A putative helical cytokine functioning in innate immune signalling in Drosophila melanogaster

In invertebrates and vertebrates, innate immunity is considered the first line of defense mechanism against non-self material. In vertebrates, cytokines play a critical role in innate immune signalling. To date, however, the existence of genes encoding for invertebrate helical cytokines has been anticipated, but never demonstrated. Here, we report the first structural and functional evidence of a gene encoding for a putative helical cytokine in Drosophila melanogaster. Functional experiments demonstrate that its expression, as well as that of the antimicrobial factors defensin and cecropin A1, is significantly increased after immune stimulation. These observations suggest the involvement of helical cytokines in the innate immune response of invertebrates.     

An ancient interleukin-16–like molecule regulates hemocyte proliferation via integrin β1 in invertebrates

Interleukins (ILs) are cytokines with crucial functions in innate and adaptive immunity. IL genes are only found in vertebrates, except for IL-16, which has been cloned in some arthropod species. However, the function of this gene in invertebrates is unknown. In the present study, an IL-16–like gene (EsIL-16) was identified from the Chinese mitten crab Eriocheir sinensis. EsIL-16 was predicted to encode a precursor (proEsIL-16) that shares similarities with pro-IL-16 proteins from insects and vertebrates. We show that caspase-3 processes proEsIL-16 into an approximately 144-kDa N-terminal prodomain with nuclear import activity and an approximately 34-kDa mature peptide that might be secreted into the extracellular region. EsIL-16 mRNA could be detected in all analyzed tissues and was significantly upregulated after immune challenge both in vitro and in vivo. T7 phage display library screening suggested potential binding activity between EsIL-16 and integrin, which was confirmed by coimmunoprecipitation assay. Interestingly, EsIL-16 promoted cell proliferation via integrin β1 in primary cultured crab hemocytes and Drosophila S2 cells. Furthermore, the interaction between EsIL-16 and integrin β1 was necessary to efficiently protect the host from bacterial infection. To our knowledge, this study revealed integrin β1 as a receptor for IL-16 and the function of this interaction in hemocyte proliferation in invertebrates for the first time. These results provide new insights into the regulation of innate immune responses in invertebrates and shed the light on the evolution of ILs within the animal kingdom.     

无脊椎动物先天免疫模式识别受体研究进展

免疫系统的基本功能是“自己”与“非己”识别.对入侵物的识别是免疫防御的起始,最终引发效应物反应系统,包括吞噬作用、包被作用、激活蛋白酶级联反应和黑化作用以及诱导抗菌肽的合成等,从而清除或消灭入侵物.研究证明,这种“非己”识别是因为存在某些特异性的、可溶的或与细胞膜结合的模式识别受体,可以识别或结合微生物表面保守的、而在宿主中又不存在的病原相关分子模式.模式识别受体通过对病原相关分子的识别启动先天免疫防御.近年来这方面的研究进展很快,已经在无脊椎动物中确定了多种模式识别受体,包括肽聚糖识别蛋白、含硫酯键蛋白、革兰氏阴性菌结合蛋白、清除受体、C型凝集素、硫依赖型凝集素、Toll样受体和血素等,并对其性质和功能进行了研究.     

The amphioxus genome provides unique insight into the evolution of immunity

Immune systems evolve as essential strategies to maintain homeostasis with the environment, prevent microbial assault and recycle damaged host tissues. The immune system is composed of two components, innate and adaptive immunity. The former is common to all animals while the latter consists of a vertebrate-specific system that relies on somatically derived lymphocytes and is associated with near limitless genetic diversity as well as long-term memory. Deuterostome invertebrates provide a view of immune repertoires in phyla that immediately predate the origins of vertebrates. Genomic studies in amphioxus, a cephalochordate, have revealed homologs of genes encoding most innate immune receptors found in vertebrates; however, many of the gene families have undergone dramatic expansions, greatly increasing the innate immune repertoire. In addition, domain-swapping accounts for the innovation of new predicted pathways of receptor function. In both amphioxus and Ciona, a urochordate, the VCBPs (variable region containing chitin-binding proteins), which consist of immunoglobulin V (variable) and chitin binding domains, mediate recognition through the V domains. The V domains of VCBPs in amphioxus exhibit high levels of allelic complexity that presumably relate to functional specificity. Various features of the amphioxus immune repertoire reflect novel selective pressures, which likely have resulted in innovative strategies. Functional genomic studies underscore the value of amphioxus as a model for studying innate immunity and may help reveal how unique relationships between innate immune receptors and both pathogens and symbionts factored in the evolution of adaptive immune systems.     

