The cellular pathway of CD1e in immature and maturing dendritic cells

Dysregulated inflammatory response to urogynecologic meshes in women with diabetes and its implications

BACKGROUND

Diabetes is an independent risk factor for mesh complications in women undergoing mesh-augmented surgical repairs of stress urinary incontinence and/or pelvic organ prolapse. The underlying mechanism remains unclear.

OBJECTIVE

This study aimed to define the diabetes-associated alterations in the host inflammatory response to mesh and correlate them with perioperative glucose management.

STUDY DESIGN

Deidentified demographics and medical records of patients who underwent mesh removal and participated in a mesh biorepository study were reviewed (n=200). In patients with diagnosed diabetes (n=25), blood glucose management before initial mesh implantation and before and after mesh removal was assessed by blood glucose and hemoglobin A1c levels. Age- and body mass index-matched tissue samples excised from patients with and without diabetes were examined. Transcriptomic profiles of immune cell markers, immune mediators, key inflammatory regulators, cell senescence, and epigenetic enzymes were determined by multiplex transcriptomic assays (NanoString). Ratios of apoptotic cells to CD68+ macrophages were examined with immunofluorescence. Protein profiles of 12 molecules involved in apoptotic cell clearance were examined with a multiplex protein assay (Luminex).

RESULTS

Demographic and clinical characteristics, including duration between mesh implantation and removal, reason for removal, and type of mesh, etc., were comparable between patients with and without diabetes, except for 11.6% higher body mass index in the former (P=.005). In patients with diabetes, suboptimal management of blood glucose following mesh implantation was observed, with 59% of the patients having loosely or poorly controlled glucose before and after the mesh removal. Ongoing chronic inflammatory response was observed in the excised mesh-tissue complexes in both groups, whereas markers for M2 macrophages (Mrc1 [mannose receptor C-type 1]) and helper T cells (Cd4 [CD4 molecule]) were increasingly expressed in the diabetic vs nondiabetic group (P=.023 and .047, respectively). Furthermore, the gene expressions of proinflammatory Ccl24 (C-C motif chemokine ligand 24) and Ccl13 (C-C motif chemokine ligand 13) were upregulated by 1.5- and 1.8-fold (P=.035 and .027, respectively), whereas that of Il1a (interleukin 1 alpha) was paradoxically downregulated by 2.2-fold (P=.037) in the diabetic vs nondiabetic group. Interestingly, strong positive correlations were found between the expression of Ccl13, Setdb2 (SET domain bifurcated histone lysine methyltransferase 2), and M2 macrophage markers, and between the expression of Il1a, Fosl1 (activator protein-1 transcription factor subunit), and dendritic cell markers, suggesting the involvement of macrophages and dendritic cells in the diabetes-dysregulated proinflammatory response. Supportively, apoptotic cell clearance, which is an important function of macrophages, appeared to be impaired in the diabetic group, with a significantly increased protein level of CALR (calreticulin), an "eat-me" signal on the surface of apoptotic cells (P=.031), along with an increase of AXL (AXL receptor tyrosine kinase) (P=.030), which mediates apoptotic cell clearance.

CONCLUSION

Diabetes was associated with altered long-term inflammatory response in complicated mesh implantation, particularly involving innate immune cell dysfunction. Suboptimal blood glycemic control following mesh implantation may contribute to this immune dysregulation, necessitating further mechanistic studies.

In silico identification and characterization of small molecule binding to the CD1d immunoreceptor

CD1 immunoreceptors are a non-classical major histocompatibility complex (MHC) that present antigens to T cells to elucidate immune responses against disease. The antigen repertoire of CD1 has been composed primarily of lipids until recently when CD1d-restricted T cells were shown to be activated by non-lipidic small molecules, such as phenyl pentamethyl dihydrobenzofuran sulfonate (PPBF) and related benzofuran sulfonates. To date structural insights into PPBF/CD1d interactions are lacking, so it is unknown whether small molecule and lipid antigens are presented and recognized through similar mechanisms. Furthermore, it is unknown whether CD1d can bind to and present a broader range of small molecule metabolites to T cells, acting out functions analogous to the MHC class I related protein MR1. Here, we perform in silico docking and molecular dynamics simulations to structurally characterize small molecule interactions with CD1d. PPBF was supported to be presented to T cell receptors through the CD1d F' pocket. Virtual screening of CD1d against more than 17,000 small molecules with diverse geometry and chemistry identified several novel scaffolds, including phytosterols, cholesterols, triterpenes, and carbazole alkaloids, that serve as candidate CD1d antigens. Protein-ligand interaction profiling revealed conserved residues in the CD1d F' pocket that similarly anchor small molecules and lipids. Our results suggest that CD1d could have the intrinsic ability to bind and present a broad range of small molecule metabolites to T cells to carry out its function beyond lipid antigen presentation.Communicated by Ramaswamy H. Sarma.

A novel immunogenomic classification for prognosis in non-small cell lung cancer

OBJECTIVE

To facilitate immunotherapy and prognostic assessment of non-small cell lung cancer (NSCLC), we established a novel immunogenomic classification to provide valid identification criteria.

METHODS

The immune enrichment scores were calculated by single sample gene set enrichment analysis (ssGSEA) and clustered into Immunity_L and Immunity_H, and the reliability of this classification was demonstrated. Immune microenvironment score and immune cell infiltration analysis of NSCLC were also performed. Randomly divided into training group and test group, a prognosis-related immune profile was developed using least absolute shrinkage and selection operator (LASSO) and stepwise COX proportional hazards model to construct a prognostic mode.

RESULTS

The risk score for this immune profile was identified as an independent prognostic factor and can be used as a powerful prognostic tool to refine tumor immunotherapy. Our study identified two NSCLC classifications based on immunomic profiling, Immunity_H and Immunity_L.

CONCLUSION

In conclusion, Immunogenomic classification can distinguish the immune status of different types of NSCLC patients and contribute to the immunotherapy of NSCLC patients.

