The expression of legumain, an asparaginyl endopeptidase that controls antigen processing, is reduced in endotoxin-tolerant monocytes

Bacterial infection-biased abundance of proteins in the skin mucus of obscure puffer (Takifugu Obscurus)

The skin mucus of fish is equipped with immunological and antimicrobial peptides that confer protection against invading pathogens. The skin mucus has been studied in fish however information regarding its immunological roles in bacterial infection is rare. This study highlighted the proteins and peptides in the skin mucus of Obscure puffer Takifugu obscurus that quantitatively altered against Aeromonas hydrophila infection. We infected the fish through bath immersion, intraperitonially, and treated with PBS (control) then compared the level of proteins in the skin mucus among the groups using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. The Tandem Mass Tag (TMT) based quantification showed that 4896 proteins were Deferentially Quantified Proteins (DQPs), based on 19,751 unique peptides. Of which 170 were depleted (decreased in abundance) and 69 were abundant in comparison of Bath Treated (BT) vs Control (C) groups. Similarly, 76 DQPs were depleted and 70 were abundant in comparison of Treated (T) vs BT groups. Further, 126 DQPs were depleted, and 34 were abundant in comparison to T vs C groups. The DQPs we report were mostly immunological and were involved in unique biological functions and pathways. The interesting protein we report, where some of the proteins are for the first time in fish, shows the protein-rich structure of the mucus of fish, which may act as a biomarker to be targeted for bacterial disease therapy in fish and ultimately hint to the way of making resistance in fish against bacterial pathogens.

The transcriptional and phenotypic characteristics that define alveolar macrophage subsets in acute hypoxemic respiratory failure

The transcriptional and phenotypic characteristics that define alveolar monocyte and macrophage subsets in acute hypoxemic respiratory failure (AHRF) are poorly understood. Here, we apply CITE-seq (single-cell RNA-sequencing and cell-surface protein quantification) to bronchoalveolar lavage and blood specimens longitudinally collected from participants with AHRF to identify alveolar myeloid subsets, and then validate their identity in an external cohort using flow cytometry. We identify alveolar myeloid subsets with transcriptional profiles that differ from other lung diseases as well as several subsets with similar transcriptional profiles as reported in healthy participants (Metallothionein) or patients with COVID-19 (CD163/LGMN). We use information from CITE-seq to determine cell-surface proteins that distinguish transcriptional subsets (CD14, CD163, CD123, CD71, CD48, CD86 and CD44). In the external cohort, we find a higher proportion of CD163/LGMN alveolar macrophages are associated with mortality in AHRF. We report a parsimonious set of cell-surface proteins that distinguish alveolar myeloid subsets using scalable approaches that can be applied to clinical cohorts.

Potential relevance of salivary legumain for the clinical diagnostic of hand, foot, and mouth disease

The fight against hand, foot, and mouth disease (HFMD) remains an arduous challenge without existing point-of-care (POC) diagnostic platforms for accurate diagnosis and prompt case quarantine. Hence, the purpose of this salivary biomarker discovery study is to set the fundamentals for the realization of POC diagnostics for HFMD. Whole salivary proteome profiling was performed on the saliva obtained from children with HFMD and healthy children, using a reductive dimethylation chemical labeling method coupled with high-resolution mass spectrometry-based quantitative proteomics technology. We identified 19 upregulated (fold change = 1.5-5.8) and 51 downregulated proteins (fold change = 0.1-0.6) in the saliva samples of HFMD patients in comparison to that of healthy volunteers. Four upregulated protein candidates were selected for dot blot-based validation assay, based on novelty as biomarkers and exclusions in oral diseases and cancers. Salivary legumain was validated in the Singapore (n = 43 healthy, 28 HFMD cases) and Taiwan (n = 60 healthy, 47 HFMD cases) cohorts with an area under the receiver operating characteristic curve of 0.7583 and 0.8028, respectively. This study demonstrates the feasibility of a broad-spectrum HFMD POC diagnostic test based on legumain, a virus-specific host systemic signature, in saliva.

The Peptide Ligase Activity of Human Legumain Depends on Fold Stabilization and Balanced Substrate Affinities

Protein modification by enzymatic breaking and forming of peptide bonds significantly expands the repertoire of genetically encoded protein sequences. The dual protease-ligase legumain exerts the two opposing activities within a single protein scaffold. Primarily localized to the endolysosomal system, legumain represents a key enzyme in the generation of antigenic peptides for subsequent presentation on the MHCII complex. Here we show that human legumain catalyzes the ligation and cyclization of linear peptides at near-neutral pH conditions, where legumain is intrinsically unstable. Conformational stabilization significantly enhanced legumain's ligase activity, which further benefited from engineering the prime substrate recognition sites for improved affinity. Additionally, we provide evidence that specific legumain activation states allow for differential regulation of its activities. Together these results set the basis for engineering legumain proteases and ligases with applications in biotechnology and drug development.

MS-Based HLA-II Peptidomics Combined With Multiomics Will Aid the Development of Future Immunotherapies

Immunotherapies have emerged to treat diseases by selectively modulating a patient's immune response. Although the roles of T and B cells in adaptive immunity have been well studied, it remains difficult to select targets for immunotherapeutic strategies. Because human leukocyte antigen class II (HLA-II) peptides activate CD4+ T cells and regulate B cell activation, proliferation, and differentiation, these peptide antigens represent a class of potential immunotherapy targets and biomarkers. To better understand the molecular basis of how HLA-II antigen presentation is involved in disease progression and treatment, systematic HLA-II peptidomics combined with multiomic analyses of diverse cell types in healthy and diseased states is required. For this reason, MS-based innovations that facilitate investigations into the interplay between disease pathologies and the presentation of HLA-II peptides to CD4+ T cells will aid in the development of patient-focused immunotherapies.

