lymphoid architecture that occur during disease progression to AIDS.     

Immunoglobulin g antibody-mediated enhancement of measles virus infection can bypass the protective antiviral immune response

Antibodies to viral surface glycoproteins play a crucial role in immunity to measles by blocking both virus attachment and subsequent fusion with the host cell membrane. Here, we demonstrate that certain immunoglobulin G (IgG) antibodies can also enhance the entry of measles virus (MV) into monocytes and macrophages. Antibody-dependent enhancement of infectivity was observed in mouse and human macrophages using virions opsonized by a murine monoclonal antibody against the MV hemagglutinin (H) glycoprotein, polyclonal mouse anti-MV IgG, or diluted measles-immune human sera. Neither H-specific Fab fragments nor H-specific IgM could enhance MV entry in monocytes or macrophages, indicating involvement of a Fc γ receptor (FcγR)-mediated mechanism. Preincubation with an anti-fusion protein (anti-F) monoclonal antibody or a fusion-inhibitory peptide blocked infection, indicating that a functional F protein was required for viral internalization. Classical complement pathway activation did not promote infection through complement receptors and inhibited anti-H IgG-mediated enhancement. In vivo, antibody-enhanced infection allowed MV to overcome a highly protective systemic immune response in preimmunized IfnarKo-Ge46 transgenic mice. These data demonstrate a previously unidentified mechanism that may contribute to morbillivirus pathogenesis where H-specific IgG antibodies promote the spread of MV infection among FcγR-expressing host cells. The findings point to a new model for the pathogenesis of atypical MV infection observed after immunization with formalin-inactivated MV vaccine and underscore the importance of the anti-F response after vaccination.     

Distinct expression patterns of CD69 in mucosal and systemic lymphoid tissues in primary SIV infection of rhesus macaques

Although the intestinal tract plays a major role in early human immunodeficiency virus (HIV) infection, the role of immune activation and viral replication in intestinal tissues is not completely understood. Further, increasing evidence suggests the early leukocyte activation antigen CD69 may be involved in the development or regulation of important T cell subsets, as well as a major regulatory molecule of immune responses. Using the simian immunodeficiency virus (SIV) rhesus macaque model, we compared expression of CD69 on T cells from the intestine, spleen, lymph nodes, and blood of normal and SIV-infected macaques throughout infection. In uninfected macaques, the majority of intestinal lamina propria CD4+ T cells had a memory (CD95+) phenotype and co-expressed CD69, and essentially all intestinal CCR5+ cells co-expressed CD69. In contrast, systemic lymphoid tissues had far fewer CD69+ T cells, and many had a naïve phenotype. Further, marked, selective depletion of intestinal CD4+CD69+ T cells occurred in early SIV infection, and this depletion persisted throughout infection. Markedly increased levels of CD8+CD69+ T cells were detected after SIV infection in virtually all tissues, including the intestine. Further, confocal microscopy demonstrated selective, productive infection of CD3+CD69+ T cells in the intestine in early infection. Combined, these results indicate CD69+CD4+ T cells are a major early target for viral infection, and their rapid loss by direct infection may have profound effects on intestinal immune regulation in HIV infected patients.     

CD16+ monocyte-derived macrophages activate resting T cells for HIV infection by producing CCR3 and CCR4 ligands

The CD16(+) monocyte (Mo) subset produces proinflammatory cytokines and is expanded in peripheral blood during progression to AIDS, but its contribution to HIV pathogenesis is unclear. In this study, we investigate the capacity of human CD16(+) and CD16(-) Mo subsets to render resting CD4(+) T cells permissive for HIV replication. We demonstrate that CD16(+) Mo preferentially differentiate into macrophages (Mphi) that activate resting T cells for productive HIV infection by producing the CCR3 and CCR4 ligands CCL24, CCL2, CCL22, and CCL17. CD16(+), but not CD16(-), Mo-derived Mphi from HIV-infected and -uninfected individuals constitutively produce CCL24 and CCL2. Furthermore, these chemokines stimulate HIV replication in CD16(-) Mo:T cell cocultures. Engagement of CCR3 and CCR4 by CCL24 and CCL2, respectively, along with stimulation via CD3/CD28, renders T cells highly permissive for productive HIV infection. Moreover, HIV replicates preferentially in CCR3(+) and CCR4(+) T cells. These findings reveal a new pathway of T cell costimulation for increased susceptibility to HIV infection via engagement of CCR3 and CCR4 by chemokines constitutively produced by CD16(+) Mo/Mphi. Thus, expansion of CD16(+) Mo in peripheral blood of HIV-infected patients and their subsequent recruitment into tissues may contribute to chronic immune activation and establishment of viral reservoirs in resting T cells.     