Optimization of 3D Immunofluorescence Analysis and Visualization Using IMARIS and MeshLab

The precision of colocalization analysis is enhanced by 3D and is potentially more accurate than 2D. Even though 3D improves the visualization of colocalization analysis, rendering a colocalization model may generate a model with numerous polygons. We developed a 3D colocalization model of FtMt/LC3 followed by simplification. Double immunofluorescence staining of FtMt and LC3 was conducted, and stacked images were acquired. We used IMARIS to render the 3D colocalization model of FtMt/LC3 and further processed it with MeshLab to decimate and generate a less complex colocalization model. We examined the available simplification algorithm using MeshLab in detail and evaluated the feasibility of each procedure in generating a model with less complexity. The quality of the simplified model was subsequently assessed. MeshLab's available shaders were scrutinized to facilitate the spatial colocalization determination. Finally, we showed that QECD was the most effective method for reducing the polygonal complexity of the colocalization model without compromising its quality. In addition, we would recommend implementing the x-ray shader, which we found useful for visualizing colocalization. As 3D was found to be more accurate in quantifying colocalization, our study provides a novel and dependable method for rendering 3D models for colocalization analysis.

Dissecting the process of human neutrophil lineage determination by using alpha-lipoic acid inducing neutrophil deficiency model

Granulocyte-monocyte progenitors (GMPs) differentiate into both neutrophils and monocytes. Recently, uni-potential neutrophil progenitors have been identified both in mice and humans using an array of surface markers. However, how human GMPs commit to neutrophil progenitors and the regulatory mechanisms of fate determination remain incompletely understood. In the present study, we established a human neutrophil deficiency model using the small molecule alpha-lipoic acid. Using this neutrophil deficiency model, we determined that the neutrophil progenitor commitment process from CD371⁺ CD115^– GMPs defined by CD34 and CD15 and discovered that critical signals generated by RNA splicing and rRNA biogenesis regulate the process of early commitment for human early neutrophil progenitors derived from CD371⁺ CD115^– GMPs. These processes were elucidated by single-cell RNA sequencing both in vitro and in vivo derived cells. Sequentially, we identified that the transcription factor ELK1 is essential for human neutrophil lineage commitment using the alpha-lipoic acid (ALA)-inducing neutrophil deficiency model. Finally, we also revealed differential roles for long-ELK1 and short-ELK1, balanced by SF3B1, in the commitment process of neutrophil progenitors. Taken together, we discovered a novel function of ALA in regulating neutrophil lineage specification and identified that the SF3B1-ELK axis regulates the commitment of human neutrophil progenitors from CD371⁺ CD115^– GMPs.

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ALA completely blocks the differentiation of human neutrophils derived from CD34⁺ stem cells in ex-vivo culture.

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CD34 and CD15 could be used to define the early differentiation stages of human neutrophil lineage determination.

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SF3B1-ELK1 signal axis regulates human neutrophil lineage determination.

Identification of glioblastoma immune subtypes and immune landscape based on a large cohort

Glioblastomas (GBM) are the most common primary brain malignancy and also the most aggressive one. In addition, GBM have to date poor treatment options. Therefore, understanding the GBM microenvironment may help to design immunotherapy treatments and rational combination strategies. In this study, the gene expression profiles and clinical follow-up data were downloaded from TCGA-GBM, and the molecular subtypes were identified using ConsensusClusterPlus. Univariate and multivariate Cox regression were used to evaluate the prognostic value of immune subtypes. The Graph Structure Learning method was used for dimension reduction to reveal the internal structure of the immune system. A Weighted Correlation Network Analysis (WGCNA) was used to identify immune-related gene modules. Four immune subtypes (IS1, IS2, IS3, IS4) with significant prognosis differences were obtained. Interestingly, IS4 had the highest mutation rate. We also found significant differences in the distribution of the four subtypes at immune checkpoints, molecular markers, and immune characteristics. WGCNA identified 11 co-expressed module genes, and there were significant differences among the four subtypes. Finally, CD1A, CD1E, and IL23R genes with significant prognostic significance were selected as the final feature genes in the brown module. Overall, this study provided a conceptual framework for understanding the tumor immune microenvironment of GBM.

Ethnic differences in CD1E, but not CD1A, gene polymorphisms between Sub-Saharan Africans, West Asians and Europeans

The five closely linked CD1A-E genes encode the human CD1 family of proteins. Few studies of the allele frequencies of these genes in African populations have been published so far. This study aimed to genotype CD1A and CD1E variants and to compare their frequencies in Sub-Saharan Africans from Gabon and Ivory Coast, and Non-Africans from Syria and France. A restriction analysis of DNA fragments generated by PCR was performed to detect CD1A and CD1E alleles in 105 subjects from Gabon, 169 subjects from Ivory Coast, 107 subjects from Syria and 181 subjects from France. The frequencies of the CD1E*02 allele were high among Sub-Saharan Africans (87%) and low in West Asians (44%) and Europeans (36%), whereas the contrary was obtained for the CD1E*01 allele (7%, 55% and 64% respectively). Frequencies of CD1A alleles were similar between all groups, the CD1A*02 allele was most prevalent (91%). The high frequency of the CD1E*02 allele in Sub-Saharan Africans suggest that future work should investigate the relationship between CD1 polymorphism and infectious diseases.

The processing and presentation of lipids and glycolipids to the immune system

The recognition of CD1-lipid complexes by T cells was discovered 20 years ago and has since been an emerging and expanding field of investigation. Unlike protein antigens, which are presented on MHC class I and II molecules, lipids can only be presented by CD1 molecules, a unique family of MHC-like proteins whose singularity is a hydrophobic antigen-binding groove. The processing and loading of lipid antigens inside this groove of CD1 molecules require localization to endosomal and lysosomal subcellular compartments and their acidic pHs. This particular environment provides the necessary glycolytic enzymes and lipases that process lipid and glycolipid antigens, as well as a set of lipid transfer proteins that load the final version of the antigen inside the groove of CD1. The overall sequence of events needed for efficient presentation of lipid antigens is now understood and presented in this review. However, a large number of important details have been elusive. This elusiveness is linked to the inherent technical difficulties of studying lipids and the lipid-protein interface in vitro and in vivo. Here, we will expose some of those limitations and describe new approaches to address them during the characterization of lipids and glycolipids antigen presentation.

Mammalian CD1 and MR1 genes

All higher vertebrates share the fundamental components of the adaptive immune system: the B cell receptor, the T cell receptor, and classical MHC proteins. At a more detailed level, their immune systems vary considerably, especially with respect to the non-polymorphic MHC class I-like proteins. In mammals, the CD1 family of lipid-presenting proteins is encoded by clusters of genes of widely divergent sizes and compositions. Another MHC class I-like protein, MR1, is typically encoded by a single gene that is highly conserved among species. Based on mammalian genomes and the available data on cellular expression profiles and protein structure, we review MR1 genes and families of CD1 genes in modern mammals from a genetic and functional perspective. Understanding the CD1 and MR1 systems across animal species provides insights into the specialized functions of the five types of CD1 proteins and facilitates careful consideration of animal models for human diseases in which immune responses to lipids and bacterial metabolites play a role.