Transcriptomic analysis of immunity in rainbow trout (Oncorhynchus mykiss) gills infected by Ichthyophthirius multifiliis

The parasite Ichthyophthirius multifiliis infecting skin, fins and gills of a wide range of freshwater fish species, including rainbow trout, is known to induce a protective immune response in the host. Although a number of studies have reported activation of several immune genes in infected fish host, the immune response picture is still considered incomplete. In order to address this issue, a comparative transcriptomic analysis was performed on infected versus uninfected rainbow trout gills and it showed that a total of 3352 (7.2%) out of 46,585 identified gene sequences were significantly regulated after parasite infection. Of differentially expressed gene sequences, 1796 genes were up-regulated and 1556 genes were down-regulated. These were classified into 61 Gene Ontology (GO) terms and mapped to 282 reference canonical pathways in the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. Infection of I. multifiliis induced a clear differential expression of immune genes, related to both innate and adaptive immunity. A total of 268 (6.86%) regulated gene sequences were known to take part in 16 immune-related pathways. These involved pathways related to the innate immunity such as the Chemokine signaling pathway, Platelet activation, Toll-like receptor signaling pathway, NOD-like receptor signaling pathway, and Leukocyte transendothelial migration. Elevated transcription of genes encoding the TLR 8 gene and chemokines (CCL4, CCL19, CCL28, CXCL8, CXCL11, CXCL13, CXCL14) was recorded indicating their roles in recognition of I. multifiliis and subsequent induction of the inflammatory response, respectively. A number of upregulated genes in infected gills were associated with antigen processing/presentation and T and B cell receptor signaling (including B cell marker CD22 involved in B cell development). Overall the analysis supports the notion that I. multifiliis induces a massive and varied innate response upon which a range of adaptive immune responses are established which may contribute to the long lasting protection of immunized rainbow trout.

Physiological and transcriptomic responses to fishmeal-based diet and rapeseed meal-based diet in two strains of gibel carp (Carassius gibelio)

The present study investigated differences in the utilization of fishmeal (FM) and rapeseed meal (RM) by gibel carp (Carassius gibelio) and explored the effects of protein sources on the responses of different genotypes. Gibel carp strains A (4.12 ± 0.03 g) and F (3.47 ± 0.00 g) were fed FM diet or RM diet for 56 days, and after which, growth performance, body composition, hematologic indices, and hepatic transcriptomes were measured. The effects of strain and diet on growth performance, body composition, and hematologic indices were analyzed by two-way analysis of covariance (ANCOVA). The results revealed that total replacement of FM with RM caused poor growth and feed utilization in both strains as well as the existence of genotype-diet interactions. Strain A showed better growth performance than strain F in the FM group, while the strain F grew better than strain A in the RM group. Transcriptomic analysis showed that the three main biological processes affected by the RM diet were amino acid metabolism, lipid metabolism, and digestive system. The different responses to the RM diet between strains were involved in amino acid metabolism, immune responses, and lipid metabolism. Identifying the underlying mechanisms by which different strains differently respond to meal sources might be the basis to develop a selective breeding program towards strains accepting alternative meal sources.

Vaccine antigens modulate the innate response of monocytes to Al(OH)3

Aluminum-based adjuvants have widely been used in human vaccines since 1926. In the absence of antigens, aluminum-based adjuvants can initiate the inflammatory preparedness of innate cells, yet the impact of antigens on this response has not been investigated so far. In this study, we address the modulating effect of vaccine antigens on the monocyte-derived innate response by comparing processes initiated by Al(OH)₃ and by Infanrix, an Al(OH)₃-adjuvanted trivalent combination vaccine (DTaP), containing diphtheria toxoid (D), tetanus toxoid (T) and acellular pertussis (aP) vaccine antigens. A systems-wide analysis of stimulated monocytes was performed in which full proteome analysis was combined with targeted transcriptome analysis and cytokine analysis. This comprehensive study revealed four major differences in the monocyte response, between plain Al(OH)₃ and DTaP stimulation conditions: (I) DTaP increased the anti-inflammatory cytokine IL-10, whereas Al(OH)₃ did not; (II) Al(OH)₃ increased the gene expression of IFNγ, IL-2 and IL-17a in contrast to the limited induction or even downregulation by DTaP; (III) increased expression of type I interferons-induced proteins was not observed upon DTaP stimulation, but was observed upon Al(OH)₃ stimulation; (IV) opposing regulation of protein localization pathways was observed for Al(OH)₃ and DTaP stimulation, related to the induction of exocytosis by Al(OH)₃ alone. This study highlights that vaccine antigens can antagonize Al(OH)₃-induced programming of the innate immune responses at the monocyte level.

Novel identified aluminum hydroxide-induced pathways prove monocyte activation and pro-inflammatory preparedness

Aluminum-based adjuvants are the most widely used adjuvants in human vaccines. A comprehensive understanding of the mechanism of action of aluminum adjuvants at the molecular level, however, is still elusive. Here, we unravel the effects of aluminum hydroxide Al(OH)₃ by a systems-wide analysis of the Al(OH)₃-induced monocyte response. Cell response analysis by cytokine release was combined with (targeted) transcriptome and full proteome analysis. Results from this comprehensive study revealed two novel pathways to become activated upon monocyte stimulation with Al(OH)₃: the first pathway was IFNβ signaling possibly induced by DAMP sensing pathways like TLR or NOD1 activation, and second the HLA class I antigen processing and presentation pathway. Furthermore, known mechanisms of the adjuvant activity of Al(OH)₃ were elucidated in more detail such as inflammasome and complement activation, homeostasis and HLA-class II upregulation, possibly related to increased IFNγ gene expression. Altogether, our study revealed which immunological pathways are activated upon stimulation of monocytes with Al(OH)₃, refining our knowledge on the adjuvant effect of Al(OH)₃ in primary monocytes.

