Irene S. Ludwig

Lewis X component in human milk binds DC-SIGN and inhibits HIV-1 transfer to CD4+ T lymphocytes

DC-specific ICAM3-grabbing non-integrin (DC-SIGN), which is expressed on DCs, can interact with a variety of pathogens such as HIV-1, hepatitis C, Ebola, cytomegalovirus, Dengue virus, Mycobacterium, Leishmania, and Candida albicans. We demonstrate that human milk can inhibit the DC-SIGN-mediated transfer of HIV-1 to CD4+ T lymphocytes as well as viral transfer by both immature and mature DCs. The inhibitory factor directly interacted with DC-SIGN and prevented the HIV-1 gp120 envelope protein from binding to the receptor. The human milk proteins lactoferrin, alpha-lactalbumin, lysozyme, beta-casein, and secretory leukocyte protease inhibitor did not bind DC-SIGN or demonstrate inhibition of viral transfer. The inhibitory effect could be fully alleviated with an Ab recognizing the Lewis X (LeX) sugar epitope, commonly found in human milk. LeX in polymeric form or conjugated to protein could mimic the inhibitory activity, whereas free LeX sugar epitopes could not. We reveal that a LeX motif present in human milk can bind to DC-SIGN and thereby prevent the capture and subsequent transfer of HIV-1 to CD4+ T lymphocytes. The presence of such a DC-SIGN-binding molecule in human milk may both influence antigenic presentation and interfere with pathogen transfer in breastfed infants.

Hepatitis C Virus Targets DC-SIGN and L-SIGN To Escape Lysosomal Degradation

ABSTRACT Hepatitis C virus (HCV) is a major health problem. However, the mechanism of hepatocyte infection is largely unknown. We demonstrate that the dendritic cell (DC)-specific C-type lectin DC-SIGN and its liver-expressed homologue L-SIGN/DC-SIGNR are important receptors for HCV envelope glycoproteins E1 and E2. Mutagenesis analyses demonstrated that both HCV E1 and E2 bind the same binding site on DC-SIGN as the pathogens human immunodeficiency virus type 1 (HIV-1) and mycobacteria, which is distinct from the cellular ligand ICAM-3. HCV virus-like particles are efficiently captured and internalized by DCs through binding of DC-SIGN. Antibodies against DC-SIGN specifically block HCV capture by both immature and mature DCs, demonstrating that DC-SIGN is the major receptor on DCs. Interestingly, internalized HCV virus-like particles were targeted to nonlysosomal compartments within immature DCs, where they are protected from lysosomal degradation in a manner similar to that demonstrated for HIV-1. Lewis X antigen, another ligand of DC-SIGN, was internalized to lysosomes, demonstrating that the internalization pathway of DC-SIGN-captured ligands may depend on the structure of the ligand. Our results suggest that HCV may target DC-SIGN to “hide” within DCs and facilitate viral dissemination. L-SIGN, expressed by THP-1 cells, internalized HCV particles into similar nonlysosomal compartments, suggesting that L-SIGN on liver sinusoidal endothelial cells may capture HCV from blood and transmit it to hepatocytes, the primary target for HCV. We therefore conclude that both DCs and liver sinusoidal endothelial cells may act as reservoirs for HCV and that the C-type lectins DC-SIGN and L-SIGN, as important HCV receptors, may represent a molecular target for clinical intervention in HCV infection.

Interactions of DC-SIGN with Mac-1 and CEACAM1 regulate contact between dendritic cells and neutrophils

Early during infection neutrophils are the most important immune cells that are involved in killing of pathogenic bacteria and regulation of innate immune responses at the site of infection. It has become clear that neutrophils also modulate adaptive immunity through interactions with dendritic cells (DCs) that are pivotal in the induction of T cell responses. Upon activation, neutrophils release TNF‐α and induce maturation of DCs that enables these antigen‐presenting cells to stimulate T cell proliferation and to induce T helper 1 polarization. DC maturation by neutrophils also requires cellular interactions that are mediated by binding of the DC‐specific receptor DC‐SIGN to Mac‐1 on the neutrophil. Here, we demonstrate that also CEACAM1 is an important ligand for DC‐SIGN on neutrophils. Binding of DC‐SIGN to both CEACAM1 and Mac‐1 is required to establish cellular interactions with neutrophils. DC‐SIGN is a C‐type lectin that has specificity for Lewisx, and we show that DC‐SIGN mediates binding to CEACAM1 through Lewisx moieties that are specifically expressed on CEACAM1 derived from neutrophils. This indicates that glycosylation‐driven binding of both Mac‐1 and CEACAM1 to DC‐SIGN is essential for interactions of neutrophils with DCs and enables neutrophils to modulate T cell responses through interactions with DCs.

