Endosomal proteolysis and MHC class II function

Transcriptome analysis in the spleen of Northern Snakehead (Channa argus) challenged with Nocardia seriolae

Northern snakehead (Channa argus) is an indigenous fish species and is one of popularly cultured snakeheads in China and other Asian countries. Unfortunately, Nocardia seriolae infections have caused considerable losses in the snakehead aquaculture industry. However, the infectivity and the immune response induced by N. seriolae in snakehead are unclear. In order to better understand the immune response of Northern snakehead in a series of time points after N. seriolae challenge, we conducted the transcriptomic comparison in snakehead spleen at 48, 96, and 144 h after the challenge of N. seriola against their control counterparts. Gene annotation and pathway analysis of differentially expressed genes (DEGs) were carried out to understand the functions of the DEGs. Additionally, protein-protein interaction networks were conducted to obtain the interaction relationships of immune-related DEGs. These results revealed the expression changes of multiple DEGs and signaling pathways involved in immunity during N. seriolae infection, which will facilitate our comprehensive understanding of the mechanisms involved in the immune response to bacterial infection in the northern snakehead.

Antigen Presentation and Autophagy in Teleost Adaptive Immunity

Infectious diseases are a burden for aquaculture. Antigen processing and presentation (APP) to the immune effector cells that fight pathogens is key in the adaptive immune response. At the core of the adaptive immunity that appeared in lower vertebrates during evolution are the variable genes encoding the major histocompatibility complex (MHC). MHC class I molecules mainly present peptides processed in the cytosol by the proteasome and transported to the cell surface of all cells through secretory compartments. Professional antigen-presenting cells (pAPC) also express MHC class II molecules, which normally present peptides processed from exogenous antigens through lysosomal pathways. Autophagy is an intracellular self-degradation process that is conserved in all eukaryotes and is induced by starvation to contribute to cellular homeostasis. Self-digestion during autophagy mainly occurs by the fusion of autophagosomes, which engulf portions of cytosol and fuse with lysosomes (macroautophagy) or assisted by chaperones (chaperone-mediated autophagy, CMA) that deliver proteins to lysosomes. Thus, during self-degradation, antigens can be processed to be presented by the MHC to immune effector cells, thus, linking autophagy to APP. This review is focused on the essential components of the APP that are conserved in teleost fish and the increasing evidence related to the modulation of APP and autophagy during pathogen infection.

Selective inhibition of peripheral cathepsin S reverses tactile allodynia following peripheral nerve injury in mouse

Cathepsin S (CatS) is a cysteine protease found in lysosomes of hematopoietic and microglial cells and in secreted form in the extracellular space. While CatS has been shown to contribute significantly to neuropathic pain, the precise mechanisms remain unclear. In this report, we describe JNJ-39641160, a novel non-covalent, potent, selective and orally-available CatS inhibitor that is peripherally restricted (non-CNS penetrant) and may represent an innovative class of immunosuppressive and analgesic compounds and tools useful toward investigating peripheral mechanisms of CatS in neuropathic pain. In C57BL/6 mice, JNJ-39641160 dose-dependently blocked the proteolysis of the invariant chain, and inhibited both T-cell activation and antibody production to a vaccine antigen. In the spared nerve injury (SNI) model of chronic neuropathic pain, in which T-cell activation has previously been demonstrated to be a prerequisite for the development of pain hypersensitivity, JNJ-39641160 fully reversed tactile allodynia in wild-type mice but was completely ineffective in the same model in CatS knockout mice (which exhibited a delayed onset in allodynia). By contrast, in the acute mild thermal injury (MTI) model, JNJ-39641160 only weakly attenuated allodynia at the highest dose tested. These findings support the hypothesis that blockade of peripheral CatS alone is sufficient to fully reverse allodynia following peripheral nerve injury and suggest that the mechanism of action likely involves interruption of T-cell activation and peripheral cytokine release. In addition, they provide important insights toward the development of selective CatS inhibitors for the treatment of neuropathic pain in humans.

Establishment of Peritoneal and Hepatic Metastasis Mouse Xenograft Models Using Gastric Cancer Cell Lines

BACKGROUND/AIM

Establishment of mouse xenograft models is necessary for oncological research and depends on the characteristics of the cell lines and the immune system of the host. In this study, we describe the development of mouse xenograft models using human gastric cancer (GC) cell lines.

MATERIALS AND METHODS

MKN1 stably-expressing luciferase (MKN1-Luc), N87, KATO III, MKN45 stably-expressing luciferase (MKN45-Luc), NUGC4, and OCUM-1 human GC cell lines were injected intraperitoneally into mice to establish peritoneal metastasis models. MKN45-Luc were injected into subcutaneously implanted spleen, and MKN1-Luc and MKN45-Luc were injected directly into the portal veins of mice for the establishment of hepatic metastasis models.

RESULTS

Peritoneal metastasis was formed after implantation of MKN1-Luc, N87, KATO III, MKN45-Luc, and NUGC4 in nude mice, but not formed in OCUM-1 even in NOD/SCID mice. After intrasplenic injection of MKN45-Luc, we found no hepatic metastasis formation. We identified hepatic metastasis formation after direct injection of MKN45-Luc and MKN1-Luc into the portal veins of NOD/SCID mice.

CONCLUSION

Peritoneal and hepatic metastasis mouse xenograft models were successfully established using several human GC cell lines.

N-Glycosylation of Seasonal Influenza Vaccine Hemagglutinins: Implication for Potency Testing and Immune Processing

Prior to each annual flu season, health authorities recommend three or four virus strains for inclusion in the annual influenza vaccine: a type A:H1N1 virus, a type A:H3N2 virus, and one or two type B viruses. Antigenic differences between strains are found in the glycosylation patterns of the major influenza virus antigen, hemagglutinin (HA). Here we examine the glycosylation patterns of seven reference antigens containing HA used in influenza vaccine potency testing. These reagents are supplied by the Center for Biologics Evaluation and Research (CBER) or the National Institute for Biological Standards and Control (NIBSC) for use in vaccine testing. Those produced in hen egg, Madin-Darby canine kidney (MDCK), and insect (Sf9) expression systems were examined. They are closely related or identical to antigens used in commercial vaccines. The reference antigens studied were used in the 2014-2015 influenza season and included A/California/07/2009 H1N1, A/Texas/50/2012 H3N2, and B/Massachusetts/02/2012. Released glycan and HA-specific glycopeptide glycosylation patterns were examined. We also examined the sensitivity of the single radial immunodiffusion (SRID) potency test to differences in HA antigen glycosylation. Based on deglycosylation studies applied using standard assay procedures, the SRID assay was not sensitive to any HA antigen glycosylation status from any cell system. Mapping of glycosites with their occupying glycan to functional regions, including antigenic sites, lectin interaction regions, and fusion domains, was performed and has implications for immune processing, immune responses, and antigenic shielding. Differences in glycosylation patterns, as dictated by the cell system used for expression, may impact these functions.IMPORTANCE In the present study, the glycosylation patterns of the 2014-2015 influenza vaccine season standard antigens A/California/07/2009 H1N1, A/Texas/50/2012 H3N2, and B/Massachusetts/02/2012 were revealed, and the sensitivity of the single radial immunodiffusion (SRID) potency test to glycosylation was tested. Differences in hemagglutinin glycosylation site composition and heterogeneity seen in antigens produced in different cell substrates suggest differences in processing and downstream immune responses. The SRID potency test used for vaccine release is not sensitive to differences in glycosylation under standard use conditions. This work reveals important differences in vaccine antigens and may point out areas where improvements may be made concerning vaccine antigen preparation, immune processing, and testing.

