Structure and function of the macrophage mannose receptor

Talaromyces marneffei Influences Macrophage Polarization and Sterilization Ability via the Arginine Metabolism Pathway in Vitro

The opportunistic fungal pathogen Talaromyces marneffei, which is endemic across a narrow band of tropical Southeast Asia and southern China, is an intracellular pathogen that causes systemic and lethal infection through the mononuclear phagocyte system. The mechanisms by which T. marneffei successfully replicates and escapes the immune system remain unclear. To investigate the role of arginine metabolism in the escape of T. marneffei from killer macrophages, we assessed inducible nitric oxide synthase (iNOS) and arginase expression, nitric oxide (NO) production, arginase and phagocytic activity, and the killing of T. marneffei in a coculture system. Our results indicate that T. marneffei induced macrophage polarization toward the M2 phenotype and regulated the arginine metabolism pathway by prolonging infection, thereby reducing antimicrobial activity and promoting fungal survival. Moreover, inhibiting T. marneffei-induced macrophage arginase activity with Nω-hydroxy-nor-arginine restored NO synthesis and strengthened fungal killing. These findings indicate that T. marneffei affects macrophage polarization and inhibits macrophage antimicrobial function via the arginine metabolism pathway.

Killer Timing: The Temporal Uterine Natural Killer Cell Differentiation Pathway and Implications for Female Reproductive Health

Natural killer (NK) cells are the predominant maternal uterine immune cell component, and they densely populate uterine mucosa to promote key changes in the post-ovulatory endometrium and in early pregnancy. It is broadly accepted that (a) immature, inactive endometrial NK (eNK) cells in the pre-ovulatory endometrium become activated and transition into decidual NK (dNK) cells in the secretory stage, peri-implantation endometrium, and continue to mature into early pregnancy; and (b) that secretory-stage and early pregnancy dNK cells promote uterine vascular growth and mediate trophoblast invasion, but do not exert their killing function. However, this may be an overly simplistic view. Evidence of specific dNK functional killer roles, as well as opposing effects of dNK cells on the uterine vasculature before and after conception, indicates the presence of a transitory secretory-stage dNK cell (s-dNK) phenotype with a unique angiodevelopmental profile during the peri-implantation period, that is that is functionally distinct from the angiomodulatory dNK cells that promote vessel destabilisation and vascular cell apoptosis to facilitate uterine vascular changes in early pregnancy. It is possible that abnormal activation and differentiation into the proposed transitory s-dNK phenotype may have implications in uterine pathologies ranging from infertility to cancer, as well as downstream effects on dNK cell differentiation in early pregnancy. Further, dysregulated transition into the angiomodulatory dNK phenotype in early pregnancy will likely have potential repercussions for adverse pregnancy outcomes, since impaired dNK function is associated with several obstetric complications. A comprehensive understanding of the uterine NK cell temporal differentiation pathway may therefore have important translational potential due to likely NK phenotypic functional implications in a range of reproductive, obstetric, and gynaecological pathologies.

Immune cell targeting nanoparticles: a review

Immune cells are attractive targets for therapy as they are direct participants in a variety of diseases. Delivering a therapeutic agent only to cells that act on a disease by distinguishing them from other cells has the advantage of concentrating the therapeutic effect and lowering systemic side effects. Distinguishing each immune cell from other immune cells to deliver substances, including drugs and genes, can be achieved using nanotechnology. And also nanoparticles can ensure in vivo stability and sustained drug release. In addition, there is an ease of surface modification, which is an important characteristic that can be utilized in targeted drug delivery systems. This characteristic allows us to utilize various properties that are specifically expressed in each immune cell. A number of studies have delivered various substances specifically to immune cells through surface engineering with active target ligands that can target each immune cell and enzyme-responsive coating, and demonstrated high therapeutic effects compared to conventional treatments. Progress in research on target delivery has been suggested to be a breakthrough for the treatments of various diseases, including cancer treatment.

Positron emission tomography and single photon emission computed tomography imaging of tertiary lymphoid structures during the development of lupus nephritis

Lymphoid neogenesis occurs in tissues targeted by chronic inflammatory processes, such as infection and autoimmunity. In systemic lupus erythematosus (SLE), such structures develop within the kidneys of lupus-prone mice ((NZBXNZW)F1) and are observed in kidney biopsies taken from SLE patients with lupus nephritis (LN). The purpose of this prospective longitudinal animal study was to detect early kidney changes and tertiary lymphoid structures (TLS) using in vivo imaging. Positron emission tomography (PET) by tail vein injection of 18-F-fluoro-2-deoxy-D-glucose (¹⁸F-FDG)(PET/FDG) combined with computed tomography (CT) for anatomical localization and single photon emission computed tomography (SPECT) by intraperitoneal injection of ^99mTC labeled Albumin Nanocoll (^99mTC-Nanocoll) were performed on different disease stages of NZB/W mice (n = 40) and on aged matched control mice (BALB/c) (n = 20). By using one-way ANOVA analyses, we compared two different compartmental models for the quantitative measure of ¹⁸F-FDG uptake within the kidneys. Using a new five-compartment model, we observed that glomerular filtration of ^18FFDG in lupus-prone mice decreased significantly by disease progression measured by anti-dsDNA Ab production and before onset of proteinuria. We could not visualize TLS within the kidneys, but we were able to visualize pancreatic TLS using ^99mTC Nanocoll SPECT. Based on our findings, we conclude that the five-compartment model can be used to measure changes of FDG uptake within the kidney. However, new optimal PET/SPECT tracer administration sites together with more specific tracers in combination with magnetic resonance imaging (MRI) may make it possible to detect formation of TLS and LN before clinical manifestations.