A trade-off switch of two immunological memories in Caenorhabditis elegans reinfected by bacterial pathogens

Recent studies have suggested that innate immune responses exhibit characteristics associated with memory linked to modulations in both vertebrates and invertebrates. However, the diverse evolutionary paths taken, particularly within the invertebrate taxa, should lead to similarly diverse innate immunity memory processes. Our understanding of innate immune memory in invertebrates primarily comes from studies of the fruit fly Drosophila melanogaster, the generality of which is unclear. Caenorhabditis elegans typically inhabits soil harboring a variety of fatal microbial pathogens; for this invertebrate, the innate immune system and aversive behavior are the major defensive strategies against microbial infection. However, their characteristics of immunological memory remains infantile. Here we discovered an immunological memory that promoted avoidance and suppressed innate immunity during reinfection with bacteria, which we revealed to be specific to the previously exposed pathogens. During this trade-off switch of avoidance and innate immunity, the chemosensory neurons AWB and ADF modulated production of serotonin and dopamine, which in turn decreased expression of the innate immunity-associated genes and led to enhanced avoidance via the downstream insulin-like pathway. Therefore, our current study profiles the immune memories during C. elegans reinfected by pathogenic bacteria and further reveals that the chemosensory neurons, the neurotransmitter(s), and their associated molecular signaling pathways are responsible for a trade-off switch between the two immunological memories.     

Molecular evolution of the NF-κB signaling system

The mechanisms of innate immunity in vertebrates show certain overall resemblances to immune mechanisms of insects. Two hypotheses have been proposed to explain these resemblances. (1) According to the evolutionary continuity hypothesis, innate immune mechanisms evolved in the common ancestor of vertebrates and insects and have been conserved since that time. (2) In the independent-evolution hypothesis, the mechanisms of innate immunity in vertebrates evolved independently from invertebrate immune mechanisms. Phylogenetic analysis of five gene families (Pelle, Rel, IkappaB, Toll, and TRAF) whose members are involved in NF-kappaB signaling in vertebrates and insects were used to decide between these hypotheses. The phylogenies of the Rel and TRAF families strongly supported independent evolution of immune functions in vertebrates and invertebrates, and, except for a possible case in the Pelle family, orthologous molecules having immune functions in both vertebrates and invertebrates were not found. The results suggest that NF-kappaB represents an ancient, generalized signaling system that has been co-opted for immune system roles independently in vertebrate and insect lineages.     

Evolution of the lectin-complement pathway and its role in innate immunity

Discrimination between self and non-self by lectins (carbohydrate-binding proteins) is a strategy of innate immunity that is found in both vertebrates and invertebrates. In vertebrates, immune recognition mediated by ficolins (lectins that consist of a fibrinogen-like and a collagen-like domain), as well as by mannose-binding lectins, triggers the activation of the complement system, which results in the activation of novel serine proteases. The presence of a similar lectin-based complement system in ascidians, our closest invertebrate relatives, indicates that the complement system probably had a pivotal role in innate immunity before the evolution of an adaptive immune system in jawed vertebrates.     

Life is a huge compromise: Is the complexity of the vertebrate immune-neuroendocrine system an advantage or the price to pay?

Recent advances in comparative immunology have established that invertebrates produce hypervariable molecules probably related to immunity, suggesting the possibility of raising a specific immune response. “Priming” and “tailoring” are terms now often associated with the invertebrate innate immunity. Comparative immunologists contributed to eliminate the idea of a static immune system in invertebrates, making necessary to re-consider the evolutive meaning of immunological memory of vertebrates. If the anticipatory immune system represents a maximally efficient immune system, why can it be observed only in vertebrates, especially in consideration that molecular hypervariability exists also in invertebrates? Using well-established theories concerning the evolution of the vertebrate immunity as theoretical basis we analyze from an Eco-immunology-based perspective why a memory-based immune system may have represented an evolutive advantage for jawed vertebrates. We hypothesize that for cold-blooded vertebrates memory represents a complimentary component that flanks the robust and fundamental innate immunity. Conversely, immunological memory has become indispensable and fully exploited in warm-blooded vertebrates, due to their stable inner environment and high metabolic rate, respectively.     

Cytotoxicity and cytotoxic molecules in invertebrates

Although lacking the components that characterize the acquired immunity systems of vertebrates, invertebrates nevertheless possess effective general innate immune mechanisms which exhibit striking parallels with those of vertebrates. These innate immune systems include both cellular and humoral elements. Invertebrate phagocytes synthesize both oxygen-dependent and oxygen-independent molecules to combat infectious agents. Cytotoxic substances employed by invertebrates include reactive intermediates of oxygen and nitrogen, antimicrobial peptides, lectins, cytokine- and complement-like molecules, and quinoid intermediates of melanin. The signal transduction pathways that are involved in mediating the production of these substances appear to be very similar among animal species, suggesting a common ancestral origin for the innate immune systems.     