Class II transactivator knockdown limits major histocompatibility complex II expression, diminishes immune rejection, and improves survival of allogeneic bone marrow stem cells in the infarcted heart

This study was performed to investigate how to overcome immunorejection associated with allogeneic stem cell therapy in the infarcted heart. Allogeneic bone marrow mesenchymal stem cell (MSC) differentiation increases major histocompatibility complex II (MHC II) expression, inducing transition from immunoprivileged to immunogenic phenotype. MHC II expression is regulated by the class II transactivator (CIITA). We isolated and characterized mouse and human MSCs and knocked down CIITA expression. Wild-type (WT) or CIITA-knockout (CIITA(-)) mouse MSCs were implanted into infarcted mouse myocardia, and recipient allo-antibody formation, cell survival, and cardiac function were measured. WT mouse and human MSCs that were myogenically differentiated showed increased MHC II and CIITA expression. Differentiated CIITA(-) MSCs lacked MHC II induction and showed reduced cytotoxicity in allogeneic leukocyte coculture. Differentiation of human MSCs increased MHC II expression, which resulted in cytotoxicity in allogeneic leukocyte coculture and was prevented by CIITA small interfering RNA. In contrast to WT MSCs, CIITA(-) MSCs did not initiate recipient allo-antibody formation and instead survived in the injured myocardium and significantly improved ventricular function. Decreasing CIITA expression in allogeneic MSCs abolished MHC II induction during myogenic differentiation and prevented immunorejection of these cells from the infarcted myocardium, which enhanced beneficial functional effects of MSC implantation on myocardial repair.-Huang, X.-P., Ludke, A., Dhingra, S., Guo, J., Sun, Z., Zhang, L., Weisel, R. D., Li, R.-K. Class II transactivator knockdown limits major histocompatibility complex II expression, diminishes immune rejection, and improves survival of allogeneic bone marrow stem cells in the infarcted heart.

Genome-wide identification and transcript profile of the whole cathepsin superfamily in the intertidal copepod Tigriopus japonicus

Modulation of expression of cathepsins in innate immune response has previously been reported in mollusks and large crustaceans including crabs, lobsters, and shrimps in response to immune challenges. However, similar responses in copepods and the related cathepsin members remain under-investigated. To understand molecular and innate immune responses in the intertidal copepod Tigriopus japonicus, we identified the full spectra of cathepsin members (2 aspartyl proteases, 18 cysteine proteases, and 4 serine proteases) and also analyzed transcriptional expression of cathepsin (Tj-cathepsin) genes in developmental stages, lipopolysaccharide (LPS)- and two Vibrio species-exposed T. japonicus. The transcriptional levels of most Tj-cathepsin genes were highly increased during the molting transition from the nauplius to the copepodid stages. LPS treatment induced innate immune response via significant transcriptional increase of serine cathepsin (e.g., cathepsin As) members with induction of several cysteine cathepsin genes. However, Tj-aspartyl cathepsin E-like and a novel cysteine cathepsin were slightly reduced in response to LPS exposure. Interestingly, Vibrio species showed very low transcriptional sensitivity in the expression of entire cathepsins, while LPS induced several cathepsin gene-involved primitive immune responses in T. japonicus. In this paper, we discuss how whole cathepsin expression profiling can be linked to host defense mechanism to better understand and uncover the underlying mechanism of copepods' innate immunity.

Identification of a nuclear export sequence in the MHC CIITA

Initiation of an immune response through expression of MHC class II and related genes is under the control of the CIITA. Normally found in both the cytoplasm and nucleus, CIITA is tightly controlled by a variety of posttranslational modifications as well as interactions with other nuclear and cytoplasmic factors, whereas disruption of this dual subcellular localization impairs CIITA functioning and expression of target genes. Although CIITA has well-defined domains necessary for its nuclear import, the region responsible for the translocation of CIITA from the nucleus has not been characterized. In this study, we identify a leucine-rich motif at residues 717-724 that bears strong homology to known nuclear export sequence (NES) domains. Mutation of this region renders CIITA insensitive to treatment with leptomycin B, an inhibitor of nuclear export, whereas fusion of this domain to a heterologous GFP is sufficient to induce its export to the cytoplasm or cause its retention in the nucleus following leptomycin B treatment. Point mutations of specific leucine residues within the NES disrupt the normal subcellular distribution of the full-length CIITA, impair its ability to interact with the nuclear export factor CRM1, and enhance CIITA-induced gene expression from an MHC class II gene promoter. IFN-γ stimulation of class II genes is further enhanced by inhibiting the nuclear export of endogenous CIITA. Collectively, these data demonstrate the first identification of a specific NES within CIITA and place it among the other protein domains that contribute to the posttranslational regulation of CIITA activity.

Epigenome-wide differences in pathology-free regions of multiple sclerosis-affected brains

Using the Illumina 450K array and a stringent statistical analysis with age and gender correction, we report genome-wide differences in DNA methylation between pathology-free regions derived from human multiple sclerosis-affected and control brains. Differences were subtle, but widespread and reproducible in an independent validation cohort. The transcriptional consequences of differential DNA methylation were further defined by genome-wide RNA-sequencing analysis and validated in two independent cohorts. Genes regulating oligodendrocyte survival, such as BCL2L2 and NDRG1, were hypermethylated and expressed at lower levels in multiple sclerosis-affected brains than in controls, while genes related to proteolytic processing (for example, LGMN, CTSZ) were hypomethylated and expressed at higher levels. These results were not due to differences in cellular composition between multiple sclerosis and controls. Thus, epigenomic changes in genes affecting oligodendrocyte susceptibility to damage are detected in pathology-free areas of multiple sclerosis-affected brains.