Lyophilization of NOTA-sdAbs: First step towards a cold diagnostic kit for 68Ga-labeling

Lyophilization is commonly used in the production of pharmaceutical compounds to increase the stability of the Active Pharmaceutical Ingredient (API) by removing solvents. This study investigates the possibility to lyophilize an anti-HER2 and an anti-MMR single-domain antibody fragment (sdAb)-based precursor as a first step in the development of a diagnostic kit for PET imaging.

METHODS

NOTA-sdAb precursors have been lyophilized with the following formulation: 100 µg NOTA-sdAb in 0.1 M NaOAc (NaOAc), 5% (w/v%) mannitol-sucrose mix at a 2:1 ratio and 0.1 mg/mL polysorbate 80. During development of the formulation and drying cycle, factors such as cake appearance, glass transition temperature and residual moisture were analyzed to ensure qualitative and stable lyophilized samples. Stability studies of lyophilized precursor were conducted up to 18 months after storage at 2-8 °C by evaluating the precursor integrity, aggregation, functionality and ⁶⁸Ga-labeling efficiency. A comparative biodistribution study (lyophilized vs non-lyophilized precursor) was conducted in wild type mice (n = 3) and in tumor bearing mice (n = 6).

RESULTS

The lyophilized NOTA-anti-HER2 precursor shows consistent stability data in vitro for up to 12 months at 2-8 °C in three separate batches, with results indicating stability even for up to T18m. No aggregation, degradation or activity loss was observed. Radiochemical purity after ⁶⁸Ga-labeling is consistent over a period of 12 months (RCP ≥ 95% at T12m). In vivo biodistribution analyses show a typical [⁶⁸Ga]Ga-NOTA-anti-HER2 sdAb distribution profile and a comparable tumor uptake for the lyophilized compound vs non-lyophilized (5.5% vs 5.7 %IA/g, respectively). In vitro results of lyophilized NOTA-anti-MMR precursor indicates stability for up to 18 months, while in vivo data show a comparable tumor uptake (2.5% vs 2.8 %IA/g, respectively) and no significant difference in kidney retention (49.4% vs 47.5 %IA/g, respectively).

CONCLUSION

A formulation and specific freeze-drying cycle were successfully developed to lyophilize NOTA-sdAb precursors for long-term storage at 2-8 °C. In vivo data show no negative impact of the lyophilization process on the in vivo behavior or functionality of the lyophilized precursor. These results highlight the potential to develop a kit for the preparation of ⁶⁸Ga-sdAb-based radiopharmaceuticals.

Clinical characterization and therapeutic targets of vitamin A in patients with hepatocholangiocarcinoma and coronavirus disease

Recent reports indicate that patients with hepatocholangiocarcinoma (CHOL) have a higher morbidity and mortality rate for coronavirus disease (COVID-19). Anti-CHOL/COVID-19 medicines are inexistent. Vitamin A (VA) refers to a potent nutrient with anti-cytotoxic and anti-inflammatory actions. Therefore, this study aimed to determine the potential functions and molecular mechanisms of VA as a potential treatment for patients with both CHOL and COVID-19 (CHOL/COVID-19). The transcriptome data of CHOL patients were obtained from the Cancer Genome Analysis database. Furthermore, the network pharmacology approach and bioinformatics analysis were used to identify and reveal the molecular functions, therapeutic biotargets, and signaling of VA against CHOL/COVID-19. First, clinical findings identified the medical characteristics of CHOL patients with COVID-19, such as susceptibility gene, prognosis, recurrence, and survival rate. Anti-viral and anti-inflammatory pathways, and immunopotentiation were found as potential targets of VA against CHOL/COVID-19. These findings illustrated that VA may contribute to the clinical management of CHOL/COVID-19 achieved by induction of cell repair, suppression of oxidative stress and inflammatory reaction, and amelioration of immunity. Nine vital therapeutic targets (BRD2, NOS2, GPT, MAPK1, CXCR3, ICAM1, CDK4, CAT, and TMPRSS13) of VA against CHOL/COVID-19 were identified. For the first time, the potential pharmacological biotargets, function, and mechanism of action of VA in CHOL/COVID-19 were elucidated.