SIGNIFICANCE

Aluminum salts are the most used adjuvants in human vaccines but a comprehensive understanding of the working mechanism of alum adjuvants at the molecular level is still elusive. Our Systems Vaccinology approach, combining complementary molecular biological, immunological and mass spectrometry-based techniques gave a detailed insight in the molecular mechanisms and pathways induced by Al(OH)₃ in primary monocytes. Several novel immunological relevant cellular pathways were identified: type I interferon secretion potentially induced by TLR and/or NOD like signaling, the activation of the inflammasome and the HLA Class-I and Class-II antigen presenting pathways induced by IFNγ. This study highlights the mechanisms of the most commonly used adjuvant in human vaccines by combing proteomics, transcriptomics and cytokine analysis revealing new potential mechanisms of action for Al(OH)₃.

[The importance of marker proteins of the nervous tissue for morphological diagnostics of the craniocerebral injury]

The present review of the literature involves 50 publications concerning various substrates of importance as the biological markers of axonal damages with special reference to the secondary molecular and cellular mechanisms on which to base in vitro and in vivo modeling of the craniocerebral injury. The results of the investigations with the application of mass-spectrometry for the identification of the proteins specifically synthesized in response to the injury are presented; their biological functions are described. The use of the sequential microscopic imaging technique and the immunohistochemical methods made it possible to determine that the majority of the marker proteins are involved in the specific intracellular processes that are triggered in response to the traumatic impact including apoptosis, proliferation, formation of lamellipodia, axon regeneration, actin remodeling, cell migration and inflammation. In addition, a rise in the amount of intracellular actin-associated proteins has been observed. It is concluded that the investigations into the properties and the physiological role of beta-amyloid precursor protein (beta-APP) are of special value for the characteristic of nervous tissue damages and morphological diagnostics of the craniocerebral injury.

The High Mobility Group A1 (HMGA1) Transcriptome in Cancer and Development

BACKGROUND & OBJECTIVES

Chromatin structure is the single most important feature that distinguishes a cancer cell from a normal cell histologically. Chromatin remodeling proteins regulate chromatin structure and high mobility group A (HMGA1) proteins are among the most abundant, nonhistone chromatin remodeling proteins found in cancer cells. These proteins include HMGA1a/HMGA1b isoforms, which result from alternatively spliced mRNA. The HMGA1 gene is overexpressed in cancer and high levels portend a poor prognosis in diverse tumors. HMGA1 is also highly expressed during embryogenesis and postnatally in adult stem cells. Overexpression of HMGA1 drives neoplastic transformation in cultured cells, while inhibiting HMGA1 blocks oncogenic and cancer stem cell properties. Hmga1 transgenic mice succumb to aggressive tumors, demonstrating that dysregulated expression of HMGA1 causes cancer in vivo. HMGA1 is also required for reprogramming somatic cells into induced pluripotent stem cells. HMGA1 proteins function as ancillary transcription factors that bend chromatin and recruit other transcription factors to DNA. They induce oncogenic transformation by activating or repressing specific genes involved in this process and an HMGA1 "transcriptome" is emerging. Although prior studies reveal potent oncogenic properties of HMGA1, we are only beginning to understand the molecular mechanisms through which HMGA1 functions. In this review, we summarize the list of putative downstream transcriptional targets regulated by HMGA1. We also briefly discuss studies linking HMGA1 to Alzheimer's disease and type-2 diabetes.

CONCLUSION

Further elucidation of HMGA1 function should lead to novel therapeutic strategies for cancer and possibly for other diseases associated with aberrant HMGA1 expression.

De novo transcriptome sequencing and analysis of Rapana venosa from six different developmental stages using Hi-seq 2500

The carnivorous whelk Rapana venosa is regarded as a biological invader with strong ecological fitness in the United States, Argentina, France and other countries. R. venosa may seriously damage bivalve resources. Nonetheless, in China, R. venosa is an important commercial species. Larval development, especially metamorphosis, influences the natural population and industrial breeding. However, there are few studies on the early development of R. venosa, and our understanding is further limited by a lack of genomic information. In this study, de novo sequencing was performed to obtain a comprehensive transcriptome profile during early development. A Hi-seq 2500 sequencing run produced 148,737,902 raw reads that were assembled into 1,137,556 unigenes (average length of 619 nucleotides, of which 49,673 could be annotated). The unigenes were assigned to biological processes and functions after annotation in Gene Ontology, eukaryotic Ortholog Groups and Kyoto Encyclopedia of Genes and Genomes. We also identified 93,196 simple sequence repeats among the unigenes. Six unique sequences associated with neuroendocrine function were analyzed by quantitative real-time PCR. Our data represent the first comprehensive transcriptomic resource for R. venosa. Functional annotation of the unigenes involved in various biological processes could stimulate research on the mechanisms of early development in this species. Understanding the mechanism of early development and metamorphosis would benefit antifouling research and aquaculture of R. venosa.

Structure and function of legumain in health and disease

The last years have seen a steady increase in our understanding of legumain biology that is driven from two largely uncoupled research arenas, the mammalian and the plant legumain field. Research on legumain, which is also referred to as asparaginyl endopeptidase (AEP) or vacuolar processing enzyme (VPE), is slivered, however. Here we summarise recent important findings and put them into a common perspective. Legumain is usually associated with its cysteine endopeptidase activity in lysosomes where it contributes to antigen processing for class II MHC presentation. However, newly recognized functions disperse previously assumed boundaries with respect to their cellular compartmentalisation and enzymatic activities. Legumain is also found extracellularly and even translocates to the cytosol and the nucleus, with seemingly incompatible pH and redox potential. These different milieus translate into changes of legumain's molecular properties, including its (auto-)activation, conformational stability and enzymatic functions. Contrasting its endopeptidase activity, legumain can develop a carboxypeptidase activity which remains stable at neutral pH. Moreover, legumain features a peptide ligase activity, with intriguing mechanistic peculiarities in plant and human isoforms. In pathological settings, such as cancer or Alzheimer's disease, the proper association of legumain activities with the corresponding cellular compartments is breached. Legumain's increasingly recognized physiological and pathological roles also indicate future research opportunities in this vibrant field.