Retrovirus entry by endocytosis and cathepsin proteases

Retroviruses include infectious agents inducing severe diseases in humans and animals. In addition, retroviruses are widely used as tools to transfer genes of interest to target cells. Understanding the entry mechanism of retroviruses contributes to developments of novel therapeutic approaches against retrovirus-induced diseases and efficient exploitation of retroviral vectors. Entry of enveloped viruses into host cell cytoplasm is achieved by fusion between the viral envelope and host cell membranes at either the cell surface or intracellular vesicles. Many animal retroviruses enter host cells through endosomes and require endosome acidification. Ecotropic murine leukemia virus entry requires cathepsin proteases activated by the endosome acidification. CD4-dependent human immunodeficiency virus (HIV) infection is thought to occur via endosomes, but endosome acidification is not necessary for the entry whereas entry of CD4-independent HIVs, which are thought to be prototypes of CD4-dependent viruses, is low pH dependent. There are several controversial results on the retroviral entry pathways. Because endocytosis and endosome acidification are complicatedly controlled by cellular mechanisms, the retrovirus entry pathways may be different in different cell lines.

Identification of putative cathepsin S in mangrove red snapper Lutjanus argentimaculatus and its role in antigen presentation

Cathepsin S (CTSS) is a key enzyme employed in the histocompatibility complex (MHC) class II-restricted antigens, which are presented by processing class II-associated invariant chains and loaded antigen peptides into class II molecules. To date, little is known about the character and function of CTSS in fish. In the present study, we screened and identified a CTSS cDNA sequence from the mangrove red snapper head kidney cDNA library. The full-length CTSS cDNA contained 1339-bp nucleotide acids encoding 337 amino acids. The sequence shared high identity and similarity with other known cathepsins, especially CTSS (about 56-78% and 79-89%, respectively). Like other cathepsins, the deduced peptide consisted of regions with N-terminal signal peptides, propeptides, and mature peptides. A typical ERWNIN motif in L-like cathepsins and three conservative catalytic activity sites forming a catalytic triad active center were respectively identified in the pro-peptide and mature peptide regions of CTSS. Phylogenetic analysis revealed that mangrove red snapper CTSS was located in the CTSS clade belonging to the L-like cathepsin group, and evolved from the same ancestry. To further characterize the biological activity of the putative CTSS of mangrove snapper, CTSS was expressed in Escherichia coli M15 strains. Like other mammalian CTSS, the recombinant CTSS (rCTSS) had autocatalytic activation properties, can remove pro-peptides, and can release active mature peptides. Active CTSS had the ability to catalyze Z-Phe-Arg-AMC substrates in acidic conditions (pH 5.0) and weak alkaline environments (pH 7.5); this activity could be blocked by the cysteine protease inhibitor E-64. Active CTSS can process recombinant Ii chains (invariant chains) in a stepwise manner in vitro. The results indicate that mangrove red snapper CTSS is a lysosomal cysteine protease family member with a key role in antigen processing in fish.

Shark class II invariant chain reveals ancient conserved relationships with cathepsins and MHC class II

The invariant chain (Ii) is the critical third chain required for the MHC class II heterodimer to be properly guided through the cell, loaded with peptide, and expressed on the surface of antigen presenting cells. Here, we report the isolation of the nurse shark Ii gene, and the comparative analysis of Ii splice variants, expression, genomic organization, predicted structure, and function throughout vertebrate evolution. Alternative splicing to yield Ii with and without the putative protease-protective, thyroglobulin-like domain is as ancient as the MHC-based adaptive immune system, as our analyses in shark and lizard further show conservation of this mechanism in all vertebrate classes except bony fish. Remarkable coordinate expression of Ii and class II was found in shark tissues. Conserved Ii residues and cathepsin L orthologs suggest their long co-evolution in the antigen presentation pathway, and genomic analyses suggest 450 million years of conserved Ii exon/intron structure. Other than an extended linker preceding the thyroglobulin-like domain in cartilaginous fish, the Ii gene and protein are predicted to have largely similar physiology from shark to man. Duplicated Ii genes found only in teleosts appear to have become sub-functionalized, as one form is predicted to play the same role as that mediated by Ii mRNA alternative splicing in all other vertebrate classes. No Ii homologs or potential ancestors of any of the functional Ii domains were found in the jawless fish or lower chordates.

Clinical utility of serum autoantibodies detected by protein microarray in melanoma

Better prognostic and predictive markers in melanoma are needed to select patients for therapy. We utilized a dual-lectin affinity chromatography and a natural protein microarray-based analysis to select a subproteome of target glycoproteins to profile serum antibodies against melanoma associated antigens that may predict nodal positivity. We identified 5 melanoma-associated antigens using this microarray coupled to mass spectrometry; GRP75, GRP94, ASAH1, CTSD and LDHB. We evaluated their predictive value for nodal status adjusting for age, gender, Breslow thickness, mitotic rate and ulceration using standard logistic regression. After adjustment, ASAH1, CTSD and LDHB were significantly negatively associated with nodal status (P = 0.0008) and GRP94 was significantly positively associated (P = 0.014). Our best multivariate model for nodal positivity included Breslow thickness, presence of serum anti-ASAH1, anti-LDHB or anti-CTSD, and presence of serum anti-GRP94, with an area under the ROC curve of 0.869. If validated, these results show promise for selecting clinically node negative patients for SLN biopsy. In addition, there is strong potential for glycoprotein microarray to screen serum autoantibodies that may identify patients at high risk of distant metastases or those likely or unlikely to respond to treatment, and these proteins may serve as targets for intervention.

Azepanone-based inhibitors of human cathepsin S: optimization of selectivity via the P2 substituent

A series of azepanone inhibitors of cathepsin S is described. Selectivity over both cathepsin K and cathepsin L was achieved by varying the P2 substituent. Ultimately, a balanced potency and selectivity profile was achieved in compound 39 possessing a 1-methylcyclohexyl alanine at P2 and nicotinamide as the P' substituent. The cellular potency of selected analogs is also described.

Processing and presentation of (pro)-insulin in the MHC class II pathway: the generation of antigen-based immunomodulators in the context of type 1 diabetes mellitus

Both CD4(+) and CD8(+) T lymphocytes play a crucial role in the autoimmune process leading to T1D. Dendritic cells take up foreign antigens and autoantigens; within their endocytic compartments, proteases degrade exogenous antigens for subsequent presentation to CD4(+) T cells via MHC class II molecules. A detailed understanding of autoantigen processing and the identification of autoantigenic T cell epitopes are crucial for the development of antigen-based specific immunomodulators. APL are peptide analogues of auto-immunodominant T cell epitopes that bind to MHC class II molecules and can mediate T cell activation. However, APL can be rapidly degraded by proteases occurring in the extracellular space and inside cells, substantially weakening their efficiency. By contrast, protease-resistant APL function as specific immunomodulators and can be used at low doses to examine the functional plasticity of T cells and to potentially interfere with autoimmune responses. Here, we review the latest achievements in (pro)-insulin processing in the MHC class II pathway and the generation of APL to mitigate autoreactive T cells and to activate Treg cells.