Decorating sdAbs with Chelators: Effect of Conjugation on Biodistribution and Functionality

Single domain antibodies (sdAbs) have proven to be valuable probes for molecular imaging. In order to produce such probes, one strategy is the functionalization of the reactive amine side chain of lysines with a chelator, resulting in a mixture of compounds with a different degree of conjugation. In this study, we implemented anion exchange chromatography (AEX) to separate the different compounds or fractions that were further characterized and evaluated to study the impact of the conjugation degree on pharmacokinetic properties and functionality. Anti-HER2 and anti-MMR sdAbs were functionalized with NOTA or DTPA chelator. Anion exchange chromatography was performed using 0.02 mol/L Tris pH 7.5 as the first solvent and 0.25 M or 0.4 M NaCl (in case of NOTA chelator or DTPA chelator, respectively) as the second solvent applied as a gradient. The fractions were characterized via mass spectrometry (MS), surface plasmon resonance (SPR), and isoelectric focusing gel electrophoresis (IEF), while in vivo studies were performed after radiolabeling with either ⁶⁸Ga (NOTA) or ¹¹¹In (DTPA) to assess the impact of the conjugation degree on pharmacokinetics. AEX could successfully be applied to separate fractions of (chelator)_n-anti-HER2 and (chelator)_n-anti-MMR sdAb constructs. MS confirmed the identity of different peaks obtained in the separation process. SPR measurement suggests a small loss of affinity for (chelator)₃-anti-sdAb, while IEF revealed a correlated decrease in isoelectric point (pI) with the number of conjugated chelators. Interestingly, both the reduction in affinity and in pI was stronger with the DTPA chelator than with NOTA for both sdAbs. In vivo data showed no significant differences in organ uptake for any construct, except for (DTPA)_n-anti-MMR, which showed a significantly higher liver uptake for (DTPA)₁-anti-MMR compared to (DTPA)₂-anti-MMR and (DTPA)₃-anti-MMR. For all constructs in general, high kidney uptake was observed, due to the typical renal clearance of sdAb-based tracers. The kidney uptake showed significant differences between fractions of a same construct and indicates that a higher conjugation degree improves kidney clearance. AEX allows the separation of sdAbs with a different degree of conjugation and provides the opportunity to further characterize individual fractions. The conjugation of a chelator to sdAbs can alter some properties of the tracers, such as pI; however, the impact on the general biodistribution profile and tumor targeting was minimal.

Newly synthesized surfactants for surface mannosylation of respirable SLN assemblies to target macrophages in tuberculosis therapy

The present study reports about new solid lipid nanoparticle assemblies (SLNas) loaded with rifampicin (RIF) surface-decorated with novel mannose derivatives, designed for anti-tuberculosis (TB) inhaled therapy by dry powder inhaler (DPI). Mannose is considered a relevant ligand to achieve active drug targeting being mannose receptors (MR) overexpressed on membranes of infected alveolar macrophages (AM), which are the preferred site of Mycobacterium tuberculosis. Surface decoration of SLNas was obtained by means of newly synthesized functionalizing compounds used as surfactants in the preparation of carriers. SLNas were fully characterized in vitro determining size, morphology, drug loading, drug release, surface mannosylation, cytotoxicity, macrophage internalization extent and ability to bind MR, and intracellular RIF concentration. Moreover, the influence of these new surface functionalizing agents on SLNas aerodynamic performance was assessed by measuring particle respirability features using next generation impactor. SLNas exhibited suitable drug payload, in vitro release, and more efficient ability to enter macrophages (about 80%) compared to bare RIF (about 20%) and to non-functionalized SLNas (about 40%). The involvement of MR-specific binding has been demonstrated by saturating MR of J774 cells causing a decrease of RIF intracellular concentration of about 40%. Furthermore, it is noteworthy that the surface decoration of particles produced a poor cohesive powder with an adequate respirability (fine particle fraction ranging from about 30 to 50%). Therefore, the proposed SLNas may represent an encouraging opportunity in a perspective of an efficacious anti-TB inhaled therapy.

C-Type lectin receptor(s)-targeted nanoliposomes: an intelligent approach for effective cancer immunotherapy

Aim: The purpose of present approach is to target C-Type lectin (CTL) receptors for preferential uptake by the macrophages/dendritic cells and improving the cross-presentation of ovalbumin. Materials & methods: Conventional and engineered nanoliposomes (MPNLs) were fabricated and extensively characterized. The nanoliposome(s) was spherical in shape; and their ζ potential, size and ovalbumin loading efficiency were recorded to be 268 ± 4.15 nm, 23.4 ± 0.35 mV, 46.65 ± 1.84%, respectively. Results: The findings demonstrate that MPNLs significantly improved the antigen uptake and its cross-presentation to evoke Th CD8+ cell-mediated cellular immunity. Conclusion: In a nutshell, this engineered approach mannose surface modification for active targeting to dendritic cells/macrophages and pH-dependent quick endosomal antigen release is a promising system for efficient cancer immunotherapy.