Cross-talk among immune and neuroendocrine systems in molluscs and other invertebrate models

The comparison between immune and neuroendocrine systems in vertebrates and invertebrates suggest an ancient origin and a high degree of conservation for the mechanisms underlying the integration between immune and stress responses. This suggests that in both vertebrates and invertebrates the stress response involves the integrated network of soluble mediators (e.g., neurotransmitters, hormones and cytokines) and cell functions (e.g., chemotaxis and phagocytosis), that interact with a common objective, i.e., the maintenance of body homeostasis. During evolution, several changes observed in the stress response of more complex taxa could be the result of new roles of ancestral molecules, such as ancient immune mediators may have been recruited as neurotransmitters and hormones, or vice versa. We review older and recent evidence suggesting that immune and neuro-endocrine functions during the stress response were deeply intertwined already at the dawn of multicellular organisms. These observations found relevant reflections in the demonstration that immune cells can transdifferentiate in olfactory neurons in crayfish and the recently re-proposed neural transdifferentiation in humans.     

Cloning,characterization and expression of tyrosinase-like gene in amphioxus Branchiostoma japonicum

Prophenoloxidase (tyrosinase) widely distributed in invertebrates and vertebrates, and plays a crucial role in the innate immune. In the present study, the full-length cDNA of a tyrosinase-like (designated AmphiTYR) was cloned from amphioxus Branchiostoma japonicum by PCR techniques. The full-length cDNA of AmphiTYR is 2314 bp, and its predicted open-reading frame codes for a protein of 544 amino acids with a predicted molecular mass of approximately 60.9 kDa and an isoelectric point of 5.65. It has a conserved putative copper-binding domain with six histidines in tyrosinase proteins. Six potential N-linked glycosylation sites and 14 conserved cysteine residues were also predicted to be present in B. japonicum tyrosinase. Homology analysis revealed that AmphiTYR was higher similar to vertebrates tyrosinases (32.5–40.5%) than to invertebrates phenoloxidase (6.4–25.4%). In the adult, AmphiTYR mRNA was expressed in the muscle, epidermis, notochord, ovary, hepatic caecum, pharynx and gill, but not in the neural tube, intestines and testis. During the different development stages from unfertilized egg to larvae of amphioxus, AmphiTYR expressed during all the amphioxus development. These results indicated that AmphiTYR gene not only play a pivotal role in innate immune but also play an important role during embryonic development of cephalochordate amphioxus.     

鱼类Toll样受体及其信号传导的研究进展

鱼类是脊椎动物中的一个重要类群, 在其生存与进化的过程中, 免疫系统担负着保护鱼类免受病原感染的重任, 其中Toll样受体家族等介导的先天性免疫是鱼类抗病免疫的第一道防线, 并在连接先天性免疫与获得性免疫反应中起着桥梁作用. 虽然从无脊椎动物到高等脊椎动物, Toll样受体家族内多数成员在蛋白质结构与功能上都较为保守, 但是鱼类作为最低等的脊椎动物, 在其进化过程中又形成了一些特有Toll样受体分子, 其剪接类型也更丰富; 鱼类Toll样受体家族介导的免疫识别、免疫信号传导、激活和调控方式与高等脊椎动物也不尽相同. 文章主要综述了鱼类Toll样受体的结构、种类、功能、多样性、免疫信号传导及其调控特点, 为深入了解鱼类的免疫反应奠定基础.       

The evolution and genetics of innate immunity

The immune system provides protection from a wide range of pathogens. One component of immunity, the phylogenetically ancient innate immune response, fights infections from the moment of first contact and is the fundamental defensive weapon of multicellular organisms. The Toll family of receptors has a crucial role in immune defence. Studies in fruitflies and in mammals reveal that the defensive strategies of invertebrates and vertebrates are highly conserved at the molecular level, which raises the exciting prospects of an increased understanding of innate immunity.     

The expression of protein disulfide isomerase from Litopenaeus vannamei hemocytes is regulated by bacterial inoculation

A partial clone encoding a member of the protein disulfide isomerase (PDI) was isolated from a Litopenaeus vannamei hemocyte cDNA library. The 5′-end sequence was obtained by RACE. The complete sequence encodes for a 502-residues protein that contains two thioredoxin domains and the typical endoplasmic reticulum retention KDEL motif. Shrimp PDI is highly similar to the homologue protein described in both vertebrates and invertebrates. Changes in the shrimp PDI mRNA expression were observed after injection of Vibrio alginolyticus, suggesting that PDI is implicated in the immune defense system. This is the first report of a PDI in crustaceans.     