MHC class II epitope predictive algorithms

SUMMARY

Major histocompatibility complex class II (MHC-II) molecules sample peptides from the extracellular space, allowing the immune system to detect the presence of foreign microbes from this compartment. To be able to predict the immune response to given pathogens, a number of methods have been developed to predict peptide-MHC binding. However, few methods other than the pioneering TEPITOPE/ProPred method have been developed for MHC-II. Despite recent progress in method development, the predictive performance for MHC-II remains significantly lower than what can be obtained for MHC-I. One reason for this is that the MHC-II molecule is open at both ends allowing binding of peptides extending out of the groove. The binding core of MHC-II-bound peptides is therefore not known a priori and the binding motif is hence not readily discernible. Recent progress has been obtained by including the flanking residues in the predictions. All attempts to make ab initio predictions based on protein structure have failed to reach predictive performances similar to those that can be obtained by data-driven methods. Thousands of different MHC-II alleles exist in humans. Recently developed pan-specific methods have been able to make reasonably accurate predictions for alleles that were not included in the training data. These methods can be used to define supertypes (clusters) of MHC-II alleles where alleles within each supertype have similar binding specificities. Furthermore, the pan-specific methods have been used to make a graphical atlas such as the MHCMotifviewer, which allows for visual comparison of specificities of different alleles.

The Story So Far:Helicobacter Pyloriand Gastric Autoimmunity

The gastric mucosal pathogen Helicobacter pylori induces autoantibodies directed against the gastric proton pump H+,K+-ATPase in 20-30% of infected patients. The presence of these autoantibodies is associated with severity of gastritis, increased atrophy, and apoptosis in the corpus mucosa, and patients with these autoantibodies infected with H. pylori display histopathological and clinical features that are similar to those of autoimmune gastritis (AIG). This review will focus on the T helper cell responses, cytokines, and adhesion molecules involved in corpus mucosal atrophy in chronic H. pylori gastritis and in AIG, and the role of H. pylori in the onset of AIG.

Peptidomimetic 2-cyanopyrrolidines as potent selective cathepsin L inhibitors

Cathepsins have been found to have important physiological roles. The implication of cathepsin L in various types of cancers is well established. In a search for selective cathepsin L inhibitors as anticancer agents, a series of 2-cyanoprrolidine peptidomimetics, carrying a nitrile group as warhead, were designed. Two series of compounds, one with a benzyl moiety and a second with an isobutyl moiety at P(2) position of the enzyme were synthesized. The synthesized compounds were evaluated for inhibitory activity against human cathepsin L and cathepsin B. Although, none of the compounds showed promising inhibitory activity, (E)N-{(S)1-[(S)2-cyano-1-pyrrolidinecarbonyl]-3-methylbutyl}-2,3-diphenylacrylamide (24) with an isobutyl moiety at P(2) was found to show selectivity as a cathepsin L inhibitor (Ki 5.3 microM for cathepsin L and Ki > 100 microM for cathepsin B). This compound could act as a new lead for the further development of improved inhibitors within this inhibitor type.

Dominance of an alternative CLIP sequence in the celiac disease associated HLA-DQ2 molecule

During assembly, HLA class II molecules associate with the invariant chain. As the result, the peptide-binding groove is occupied by an invariant chain peptide termed CLIP (class-II-associated invariant chain peptide; sequence MRMATPLLM). By mass spectrometry, we have now characterized peptides that are naturally present in HLA-DQ2. This analysis revealed that 22 variants of Ii-derived peptides are associated with HLA-DQ2. Strikingly, the large majority of those do not contain the conventional CLIP sequence MRMATPLLM, but instead a peptide that partially overlaps with CLIP, sequence TPLLMQALPM. Peptide binding studies indicate that this alternative CLIP peptide has superior HLA-DQ2 binding properties compared to the conventional CLIP and that the minimal nine-amino-acid binding core consists of the sequence PLLMQALPM, findings that could be corroborated by molecular simulation. The alternative CLIP peptide was also found to be present in HLA-DQ2 molecules isolated from human thymus. Moreover, the alternative CLIP peptide was also found in association with HLA-DQ8. Together, these results indicate that HLA-DQ2 and HLA-DQ8 associate with an alternative CLIP sequence, a property that may relate to the strong association between HLA-DQ molecules and human autoimmune diseases.

A study on serum IgE and clinical symptomatology of atopy in patients suffering from the lysosomal storage disorder Fabry disease

BACKGROUND

Lysosomal storage disorders may impair intracellular lysosomal processing of antigen with consequences for antibody production [e.g. immunoglobulin E (IgE)] and atopic disease status.

AIMS

Serum concentration of total IgE as well as clinical symptoms of atopic disorders as an indirect consequence of lysosomal impairment of antigen processing were studied in male and female Fabry disease (FD) patients with and without replacement of the missing lysosomal enzyme, alpha-galactosidase A (alpha-Gal A).

METHODS

Observational study in 31 adult FD patients with measurements of total serum IgE concentration. Questionnaire-derived data were obtained for atopic eczema (AE) skin lesions, allergic rhinoconjunctivitis (RCA) and allergic asthma (AA) at present or in the past.

RESULTS

Among 12 FD males under enzyme replacement therapy (ERT), 2 showed total IgE concentrations above 100 kU/L. Clinical symptoms for AA were found in 2, RCA and AE in 1, respectively. Among 10 FD females under ERT, 4 showed total IgE concentrations above 100 kU/L. Clinical symptoms for AA were found in 4, RCA in 2 and AE in 2. Among 9 females without ERT, 2 showed total IgE concentrations above 100 kU/L. Clinical symptoms for AA were found in 2, RCA in 2 and AE in none.

CONCLUSIONS

FD patients may demonstrate an increased total serum IgE concentration and may show symptoms of atopic disorders (AA, RCA, AE) in a prevalence rate comparable to international experience for individuals without FD. There was no difference between patients with and without ERT. Lack of detection of AE in females without ERT is suggested to be caused by the small sample size. FD patients without any alpha-Gal A activity prior to initiation of ERT should be in the focus of future studies.

Immune system irregularities in lysosomal storage disorders

Lysosomal storage disorders (LSDs) are genetically inherited diseases characterized by the accumulation of disease-specific biological materials such as proteolipids or metabolic intermediates within the lysosome. The lysosomal compartment's central importance to normal cellular function can be appreciated by examining the various pathologies that arise in LSDs. These disorders are invariably fatal, and many display profound neurological impairment that begins in childhood. However, recent studies have revealed that several LSDs also have irregularities in the function of the immune system. Gaucher disease, mucopolysaccharidosis VII, and alpha-mannosidosis are examples of a subset of LSD patients that are predisposed towards immune suppression. In contrast, GM2 gangliosidosis, globoid cell leukodystrophy, Niemann-Pick disease type C1 and juvenile neuronal ceroid lipofuscinosis are LSDs that are predisposed towards immune system hyperactivity. Antigen presentation and processing by dedicated antigen presenting cells (APCs), secretion of pore-forming perforins by cytotoxic-T lymphocytes, and release of pro-inflammatory mediators by mast cells are among the many crucial immune system functions in which the lysosome plays a central role. Although the relationship between the modification of the lysosomal compartment in LSDs and modulation of the immune system remains unknown, there is emerging evidence for early neuroimmune responses in a variety of LSDs. In this review we bridge biochemical studies on the lysosomal compartment's role in the immune system with clinical data on immune system irregularities in a subset of LSDs.