Structure-Function Assessment of Mannosylated Poly(β-amino esters) upon Targeted Antigen Presenting Cell Gene Delivery

Antigen presenting cell (APC) gene delivery is a promising avenue for modulating immunological outcomes toward a desired state. Recently, our group developed a delivery methodology to elicit targeted and elevated levels of APC-mediated gene delivery. During these initial studies, we observed APC-specific structure-function relationships with the vectors used during gene delivery that differ from current non-APC cell lines, thus, emphasizing a need to re-evaluate vector-associated parameters in the context of APC gene transfer. Thus, we describe the synthesis and characterization of a second-generation mannosylated poly(β-amino ester) library stratified by molecular weight. To better understand the APC-specific structure-function relationships governing polymeric gene delivery, the library was systematically characterized by (1) polymer molecular weight, (2) relative mannose content, (3) polyplex biophysical properties, and (4) gene delivery efficacy. In this library, polymers with the lowest molecular weight and highest relative mannose content possessed gene delivery transfection efficiencies as good as or better than commercial controls. Among this group, the most effective polymers formed the smallest polymer-plasmid DNA complexes (∼300 nm) with moderate charge densities (<10 mV). This convergence in polymer structure and polyplex biophysical properties suggests a unique mode of action and provides a framework within which future APC-targeting polymers can be designed.

Alterations in microglial phenotype and hippocampal neuronal function in transgenic mice with astrocyte-targeted production of interleukin-10

Interleukin-10 (IL-10) is a cytokine classically linked with anti-inflammatory and protective functions in the central nervous system (CNS) in different neurodegenerative and neuroinflammatory conditions. In order to study the specific role of local CNS produced IL-10, we have created a new transgenic mouse line with astrocyte-targeted production of IL-10 (GFAP-IL10Tg). In the present study, the effects of local CNS IL-10 production on microglia, astrocytes and neuronal connectivity under basal conditions were investigated using immunohistochemistry, molecular biology techniques, electrophysiology and behavioural studies. Our results showed that, in GFAP-IL10Tg animals, microglia displayed an increase in density and a specific activated phenotype characterised by morphological changes in specific areas of the brain including the hippocampus, cortex and cerebellum that correlated with the level of transgene expressed IL-10 mRNA. Distinctively, in the hippocampus, microglial cells adopted an elongated morphology following the same direction as the dendrites of pyramidal neurons. Moreover, this IL-10-induced microglial phenotype showed increased expression of certain molecules including Iba1, CD11b, CD16/32 and F4/80 markers, "de novo" expression of CD150 and no detectable levels of either CD206 or MHCII. To evaluate whether this specific activated microglial phenotype was associated with changes in neuronal activity, the electrophysiological properties of pyramidal neurons of the hippocampus (CA3-CA1) were analysed in vivo. We found a lower excitability of the CA3-CA1 synapses and absence of long-term potentiation (LTP) in GFAP-IL10Tg mice. This study is the first description of a transgenic mouse with astrocyte-targeted production of the cytokine IL-10. The findings indicate that IL-10 induces a specific activated microglial phenotype concomitant with changes in hippocampal LTP responses. This transgenic animal will be a very useful tool to study IL-10 functions in the CNS, not only under basal conditions, but also after different experimental lesions or induced diseases.

Mannosylated poly(beta-amino esters) for targeted antigen presenting cell immune modulation

Given the rise of antibiotic resistance and other difficult-to-treat diseases, genetic vaccination is a promising preventative approach that can be tailored and scaled according to the vector chosen for gene delivery. However, most vectors currently utilized rely on ubiquitous delivery mechanisms that ineffectively target important immune effectors such as antigen presenting cells (APCs). As such, APC targeting allows the option for tuning the direction (humoral vs cell-mediated) and strength of the resulting immune responses. In this work, we present the development and assessment of a library of mannosylated poly(beta-amino esters) (PBAEs) that represent a new class of easily synthesized APC-targeting cationic polymers. Polymeric characterization and assessment methodologies were designed to provide a more realistic physiochemical profile prior to in vivo evaluation. Gene delivery assessment in vitro showed significant improvement upon PBAE mannosylation and suggested that mannose-mediated uptake and processing influence the magnitude of gene delivery. Furthermore, mannosylated PBAEs demonstrated a strong, efficient, and safe in vivo humoral immune response without use of adjuvants when compared to genetic and protein control antigens. In summary, the gene delivery effectiveness provided by mannosylated PBAE vectors offers specificity and potency in directing APC activation and subsequent immune responses.