Bile Salt-Stimulated Lipase from Human Milk Binds DC-SIGN and Inhibits Human Immunodeficiency Virus Type 1 Transfer to CD4^+ T Cells

ABSTRACT A wide range of pathogens, including human immunodeficiency virus type 1 (HIV-1), hepatitis C virus, Ebola virus, cytomegalovirus, dengue virus, Mycobacterium, Leishmania, and Helicobacter pylori, can interact with dendritic cell (DC)-specific ICAM3-grabbing nonintegrin (DC-SIGN), expressed on DCs and a subset of B cells. More specifically, the interaction of the gp120 envelope protein of HIV-1 with DC-SIGN can facilitate the transfer of virus to CD4+ T lymphocytes in trans and enhance infection. We have previously demonstrated that a multimeric LeX component in human milk binds to DC-SIGN, preventing HIV-1 from interacting with this receptor. Biochemical analysis reveals that the compound is heat resistant, trypsin sensitive, and larger than 100 kDa, indicating a specific glycoprotein as the inhibitory compound. By testing human milk from three different mothers, we found the levels of DC-SIGN binding and viral inhibition to vary between samples. Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting, and matrix-assisted laser desorption ionization analysis, we identified bile salt-stimulated lipase (BSSL), a Lewis X (LeX)-containing glycoprotein found in human milk, to be the major variant protein between the samples. BSSL isolated from human milk bound to DC-SIGN and inhibited the transfer of HIV-1 to CD4+ T lymphocytes. Two BSSL isoforms isolated from the same human milk sample showed differences in DC-SIGN binding, illustrating that alterations in the BSSL forms explain the differences observed. These results indicate that variations in BSSL lead to alterations in LeX expression by the protein, which subsequently alters the DC-SIGN binding capacity and the inhibitory effect on HIV-1 transfer. Identifying the specific molecular interaction between the different forms may aid in the future design of antimicrobial agents.

Branched oligosaccharide structures on HBV prevent interaction with both DC-SIGN and L-SIGN

Summary.  Hepatitis B virus (HBV) is a DNA virus that infects the liver as primary target. Currently, a high affinity receptor for HBV is still unknown. The dendritic cell specific C‐type lectin DC‐SIGN is involved in pathogen recognition through mannose and fucose containing carbohydrates leading to the induction of an anti‐viral immune response. Many glycosylated viruses subvert this immune surveillance function and exploit DC‐SIGN as a port of entry and for trans‐infection of target cells. The glycosylation pattern on HBV surface antigens (HBsAg) together with the tissue distribution of HBV would allow interaction between HBV and DC‐SIGN and its liver‐expressed homologue L‐SIGN. Therefore, a detailed study to investigate the binding of HBV to DC‐SIGN and L‐SIGN was performed. For HCV, both DC‐SIGN and L‐SIGN are known to bind envelope glycoproteins E1 and E2. Soluble DC‐SIGN and L‐SIGN specifically bound HCV virus‐like particles, but no interaction with either HBsAg or HepG2.2.15‐derived HBV was detected. Also, neither DC‐SIGN nor L‐SIGN transfected Raji cells bound HBsAg. In contrast, highly mannosylated HBV, obtained by treating HBV producing HepG2.2.15 cells with the α‐mannosidase I inhibitor kifunensine, is recognized by DC‐SIGN. The α‐mannosidase I trimming of N‐linked oligosaccharide structures thus prevents recognition by DC‐SIGN. On the basis of these findings, it is tempting to speculate that HBV exploits mannose trimming as a way to escape recognition by DC‐SIGN and thereby subvert a possible immune activation response.

Diclofenac enhances allergic responses in a mouse peanut allergy model

Cite this as: M. Bol‐Schoenmakers, R. Bleumink, M. Marcondes Rezende, E. Mouser, I. Hassing, I. Ludwig, J. J. Smit and R. H. H. Pieters, Clinical & Experimental Allergy, 2011 (41) 424–433.

An Arthritis-Suppressive and Treg Cell-Inducing CD4+ T Cell Epitope Is Functional in the Context of HLA-Restricted T Cell Responses.

We previously showed that mycobacterial Hsp70‐derived peptide B29 induced B29‐specific Treg cells that suppressed experimental arthritis in mice via cross‐recognition of their mammalian Hsp70 homologs. The aim of the current study was to characterize B29 binding and specific CD4+ T cell responses in the context of human major histocompatibility complex (MHC) molecules.