T cell responses in melanoma patients after vaccination with tumor-mRNA transfected dendritic cells

We have developed an individualized melanoma vaccine based on autologous dendritic cells (DCs) transfected with autologous tumor-mRNA. The vaccine targets the unique spectrum of tumor antigens in each patient and may recruit multiple T cell clones. In a recent phase I/II trial, we demonstrated T cell responses against vaccine antigens in 9/19 patients evaluable by T cell assays. Here, we report a follow-up study that was conducted to characterize interesting T cell responses and to investigate the effects of long-term booster vaccination. Two patients were selected for continued vaccine therapy. The clinical follow-up suggested a favorable clinical development in both patients. The immunological data (T cell proliferation/IFNgamma ELISPOT/Bioplex cytokine assays) indicated sustained T cell responses and suggested an enhancing effect of booster vaccinations. Both CD4(+) and CD8(+) T cell responses were demonstrated. From post-vaccination samples, we generated 39 T cell clones that responded specifically to stimulation by mRNA-transfected DCs and 12 clones that responded to mock-transfected DCs. These data clearly indicate a two-component vaccine response, against transfected and non-transfected antigens. T cell receptor (TCR) clonotype mapping, performed on 11 tDC-specific clones, demonstrated that 10/11 clones had different TCRs. The results thus indicate a broad spectrum T cell response against antigens encoded by the transfected tumor-mRNA. We generally observed mixed Th1/Th2 cytokine profiles, even in T cell clones that were confirmed to be derived from a single cell. This finding suggests that cytokine patterns after cancer vaccination may be more complex than indicated by the classic Th1/Th2 dichotomy.

Identification of a novel class of succinyl-nitrile-based Cathepsin S inhibitors

The synthesis and in vitro activities of a series of succinyl-nitrile-based inhibitors of Cathepsin S are described. Several members of this class show nanomolar inhibition of the target enzyme as well as cellular potency. The inhibitors displaying the greatest potency contain N-alkyl substituted piperidine and pyrrolidine rings spiro-fused to the alpha-carbon of the P1 residue.

Interferon-gamma regulates cathepsin G activity in microglia-derived lysosomes and controls the proteolytic processing of myelin basic protein in vitro

The serine protease cathepsin (Cat) G dominates the proteolytic processing of the multiple sclerosis (MS)-associated autoantigen myelin basic protein (MBP) in lysosomes from primary human B cells and dendritic cells. This is in contrast to B-lymphoblastoid cell lines, where the asparagine endopeptidase (AEP) is responsible for this task. We have analysed microglia-derived lysosomal proteases for their ability to process MBP in vitro. In lysosomes derived from primary murine microglia, CatD, CatS, AEP and CatG were involved in the processing of MBP. Interestingly, when microglia were treated with interferon-gamma to mimic a T helper type 1-biased cytokine milieu in MS, CatG was drastically down-regulated, in contrast to CatS, CatB, CatL, CatD or AEP. This resulted in significantly increased stability of MBP and a selective lack of CatG-derived proteolytic fragments; however, it did not affect the gross pattern of MBP processing. Inhibition of serine proteases eliminated the processing differences between lysosomal extracts from resting microglia compared to interferon-stimulated microglia. Thus, the cytokine environment modulates lysosomal proteases in microglia by a selective down-regulation of CatG, leading to decreased MBP-processing by microglia-derived lysosomal proteases in vitro.

An orally active reversible inhibitor of cathepsin S inhibits human trans vivo delayed-type hypersensitivity

Cathepsin S is a major histocompatibility complex (MHC) class II associated invariant chain (Ii) degrading enzyme expressed in antigen presenting cells such as B cells and dendritic cells. This enzyme is essential for MHC class II associated antigen processing and presentation to CD4(+) T cells. Compound I, a selective, reversible and orally bioavailable, inhibitor of cathepsin S, with molecular IC(50)=9 nM, has been recently described. We have tested the effects of compound I in a trans vivo model of delayed-type hypersensitivity. Human peripheral blood mononuclear cells (7-10 x 10(6)) from tetanus-sensitized donors were co-injected with tetanus toxoid (0.25 Lf) into C57Bl/6 mouse footpads. At 24 h, significant footpad swelling (+0.024+/-0.001 cm) characterized by an influx of mouse neutrophils and monocytes was observed. Injection of peripheral blood mononuclear cells alone caused negligible swelling (0.002+/-0.0002 cm). Anti-human MHC class II (HLA-DR, DP, DQ) antibody (5 mg/kg, i.p.) inhibited the swelling 91+/-7%, thus demonstrating a role of human antigen presenting cells in this model. Compound I (10, 30, and 100 mg/kg, p.o.) inhibited the response with an ED50 of approximately 18 mg/kg. Compound III, a less active analogue (molecular IC50>20 microM) had no effect. Furthermore, pretreatment of peripheral blood mononuclear cells with 10 nM compound II, an irreversible inhibitor (molecular IC50=11 nM) inhibited swelling 87+/-4%. These findings support the role of cathepsin S in human delayed-type hypersensitivity. Inhibition of cathepsin S with compound I may be useful in the treatment of human autoimmune diseases like rheumatoid arthritis and multiple sclerosis.

Viral strategies for evading antiviral cellular immune responses of the host

The host invariably responds to infecting viruses by activating its innate immune system and mounting virus-specific humoral and cellular immune responses. These responses are aimed at controlling viral replication and eliminating the infecting virus from the host. However, viruses have evolved numerous strategies to counter and evade host's antiviral responses. Providing specific examples from the published literature, we discuss in this review article various strategies that viruses have developed to evade antiviral cellular responses of the host. Unraveling these viral strategies allows a better understanding of the host-pathogen interactions and their coevolution. This knowledge is important for identifying novel molecular targets for developing antiviral reagents. Finally, it may also help devise new knowledge-based strategies for developing antiviral vaccines.

Compartmentalization of class II antigen presentation: contribution of cytoplasmic and endosomal processing

During antigen processing, peptides are generated and displayed in the context of major histocompatibility complex (MHC) class II molecules on the surface of antigen-presenting cells (APCs) to modulate immune responses to foreign antigens and guide self-tolerance. Exogenous and cytoplasmic antigens are processed by distinct routes within APCs to yield class II ligands. Exogenous antigens are internalized, processed, and bound to class II molecules within endosomal and lysosomal compartments of APCs. Studies reviewed here demonstrate the importance of reduction in regulating exogenous antigen presentation. The differential expression of a gamma-interferon-inducible lysosomal thiol reductase in professional APCs and melanomas is discussed in the context of tumor immune evasion. Cytoplasmic autoantigens, by contrast, are degraded by the proteasome and other enzymes in the cytosol, with the resulting peptides translocating to endosomal and lysosomal compartments for intersection with class II molecules. Processing and editing of these antigenic peptides within endosomes and lysosomes may be critical in regulating their display via class II proteins. Multiple pathways may regulate the transit of cytosolic peptides to class II molecules. The role of lysosome-associated membrane protein-2a and heat-shock cognate protein 70 in promoting cytoplasmic peptide presentation by MHC class II molecules is discussed.

