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1.
The insect cellular immune response   总被引:8,自引:0,他引:8  
The innate immune system of insects is divided into humoral defenses that include the production of soluble effector molecules and cellular defenses like phagocytosis and encapsulation that are mediated by hemocytes. This review summarizes current understand- ing of the cellular immune response. Insects produce several terminally differentiated types of hemocytes that are distinguished by morphology, molecular and antigenic markers, and function. The differentiated hemocytes that circulate in larval or nymphal stage insects arise from two sources: progenitor cells produced during embryogenesis and mesodermally derived hematopoietic organs. Regulation of hematopoiesis and hemocyte differentiation also involves several different signaling pathways. Phagocytosis and encapsulation require that hemocytes first recognize a given target as foreign followed by activation of downstream signaling and effector responses. A number of humoral and cellular receptors have been identified that recognize different microbes and multicellular parasites. In turn, activation of these receptors stimulates a number of signaling pathways that regulate different hemocyte functions. Recent studies also identify hemocytes as important sources Of a number of humoral effector molecules required for killing different foreign invaders.  相似文献   

2.
A number of cytochemical parameters of the hemocytes of larval Galleria mellonella, an insect frequently used as a model by comparative cellular immunologists, are described. Cytochemical methods were used to quantify hemocyte granule-associated components, the results are compared to those obtained for leukocytes from higher animals. Granulocytes contained a population of nonlysosomal granules rich in mucopolysaccharide not seen in plasmatocytes. The numbers and dimensions of these granules showed a positive correlation to cell size, probably reflecting a developmental sequence in granulocyte maturation. Both granulocytes and plasmatocytes had other granules containing the typical lysosomal enzymes, acid phosphatase, beta-glucuronidase, esterase, and lysozyme. The nonlysosomal enzyme alkaline phosphatase was not found in Galleria hemocytes; it is also absent from vertebrate monocytes, macrophages, and immature polymorphonuclear leukocytes. Insect hemocytes appear to lack certain components of antibacterial systems typical of mammalian blood cells, such as H2O2-generating systems, cationic proteins, and myeloperoxidase. The bactericidal mechanisms of hemocytes probably involve lysozyme, as well as other biologically active cellular and humoral factors unique to insects.  相似文献   

3.
Cell-mediated immune responses of insects involve interactions of two main classes of blood cells (hemocytes) known as granular cells and plasmatocytes. In response to a foreign surface, these hemocytes suddenly transform from circulating, non-adherent cells to cells that interact and adhere to each other and the foreign surface. This report presents evidence that during this adhesive transformation the extracellular matrix (ECM) proteins lacunin and a ligand for peanut agglutinin (PNA) lectin are released by granular cells and bind to surfaces of both granular cells and plasmatocytes. ECM protein co-localizes on cell surfaces with the adhesive receptors integrin and neuroglian, a member of the immunoglobulin superfamily. The ECM protein(s) secreted by granular cells are hypothesized to interact with adhesion receptors such as neuroglian and integrin by cross linking and clustering them on hemocyte surfaces. This clustering of receptors is known to enhance the adhesiveness (avidity) of interacting mammalian immune cells. The formation of ring-shaped clusters of these adhesion receptors on surfaces of insect immune cells represents an evolutionary antecedent of the mammalian immunological synapse.  相似文献   

4.
Insect hemocytes have historically been identified on the basis of morphology, ultrastructure and hypothesized function. Among insects in the order Lepidoptera, five hemocyte classes are usually recognized: granular cells, plasmatocytes, spherule cells, oenocytoids and prohemocytes. We have generated a panel of monoclonal antibodies (mAbs) against hemocytes of the moth Pseudoplusia includens. In this study, hemocyte identification using 16 different mAbs was compared to identification methods using morphological characters. Three main categories of mAb binding activity were identified: (1) mAbs that specifically labeled only one morphological class of hemocytes, (2) mAbs that labeled granular cells and spherule cells, and (3) mAbs that labeled plasmatocytes and oenocytoids. With one exception, none of the antibodies bound to other tissues in P. includens. However, certain mAbs that specifically labeled granular cells and/or spherule cells in separated hemocyte populations also labeled plasmatocytes co-cultured with granular cells or cultured in granular cell conditioned medium. Overall, our results suggest that granular cells are antigenically related to spherule cells, and that plasmatocytes are antigenically related to oenocytoids. The use of mAbs as hemocyte markers are discussed.  相似文献   

5.
The hemocytes, the blood cells of Drosophila, participate in the humoral and cellular immune defense reactions against microbes and parasites [1-8]. The plasmatocytes, one class of hemocytes, are phagocytically active and play an important role in immunity and development by removing microorganisms as well as apoptotic cells. On the surface of circulating and sessile plasmatocytes, we have now identified a protein, Nimrod C1 (NimC1), which is involved in the phagocytosis of bacteria. Suppression of NimC1 expression in plasmatocytes inhibited the phagocytosis of Staphylococcus aureus. Conversely, overexpression of NimC1 in S2 cells stimulated the phagocytosis of both S. aureus and Escherichia coli. NimC1 is a 90-100 kDa single-pass transmembrane protein with ten characteristic EGF-like repeats (NIM repeats). The nimC1 gene is part of a cluster of ten related nimrod genes at 34E on chromosome 2, and similar clusters of nimrod-like genes are conserved in other insects such as Anopheles and Apis. The Nimrod proteins are related to other putative phagocytosis receptors such as Eater and Draper from D. melanogaster and CED-1 from C. elegans. Together, they form a superfamily that also includes proteins that are encoded in the human genome.  相似文献   