The CD1 family: serving lipid antigens to T cells since the Mesozoic era

Class I-like CD1 molecules are in a family of antigen-presenting molecules that bind lipids and lipopeptides, rather than peptides for immune surveillance by T cells. Since CD1 lacks the high degree of polymorphism found in their major histocompatibility complex (MHC) class I molecules, different species express different numbers of CD1 isotypes, likely to be able to present structurally diverse classes of lipid antigens. In this review, we will present a historical overview of the structures of the different human CD1 isotypes and also discuss species-specific adaptations of the lipid-binding groove. We will discuss how single amino acid changes alter the shape and volume of the CD1 binding groove, how these minor changes can give rise to different numbers of binding pockets, and how these pockets affect the lipid repertoire that can be presented by any given CD1 protein. We will compare the structures of various lipid antigens and finally, we will discuss recognition of CD1-presented lipid antigens by antigen receptors on T cells (TCRs).

Role of Group 1 CD1-Restricted T Cells in Infectious Disease

The evolutionarily conserved CD1 family of antigen-presenting molecules presents lipid antigens rather than peptide antigens to T cells. CD1 molecules, unlike classical MHC molecules, display limited polymorphism, making CD1-restricted lipid antigens attractive vaccine targets that could be recognized in a genetically diverse human population. Group 1 CD1 (CD1a, CD1b, and CD1c)-restricted T cells have been implicated to play critical roles in a variety of autoimmune and infectious diseases. In this review, we summarize current knowledge and recent discoveries on the development of group 1 CD1-restricted T cells and their function in different infection models. In particular, we focus on (1) newly identified microbial and self-lipid antigens, (2) kinetics, phenotype, and unique properties of group 1 CD1-restricted T cells during infection, and (3) the similarities of group 1 CD1-restricted T cells to the closely related group 2 CD1-restricted T cells.

CD1 and mycobacterial lipids activate human T cells

For decades, proteins were thought to be the sole or at least the dominant source of antigens for T cells. Studies in the 1990s demonstrated that CD1 proteins and mycobacterial lipids form specific targets of human αβ T cells. The molecular basis by which T-cell receptors (TCRs) recognize CD1-lipid complexes is now well understood. Many types of mycobacterial lipids function as antigens in the CD1 system, and new studies done with CD1 tetramers identify T-cell populations in the blood of tuberculosis patients. In human populations, a fundamental difference between the CD1 and major histocompatibility complex systems is that all humans express nearly identical CD1 proteins. Correspondingly, human CD1 responsive T cells show evidence of conserved TCRs. In addition to natural killer T cells and mucosal-associated invariant T (MAIT cells), conserved TCRs define other subsets of human T cells, including germline-encoded mycolyl-reactive (GEM) T cells. The simple immunogenetics of the CD1 system and new investigative tools to measure T-cell responses in humans now creates a situation in which known lipid antigens can be developed as immunodiagnostic and immunotherapeutic reagents for tuberculosis disease.

Septin6 and Septin7 GTP binding proteins regulate AP-3- and ESCRT-dependent multivesicular body biogenesis

Septins (SEPTs) form a family of GTP-binding proteins implicated in cytoskeleton and membrane organization, cell division and host/pathogen interactions. The precise function of many family members remains elusive. We show that SEPT6 and SEPT7 complexes bound to F-actin regulate protein sorting during multivesicular body (MVB) biogenesis. These complexes bind AP-3, an adapter complex sorting cargos destined to remain in outer membranes of maturing endosomes, modulate AP-3 membrane interactions and the motility of AP-3-positive endosomes. These SEPT-AP interactions also influence the membrane interaction of ESCRT (endosomal-sorting complex required for transport)-I, which selects ubiquitinated cargos for degradation inside MVBs. Whereas our findings demonstrate that SEPT6 and SEPT7 function in the spatial, temporal organization of AP-3- and ESCRT-coated membrane domains, they uncover an unsuspected coordination of these sorting machineries during MVB biogenesis. This requires the E3 ubiquitin ligase LRSAM1, an AP-3 interactor regulating ESCRT-I sorting activity and whose mutations are linked with Charcot-Marie-Tooth neuropathies.

MICAL-like1 in endosomal signaling

Small GTPase Rabs are required for membrane protein sorting/delivery to precise membrane domains. Rab13 regulates tight junction assembly and polarized membrane transport in epithelial cells. Using yeast two-hybrid screen, we identified MICAL-like1 (MICAL-L1), a protein that interacts with GTP-bound Rab13 and shares a similar domain organization with MICAL protein family. MICAL-L1 has a calponin homology, Lin11, Isl-1 & Mec-3 (LIM), proline-rich, and coiled-coil domains. It is associated with late and recycling endosomes. Time-lapse video microscopy shows that GFP-Rab7 and cherry-MICAL-L1 are present within vesicles that move rapidly in the cytoplasm. Depletion of MICAL-L1 by short hairpin RNA does not alter the distribution of tight junction proteins, but affects the trafficking of epidermal growth factor receptor (EGFR). Overexpression of MICAL-L1 leads to the accumulation of EGFR in late endosomal compartments. In contrast, knocking down MICAL-L1 results in the distribution of internalized EGFR in vesicles spread throughout the cytoplasm and promotes its degradation. Our data show that MICAL-L1 inhibits EGFR degradation, suggesting that MICAL-L1 is involved in sorting/targeting the receptor to the recycling pathway. They provide novel insights into MICAL-L1/Rab protein complex that can regulate EGFR trafficking/signaling.