Genome-wide investigation reveals pathogen-specific and shared signatures in the response of <Emphasis Type="Italic">Caenorhabditis elegans</Emphasis>to infection

Background  

There are striking similarities between the innate immune systems of invertebrates and vertebrates. Caenorhabditis elegans is increasingly used as a model for the study of innate immunity. Evidence is accumulating that C. elegans mounts distinct responses to different pathogens, but the true extent of this specificity is unclear. Here, we employ direct comparative genomic analyses to explore the nature of the host immune response.     

抗病毒天然免疫研究

病毒是一种极具感染性和传染性的病原微生物．当病毒感染机体以后,机体会通过激活免疫系统来进行防御．高等哺乳动物的免疫系统分为两大类：适应性免疫系统和天然免疫系统．适应性免疫系统主要通过T淋巴细胞和B淋巴细胞特异性地识别入侵的病毒并将其清除．而天然免疫系统主要通过模式识别受体识别病毒的入侵,进而产生一系列的细胞因子抵抗病毒的入侵．其中,天然免疫系统作为抵御病毒入侵的第一道防线和激活后续适应性免疫的先决条件在整个抗病毒免疫反应中发挥着十分重要的作用．     

c-di-GMP Enhances Protective Innate Immunity in a Murine Model of Pertussis

Innate immunity represents the first line of defense against invading pathogens in the respiratory tract. Innate immune cells such as monocytes, macrophages, dendritic cells, NK cells, and granulocytes contain specific pathogen-recognition molecules which induce the production of cytokines and subsequently activate the adaptive immune response. c-di-GMP is a ubiquitous second messenger that stimulates innate immunity and regulates biofilm formation, motility and virulence in a diverse range of bacterial species with potent immunomodulatory properties. In the present study, c-di-GMP was used to enhance the innate immune response against pertussis, a respiratory infection mainly caused by Bordetella pertussis. Intranasal treatment with c-di-GMP resulted in the induction of robust innate immune responses to infection with B. pertussis characterized by enhanced recruitment of neutrophils, macrophages, natural killer cells and dendritic cells. The immune responses were associated with an earlier and more vigorous expression of Th1-type cytokines, as well as an increase in the induction of nitric oxide in the lungs of treated animals, resulting in significant reduction of bacterial numbers in the lungs of infected mice. These results demonstrate that c-di-GMP is a potent innate immune stimulatory molecule that can be used to enhance protection against bacterial respiratory infections. In addition, our data suggest that priming of the innate immune system by c-di-GMP could further skew the immune response towards a Th1 type phenotype during subsequent infection. Thus, our data suggest that c-di-GMP might be useful as an adjuvant for the next generation of acellular pertussis vaccine to mount a more protective Th1 phenotype immune response, and also in other systems where a Th1 type immune response is required.     

Reconstructing immune phylogeny: new perspectives

Numerous studies of the mammalian immune system have begun to uncover profound interrelationships, as well as fundamental differences, between the adaptive and innate systems of immune recognition. Coincident with these investigations, the increasing experimental accessibility of non-mammalian jawed vertebrates, jawless vertebrates, protochordates and invertebrates has provided intriguing new information regarding the likely patterns of emergence of immune-related molecules during metazoan phylogeny, as well as the evolution of alternative mechanisms for receptor diversification. Such findings blur traditional distinctions between adaptive and innate immunity and emphasize that, throughout evolution, the immune system has used a remarkably extensive variety of solutions to meet fundamentally similar requirements for host protection.     

Proteome modifications of the medicinal leech nervous system under bacterial challenge

Once considered as lacking intrinsic immune mechanisms, the CNS of vertebrates is now known to be capable of mounting its own innate immune response. Interestingly, while invertebrates have been very useful in the interpretation of general vertebrate innate immunity mechanisms, only scarce data are available on the immune response of nervous tissue within this group. This study provides new data on the innate immune response of medicinal leech Hirudo medicinalis CNS. We identified several spots in 2-D gels of leech CNS proteins that showed specific changes following bacterial challenge, thus demonstrating the ability of the leech nervous system to mount a response to an immune stress. Protein identifications were based on comparison of sequence data with publicly available databases and a recently established leech ESTs database. The broad nature of the identified proteins suggests a clear involvement of cytoskeletal rearrangements, endoplasmic reticulum stress, modulation of synaptic activity and calcium mobilization, all during the first 24 hours of this response. Moreover, several of these proteins are specifically expressed in glial cells, suggesting an important role for glial cells in the immune response of the leech nervous system, similar to what has been observed in vertebrates.