Receptor-mediated endocytosis and brain delivery of therapeutic biologics

Transport of macromolecules across the blood-brain-barrier (BBB) requires both specific and nonspecific interactions between macromolecules and proteins/receptors expressed on the luminal and/or the abluminal surfaces of the brain capillary endothelial cells. Endocytosis and transcytosis play important roles in the distribution of macromolecules. Due to the tight junction of BBB, brain delivery of traditional therapeutic proteins with large molecular weight is generally not possible. There are multiple pathways through which macromolecules can be taken up into cells through both specific and nonspecific interactions with proteins/receptors on the cell surface. This review is focused on the current knowledge of receptor-mediated endocytosis/transcytosis and brain delivery using the Angiopep-2-conjugated system and the molecular Trojan horses. In addition, the role of neonatal Fc receptor (FcRn) in regulating the efflux of Immunoglobulin G (IgG) from brain to blood, and approaches to improve the pharmacokinetics of therapeutic biologics by generating Fc fusion proteins, and increasing the pH dependent binding affinity between Fc and FcRn, are discussed.

Mannosylated mucin-type immunoglobulin fusion proteins enhance antigen-specific antibody and T lymphocyte responses

Targeting antigens to antigen-presenting cells (APC) improve their immunogenicity and capacity to induce Th1 responses and cytotoxic T lymphocytes (CTL). We have generated a mucin-type immunoglobulin fusion protein (PSGL-1/mIgG(2b)), which upon expression in the yeast Pichia pastoris became multivalently substituted with O-linked oligomannose structures and bound the macrophage mannose receptor (MMR) and dendritic cell-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN) with high affinity in vitro. Here, its effects on the humoral and cellular anti-ovalbumin (OVA) responses in C57BL/6 mice are presented.OVA antibody class and subclass responses were determined by ELISA, the generation of anti-OVA CTLs was assessed in (51)Cr release assays using in vitro-stimulated immune spleen cells from the different groups of mice as effector cells and OVA peptide-fed RMA-S cells as targets, and evaluation of the type of Th cell response was done by IFN-γ, IL-2, IL-4 and IL-5 ELISpot assays.Immunizations with the OVA - mannosylated PSGL-1/mIgG(2b) conjugate, especially when combined with the AbISCO®-100 adjuvant, lead to faster, stronger and broader (with regard to IgG subclass) OVA IgG responses, a stronger OVA-specific CTL response and stronger Th1 and Th2 responses than if OVA was used alone or together with AbISCO®-100. Also non-covalent mixing of mannosylated PSGL-1/mIgG(2b), OVA and AbISCO®-100 lead to relatively stronger humoral and cellular responses. The O-glycan oligomannoses were necessary because PSGL-1/mIgG(2b) with mono- and disialyl core 1 structures did not have this effect.Mannosylated mucin-type fusion proteins can be used as versatile APC-targeting molecules for vaccines and as such enhance both humoral and cellular immune responses.

The increase in mannose receptor recycling favors arginase induction and Trypanosoma cruzi survival in macrophages

The macrophage mannose receptor (MR) is a pattern recognition receptor of the innate immune system that binds to microbial structures bearing mannose, fucose and N-acetylglucosamine on their surface. Trypanosoma cruzi antigen cruzipain (Cz) is found in the different developmental forms of the parasite. This glycoprotein has a highly mannosylated C-terminal domain that participates in the host-antigen contact. Our group previously demonstrated that Cz-macrophage (Mo) interaction could modulate the immune response against T. cruzi through the induction of a preferential metabolic pathway. In this work, we have studied in Mo the role of MR in arginase induction and in T. cruzi survival using different MR ligands. We have showed that pre-incubation of T. cruzi infected cells with mannose-Bovine Serum Albumin (Man-BSA, MR specific ligand) biased nitric oxide (NO)/urea balance towards urea production and increased intracellular amastigotes growth. The study of intracellular signals showed that pre-incubation with Man-BSA in T. cruzi J774 infected cells induced down-regulation of JNK and p44/p42 phosphorylation and increased of p38 MAPK phosphorylation. These results are coincident with previous data showing that Cz also modifies the MAPK phosphorylation profile induced by the parasite. In addition, we have showed by confocal microscopy that Cz and Man-BSA enhance MR recycling. Furthermore, we studied MR behavior during T. cruzi infection in vivo. MR was up-regulated in F4/80+ cells from T. cruzi infected mice at 13 and 15 days post infection. Besides, we investigated the effect of MR blocking antibody in T. cruzi infected peritoneal Mo. Arginase activity and parasite growth were decreased in infected cells pre-incubated with anti-MR antibody as compared with infected cells treated with control antibody. Therefore, we postulate that during T. cruzi infection, Cz may contact with MR, increasing MR recycling which leads to arginase activity up-regulation and intracellular parasite growth.