Interleukin-22: immunobiology and pathology

Interleukin-22 (IL-22) is a recently described IL-10 family cytokine that is produced by T helper (Th) 17 cells, γδ T cells, NKT cells, and newly described innate lymphoid cells (ILCs). Knowledge of IL-22 biology has evolved rapidly since its discovery in 2000, and a role for IL-22 has been identified in numerous tissues, including the intestines, lung, liver, kidney, thymus, pancreas, and skin. IL-22 primarily targets nonhematopoietic epithelial and stromal cells, where it can promote proliferation and play a role in tissue regeneration. In addition, IL-22 regulates host defense at barrier surfaces. However, IL-22 has also been linked to several conditions involving inflammatory tissue pathology. In this review, we assess the current understanding of this cytokine, including its physiologic and pathologic effects on epithelial cell function.

Structure and mechanism of an aspartimide-dependent peptide ligase in human legumain

Peptide ligases expand the repertoire of genetically encoded protein architectures by synthesizing new peptide bonds, energetically driven by ATP or NTPs. Here, we report the discovery of a genuine ligase activity in human legumain (AEP) which has important roles in immunity and tumor progression that were believed to be due to its established cysteine protease activity. Defying dogma, the ligase reaction is independent of the catalytic cysteine but exploits an endogenous energy reservoir that results from the conversion of a conserved aspartate to a metastable aspartimide. Legumain's dual protease-ligase activities are pH- and thus localization controlled, dominating at acidic and neutral pH, respectively. Their relevance includes reversible on-off switching of cystatin inhibitors and enzyme (in)activation, and may affect the generation of three-dimensional MHC epitopes. The aspartate-aspartimide (succinimide) pair represents a new paradigm of coupling endergonic reactions in ATP-scarce environments.

Identification of injury specific proteins in a cell culture model of traumatic brain injury

The complicated secondary molecular and cellular mechanisms following traumatic brain injury (TBI) are still not fully understood. In the present study, we have used mass spectrometry to identify injury specific proteins in an in vitro model of TBI. A standardized injury was induced by scalpel cuts through a mixed cell culture of astrocytes, oligodendrocytes and neurons. Twenty-four hours after the injury, cell culture medium and whole-cell fractions were collected for analysis. We found 53 medium proteins and 46 cell fraction proteins that were specifically expressed after injury and the known function of these proteins was elucidated by an extensive literature survey. By using time-lapse microscopy and immunostainings we could link a large proportion of the proteins to specific cellular processes that occur in response to trauma; including cell death, proliferation, lamellipodia formation, axonal regeneration, actin remodeling, migration and inflammation. A high percentage of the proteins uniquely expressed in the medium after injury were actin-related proteins, which normally are situated intracellularly. We show that two of these, ezrin and moesin, are expressed by astrocytes both in the cell culture model and in mouse brain subjected to experimental TBI. Interestingly, we found many inflammation-related proteins, despite the fact that cells were present in the culture. This study contributes with important knowledge about the cellular responses after trauma and identifies several potential cell-specific biomarkers.

Th22 and related cytokines in inflammatory and autoimmune diseases

INTRODUCTION

Th22 and related cytokines regulate various processes and have been linked to diverse effects. The levels of Th22 and cytokine IL-22 are increased in several disorders and positively related to some autoimmune diseases. Preclinical studies have suggested that the inhibition or stimulation of IL-22 is an attractive approach to reverse the immune disorders. Simultaneously, considering many patients with refractory autoimmune diseases respond poorly to the therapies which are highly toxic, more effective therapies are to be examined.

AREAS COVERED

The role of Th22 cells and related cytokines and therapeutic strategies targeting them in many illnesses, especially inflammatory and autoimmune diseases.

EXPERT OPINION

Th22 cells and related cytokine IL-22 regulate multiple biological functions and play an important role in a number of inflammatory and autoimmune diseases. They have unique and attractive advantages for targeting. Targeting IL-22 has already been trialed in many mice experiments, showing better efficacy and fewer side effects compared with classical drugs. Targeting IL-22 or Th22 might provide pathogenetic treatment. However, Th22 subset is a recently identified Th subset and its associated research is extremely limited. Therefore, there are still many unanswered questions and further researches are warranted.

Targeting cell surface alpha(v)beta(3) integrin increases therapeutic efficacies of a legumain protease-activated auristatin prodrug

Novel monomethylauristatin E (MMAE) prodrug 8 was designed and prepared that bound cell surface glycoprotein integrin αvβ3, and was activated using legumain protease as a catalyst. Upon activation, prodrug 8 strongly induced the death of MDA-MB-435 cells that express integrin αvβ3 on cell surface. Efficacies of prodrug 8 were also determined in vivo using animal models of 4T1 murine breast cancer, D121 Lewis lung carcinoma, and MDA-MB-435 human breast cancer. The results demonstrated that prodrug 8 decreased tumor growth and metastasis effectively. In comparison to the parent cytotoxin, MMAE, and prodrug 3, prodrug 8 was less toxic to mouse white blood cells. The latter caused no loss in weight gain of mice at a dose 3 mg/kg, which is over 30 times in excess to MMAE (0.1 mg/kg). We hypothesize that overexpression and colocalization of integrin αvβ3 and legumain protease on tumor cells, tumor vasculature, and/or tumor microenvironments can be exploited to enhance the efficacy and selectivity of potent cytotoxins, such as MMAE, which is otherwise too toxic to use for therapy.