The T-Cell Response to Lipid Antigens of Mycobacterium tuberculosis

T-cells recognize lipid antigens presented by dedicated antigen-presenting molecules that belong to the CD1 family. This review discusses the structural properties of CD1 molecules, the nature of mycobacterial lipid antigens, and the phenotypic and functional properties of T-cells recognizing mycobacterial lipids. In humans, the five CD1 genes encode structurally similar glycoproteins that recycle in and thus survey different cellular endosomal compartments. The structure of the CD1-lipid-binding pockets, their mode of intracellular recycling and the type of CD1-expressing antigen-presenting cells all contribute to diversify lipid immunogenicity and presentation to T-cells. Mycobacteria produce a large variety of lipids, which form stable complexes with CD1 molecules and stimulate specific T-cells. The structures of antigenic lipids may be greatly different from each other and each lipid may induce unique T-cells capable of discriminating small lipid structural changes. The important functions of some lipid antigens within mycobacterial cells prevent the generation of negative mutants capable of escaping this type of immune response. T-cells specific for lipid antigens are stimulated in tuberculosis and exert protective functions. The mechanisms of antigen recognition, the type of effector functions and the mode of lipid-specific T-cell priming are discussed, emphasizing recent evidence of the roles of lipid-specific T-cells in tuberculosis.

Lysosomal-associated transmembrane protein 5 (LAPTM5) is a molecular partner of CD1e

The CD1e protein participates in the presentation of lipid antigens in dendritic cells. Its transmembrane precursor is transported to lysosomes where it is cleaved into an active soluble form. In the presence of bafilomycin, which inhibits vacuolar ATPase and consequently the acidification of endosomal compartments, CD1e associates with a 27 kD protein. In this work, we identified this molecular partner as LAPTM5. The latter protein and CD1e colocalize in trans-Golgi and late endosomal compartments. The quantity of LAPTM5/CD1e complexes increases when the cells are treated with bafilomycin, probably due to the protection of LAPTM5 from lysosomal proteases. Moreover, we could demonstrate that LAPTM5/CD1e association occurs under physiological conditions. Although LAPTM5 was previously shown to act as a platform recruiting ubiquitin ligases and facilitating the transport of receptors to lysosomes, we found no evidence that LATPM5 controls either CD1e ubiquitination or the generation of soluble lysosomal CD1e proteins. Notwithstanding these last observations, the interaction of LAPTM5 with CD1e and their colocalization in antigen processing compartments both suggest that LAPTM5 might influence the role of CD1e in the presentation of lipid antigens.

Deciphering the role of CD1e protein in mycobacterial phosphatidyl-myo-inositol mannosides (PIM) processing for presentation by CD1b to T lymphocytes

Lipids are important antigens that induce T cell-mediated specific immune responses. They are presented to T lymphocytes by a specific class of MHC-I like proteins, termed CD1. The majority of the described CD1-presented mycobacterial antigens are presented by the CD1b isoform. We previously demonstrated that the stimulation of CD1b-restricted T cells by the hexamannosylated phosphatidyl-myo-inositol (PIM(6)), a family of mycobacterial antigens, requires a prior partial digestion of the antigen oligomannoside moiety by α-mannosidase and that CD1e is an accessory protein absolutely required for the generation of the lipid immunogenic form. Here, we show that CD1e behaves as a lipid transfer protein influencing lipid immunoediting and membrane transfer of PIM lipids. CD1e selectively assists the α-mannosidase-dependent digestion of PIM(6) species according to their degree of acylation. Moreover, CD1e transfers only diacylated PIM from donor to acceptor liposomes and also from membranes to CD1b. This study provides new insight into the molecular mechanisms by which CD1e contributes to lipid immunoediting and CD1-restricted presentation to T cells.

Novel insights into lipid antigen presentation

T cells recognizing lipid antigens are present in large numbers in circulating blood. They exert multiple functions including immunoregulation, tumour surveillance and protection during infection. Here, we review the latest information on the mechanisms of lipid antigen presentation by CD1 molecules. Recent studies have provided insight into CD1 trafficking within the cell, lipid distribution and handling, CD1 maturation, lipid antigen processing and loading. The structural resolution of all human CD1 molecules has revealed unique features that correlate with function. Molecular mechanisms regulating CD1 expression and multiple evasion mechanisms evolved by viral and bacterial pathogens have been disclosed. With rapid progression, these studies have decoded lipid-specific immunity and have revealed the important immunological role of this type of antigen recognition.

MICAL-like1 mediates epidermal growth factor receptor endocytosis

Small GTPase Rabs are required for membrane protein sorting/delivery to precise membrane domains. Rab13 regulates epithelial tight junction assembly and polarized membrane transport. Here we report that Molecule Interacting with CasL (MICAL)-like1 (MICAL-L1) interacts with GTP-Rab13 and shares a similar domain organization with MICAL. MICAL-L1 has a calponin homology (CH), LIM, proline rich and coiled-coil domains. It is associated with late endosomes. Time-lapse video microscopy shows that green fluorescent protein-Rab7 and mcherry-MICAL-L1 are present within vesicles that move rapidly in the cytoplasm. Depletion of MICAL-L1 by short hairpin RNA does not alter the distribution of a late endosome/lysosome-associated protein but affects the trafficking of epidermal growth factor receptor (EGFR). Overexpression of MICAL-L1 leads to the accumulation of EGFR in the late endosomal compartment. In contrast, knocking down MICAL-L1 results in the distribution of internalized EGFR in vesicles spread throughout the cytoplasm and promotes its degradation. Our data suggest that the N-terminal CH domain associates with the C-terminal Rab13 binding domain (RBD) of MICAL-L1. The binding of Rab13 to RBD disrupts the CH/RBD interaction, and may induce a conformational change in MICAL-L1, promoting its activation. Our results provide novel insights into the MICAL-L1/Rab protein complex that can regulate EGFR trafficking at late endocytic pathways.

Fine tuning by human CD1e of lipid-specific immune responses

CD1e is a member of the CD1 family that participates in lipid antigen presentation without interacting with the T-cell receptor. It binds lipids in lysosomes and facilitates processing of complex glycolipids, thus promoting editing of lipid antigens. We find that CD1e may positively or negatively affect lipid presentation by CD1b, CD1c, and CD1d. This effect is caused by the capacity of CD1e to facilitate rapid formation of CD1-lipid complexes, as shown for CD1d, and also to accelerate their turnover. Similar results were obtained with antigen-presenting cells from CD1e transgenic mice in which lipid complexes are assembled more efficiently and show faster turnover than in WT antigen-presenting cells. These effects maximize and temporally narrow CD1-restricted responses, as shown by reactivity to Sphingomonas paucimobilis-derived lipid antigens. CD1e is therefore an important modulator of both group 1 and group 2 CD1-restricted responses influencing the lipid antigen availability as well as the generation and persistence of CD1-lipid complexes.