Endosomal proteolysis of insulin-like growth factor-I at its C-terminal D-domain by cathepsin B

IGF-I is degraded within the endosomal apparatus as a consequence of receptor-mediated endocytosis. However, the nature of the responsible protease and the position of the cleavage sites in the IGF-I molecule remain undefined. In vitro proteolysis of IGF-I using an endosomal lysate required an acidic pH and was sensitive to CA074, an inhibitor of the cathepsin B enzyme. By nondenaturing immunoprecipitation, the acidic IGF-I-degrading activity was attributed to the luminal species of endosomal cathepsin B with apparent molecular masses of 32- and 28-kDa. The cathepsin B precursor, procathepsin B, was processed in vitro within isolated endosomes at pH 5 or at 7 in the presence of ATP, the substrate of the vacuolar H(+)-ATPase. The rate of IGF-I hydrolysis using an endosomal lysate or pure cathepsin B was found to be optimal at pH 5-6 and moderate at pH 4 and 7. Competition studies revealed that EGF and IGF-I share a common binding site on the cathepsin B enzyme, with native IGF-I displaying the lowest affinity for the protease (IC50 approximately 1.5 microM). Hydrolysates of IGF-I generated at low pH by endosomal IGF-I-degrading activity and analyzed by reverse-phase HPLC and mass spectrometry revealed cleavage sites at Lys68-Ser69, Ala67-Lys68, Pro66-Ala67 and Lys65-Pro66 within the C-terminal D-domain of IGF-I. Treatment of human HepG2 hepatoma cells with the cathepsin B proinhibitor CA074-Me reduced, in vivo, the intracellular degradation of internalized [125I]IGF-I and, in vitro, the degradation of exogenous [125I]IGF-I incubated with the cell-lysates at pH 5. Inhibitors of cathepsin B and pro-cathepsin B processing, which abolish endosomal proteolysis of IGF-I and alter tumor cell growth and IGF-I receptor signalling, merit investigation as antimetastatic drugs.

The nipah virus fusion protein is cleaved within the endosomal compartment

Nipah virus (NiV) is a recently emerged and highly pathogenic paramyxovirus that causes a systemic infection in animals and humans and can infect a wide range of cultured cells. Interestingly, the NiV fusion (F) protein has a single arginine at the cleavage site similar to paramyxoviruses that are activated by exogenous trypsin-like enzymes only present in specific cells and tissues and therefore only cause localized infections. We show here that NiV F activation is not mediated by an exogenous serum protease but by an endogenous ubiquitous cellular protease after endocytosis of the protein. In addition to endocytosis, acidification of the endosome is a prerequisite for F cleavage. These results show that activation of the NiV F protein depends on a type of proteolytic cleavage that is clearly different from what is known for other paramyxoviral and orthomyxoviral fusion proteins. To our knowledge, this is the first example of a viral class I fusion protein whose activation depends on clathrin-mediated constitutive endocytosis.

Antibodies generated by a novel DNA vaccination identify the MHC class III encoded BAT2 polypeptide

Recombinant vaccines containing Ii sequences were employed to elicit an antibody response. Gene gun immunisation of mice with the recombinant Ii-antigen-encoding vectors induced antigen-specific antibodies. Antibody levels were substantially elevated when the DNA construct was extended by a sequence encoding the protease inhibitory domain of the invariant chain isoform Ii41. Employing this approach, we raised antibodies specific for a novel MHC class III encoded protein. The antibodies identify the 216 kDa BAT2 polypeptide. Immunostaining of embryonic tissue sections showed specific expression, especially in central nervous tissue, and suggests BAT2 as a novel differentiation marker.

Presentation of Endogenously Synthesized MHC Class II-Restricted Epitopes by MHC Class II Cancer Vaccines Is Independent of Transporter Associated with Ag Processing and the Proteasome

Cell-based vaccines consisting of invariant chain-negative tumor cells transfected with syngeneic MHC class II (MHC II) and costimulatory molecule genes are prophylactic and therapeutic agents for the treatment of murine primary and metastatic cancers. Vaccine efficacy is due to direct presentation of endogenously synthesized, MHC II-restricted tumor peptides to CD4+ T cells. Because the vaccine cells lack invariant chain, we have hypothesized that, unlike professional APC, the peptide-binding groove of newly synthesized MHC II molecules may be accessible to peptides, allowing newly synthesized MHC II molecules to bind peptides that have been generated in the proteasome and transported into the endoplasmic reticulum via the TAP complex. To test this hypothesis, we have compared the Ag presentation activity of multiple clones of TAP-negative and TAP-positive tumor cells transfected with I-Ak genes and the model Ag hen egg white lysozyme targeted to the endoplasmic reticulum or cytoplasm. Absence of TAP does not diminish Ag presentation of three hen egg white lysozyme epitopes. Likewise, cells treated with proteasomal and autophagy inhibitors are as effective APC as untreated cells. In contrast, drugs that block endosome function significantly inhibit Ag presentation. Coculture experiments demonstrate that the vaccine cells do not release endogenously synthesized molecules that are subsequently endocytosed and processed in endosomal compartments. Collectively, these data indicate that vaccine cell presentation of MHC II-restricted endogenously synthesized epitopes occurs via a mechanism independent of the proteasome and TAP complex, and uses a pathway that overlaps with the classical endosomal pathway for presentation of exogenously synthesized molecules.

Proteinases participating in the processing and activation of prolegumain in primary cultured rat macrophages

The mammalian legumain is a recently identified lysosomal cysteine proteinase belonging to the clan CD and homologous to plant legumain. This enzyme has the characteristic of specifically hydrolyzing peptide bonds after asparagine residues. As in the case of papain-type cysteine proteinases, legumain is synthesized as an inactive zymogen, and processed into a mature form localized in lysosomes. However, the mechanism of its activation remains unclear. In this study, we analyze which types of proteinases may participate in the processing of legumain in rat primary cultured macrophages using various proteinase inhibitors after 24 h treatment with Bafilomycin A1, a vacuolar ATPase inhibitor. The processing of legumain in macrophages was accomplished by papain-type cysteine proteinases other than cathepsin B.