Proliferation of uterine natural killer cells is induced by human chorionic gonadotropin and mediated via the mannose receptor

The endometrial lining of the human uterus contains a population of phenotypically distinct (CD56(bright), CD16(dim)), tissue-specific, natural killer [uterine natural killer (uNK)] cells that play a key role in the establishment of a successful pregnancy. An increase in the number of endometrial uNK cells occurs when the conceptus implants, and there is a further increase during the early stages of placentation. Here, we describe studies that have identified human chorionic gonadotrophin (hCG), a glycoprotein synthesized by the preimplantation conceptus, as a novel regulator of uNK cell proliferation. The impact of hCG on uNK cells was mediated via the mannose receptor (CD206) rather than by the classical hCG/LH receptor that was not expressed. The mannose receptor and hCG were colocalized on the surface of uNK cells, and proliferation did not occur if cells were incubated with deglycosylated hCG or intact hCG in the presence of excess d-Mannose. These novel observations provide new insight into the endocrine-immune dialogue that exists between the conceptus and immune cells within the receptive endometrium, and have implications for the role of uNK cell-trophoblast interactions and pregnancy outcome.

Non-opsonic recognition of Mycobacterium tuberculosis by phagocytes

The interactions between Mycobacterium tuberculosis and host phagocytes such as macrophages and dendritic cells are central to both immunity and pathogenesis. Many receptors have been implicated in recognition and binding of M. tuberculosis such as the mannose receptor, dendritic-cell-specific intercellular adhesion molecule-3 grabbing nonintegrin, dectin-1 and complement receptor 3 as well as Toll-like receptors, scavenger receptors and CD14. While in vitro studies have demonstrated clear roles for particular receptor(s), in vivo work in receptor-deficient animals often revealed only a minor, or no role, in infection with M. tuberculosis. The initial encounter of phagocytic cells with myco- bacteria appears to be complex and depends on various parameters. It seems likely that infection with M. tuberculosis does not occur via a single receptor-mediated pathway. Rather, multiple receptors play different roles in M. tuberculosis infection, and the overall effect depends on the expression and availability of a particular receptor on a particular cell type and its triggered downstream responses. Moreover, the role of membrane cholesterol for M. tuberculosis interactions with phagocytes adds to the complexity of mycobacterial recognition and response. This review summarizes current knowledge on non-opsonic receptors involved in binding of mycobacteria and discusses the contribution of individual receptors to the recognition process.

Macrophage mannose receptor on lymphatics controls cell trafficking

Macrophage mannose receptor (MR) participates in pathogen recognition, clearance of endogenous serum glycoproteins, and antigen presentation. MR is also present on lymphatic vessels, where its function is unknown. Here we show that migration of lymphocytes from the skin into the draining lymph nodes through the afferent lymphatics is reduced in MR-deficient mice, while the structure of lymphatic vasculature remains normal in these animals. Moreover, in a tumor model the primary tumors grow significantly bigger in MR−/− mice than in the wild-type (WT) controls, whereas the regional lymph node metastases are markedly smaller. Adhesion of both normal lymphocytes and tumor cells to lymphatic vessels is significantly decreased in MR-deficient mice. The ability of macrophages to present tumor antigens is indistinguishable between the 2 genotypes. Thus, MR on lymphatic endothelial cells is involved in leukocyte trafficking and contributes to the metastatic behavior of cancer cells. Blocking of MR may provide a new approach to controlling inflammation and cancer metastasis by targeting the lymphatic vasculature.

Antigenic targeting of the human mannose receptor induces tumor immunity

Pattern recognition receptors are preferentially expressed on APCs allowing selective uptake of pathogens for the initiation of antimicrobial immunity. In particular, C-type lectin receptors, including the mannose receptor (MR), facilitate APC-mediated adsorptive endocytosis of microbial glyconjugates. We have investigated the potential of antigenic targeting to the MR as a means to induce Ag-specific humoral and cellular immunity. hMR transgenic (hMR Tg) mice were generated to allow specific targeting with the anti-hMR Ab, B11. We show that hMR targeting induced both humoral and cellular antigenic specific immunity. Immunization of hMR Tg mice with B11 mAbs induced potent humoral responses independent of adjuvant. Injection of hMR Tg mice with mouse anti-hMR Ab clone 19.2 elicited anti-Id-specific humoral immunity while non-Tg mice were unresponsive. B11-OVA fusion proteins (B11-OVA) were efficiently presented to OVA-specific CD4 and CD8 T cells in MR Tg, but not in non-Tg, mice. Effector differentiation of responding T cells in MR Tg mice was significantly enhanced with concomitant immunization with the TLR agonist, CpG. Administration of both CpG and B11-OVA to hMR Tg mice induced OVA-specific tumor immunity while WT mice remained unprotected. These studies support the clinical development of immunotherapeutic approaches in cancer using pattern recognition receptor targeting systems for the selective delivery of tumor Ags to APCs.