The asparaginyl endopeptidase legumain after experimental stroke

Various proteases in the brain contribute to ischemic brain injury. We investigated the involvement of the asparaginyl endopeptidase legumain after experimental stroke. On the basis of gene array studies and in situ hybridizations, we observed an increase of legumain expression in the peri-infarct area of rats after transient occlusion of the middle cerebral artery (MCAO) for 120 mins with a maximum expression at 24 and 48 h. Immunohistochemical analyses revealed the expression of legumain in Iba1(+) microglial cells and glial fibrillary acidic protein-positive astrocytes of the peri-infarct area in mice after MCAO. Post-stroke recovery was also studied in aged legumain-deficient mice (45 to 58 weeks old). Legumain-deficient mice did not show any differences in physiologic parameters compared with respective littermates before, during MCAO (45 mins), and the subsequent recovery period of 8 days. Moreover, legumain deficiency had no effect on mortality, infarct volume, and the neurologic deficit determined by the rotating pole test, a standardized grip strength test, and the pole test. However, a reduced number of invading CD74(+) cells in the ischemic hemisphere indicates an involvement in post-stroke inflammation. We conclude that legumain is not essential for the functional deficit after MCAO but may be involved in mechanisms of immune cell invasion.

Structural analysis of cytokines comprising the IL-10 family

Interleukin-10 (IL-10) family of cytokines includes a number of its viral homologs and eight cellular cytokines (IL-19, IL-20, IL-22, IL-24, IL-26, IL-28A, IL-28B, and IL-29). The latter three proteins are also known as IFN-λ2, IFN-λ3, and IFN-λ1, and are recognized as type III (or λ) interferons. Most of the cellular homologs of IL-10 are monomeric in solution, whereas IL-10 and its viral homologs are intercalated dimers consisting of two helical bundle domains topologically similar to the monomeric members of the family. A classical four-helix bundle, a signature element of all helical cytokines, is always found as part of the domain of each member of the IL-10 family. The only crystal structures of these cytokine receptors that have been determined to date are for their extracellular domains (ECDs). Each ECD consists of two β-sandwich domains connected in the middle by a linkage. Signal transduction occurs when a cytokine binds to its two appropriate receptor chains. IL-10 and its viral homologs use the same IL-10 receptor system, whereas the cellular homologs of IL-10 use their own receptors, which in some cases may overlap and be used in different pairwise combinations. The known structures of binary complexes allowed for marking of the receptor binding site, which always includes helix A, loop AB and helix F (IL-10 notations) on the side of a ligand, loops of the N-terminal and C-terminal domains directed toward the ligand, and the interdomain linkage of the ECD. An analysis of the published structures of both the binary and ternary complexes of all helical cytokines allowed for the generation of a model of the signaling complex of IL-10. The receptor binding site I of the high affinity receptor IL-10R1 is exactly the same as in the crystal structure of the binary IL-10/sIL-10R1 complex, whereas the receptor binding site II is located on the surface of the first and the third helices of the four-helix bundle. The receptor/receptor interface, or site III, is formed between the C-terminal domains of IL-10R1 and IL-10R2.

Structure and function of interleukin-22 and other members of the interleukin-10 family

The IL-10 family of cytokines is comprised of IL-10, IL-19, IL-20, IL-22, IL-24, IL-26, and IFN-lambdas (IL-28A, IL-28B, and IL-29). The IL-10 family members bind to shared class II cytokine receptor chains that associate in various combinations in heterodimeric complexes. Upon interleukin/receptor complex formation, these proteins switch on the Jak/STAT pathway and elicit pleiotropic biological responses whose variety sharply contrasts with their structural similarities. IL-10 family members are involved in several human diseases and health conditions and hence their structural analyses may provide valuable information to design specific therapeutic strategies. In this review, we describe the human interleukin-10 family of cytokines, focusing on their structures and functions, with particular attention given to IL-22 and IL-10. We report on the recently published structures of IL-10 cytokine family members and their complexes with cognate transmembrane and soluble receptors as well as on interleukin physiology and physiopathology.

Interleukin-28 and interleukin-29: novel regulators of skin biology

The skin forms an essential barrier between the inside of an organism and the environment. In addition to its function in insulation, temperature regulation, and sensation, it protects the body against physical trauma, pathogens, UV radiation, and excessive water loss. Many processes necessary for maintaining the skin integrity, including antimicrobial/antiviral defense, wound healing, and removal of tumors, are regulated by cytokines. Accumulating results lead us to assume that interleukin (IL)-28 and IL-29, 2 novel members of the IL-10-interferon cytokine family, are important regulators of some of these processes. In the skin, IL-28 and IL-29 can be produced by virus-infected cells, maturing dendritic cells (DCs), and regulatory T-cells, and they mainly influence keratinocytes and melanocytes. In keratinocytes, IL-28 and IL-29 induce growth inhibition. Simultaneously, these cytokines increase the cellular synthesis of proteins that directly hinder virus replication and enhance the readiness to present viral antigens to immune cells. Further, IL-28 and IL-29 upregulate expression of viral and microbial sensing cellular receptors, including toll-like receptor (TLR)3, TLR2, and melanoma differentiation associated gene 5, and strengthen the cellular response to these receptors' ligands. Thereby, in the noninfected skin IL-28 and IL-29 enhance the capacity of keratinocytes to react to viral and microbial products and at least indirectly upregulate their inflammatory potential and innate immunity. IL-28 and IL-29 can act synergistically with other mediators secreted during DC maturation (eg, IL-20). In summary, IL-28/IL-29 may play an important role in the skin in the clearance of viral and microbial infections and in the removal of tumors.

High systemic levels of interleukin-10, interleukin-22 and C-reactive protein in Indian patients are associated with low in vitro replication of HIV-1 subtype C viruses

BACKGROUND

HIV-1 subtype C (HIV-1C) accounts for almost 50% of all HIV-1 infections worldwide and predominates in countries with the highest case-loads globally. Functional studies suggest that HIV-1C is unique in its biological properties, and there are contradicting reports about its replicative characteristics. The present study was conducted to evaluate whether the host cytokine environment modulates the in vitro replication capacity of HIV-1C viruses.