Crystal structure of human CD1e reveals a groove suited for lipid-exchange processes

CD1e is the only human CD1 protein existing in soluble form in the late endosomes of dendritic cells, where it facilitates the processing of glycolipid antigens that are ultimately recognized by CD1b-restricted T cells. The precise function of CD1e remains undefined, thus impeding efforts to predict the participation of this protein in the presentation of other antigens. To gain insight into its function, we determined the crystal structure of recombinant CD1e expressed in human cells at 2.90-Å resolution. The structure revealed a groove less intricate than in other CD1 proteins, with a significantly wider portal characterized by a 2 Å-larger spacing between the α1 and α2 helices. No electron density corresponding to endogenous ligands was detected within the groove, despite the presence of ligands unequivocally established by native mass spectrometry in recombinant CD1e. Our structural data indicate that the water-exposed CD1e groove could ensure the establishment of loose contacts with lipids. In agreement with this possibility, lipid association and dissociation processes were found to be considerably faster with CD1e than with CD1b. Moreover, CD1e was found to mediate in vitro the transfer of lipids to CD1b and the displacement of lipids from stable CD1b-antigen complexes. Altogether, these data support that CD1e could have evolved to mediate lipid-exchange/editing processes with CD1b and point to a pathway whereby the repertoire of lipid antigens presented by human dendritic cells might be expanded.

Increased flexibility and liposome-binding capacity of CD1e at endosomal pH

The plasma membrane proteins CD1a, CD1b and CD1c are expressed by human dendritic cells, the professional antigen-presenting cells of the immune system, and present lipid antigens to T lymphocytes. CD1e belongs to the same family of molecules, but accumulates as a membrane-associated form in the Golgi compartments of immature dendritic cells and as a soluble cleaved form in the lysosomes of mature dendritic cells. In lysosomes, the N-terminal propeptide of CD1e is also cleaved, but the functional consequences of this step are unknown. Here, we investigated how the pH changes encountered during transport to lysosomes affect the structure of CD1e and its ligand-binding properties. Circular dichroism studies demonstrated that the secondary and tertiary structures of recombinant CD1e were barely altered by pH changes. Nevertheless, at acidic pH, guanidium chloride-induced unfolding of CD1e molecules required lower concentrations of denaturing agent. The nonfunctional L194P allelic variant was found to be structurally less stable at acidic pH than the functional forms, providing an explanation for the lack of its detection in lysosomes. The number of water-exposed hydrophobic patches that bind 8-anilinonaphthalene-1-sulfonate was higher in acidic conditions, especially for the L194P variant. CD1e molecules interacted with lipid surfaces enriched in anionic lipids, such as bis(monoacylglycero)phosphate, a late endosomal/lysosomal lipid, especially at acidic pH, or when the propeptide was present. Altogether, these data indicate that, in the late endosomes/lysosomes of DCs, the acid pH promotes the binding of lipid antigens to CD1e through increased hydrophobic and ionic interactions.

Endogenous and Exogenous CD1-Binding Glycolipids

In the same way that peptide antigens are presented by major histocompatibility complex (MHC) molecules, glycolipid antigens can also activate the immune response via binding to CD1 proteins on antigen-presenting cells (APCs) and stimulate CD1-restricted T cells. In humans, there are five members of the CD1 family, termed CD1a–e, of which CD1a–d are involved in glycolipid presentation at the cell surface, while CD1e is involved in the intracellular trafficking of glycolipid antigens. Both endogenous (self-derived) and exogenous (non-self-derived) glycolipids have been shown to bind to members of the CD1 family with varying degrees of specificity. In this paper we focus on the key glycolipids that bind to the different members of the CD1 family.

CD1A and CD1E Gene Polymorphisms are Associated with Susceptibility to Multiple Sclerosis

Multiple sclerosis (MS) is thought to be an autoimmune T-cell-mediated disease directed at myelin antigens of the central nervous system. Besides myelin proteins, lipid components of CNS are supposed to play a role as antigens for T cells in MS. CD1 is a family of MHC-like glycoproteins specialized in capturing and presenting a variety of microbial and self lipids and glycolipids to antigen-specific T cells. CD1-restricted T cells specific for gangliosides and sulfatide have been isolated from subjects with MS and in mice with experimental allergic encephalopathy. We genotyped exon 2 of CD1A and CD1E in 205 MS patients and 223 unrelated healthy controls and determined their association with the presence of anti-ganglioside and anti-sulfatide antibodies. CD1E 01-01 is associated with a reduced risk of MS (OR 0.54, p=0.001); CD1A 02-02 (OR 1.99, p=0.012) or CD1E 02-02 (OR 2.45, p=0.000) with an increased risk. The combination of the genotypes CD1A 02-02 and CD1E 02-02 is present in 90.7% of patients but in only 9.4% controls (OR 94.16, p= 0.000). CD1A and CD1E polymorphisms contribute to the polygenic susceptibility to MS. The functional effects of CD1 polymorphisms are unknown, however changes in CD1 alleles may affect numerous immunological functions.

Integrins stimulate E-cadherin-mediated intercellular adhesion by regulating Src-kinase activation and actomyosin contractility

Cadherins and integrins are major adhesion molecules regulating cell-cell and cell-matrix interactions. In vitro and in vivo studies have demonstrated the existence of crosstalk between integrins and cadherins in cell adhesion and motility. We used a dual pipette assay to measure the force required to separate E-cadherin-producing cell doublets and to investigate the role of integrin in regulating the strength of intercellular adhesion. A greater force was required to separate cell doublets bound to fibronectin or vitronectin-coated beads than for doublets bound to polylysine-coated beads. This effect depended on cell spreading and the duration of stimulation. Cells expressing type II cadherin-7 also responded to fibronectin stimulation to produce a higher intercellular adhesion. Establishment of cadherin-mediated adhesion needed ROCK, MLCK and myosin ATPase II activity. The regulation of intercellular adhesion strength by integrin stimulation required activation of Src family kinases, ROCK and actomyosin contractility. These findings highlight the importance and mechanisms of molecular crosstalk between cadherins and integrins in the control of cell plasticity during histogenesis and morphogenesis.