Cathepsin G, and Not the Asparagine-Specific Endoprotease, Controls the Processing of Myelin Basic Protein in Lysosomes from Human B Lymphocytes

The asparagine-specific endoprotease (AEP) controls lysosomal processing of the potential autoantigen myelin basic protein (MBP) by human B lymphoblastoid cells, a feature implicated in the immunopathogenesis of multiple sclerosis. In this study, we demonstrate that freshly isolated human B lymphocytes lack significant AEP activity and that cleavage by AEP is dispensable for proteolytic processing of MBP in this type of cell. Instead, cathepsin (Cat) G, a serine protease that is not endogenously synthesized by B lymphocytes, is internalized from the plasma membrane and present in lysosomes from human B cells where it represents a major functional constituent of the proteolytic machinery. CatG initialized and dominated the destruction of intact MBP by B cell-derived lysosomal extracts, degrading the immunodominant MBP epitope and eliminating both its binding to MHC class II and a MBP-specific T cell response. Degradation of intact MBP by CatG was not restricted to a lysosomal environment, but was also performed by soluble CatG. Thus, the abundant protease CatG might participate in eliminating the immunodominant determinant of MBP. Internalization of exogenous CatG represents a novel mechanism of professional APC to acquire functionally dominant proteolytic activity that complements the panel of endogenous lysosomal enzymes.

Human B lymphoblastoid cells contain distinct patterns of cathepsin activity in endocytic compartments and regulate MHC class II transport in a cathepsin S-independent manner

Endocytic proteolysis represents a major functional component of the major histocompatibility complex class II antigen-presentation machinery. Although transport and assembly of class II molecules in the endocytic compartment are well characterized, we lack information about the pattern of endocytic protease activity along this pathway. Here, we used chemical tools that visualize endocytic proteases in an activity-dependent manner in combination with subcellular fractionation to dissect the subcellular distribution of the major cathepsins (Cat) CatS, CatB, CatH, CatD, CatC, and CatZ as well as the asparagine-specific endoprotease (AEP) in human B-lymphoblastoid cells (BLC). Endocytic proteases were distributed in two distinct patterns: CatB and CatZ were most prominent in early and late endosomes but absent from lysosomes, and CatH, CatS, CatD, CatC, and AEP distributed between late endosomes and lysosomes, suggesting that CatB and CatZ might be involved in the initial proteolytic attack on a given antigen. The entire spectrum of protease activity colocalized with human leukocyte antigen-DM and the C-terminal and N-terminal processing of invariant chain (Ii) in late endosomes. CatS was active in all endocytic compartments. Surprisingly and in contrast with results from dendritic cells, inhibition of CatS activity by leucine-homophenylalanine-vinylsulfone-phenol prevented N-terminal processing of Ii but did not alter the subcellular trafficking or surface delivery of class II complexes, as deferred from pulse-chase analysis in combination with subcellular fractionation and biotinylation of cell-surface protein. Thus, BLC contain distinct activity patterns of proteases in endocytic compartments and regulate the intracellular transport and surface-delivery of class II in a CatS-independent manner.

Identification of a Potent and Selective Noncovalent Cathepsin S Inhibitor

Cathepsin S is considered crucial for normal presentation of major histocompatibility complex (MHC) class II-restricted antigens by antigen presenting cells to CD4+ T cells. It is a key enzyme for the degradation of the class II-associated invariant chain, a process that is required for effective antigen loading of class II molecules. Here, we report a selective, orally available, high-affinity cathepsin S inhibitor, 1-[3-[4-(6-Chloro-2,3-dihydro-3-methyl-2-oxo-1H-benzimidazol-1-yl)-1-piperidinyl]propyl]-4,5,6,7-tetrahydro-5-(methylsulfonyl)-3-[4-(trifluoromethyl)phenyl]-1H-pyrazolo[4,3-c]pyridine. (JNJ 10329670), that represents a novel class of immunosuppressive compounds. JNJ 10329670 is a highly potent (Ki of approximately 30 nM), nonpeptidic, noncovalent inhibitor of human cathepsin S, but it is much less active against the mouse, dog, monkey, and bovine enzymes. The compound is inactive against other proteases, including the closely related cathepsins L, F, and K. This selectivity makes JNJ 10329670 an excellent tool for exploring the role of cathepsin S in human systems. Treatment of human B cell lines and primary human dendritic cells with JNJ 10329670 resulted in the accumulation of the p10 fragment of the invariant chain (IC50 of approximately 1 microM). In contrast, inhibition of invariant chain proteolysis was much less effective in a human monocytic cell line, suggesting that other enzymes may degrade the invariant chain in this cell type. JNJ 10329670 was shown to block the proteolysis of the invariant chain in vivo by using immunocompromised mice injected with human peripheral blood mononuclear cells (PBMCs). Furthermore, this inhibitor blocks the presentation of tetanus toxoid and giant ragweed by human PBMCs. The properties of JNJ 10329670 make it a candidate for immunosuppressive therapy of allergies and autoimmune diseases.

Enhanced immunogenicity of SIV Gag DNA vaccines encoding chimeric proteins containing a C-terminal segment of Listeriolysin O

We investigated the potential of the C-terminal 59-amino acid segment of Listeriolysin O (LLO) in enhancing immune responses against the SIV Gag antigen in the context of DNA immunization. Genes with codons optimized for mammalian expression were synthesized for the SIVmac239 Gag, a secreted SIV Gag protein with the tissue plasminogen antigen (tPA) signal fused to its N-terminus (tPA/Gag), as well as their corresponding chimeric proteins Gag/LLO and tPA/Gag/LLO containing the C-terminal 59 amino acids of LLO. Analysis of immune responses to these DNA constructs in a Balb/c mouse model showed that the Gag/LLO construct induced higher levels of both CD4 and CD8 T cell responses against SIV Gag, whereas the tPA/Gag construct induced higher levels of CD4 T cell responses. Moreover, immunization with the tPA/Gag/LLO construct further enhanced both CD4 and CD8 T cell responses. DNA constructs encoding secreted Gag proteins (tPA/Gag and tPA/Gag/LLO) were also more effective in eliciting antibody responses against SIV Gag. Our results demonstrate that the C-terminal segment of LLO can be effectively employed to enhance both cellular and humoral immune responses in the context of a DNA vaccine.

Thyrotropin-mediated repression of class II trans-activator expression in thyroid cells: involvement of STAT3 and suppressor of cytokine signaling

It has been suggested that class I and class II MHC are contributing factors for numerous diseases including autoimmune thyroid diseases, type 1 diabetes, rheumatoid arthritis, Alzheimer's disease, and multiple sclerosis. The class II trans-activator (CIITA), which is a non-DNA-binding regulator of class II MHC transcription, regulates the constitutive and inducible expression of the class I and class II genes. FRTL-5 thyroid cells incubated in the presence of IFN-gamma have a significantly higher level of cell surface rat MHC class II RTI.B. However, the IFN-gamma-induced RT1.B expression was suppressed significantly in cells incubated in the presence of thyrotropin. Thyrotropin (TSH) represses IFN-gamma-induced CIITA expression by inhibiting type IV CIITA promoter activity through the suppression of STAT1 activation and IFN regulatory factor 1 induction. This study found that TSH induces transcriptional activation of the STAT3 gene through the phosphorylation of STAT3 and CREB activation. TSH induces SOCS-1 and SOCS-3, and TSH-mediated SOCS-3 induction was dependent on STAT3. The cell line stably expressing the wild-type STAT3 showed a higher CIITA induction in response to IFN-gamma and also exhibited TSH repression of the IFN-gamma-mediated induction of CIITA. However, TSH repression of the IFN-gamma-induced CIITA expression was not observed in FRTL-5 thyroid cells, which stably expresses the dominant negative forms of STAT3, STAT3-Y705F, and STAT3-S727A. This report suggests that TSH is also engaged in immunomodulation through signal cross-talk with the cytokines in thyroid cells.