The Enigma of Heat Shock Proteins in Immune Tolerance

The fundamental problem of autoimmune diseases is the failure of the immune system to downregulate its own potentially dangerous cells, which leads to destruction of tissue expressing the relevant autoantigens. Current immunosuppressive therapies offer relief but fail to restore the basic condition of self-tolerance. They do not induce long-term physiological regulation resulting in medication-free disease remissions. Heat shock proteins (HSPs) have shown to possess the capacity of inducing lasting protective immune responses in models of experimental autoimmune diseases. Especially mycobacterial HSP60 and HSP70 were shown to induce disease inhibitory IL-10-producing regulatory T cells in many different models. This in itself may seem enigmatic, since based on earlier studies, HSPs were also coined sometimes as pro-inflammatory damage-associated molecular patterns. First clinical trials with HSPs in rheumatoid arthritis and type I diabetes have also indicated their potential to restore tolerance in autoimmune diseases. Data obtained from the models have suggested three aspects of HSP as being critical for this tolerance promoting potential: 1. evolutionary conservation, 2. most frequent cytosolic/nuclear MHC class II natural ligand source, and 3. upregulation under (inflammatory) stress. The combination of these three aspects, which are each relatively unique for HSP, may provide an explanation for the enigmatic immune tolerance promoting potential of HSP.

Bystander activation of irrelevant CD4+ T cells following antigen-specific vaccination occurs in the presence and absence of adjuvant

Autoimmune and other chronic inflammatory diseases (AID) are prevalent diseases which can severely impact the quality of life of those that suffer from the disease. In most cases, the etiology of these conditions have remained unclear. Immune responses that take place e.g. during natural infection or after vaccination are often linked with the development or exacerbation of AID. It is highly debated if vaccines induce or aggravate AID and in particular adjuvants are mentioned as potential cause. Since vaccines are given on a large scale to healthy individuals but also to elderly and immunocompromised individuals, more research is warranted. Non-specific induction of naïve or memory autoreactive T cells via bystander activation is one of the proposed mechanisms of how vaccination might be involved in AID. During bystander activation, T cells unrelated to the antigen presented can be activated without (strong) T cell receptor (TCR) ligation, but via signals derived from the ongoing response directed against the vaccine-antigen or adjuvant at hand. In this study we have set up a TCR transgenic T cell transfer mouse model by which we were able to measure local bystander activation of transferred and labeled CD4+ T cells. Intramuscular injection with the highly immunogenic Complete Freund’s Adjuvant (CFA) led to local in vivo proliferation and activation of intravenously transferred CD4+ T cells in the iliac lymph node. This local bystander activation was also observed after CFA prime and Incomplete Freund’s Adjuvant (IFA) boost injection. Furthermore, we showed that an antigen specific response is sufficient for the induction of a bystander activation response and the general, immune stimulating effect of CFA or IFA does not appear to increase this effect. In other words, no evidence was obtained that adjuvation of antigen specific responses is essential for bystander activation.

Routing dependent immune responses after experimental R848-adjuvated vaccination

Most traditional vaccines are administered via the intramuscular route. Other routes of administration however, can induce equal or improved protective memory responses and might provide practical advantages such as needle-free immunization, dose sparing and induction of tissue-specific (mucosal) immunity. Here we explored the differences in immunological outcome after immunization with model antigens via two promising immunization routes (intradermal and intranasal) with or without the experimental adjuvant and TLR7/8-agonist R848. Because the adaptive immune response is largely determined by the local innate cells at the site of immunization, the effect of R848-adjuvation on local cellular recruitment, antigenic uptake by antigen-presenting cells and the initiation of the adaptive response were analyzed for the two routes of administration. We show a general immune-stimulating effect of R848 irrespective of the route of administration. This includes influx of neutrophils, macrophages and dendritic cells to the respective draining lymph nodes and an increase in antigen-positive antigen-presenting cells which leads for both intradermal and intranasal immunization to a mainly TH1 response. Furthermore, both intranasal and intradermal R848-adjuvated immunization induces a local shift in DC subsets; frequencies of CD11b+DC increase whereas CD103+DC decrease in relative abundance in the draining lymph node. In spite of these similarities, the outcome of immune responses differs for the respective immunization routes in both magnitude and cytokine profile. Via the intradermal route, the induced T-cell response is higher compared to that after intranasal immunization, which corresponds with the local higher uptake of antigen by antigen-presenting cells after intradermal immunization. Furthermore, R848-adjuvation enhances ex vivo IL-10 and IL-17 production after intranasal, but not intradermal, T-cell activation. Quite the opposite, intradermal immunization leads to a decrease in IL-10 production by the vaccine induced T-cells. This knowledge may lead to a more rational development of novel adjuvanted vaccines administered via non-traditional routes.