Activation state and intracellular trafficking contribute to the repertoire of endogenous glycosphingolipids presented by CD1d [corrected]

Myeloid antigen-presenting cells (APC) express CD1d molecules that present exogenous and endogenous lipid antigens that activate CD1d-restricted T cells, natural killer T (NKT) cells. NKT cell activation has been shown to mediate the potent downstream activation of other immune cells through cell-cell interactions and rapid, prolific cytokine production. Foreign antigens are not required for NKT cell activation. The endogenous lipids bound to CD1d are sufficient for activation of NKT cells in the setting of Toll-like receptor-induced cytokines. The most potent NKT cell antigens identified are glycosphingolipids (GSL). The GSL repertoire of endogenous ligands bound to CD1d molecules that are expressed in myeloid APC at steady state and in the setting of activation has not been delineated. This report identifies the range of GSL bound to soluble murine CD1d (mCD1d) molecules that sample the endoplasmic reticulum/secretory routes and cell surface-cleaved mCD1d that also samples the endocytic system. Specific GSL species are preferentially bound by mCD1d and do not solely reflect cellular GSL. GM1a and GD1a are prominent CD1d ligands for molecules following both the ER/secretory and lysosomal trafficking routes, whereas GM2 was eluted from soluble CD1d but not lysosomal trafficking CD1d. Further, after LPS activation, the quantities of soluble CD1d-bound GM3 and GM1a markedly increased. A unique alpha-galactose-terminating GSL was also found to be preferentially bound to mCD1d at steady state, and it increased with APC activation. Together, these studies identify the range of GSL presented by CD1d and how presentation varies based on CD1d intracellular trafficking and microbial activation.

Recent advances in processing and presentation of CD1 bound lipid antigens

It is well established that different populations of alphabeta T lymphocytes can recognize not only peptides in the context of MHC class I and class II molecules, but also foreign and self-lipids in association with CD1 proteins, which share structural similarities with MHC class I molecules. CD1 molecules are comprised of five isoforms, known as group 1 (CD1a, b, c, e) and group 2 (CD1d) CD1, presenting lipid antigens to conventional T lymphocytes or innate-like T cells bearing an invariant T cell receptor (TCR) and known as invariant NKT (iNKT) cells. During the last couple of years, several papers have been published describing important aspects of the mechanisms controlling the processing and presentation of endogenous and exogenous CD1 lipid antigens, which will be the main focus of this review.

The immunological functions of saposins

Saposins or sphingolipid activator proteins (SAPs) are small, nonenzymatic glycoproteins that are ubiquitously present in lysosomes. SAPs comprise the five molecules saposins A-D and the GM2 activator protein. Saposins are essential for sphingolipid degradation and membrane digestion. On the one hand, they bind the respective hydrolases required to catabolize sphingolipid molecules; on the other hand, saposins can interact with intralysosomal membrane structures to render lipids accessible to their degrading enzymes. Thus, saposins bridge the physicochemical gap between lipid substrate and hydrophilic hydrolases. Accordingly, defects in saposin function can lead to lysosomal lipid accumulation. In addition to their specific functions in sphingolipid metabolism, saposins have membrane-perturbing properties. At the low pH of lysosomes, saposins get protonated and exhibit a high binding affinity for anionic phospholipids. Based on their universal principle to interact with membrane bilayers, we present the immunological functions of saposins with regard to lipid antigen presentation to CD1-restricted T cells, processing of apoptotic bodies for antigen delivery and cross-priming, as well as their potential antimicrobial impact.

AP-1 and KIF13A coordinate endosomal sorting and positioning during melanosome biogenesis

Specialized cell types exploit endosomal trafficking to deliver protein cargoes to cell type-specific lysosome-related organelles (LROs), but how endosomes are specified for this function is not known. In this study, we show that the clathrin adaptor AP-1 and the kinesin motor KIF13A together create peripheral recycling endosomal subdomains in melanocytes required for cargo delivery to maturing melanosomes. In cells depleted of AP-1 or KIF13A, a subpopulation of recycling endosomes redistributes to pericentriolar clusters, resulting in sequestration of melanosomal enzymes like Tyrp1 in vacuolar endosomes and consequent inhibition of melanin synthesis and melanosome maturation. Immunocytochemistry, live cell imaging, and electron tomography reveal AP-1- and KIF13A-dependent dynamic close appositions and continuities between peripheral endosomal tubules and melanosomes. Our results reveal that LRO protein sorting is coupled to cell type-specific positioning of endosomes that facilitate endosome-LRO contacts and are required for organelle maturation.

Lysosomal degradation of membrane lipids

The constitutive degradation of membrane components takes place in the acidic compartments of a cell, the endosomes and lysosomes. Sites of lipid degradation are intralysosomal membranes that are formed in endosomes, where the lipid composition is adjusted for degradation. Cholesterol is sorted out of the inner membranes, their content in bis(monoacylglycero)phosphate increases, and, most likely, sphingomyelin is degraded to ceramide. Together with endosomal and lysosomal lipid-binding proteins, the Niemann-Pick disease, type C2-protein, the GM2-activator, and the saposins sap-A, -B, -C, and -D, a suitable membrane lipid composition is required for degradation of complex lipids by hydrolytic enzymes.

The surprising diversity of lipid antigens for CD1-restricted T cells

CD1 proteins have been conserved throughout mammalian evolution and function to present lipid antigens to T cells. Crystal structures of CD1-lipid complexes show that CD1 antigen-binding grooves are composed of four pockets and two antigen entry portals. This structural information now provides a detailed understanding of how CD1-binding grooves capture a surprisingly diverse array of lipid ligands. CD1-expressing APCs are able to acquire lipid antigens from their own pool of lipids and from exogenous sources, including microbial pathogens, bystander cells, or even the systemic circulation. CD1 proteins bind to certain antigens using high stringency loading reactions within endosomes that involve low pH, glycosidases, and lipid transfer proteins. Other antigens can directly load onto CD1 proteins using low stringency mechanisms that are independent of cellular factors. New evidence from in vivo systems shows that CD1-restricted T cells influence outcomes in infectious, autoimmune, and allergic diseases. These studies lead to a broader view of the natural function of alphabeta T cells, which involves recognition of both cellular proteins and lipids.

The assembly of CD1e is controlled by an N-terminal propeptide which is processed in endosomal compartments

CD1e displays unique features in comparison with other CD1 proteins. CD1e accumulates in Golgi compartments of immature dendritic cells and is transported directly to lysosomes, where it is cleaved into a soluble form. In these latter compartments, CD1e participates in the processing of glycolipid antigens. In the present study, we show that the N-terminal end of the membrane-associated molecule begins at amino acid 20, whereas the soluble molecule consists of amino acids 32–333. Thus immature CD1e includes an N-terminal propeptide which is cleaved in acidic compartments and so is absent from its mature endosomal form. Mutagenesis experiments demonstrated that the propeptide controls the assembly of the CD1e α-chain with β2-microglobulin, whereas propeptide-deleted CD1e molecules are immunologically active. Comparison of CD1e cDNAs from different mammalian species indicates that the CD1e propeptide is conserved during evolution, suggesting that it may also optimize the generation of CD1e molecules in other species.