Utilization of CD11b knockout mice to characterize the role of complement receptor 3 (CR3, CD11b/CD18) in the growth of Mycobacterium tuberculosis in macrophages

Using CD11b knockout mice as a source of macrophages (Mphi;), we show that complement receptor 3 (CR3) mediates approximately 40-50% of nonopsonic binding and 50-60% of serum-mediated binding of Mycobacterium tuberculosis to resident Mphi;. We demonstrate that opsonic binding of M. tuberculosis to Mphi; is mediated by an immunoglobulin-independent, heat-labile component of serum, in both the presence and the absence of CD11b. The survival and replication of M. tuberculosis in an in vitro Mphi; model and an in vivo mouse model of infection were not significantly affected by the absence of CD11b, indicating that CR3-mediated uptake of M. tuberculosis is not a major factor in controlling the subsequent intracellular survival of the mycobacteria. However, whether a mycobacterium will gain access to the intracellular environment, and the type of Mφ that the bacterium enters, is significantly affected by the presence or absence of CR3.     

Tolerance is dependent on complement C3 fragment iC3b binding to antigen-presenting cells

Systemic tolerance can be induced by the introduction of antigen into an immune-privileged site. Here we investigated the role of complement in the induction of tolerance after intraocular injection. We found that the development of antigen-specific tolerance is dependent on a complement activation product. The ligation of the complement C3 activation product iC3b to complement receptor type 3 (the iC3b receptor) on antigen-presenting cells resulted in the sequential production of transforming growth factor-beta2 and interleukin-10, which is essential for the induction of tolerance. These observations may extend to the development of both neonatal tolerance and other forms of acquired tolerance.     

Hepatitis B and C in dialysis units in Kosova

Background

The complement system is one of the most potent weapons of innate immunity. It is not only a mechanism for direct protection against invading pathogens but it also interacts with the adaptive immunity to optimize the pathogen-specific humoral and cellular defense cascades in the body. Complement-mediated lysis of HIV is inefficient but the presence of HIV particles results in complement activation by the generation of many C3-fragments, such as C3dg and C3d. It has been demonstrated that activation of complement can enhance HIV infection through the binding of special complement receptor type 2 expression on the surface of mature B cells and follicular dendritic cells.

Presentation of the hypothesis

Previous studies have proven that the complement-mediated antibody-dependent enhancement of HIV infection is mediated by the association of complement receptor type 2 bound to the C3 fragment and deposited on the surface of HIV virions. Thus, we hypothesize that a new activator of complement, consisting of a target domain (C3-binding region of complement receptor type 2) linked to a complement-activating human IgG1 Fc domain (CR2-Fc), can target and amplify complement deposition on HIV virions and enhance the efficiency of HIV lysis.

Testing the hypothesis

Our hypothesis was tested using cell-free HIV-1 virions cultivatedin vitro and assessment of virus opsonization was performed by incubating appropriate dilutions of virus with medium containing normal human serum and purified CR2-Fc proteins. As a control group, viruses were incubated with normal human serum under the same conditions. Virus neutralization assays were used to estimate the degree of CR2-Fc-enhanced lysis of HIV compared to untreated virus.

Implications of the hypothesis

The targeted complement activator, CR2-Fc, can be used as a novel approach to HIV therapy by abrogating the complement-enhanced HIV infection of cells.     

Complement opsonization of HIV-1 enhances the uptake by dendritic cells and involves the endocytic lectin and integrin receptor families

Interaction with the complement system is an underappreciated aspect of HIV-1 infection; even in primary infection, complement fragments are found on virions with potential to affect the interplay between the virus and dendritic cells (DC). Since opsonization may affect the efficiency of uptake and the type of receptors utilized, we compared the interactions of DC with free HIV-1 (F-HIV) and complement opsonized HIV-1 (C-HIV). We demonstrate that C-HIV significantly enhanced the uptake by immature DC (IDC) and mature DC (MDC) and that the internalization rate was dependent on both opsonization of the virus and DC maturation state. Increased DC uptake of C-HIV was not due to opsonization related increased binding of virus to the surface of DC but rather increased internalization of C-HIV despite utilizing a similar repertoire of receptors as F-HIV. Both F-HIV and C-HIV interacted with C-type lectins, integrins, and CD4 and blocking these receptor families prevented HIV-1 from binding to DC at 4°C. Blocking integrins significantly reduced the binding and uptake of F-HIV and C-HIV implicating the involvement of several integrins such as β1-integrin, CR3, LFA-1, and α4β7. Distinctive for C-HIV was usage of β1-integrin and for F-HIV, usage of β7-integrin, whereas both F-HIV and C-HIV utilized both integrin chains of CR3. We have in this study identified the receptor types used by both F-HIV and C-HIV to bind to DC. Noteworthy, C-HIV was internalized more efficiently by DC than F-HIV, probably via receptor mediated endocytosis, which may entail different intracellular processing of the virus leading to both elevated infection and altered activation of HIV specific immune responses.