METHODS

A small subset of HIV-1C isolates showing efficient replication in peripheral blood mononuclear cells (PBMC) is described, and the association of in vitro replication capacity with disease progression markers and the host cytokine response was evaluated. Viruses were isolated from patient samples, and the corresponding in vitro growth kinetics were determined by monitoring for p24 production. Genotype, phenotype and co-receptor usage were determined for all isolates, while clinical category, CD4 cell counts and viral loads were recorded for all patients. Plasmatic concentrations of cytokines and, acute-phase response, and microbial translocation markers were determined; and the effect of cytokine treatment on in vitro replication rates was also measured.

RESULTS

We identified a small number of viral isolates showing high in vitro replication capacity in healthy-donor PBMC. HIV-1C usage of CXCR4 co-receptor was rare; therefore, it did not account for the differences in replication potential observed. There was also no correlation between the in vitro replication capacity of HIV-1C isolates and patients' disease status. Efficient virus growth was significantly associated with low interleukin-10 (IL-10), interleukin-22 (IL-22), and C-reactive protein (CRP) levels in plasma (p < .0001). In vitro, pretreatment of virus cultures with IL-10 and CRP resulted in a significant reduction of virus production, whereas IL-22, which lacks action on immune cells appears to mediate its anti-HIV effect through interaction with both IL-10 and CRP, and its own protective effect on mucosal membranes.

CONCLUSIONS

These results indicate that high systemic levels of IL-10, CRP and IL-22 in HIV-1C-infected Indian patients are associated with low viral replication in vitro, and that the former two have direct inhibitory effects whereas the latter acts through downstream mechanisms that remain uncertain.

Biology of interleukin-22

Interleukin (IL)-22 is a member of the IL-10 family of cytokines and represents an important effector molecule of activated Th22, Th1, and Th17 cells, as well as Tc-cell subsets, gammadelta T cells, natural killer (NK), and NKT cells. IL-22 mediates its effects via a heterodimeric transmembrane receptor complex consisting of IL-22R1 and IL-10R2 and subsequent Janus kinase-signal transducers and activators of transcription (JAK-STAT) signaling pathways including Jak1, Tyk2, and STAT3. Whereas in some aspects, IL-22 acts synergistically with tumor necrosis factor-alpha, IL-1beta, or IL-17, most functions of IL-22 are unique. Importantly, IL-22 does not serve the communication between immune cells. It mainly acts on epithelial cells and hepatocytes, where it favors the antimicrobial defense, regeneration, and protection against damage and induces acute phase reactants and some chemokines. This chapter illuminates in detail the properties of IL-22 with respect to its gene, protein structure, cellular sources, receptors, target cells, biological effects, and, finally, its role in chronic inflammatory diseases, tumors, and infection.

Despite IFN-lambda receptor expression, blood immune cells, but not keratinocytes or melanocytes, have an impaired response to type III interferons: implications for therapeutic applications of these cytokines

Interferon (IFN)-lambda1, -2 and -3 (also designated as interleukin (IL)-29, IL-28alpha and IL-28beta) represent a new subfamily within the class II cytokine family. They show type I IFN-like antiviral and cytostatic activities in affected cells forming the basis for IFN-lambda1 therapy currently under development for hepatitis C infection. However, many aspects of IFN-lambdas are still unknown. This study aimed at identifying the target cells of IFN-lambdas within the immune system and the skin. Among skin cell populations, keratinocytes and melanocytes, but not fibroblasts, endothelial cells or subcutaneous adipocytes turned out to be targets. In contrast to these target cells, blood immune cell populations did not clearly respond to even high concentrations of these cytokines, despite an IFN-lambda receptor expression. Interestingly, immune cells expressed high levels of a short IFN-lambda receptor splice variant (sIFN-lambdaR1/sIL-28R1). Its characterization revealed a secreted, glycosylated protein that binds IFN-lambda1 with a moderate affinity (K(D) 73 nM) and was able to inhibit IFN-lambda1 effects. Our study suggests that IFN-lambda therapy should be suited for patients with verrucae, melanomas and non-melanoma skin cancers, apart from patients with viral hepatitis, and would not be accompanied by immune-mediated complications known from type I IFN application.

IL-22 and IL-20 are key mediators of the epidermal alterations in psoriasis while IL-17 and IFN-gamma are not

Psoriasis is a common chronic skin disease with a largely unknown pathogenesis. We demonstrate here that transgenic over-expression of interleukin (IL)-22 in mice resulted in neonatal mortality and psoriasis-like skin alterations including acanthosis and hypogranularity. This cutaneous phenotype may be caused by the direct influence of IL-22 on keratinocytes, since this cytokine did not affect skin fibroblasts, endothelial cells, melanocytes, or adipocytes. The comparison of cytokines with hypothesized roles in psoriasis pathogenesis determined that neither interferon (IFN)-gamma nor IL-17, but only IL-22 and, with lower potency, IL-20 caused psoriasis-like morphological changes in a three-dimensional human epidermis model. These changes were associated with inhibited keratinocyte terminal differentiation and with STAT3 upregulation. The IL-22 effect on differentiation-regulating genes was STAT3-dependent. In contrast to IL-22 and IL-20, IFN-gamma and IL-17 strongly induced T-cell and neutrophilic granulocyte-attracting chemokines, respectively. Tumor necrosis factor-alpha potently induced diverse chemokines and additionally enhanced the expression of IL-22 receptor pathway elements and amplified some IL-22 effects. This study suggests that different cytokines are players in the psoriasis pathogenesis although only the IL-10 family members IL-22 and IL-20 directly cause the characteristic epidermal alterations.