Alpha-galactosylceramide modulates the induction of indoleamine 2,3-dioxygenase in antigen presenting cells

The glycolipid alpha-galactosylceramide (alpha-GalCer), when presented on CD1 molecules by antigen presenting cells (APCs) to invariant NKT (iNKT cells), is a potent immunomodulator. Indoleamine 2,3-dioxygenase (IDO), an enzyme catalyzing the catabolism of L-tryptophan along the kynurenine pathway, is inducible in APC and represents one of the main endogenous mechanisms of T cell homeostasis, peripheral tolerance and immunosuppression. No data have been published yet on the effect of alpha-GalCer on IDO in APC. We aimed to determine if: (1) alpha-GalCer modulates IDO in APC; (2) the alpha-GalCer-induced effect on IDO correlates with the production by APC of active compounds; (3) the medium from alpha-GalCer-treated APC is able to stimulate iNKT cells. From our results alpha-GalCer alone did not modify IDO expression (RT-PCR) in APC, but when human peripheral blood mononuclear cells (PBMC), monocytes, and monocytic cell lines (THP-1), expressing high levels of CD1d, were treated with interferon-gamma (IFN-gamma) plus alpha-GalCer a significant potentiation of IDO transcription was measured. This effect was not induced by increased IFN-gamma release by APC, and it was functionally correlated with increased L-kynurenine (L-KYN) release by alpha-GalCer-treated CD1d-transfected THP-1 cells. The medium of these cells stimulated iNKT hybridoma cells to release interleukin (IL)-2, while alpha-GalCer alone resulted ineffective. The data demonstrate that alpha-GalCer: (1) does not induce IFN-gamma release by APC; (2) potentiates IFN-gamma-induced IDO expression and function in APC; (2) requires CD1d molecules for inducing these effects; (3) induces the release by APC of compounds active in stimulating iNKT cells.

CD1c presentation of synthetic glycolipid antigens with foreign alkyl branching motifs

Human CD1c is a protein that activates alphabeta T cells by presenting self antigens, synthetic mannosyl phosphodolichols, and mycobacterial mannosyl phosphopolyketides. To determine which molecular features of antigen structure confer a T cell response, we measured activation by structurally divergent Mycobacterium tuberculosis mannosyl-beta1-phosphomycoketides and synthetic analogs with either stereorandom or stereospecific methyl branching patterns. T cell responses required both a phosphate and a beta-linked mannose unit, and they showed preference for C(30-34) lipid units with methyl branches in the S-configuration. Thus, T cell responses were strongest for synthetic compounds that mimicked the natural branched lipids produced by mycobacterial polyketide synthase 12. Incorporation of methylmalonate to form branched lipids is a common bacterial lipid-synthesis pathway that is absent in vertebrates. Therefore, the preferential recognition of branched lipids may represent a new lipid-based pathogen-associated molecular pattern.

Control of the intracellular pathway of CD1e

CD1e is a membrane-associated protein predominantly detected in the Golgi compartments of immature human dendritic cells. Without transiting through the plasma membrane, it is targeted to lysosomes (Ls) where it remains as a cleaved and soluble form and participates in the processing of glycolipidic antigens. The role of the cytoplasmic tail of CD1e in the control of its intracellular pathway was studied. Experiments with chimeric molecules demonstrated that the cytoplasmic domain determines a cellular pathway that conditions the endosomal cleavage of these molecules. Other experiments showed that the C-terminal half of the cytoplasmic tail mediates the accumulation of CD1e in Golgi compartments. The cytoplasmic domain of CD1e undergoes monoubiquitinations, and its ubiquitination profile is maintained when its N- or C-terminal half is deleted. Replacement of the eight cytoplasmic lysines by arginines results in a marked accumulation of CD1e in trans Golgi network 46+ compartments, its expression on the plasma membrane and a moderate slowing of its transport to Ls. Fusion of this mutated form with ubiquitin abolishes the accumulation of CD1e molecules in the Golgi compartments and restores the kinetics of their transport to Ls. Thus, ubiquitination of CD1e appears to trigger its exit from Golgi compartments and its transport to endosomes. This ubiquitin-dependent pathway may explain several features of the very particular intracellular traffic of CD1e in dendritic cells compared with other CD1 molecules.

Presentation of lipid antigens to T cells

T cells specific for lipid antigens participate in regulation of the immune response during infections, tumor immunosurveillance, allergy and autoimmune diseases. T cells recognize lipid antigens as complexes formed with CD1 antigen-presenting molecules, thus resembling recognition of MHC-peptide complexes. The biophysical properties of lipids impose unique mechanisms for their delivery, internalization into antigen-presenting cells, membrane trafficking, processing, and loading of CD1 molecules. Each of these steps is controlled at molecular and celular levels and determines lipid immunogenicity. Lipid antigens may derive from microbes and from the cellular metabolism, thus allowing the immune system to survey a large repertoire of immunogenic molecules. Recognition of lipid antigens facilitates the detection of infectious agents and the initiation of responses involved in immunoregulation and autoimmunity. This review focuses on the presentation mechanisms and specific recognition of self and bacterial lipid antigens and discusses the important open issues.

CD1 antigen presentation: how it works

The classic concept of self-non-self discrimination by the immune system focused on the recognition of fragments from proteins presented by classical MHC molecules. However, the discovery of MHC-class-I-like CD1 antigen-presentation molecules now explains how the immune system also recognizes the abundant and diverse universe of lipid-containing antigens. The CD1 molecules bind and present amphipathic lipid antigens for recognition by T-cell receptors. Here, we outline the recent advances in our understanding of how the processes of CD1 assembly, trafficking, lipid-antigen binding and T-cell activation are achieved and the new insights into how lipid antigens differentially elicit CD1-restricted innate and adaptive T-cell responses.