Two categories of mammalian galactose-binding receptors distinguished by glycan array profiling

Profiling of the four known galactose-binding receptors in the C-type lectin family has been undertaken in parallel on a glycan array. The results are generally consistent with those of previous assays using various different formats, but they provide a direct comparison of the properties of the four receptors, revealing that they fall into two distinct groups. The major subunit of the rat asialoglycoprotein receptor and the rat Kupffer cell receptor show similar broad preferences for GalNAc-terminated glycans, while the rat macrophage galactose lectin and the human scavenger receptor C-type lectin (SRCL) bind more restricted sets of glycans. Both of these receptors bind to Lewis x-type structures, but the macrophage galactose lectin also interacts strongly with biantennary galactose- and GalNAc-terminated glycans. Although the similar glycan-binding profiles for the asialoglycoprotein receptor and the Kupffer cell receptor might suggest that these receptors are functionally redundant, analysis of fibroblasts transfected with full-length Kupffer cell receptor reveals that they fail to endocytose glycosylated ligand.

The human macrophage mannose receptor is not a professional phagocytic receptor

The macrophage mannose receptor (MR) appears to play an important role in the binding and phagocytosis of several human pathogens, but its phagocytic property and signaling pathways have been poorly defined. The general strategy to explore such topics is to express the protein of interest in nonphagocytic cells, but in the case of MR, there are few reports using the full-length MR cDNA. When we searched to clone de novo the human MR (hMR) cDNA, problems were encountered, and full-length hMR cDNA was only obtained after devising a complex cloning strategy. Chinese hamster ovary cells, which have a fully functional phagocytic machinery when expressing professional phagocytic receptors, were stably transfected, and cell clones expressing hMR at quantitatively comparable levels than human macrophages or J774E cells were obtained. They exhibited a functional hMR-mediated endocytic capacity of a soluble ligand but failed to ingest classical particulate ligands of MR such as zymosan, Mycobacterium kansasii, or trimannoside bovine serum albumin-coated latex beads. Transient expression of hMR in two human cell lines did not provide a phagocytic capacity either. In conclusion, we show that MR is not a professional phagocytic receptor, as it does not possess the ability to promote particle ingestion in nonphagocytic cells on its own. We propose that MR is a binding receptor, which requires a partner to trigger phagocytosis in some specialized cells such as macrophages. Our new expression vector could represent a useful tool to study the receptor and its partnership further.

Molecular characterization of the rat Kupffer cell glycoprotein receptor

The Kupffer cell receptor for glycoproteins has been reported to have a role in clearance of galactose- and fucose-terminated glycoproteins from circulation. Although the gene and a cDNA encoding the receptor have been described, there has been little study of the receptor protein. To address some questions about possible ligands and functions for this receptor, fragments representing portions of the extracellular domain have been expressed and characterized. The extracellular domain consists of a trimer stabilized by an extended coiled-coil of alpha-helices. The receptor displays monosaccharide-binding characteristics similar to the hepatic asialoglycoprotein receptor, but with somewhat less selectivity. The two best monosaccharide ligands are GalNAc and galactose. alpha-Methyl fucoside is a particularly poor ligand. Analysis of Kupffer cell receptor binding to glycoproteins and oligosaccharides released from them reveals highest affinity for desialylated, complex N-linked glycans. The best glycoprotein ligands contain multiple highly branched oligosaccharides. A human ortholog of the rat receptor gene does not encode a full-length protein and is not expressed in liver. These characteristics suggest that the receptor may have functions parallel to those of the hepatocyte asialoglycoprotein receptor in some (but not all) mammalian species.

A mannose-receptor is possibly involved in the phagocytosis of Saccharomyces cerevisiae by seabream (Sparus aurata L.) leucocytes

In this paper the possible involvement of the mannose-receptor on the non-specific recognition and phagocytosis of heat killed yeast cells (Saccharomyces cerevisiae) by gilthead seabream (Sparus aurata L.) head-kidney leucocytes was established by studying the ability of different sugars to inhibit the uptake of the yeast cells by leucocytes. Leucocytes were preincubated for 30min with different concentrations of sugar (alpha-mannan, d-mannose, d-fucose, l-fucose, d-glucose, d-glucosamine and n-acetyl-glucosamine, all of them described as specific ligands of the vertebrate mannose-receptor) and afterwards incubated with FITC-labelled yeast cells for phagocytosis assays. The phagocytic ability (percentage of cells with one or more ingested yeast cells within the total cell population) and capacity (number of ingested yeast cells per cell) of leucocytes was analysed by flow cytometry. The results demonstrate the potential existence of a specific receptor-sugar or receptor-yeast cell binding process, which was saturable, specific and dose-dependent. More specifically, when leucocytes were preincubated with appropriate doses of d-mannose, d- or l-fucose, d-glucose or n-acetyl-glucosamine the phagocytosis of yeast cells by head-kidney leucocytes was partially blocked. Seabream leucocytes were also preincubated with chloroquine, a lysosomotropic drug which downregulates (in a nonspecific manner) the expression of mannose-receptors in mammals, before phagocytosis assays were performed. The results demonstrated that the phagocytosis of yeast was completely blocked by this substance. The overall results seem to corroborate the presence of the mannose-receptor in seabream phagocytes, which is involved in the non-specific binding and phagocytosis of yeast cells by head-kidney leucocytes.