Maturing dendritic cells are an important source of IL-29 and IL-20 that may cooperatively increase the innate immunity of keratinocytes

IL-19, IL-20, IL-22, IL-24, IL-26, IL-28, and IL-29 are new members of the IL-10 interferon family. Monocytes are well-known sources of IL-19, IL-20, and IL-24. We demonstrated here that monocytes also expressed IL-29, and monocyte differentiation into macrophages (Mphi) or dendritic cells (DCs) strongly changed their production capacity of these cytokines. Maturation of DCs with bacterial stimuli induced high expression of IL-28/IL-29 and IL-20. Simulated T cell interaction and inflammatory cytokines induced IL-29 and IL-20 in maturing DCs, respectively. Compared with monocytes, DCs expressed only minimal IL-19 levels and no IL-24. The differentiation of monocytes into Mphi reduced their IL-19 and terminated their IL-20, IL-24, and IL-29 production capacity. Like monocytes, neither Mphi nor DCs expressed IL-22 or IL-26. The importance of maturing DCs as a source of IL-28/IL-29 was supported by the much higher mRNA levels of these mediators in maturing DCs compared with those in CMV-infected fibroblasts, and the presence of IL-28 in lymph nodes but not in liver of lipopolysaccharide-injected mice. IL-19, IL-20, IL-22, IL-24, and IL-26 do not seem to affect Mphi or DCs as deduced from the lack of corresponding receptor chains. The significance of IL-20 and IL-28/IL-29 coexpression in maturing DCs may lie in the broadly amplified innate immunity in neighboring tissue cells like keratinocytes. In fact, IL-20 induced the expression of antimicrobial proteins, whereas IL-28/IL-29 enhanced the expression of toll-like receptors (TLRs) and the response to TLR ligands. However, the strongest response to TLR2 and TLR3 activation showed keratinocytes in the simultaneous presence of IL-20 and IL-29.

Long-term interleukin-10 presence induces the development of a novel, monocyte-derived cell type

Interleukin (IL)-10 is one of the most crucial immunoregulatory cytokines. Its short-term effects have been analysed extensively, but little is known about its long-term effects. This is of considerable importance, as high systemic IL-10 levels are present for long periods in patients with persistent viral infections, certain cancers and in critical care patients. Our study investigated the effects of the long-term presence of IL-10 on human peripheral blood monocytes. In vitro, IL-10 treatment of these cells for 7 days induced the development of a novel cell type characterized by unique phenotypical and functional characteristics. These cells showed high HLA-DR expression and low expression of CD86 and other co-stimulatory molecules on their surface. The mRNA levels of both HLA-DR and CD86 were high, but no intracellular accumulation of CD86 protein was observed. With respect to its function, these cells showed strongly diminished tumour necrosis factor-alpha production following lipopolysaccharide stimulation, strongly diminished allogenic CD4(+) T cell stimulatory capacity, and even induced a hyporesponsive state in CD4(+) T cells. The phenotype remained stable despite the removal of IL-10. In vivo, we found monocytic cells from patients exhibiting this phenotype after long-term IL-10 exposure. These results complement our knowledge further about the biological effects of IL-10 and may provide an explanation for the sustained immunodeficiency in cases of the persistent presence of systemic IL-10.

Immunopathogenesis of psoriasis

Psoriasis is a chronic skin disease that affects about 1.5% of the Caucasian population and is characterized by typical macroscopic and microscopic skin alterations. Psoriatic lesions are sharply demarcated, red and slightly raised lesions with silver-whitish scales. The microscopic alterations of psoriatic plaques include an infiltration of immune cells in the dermis and epidermis, a dilatation and an increase in the number of blood vessels in the upper dermis, and a massively thickened epidermis with atypical keratinocyte differentiation. It is considered a fact that the immune system plays an important role in the pathogenesis of psoriasis. Since the early 1990s, it has been assumed that T1 cells play the dominant role in the initiation and maintenance of psoriasis. However, the profound success of anti-tumor necrosis factor-alpha therapy, when compared with T-cell depletion therapies, should provoke us to critically re-evaluate the current hypothesis for psoriasis pathogenesis. Recently made discoveries regarding other T-cell populations such as Th17 and regulatory T cells, dendritic cells, macrophages, the keratinocyte signal transduction and novel cytokines including interleukin (IL)-22, IL-23 and IL-20, let us postulate that the pathogenesis of psoriasis consists of distinct subsequent stages, in each of them different cell types playing a dominant role. Our model helps to explain the varied effectiveness of the currently tested immune modulating therapies and may enable the prediction of the success of future therapies.

IL-19 and IL-20: two novel cytokines with importance in inflammatory diseases

IL-19 and IL-20 are two cytokines that were discovered in 2000 and 2001, respectively. Based on the structure and location of their genes, their primary and secondary protein structures and the used receptor complexes, they were classified with IL-10, IL-22, IL-24, IL-26, IL-28 and IL-29 in the IL-10 family of cytokines, and form a subgroup with IL-24 within this family. IL-19 and IL-20 are produced by monocytes as well as non-immune tissue cells under inflammatory conditions. IL-19 and IL-20 act via a receptor complex that consists of the IL-20R1 and IL-20R2 chains. IL-20 is additionally able to signal via a second receptor complex (IL-22R1/IL-20R2). It is controversial whether or not IL-19 and IL-20 regulate the function of immune cells. However, the expression of their receptors aliments the perception that the cells of the skin, lungs and reproductive organs as well as various glands are major targets of these mediators. Results from animal experiments and massively increased expression of these mediators in human inflamed tissues support the assumption that they play an important role in the pathogenesis of a few inflammatory diseases. For this reason, the authors have reviewed the facts known at present regarding these cytokines and postulate that IL-19 and IL-20 are pharmacologically interesting distal elements of an inflammatory cascade.

The evaluation of psoriasis therapy with biologics leads to a revision of the current view of the pathogenesis of this disorder

Psoriasis is a common chronic, recurring skin disease that is characterised by typical macroscopic and microscopic skin alterations. It is widely accepted that the immune system plays an important role in the pathogenesis of this disorder. Since the early 1990s, the dominant role of a subpopulation of T cells, so-called T1 cells, and their prominent cytokine IFN-gamma has been assumed in the pathogenesis of psoriasis. Surprisingly, the comparison of the therapeutic success of treatments with recombinant proteins directed against defined immunological structures shows that those that directly affect T cells (alefacept, efalizumab, Hu-max-CD4, OKTcdr4a) were clearly less effective than those targeting TNF-alpha (etanercept, adalimumab, infliximab). For this reason, the authors critically re-evaluated the view of psoriasis pathogenesis and postulate that in the majority of patients the T1 cells do not play a dominant role in the clinical, visible stage of this disease.