The E5 protein of human papillomavirus type 16 perturbs MHC class II antigen maturation in human foreskin keratinocytes treated with interferon-gamma

Major histocompatibility complex (MHC) class II antigens are expressed on human foreskin keratinocytes (HFKs) following exposure to interferon gamma. The expression of MHC class II proteins on the cell surface may allow keratinocytes to function as antigen-presenting cells and induce a subsequent immune response to virus infection. Invariant chain (Ii) is a chaperone protein which plays an important role in the maturation of MHC class II molecules. The sequential degradation of Ii within acidic endocytic compartments is a key process required for the successful loading of antigenic peptide onto MHC class II molecules. Since human papillomavirus (HPV) 16 E5 can inhibit the acidification of late endosomes in HFKs, the E5 protein may be able to affect proper peptide loading onto the MHC class II molecule. To test this hypothesis, HFKs were infected with either control virus or a recombinant virus expressing HPV16 E5 and the infected cells were subsequently treated with interferon-gamma. ELISAs revealed a decrease of MHC class II expression on the surface of E5-expressing cells compared with control virus-infected cells after interferon treatment. Western blot analysis showed that, in cells treated with interferon gamma, E5 could prevent the breakdown of Ii and block the formation of peptide-loaded, SDS-stable mature MHC class II dimers, correlating with diminished surface MHC class II expression. These data suggest that HPV16 E5 may be able to decrease immune recognition of infected keratinocytes via disruption of MHC class II protein function.

Importance of lysosomal cysteine proteases in lung disease

The human lysosomal cysteine proteases are a family of 11 proteases whose members include cathepsins B, C, H, L, and S. The biology of these proteases was largely ignored for decades because of their lysosomal location and the belief that their function was limited to the terminal degradation of proteins. In the past 10 years, this view has changed as these proteases have been found to have specific functions within cells. This review highlights some of these functions, specifically their roles in matrix remodeling and in regulating the immune response, and their relationship to lung diseases.

Enhancement of immune responses to an HIV env DNA vaccine by a C-terminal segment of listeriolysin O

An effective vaccine against AIDS should induce both cellular and humoral immune responses. Here we report that immunization of mice with a DNA plasmid encoding a chimeric protein consisting of HIV89.6 Env gp140 and the listeriolysin O (LLO) C-terminal segment (59 amino acids) significantly enhanced both humoral and cellular immune responses against the HIV89.6 Env protein. Plasmid DNA expression vectors with genes codon-optimized for mammalian expression were synthesized for HIV89.6 gp140 as well as for chimeric protein gp140-LLO, in which the coding sequence for the C-terminal 59 amino acids of LLO were fused in frame to the 3' end of the codon-optimized gene for gp140. All plasmid vectors produced high levels of protein expression, and the gp140-LLO chimeric protein was cleaved and secreted as efficiently as gp140. Analysis of humoral immune responses by ELISA showed that the chimeric gp140-LLO construct induced higher antibody responses than the gp140 construct in immunized mice, more notably in the IgG2a antibody subtype. Intracellular cytokine staining and flow cytometry analysis showed that the gp140-LLO construct induced significantly higher levels of cytotoxic T lymphocyte immune responses against the HIV 89.6 Env protein than those observed with the gp140 construct. Our results thus demonstrate that the C-terminal segment of LLO can be effectively employed to enhance both cellular and humoral immune responses against the HIV89.6 Env antigen in the context of a DNA vaccine.

Cloning, expression, purification, and activity of dog (Canis familiaris) and monkey (Saimiri boliviensis) cathepsin S

Cathepsin S is the key protease responsible for the removal of the invariant chain from MHC class II molecules and, as such, has attracted much attention as a target for developing immunosuppressive drugs. To help in testing candidate compounds, the monkey (Saimiri boliviensis) and dog (Canis familiaris) cathepsin S cDNAs have been cloned. The monkey cDNA sequence encodes a 330 amino acid protein with 95% homology to human cathepsin S. The dog cDNA sequence encodes a 331 amino acid protein with 91% homology to human cathepsin S. The amino acid differences do not have a major effect on the hydrolysis of the substrate Z-VVR-AMC, but may affect the substrate specificity. As for human and bovine cathepsin S, activity against Z-VVR-AMC extends into the neutral pH range. These parameters are important for understanding the role of cathepsin S in different species and for testing inhibitors in animal models of autoimmunity.

Crystal structure of MHC class II I-Ab in complex with a human CLIP peptide: prediction of an I-Ab peptide-binding motif

Association between the class II major histocompatibility complex (MHC) and the class II invariant chain-associated peptide (CLIP) occurs naturally as an intermediate step in the MHC class II processing pathway. Here, we report the crystal structure of the murine class II MHC molecule I-A(b) in complex with human CLIP at 2.15A resolution. The structure of I-A(b) accounts, via the peptide-binding groove's unique physicochemistry, for the distinct peptide repertoire bound by this allele. CLIP adopts a similar conformation to peptides bound by other I-A alleles, reinforcing the notion that CLIP is presented as a conventional peptide antigen. When compared to the related HLA-DR3/CLIP complex structure, the CLIP peptide displays a slightly different conformation and distinct interaction pattern with residues in I-A(b). In addition, after examining the published sequences of peptides presented by I-A(b), we discuss the possibility of predicting peptide alignment in the I-A(b) binding groove using a simple scoring matrix.

Activation of lysosomal function during dendritic cell maturation

In response to a variety of stimuli, dendritic cells (DCs) transform from immature cells specialized for antigen capture into mature cells specialized for T cell stimulation. During maturation, the DCs acquire an enhanced capacity to form and accumulate peptide-MHC (major histocompatibility complex) class II complexes. Here we show that a key mechanism responsible for this alteration was the generalized activation of lysosomal function. In immature DCs, internalized antigens were slowly degraded and inefficiently used for peptide loading. Maturation induced activation of the vacuolar proton pump that enhanced lysosomal acidification and antigen proteolysis, facilitating efficient formation of peptide-MHC class II complexes. Lysosomal function in DCs thus appears to be specialized for the developmentally regulated processing of internalized antigens.