Human chorionic gonadotropin (HCG) activates monocytes to produce interleukin-8 via a different pathway from luteinizing hormone/HCG receptor system

To investigate immune-endocrine interactions between the embryo and the mother early in pregnancy, we examined the effects of human chorionic gonadotropin (HCG) on IL-8 production by peripheral blood mononuclear cells (PBMC). Recombinant HCG promoted IL-8 secretion by PBMC derived from nonpregnant women. The induction of IL-8 mRNA expression was observed after 30 min of HCG stimulation. Adsorption of the HCG with anti-HCG antibodies confirmed the specificity of this effect. The translocation of nuclear factor kappaB into the nucleus and subsequent IL-8 production were observed mainly in monocytes, and IL-8 production was reduced when a proteasome inhibitor was added to inactivate nuclear factor kappaB. Although fluorescein isothiocyanate-labeled HCG was bound to the majority of monocytes, cell surface expression of HCG receptor was hardly detected. IL-8 production by HCG was not affected by inhibitors of protein kinases A and C. In contrast, this stimulation was attenuated by D-mannose, which inhibits binding to C-type lectins. The basal IL-8 production by PBMC from women early in pregnancy was significantly elevated, compared with that from nonpregnant women. This study showed that human monocytes respond to HCG and secrete IL-8 through a pathway different from the HCG receptor system, suggesting that this glycoprotein hormone can react with not only endocrine cells but also immune cells early in pregnancy, probably via primitive systems such as C-type lectins.

Involvement of the mannose receptor in the uptake of Der p 1, a major mite allergen, by human dendritic cells

BACKGROUND

Immature dendritic cells (DCs) take up antigens in peripheral tissues and, after antigen processing, mature to efficiently stimulate T cells in secondary lymph nodes. In allergic airway diseases DCs have been shown to be involved in the induction and maintenance of a T(H)2-type profile.

OBJECTIVE

The present study was undertaken to determine pathways of Der p 1 (a house dust mite allergen) uptake by human DCs and to compare Der p 1 uptake between DCs from patients with house dust mite allergy and DCs from healthy donors.

METHODS

Monocyte-derived DCs (MD-DCs) were obtained from patients with house dust mite allergy (n = 13) and healthy donors (n = 11). Der p 1 was labeled with rhodamine. Der p 1 uptake by MD-DCs was analyzed by means of flow cytometry and confocal microscopy.

RESULTS

Rhodamine- labeled Der p 1 was demonstrated to be taken up by MD-DCs in a dose-, time-, and temperature- dependent manner. The involvement of the mannose receptor (MR) in the Der p 1 uptake was demonstrated by using (1) inhibitors of the MR- mediated endocytosis (mannan and blocking anti-MR mAb), which inhibited the Der p 1 uptake from 40 % to 50 %, and (2) confocal microscopy showing the colocalization of rhodamine-labeled Der p 1 with FITC-dextran. Interestingly, compared with DCs from healthy donors, DCs from allergic patients expressed more MR and were more efficient in Der p 1 uptake.

CONCLUSION

These results suggest that the MR could play a key role in the Der p 1 allergen uptake by DCs and in the pathogenesis of allergic diseases in dust mite -sensitive patients.

Structure and activity of glycosylphosphatidylinositol anchors of Plasmodium falciparum

The glycosylphosphatidylinositol (GPI) anchors of Plasmodium falciparum are thought to be etiologic agents of malaria based on their ability to induce proinflammatory cytokine production by macrophages and cause symptoms that resemble severe malaria illness in animals. This review summarizes the published information on the structures of P. falciparum GPIs, structure-activity relationship, and anti-GPI antibodies in the host.

Structure and function of natural killer cell receptors: multiple molecular solutions to self, nonself discrimination

In contrast to T cell receptors, signal transducing cell surface membrane molecules involved in the regulation of responses by cells of the innate immune system employ structures that are encoded in the genome rather than generated by somatic recombination and that recognize either classical MHC-I molecules or their structural relatives (such as MICA, RAE-1, or H-60). Considerable progress has recently been made in our understanding of molecular recognition by such molecules based on the determination of their three-dimensional structure, either in isolation or in complex with their MHC-I ligands. Those best studied are the receptors that are expressed on natural killer (NK) cells, but others are found on populations of T cells and other hematopoietic cells. These molecules fall into two major structural classes, those of the immunoglobulin superfamily (KIRs and LIRs) and of the C-type lectin-like family (Ly49, NKG2D, and CD94/NKG2). Here we summarize, in a functional context, the structures of the murine and human molecules that have recently been determined, with emphasis on how they bind different regions of their MHC-I ligands, and how this allows the discrimination of tumor or virus-infected cells from normal cells of the host.