Reduced monocyte CD86 expression in postinflammatory immunodeficiency

OBJECTIVE

Major surgery, polytrauma, stroke, and pancreatitis frequently lead to a compensatory anti-inflammatory response syndrome that often predisposes patients to lethal infections. This temporary postinflammatory immunodeficiency is characterized by altered function of blood monocytes. These cells show strongly reduced inflammatory and antigen-presentation capacity. Diminished monocyte expression of the major histocompatibility complex class II molecule human leukocyte antigen (HLA)-DR is a well-established diagnostic marker of this immunodeficiency. To further characterize the monocytic cells in this clinical state, we analyzed their expression of CD86, the most important co-stimulatory molecule.

DESIGN

Analysis of blood samples that entered the clinical immunologic diagnostics and of cells from an in vitro model of postinflammatory immunodeficiency.

SETTING

University laboratory.

SUBJECTS

Healthy donors and intensive care unit (ICU) patients at the university hospital.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The expression of HLA-DR on monocytes and of CD86 and CD80 on monocytes and B cells was analyzed by flow cytometry. Messenger RNA expression of CD86 was analyzed in isolated monocytes by real-time polymerase chain reaction on reverse transcribed. The normal range of monocyte CD86 expression in healthy subjects was established to be from 2128 to 5102 surface molecules per cell and was independent of age, gender, and leukocyte and monocyte count. The CD86 expression on monocytes in ICU patients correlated with HLA-DR expression. Approximately 40% of the ICU patients with long-term reduced monocyte HLA-DR expression had a long-term reduction of CD86 expression. Patients in whom the expression of both molecules was diminished had an unfavorable prognosis. The diminished number of CD86 surface molecules on monocytes was associated with reduced CD86 messenger RNA levels in these cells. The expression of CD86 in B cells was not diminished in immunodeficient patients. The expression of CD80 in both monocytes and B-cells was minimal in healthy donors and not clearly changed in patients.

CONCLUSIONS

The monocyte CD86 expression may be a helpful diagnostic variable in ICU patients.

Interleukin (IL)-19, IL-20 and IL-24 are produced by and act on keratinocytes and are distinct from classical ILs

Due to their structural similarity, interleukin (IL)-19, IL-20, IL-22, IL-24 and IL-26 were combined with IL-10 in the so-called IL-10 family. To expand the knowledge on IL-19, IL-20 and IL-24, we systematically and quantitatively analysed the expression of these mediators and their receptor chains in vitro and in vivo under various conditions and in comparison with other IL-10 family members. In vitro, IL-19, IL-20 and IL-24 were produced not only by activated immune cells, particularly monocytes, but also to a similar extent by keratinocytes. IL-1beta increased the expression of these mediators 1000-fold (IL-19) and 10-fold (IL-20 and IL-24) in keratinocytes. In vivo, these cytokines were expressed preferentially in inflamed tissues. The absence of either R1 chain for the two types of receptor complexes for these cytokines (IL-20R1/IL-20R2 and IL-22R1/IL-20R2) on immune cells implies that they cannot act on these cells. In fact, IL-19, IL-20 and IL-24 did not induce activation of signal transducer and activator of transcription (STAT) molecules in immune cells. Instead, several tissues, particularly the skin, tissues from the reproductive and respiratory systems, and various glands appeared to be the main targets of these mediators. Keratinocytes expressed both receptor complexes; however, the expression of IL-22R1 was 10 times higher than that of IL-20R1. Interferon-gamma further increased the expression of IL-22R1 and decreased that of IL-20R1, suggesting that under T1 cytokine conditions these mediators primarily affect keratinocytes via the IL-22R1/IL-20R2 complex. In summary, these data support the notion that IL-19, IL-20 and IL-24 are distinct from classical ILs and constitute a separate subfamily of mediators within the IL-10 family.

A model of the ternary complex of interleukin-10 with its soluble receptors

BACKGROUND

Interleukin-10 (IL-10) is a cytokine whose main biological function is to suppress the immune response by induction of a signal(s) leading to inhibition of synthesis of a number of cytokines and their cellular receptors. Signal transduction is initiated upon formation of a ternary complex of IL-10 with two of its receptor chains, IL-10R1 and IL-10R2, expressed on the cell membrane. The affinity of IL-10R1 toward IL-10 is very high, which allowed determination of the crystal structure of IL-10 complexed with the extracellular/soluble domain of IL-10R1, while the affinity of IL-10R2 toward either IL-10 or IL-10/sIL-10R1 complex is quite low. This so far has prevented any attempts to obtain structural information about the ternary complex of IL-10 with its receptor chains.

RESULTS

Structures of the second soluble receptor chain of interleukin-10 (sIL-10R2) and the ternary complex of IL-10/sIL-10R1/sIL-10R2 have been generated by homology modeling, which allowed us to identify residues involved in ligand-receptor and receptor-receptor interactions.

CONCLUSION

The previously experimentally determined structure of the intermediate/binary complex IL-10/sIL-10R1 is the same in the ternary complex. There are two binding sites for the second receptor chain on the surface of the IL-10/sIL-10R1 complex, involving both IL-10 and sIL-10R1. Most of the interactions are hydrophilic in nature, although each interface includes two internal hydrophobic clusters. The distance between C-termini of the receptor chains is 25 A, which is common for known structures of ternary complexes of other cytokines. The structure is likely to represent the biologically active signaling complex of IL-10 with its receptor on the surface of the cell membrane.