Importance of N-linked glycosylation in the functional expression of murine CD1d1

The mouse CD1d1 glycoprotein is specialized in presenting lipid antigens to a novel class of T cells called natural killer T (NKT) cells. CD1d1 is predicted to contain five potential N-linked glycosylation sites (asparagine residues at positions 25, 38, 60, 128, and 183). Glycosylation has been shown to invariably affect the molecular and functional properties of various glycoproteins, and in the current report it was found that a conservative change of the individual endogenous asparagine residues in CD1d1 to glutamine differentially affected its functional expression. Although the maturation rate of the glycosylation mutants was comparable to that of wild type, they differed in their relative levels of surface expression and in their ability to stimulate NKT cells. Mutating all five glycosylation residues resulted in the absence of detectable CD1d1 expression, with a concomitant lack of NKT cell activation. Therefore, these results demonstrate that glycosylation plays a significant role in the functional expression of CD1d1.

CD1 expression on antigen-presenting cells

CD1 proteins present self and microbial glycolipids to CD 1-restricted T cells, or in the case of CD1d, to NKT cells. The CD1 family in humans consists of group I proteins CDla, CDlb, CDlc, and CDle and the group II protein CDld. Rodents express only CDld, but as CD1d is broadly expressed and traffics to all endosomal compartments, this single CD1 family member is thereby able to acquire antigens in many subcellular compartments. A complete understanding of the CD 1 family requires an appreciation of which cells express CD1 and how CD1 contributes to the unique function of each cell type. While group I CD 1 expression is limited to thymocytes and professional APCs, CD1d has a wider tissue distribution and can be found on many nonhematopoietic cells. The expression and regulation of CD1 are presented here with particular emphasis on the function of CD1 in thymocytes, B cells, monocytes and macrophages, dendritic cells (DCs), and intestinal epithelial cells (IECs). Altered expression of CD 1 in cancer, autoimmunity, and infectious disease is well documented, and the implication of CD 1 expression in these diseases is discussed.

How pattern recognition receptor triggering influences T cell responses: a new look into the system

Signaling through pattern recognition receptors (PRRs) in antigen-presenting cells (APCs) is required for the induction of T cell responses. PRR triggering in APCs induces important cellular modifications that have profound effects on antigen internalization, processing, MHC loading and antigen presentation. Accumulating experimental evidence also suggests that the fate of T cell responses depends strongly on the type of PRR triggered and the timing of PRR signaling. Here, we discuss the beneficial effects of PRR stimulation in the context of priming naive T cells, the generation and maintenance of effector/memory T cells, and the induction or break of tolerance. We propose a new classification into opsonic, phagocytic and instructive PRRs based on the functional properties of the receptors.

Dendritic cells and skin sensitization: Biological roles and uses in hazard identification

Recent advances have been made in our understanding of the roles played by cutaneous dendritic cells (DCs) in the induction of contact allergy. A number of associated changes in epidermal Langerhans cell phenotype and function required for effective skin sensitization are providing the foundations for the development of cellular assays (using DC and DC-like cells) for skin sensitization hazard identification. These alternative approaches to the identification and characterization of skin sensitizing chemicals were the focus of a Workshop entitled "Dendritic Cells and Skin Sensitization: Biological Roles and Uses in Hazard Identification" that was given at the annual Society of Toxicology meeting held March 6-9, 2006 in San Diego, California. This paper reports information that was presented during the Workshop.

Rab11A controls the biogenesis of Birbeck granules by regulating Langerin recycling and stability

The extent to which Rab GTPases, Rab-interacting proteins, and cargo molecules cooperate in the dynamic organization of membrane architecture remains to be clarified. Langerin, a recycling protein accumulating in the Rab11-positive compartments of Langerhans cells, induces the formation of Birbeck granules (BGs), which are membrane subdomains of the endosomal recycling network. We investigated the role of Rab11A and two members of the Rab11 family of interacting proteins, Rip11 and RCP, in Langerin traffic and the biogenesis of BGs. The overexpression of a dominant-negative Rab11A mutant or Rab11A depletion strongly influenced Langerin traffic and stability and the formation of BGs, whereas modulation of other Rab proteins involved in dynamic regulation of the endocytic-recycling pathway had no effect. Impairment of Rab11A function led to a missorting of Langerin to lysosomal compartments, but inhibition of Langerin degradation by chloroquine did not restore the formation of BGs. Loss of RCP, but not of Rip11, also had a modest, but reproducible effect on Langerin stability and BG biogenesis, pointing to a role for Rab11A-RCP complexes in these events. Our results show that Rab11A and Langerin are required for BG biogenesis, and they illustrate the role played by a Rab GTPase in the formation of a specialized subcompartment within the endocytic-recycling system.

Pathways of CD1 and lipid antigen delivery, trafficking, processing, loading, and presentation

Specific T cell responses to a variety of self and microbial lipids depend on proper assembly and intracellular trafficking of CD 1 molecules that intersect with and load processed lipid antigens. These pathways involve unique membrane trafficking and chaperones that are distinct from those utilized for major histocompatibility complex (MHC)-mediated presentation of peptide antigens, and thus define unique lipid antigen presentation pathways. Furthermore, recent studies have identified components of lipid metabolism that participate in lipid delivery, uptake, processing and loading onto CD1 molecules. Defects in these pathways result in impaired T cell development and function, underscoring their critical role in the lipid-specific T cell immune responses.

Architecture of CD1 proteins

The CD1 family of glycosylated cell surface receptors binds and presents lipid antigens for T cell recognition and activation. Crystal structures of CD1-lipid complexes reveal differences in the mode of presentation of lipids by CD1 group 1 (CDla, CDlb, and CDlc) and group 2 isoforms (CDld). For group 1, especially CDla and CD1b, the lipid backbone is anchored inside the hydrophobic binding grooves (lipid anchoring), whereas, for group 2 CDld, a precise hydrogen-bonding network positions the polar ligand headgroups in well-defined orientation at the T cell recognition surface (headgroup positioning). In addition, small, but important, structural changes occur on the surface of CDld upon binding of the potent invariant NKT cell agonist alpha-galactosylceramide due to increased polar interaction with the alphal and alpha2 helices. No such ligand-induced, conformational changes have yet been reported for any group 1 CD1 complexes, even upon binding of chemically diverse antigens, such as dual alkyl chain sphingolipids vs single alkyl chain lipopeptides. These structural data have already been successfully translated into the design of enhanced lipid activators of NKT cells and will likely continue for design of other chemotherapeutic agents or immunostimulatory compounds for a variety of immune-mediated diseases.