6.
Insect immune system comprises of both humoral and cellular defenses. Nodulation is one of the major, yet very poorly understood cellular responses against microbial infections in insects. Through screening for novel immune genes from an Indian saturniid silkmoth Antheraea mylitta, we identified a protein up-regulated in hemolymph within minutes upon bacterial challenge. We have shown here, for first time, the involvement of this novel protein in mediating nodulation response against bacteria and hence designated it as Noduler. Noduler possessed a characteristic reeler domain found in several extracellular matrix vertebrate proteins. Noduler was shown in vitro to bind a wide range of bacteria, yeast, and also insect hemocytes. Furthermore, Noduler specifically bound LPS, lipotechoic acid, and beta-1, 3 glucan components of microbial cell walls. RNA-interference mediated knock-down of the Noduler resulted in significant reduction in the number of nodules and consequent increase in bacterial load in larval hemolymph. The results suggest that the Noduler is widely conserved and is involved in very early clearance of bacteria by forming nodules of hemocytes and bacterial complexes in insects. The results would promote further studies for understanding of the crucial but hitherto overlooked nodulation mechanism in insects and also provide cues for the study of similar mammalian proteins whose function is not understood.  相似文献   

7.
Mosquitoes are important vectors of disease. These insects respond to invading organisms with strong cellular and humoral immune responses that share many similarities with vertebrate immune systems. The strength and specificity of these responses are directly correlated to a mosquito's ability to transmit disease. In the current study, we characterized the hemocytes (blood cells) of Armigeres subalbatus by morphology (ultrastructure), lectin binding, enzyme activity, immunocytochemistry, and function. We found four hemocyte types: granulocytes, oenocytoids, adipohemocytes, and thrombocytoids. Granulocytes contained acid phosphatase activity and bound the exogenous lectins Helix pomatia agglutinin, Galanthus nivalis lectin, and wheat germ agglutinin. Following bacteria inoculation, granulocytes mounted a strong phagocytic response as early as 5 min postexposure. Bacteria also elicited a hemocyte-mediated melanization response. Phenoloxidase, the rate-limiting enzyme in the melanization pathway, was present exclusively in oenocytoids and in many of the melanotic capsules enveloping bacteria. The immune responses mounted against different bacteria were not identical; gram(–) Escherichia coli were predominantly phagocytosed and gram(+) Micrococcus luteus were melanized. These studies implicate hemocytes as the primary line of defense against bacteria.This work was supported by NIH grant AI19769 to B.M.C. and NIH grant F31 AI50252 to J.F.H.  相似文献   

8.
The present study focuses on the ability of Pterostichus melas italicus Dejean to mount cellular and humoral immune responses against invading pathogens. Ultrastructural analyses revealed the presence of five morphologically distinct types of hemocytes: prohemocytes, plasmatocytes, granulocytes, oenocytoids and macrophage-like cells. Differential hemocyte counts showed that plasmatocytes and granulocytes were the most abundant circulating cell types and plasmatocytes exhibited phagocytic activity following the latex bead immune challenge. Macrophage-like cells were recruited after the immune challenge to remove exhausted phagocytizing cells, apoptotic cells and melanotic capsules formed to immobilize the latex beads. Total hemocyte counts showed a significant reduction of hemocytes after latex bead treatment. Phenoloxidase (PO) assays revealed an increase of total PO in hemolymph after immune system activation with lipopolysaccharide (LPS). Moreover, the LPS-stimulated hemocytes showed increased protein expression of inducible nitric oxide synthase, indicating that the cytotoxic action of nitric oxide was engaged in this antimicrobial collaborative response. These results provide a knowledge base for further studies on the sensitivity of the P. melas italicus immune system to the environmental perturbation in order to evaluate the effect of chemicals on non-target species in agroecosystems.  相似文献   

9.
The innate immune system of insects consists of humoral and cellular components involved in the recognition of and responses to intruding foreign micro- or macroorganisms. Several molecules have been identified so far that recognize molecular patterns present on microorganisms, such as lipopolysaccharides, peptidoglycans and lipoteichonic acid. These molecules, acting as opsonins, trigger immune responses such as phagocytosis, nodule formation, melanization and encapsulation. Here, we investigated the role of calreticulin (CRT) present on the surface of Pieris rapae hemocytes in phagocytosis. Comparative phagocytosis assays using yeast cells showed that hemocytes from different insects exhibit significant variation in their phagocytosing potential and relative CRT involvement.  相似文献   

10.
Drosophila has highly efficient defenses against infection. These include both cellular immune responses, such as the phagocytosis of invading microorganisms, and humoral immune responses, such as the secretion of antimicrobial peptides into the hemolymph [1] [2]. These defense systems are thought to interact, but the nature and extent of these interactions is not known. Here we describe a method for inhibiting phagocytosis in Drosophila blood cells (hemocytes) by injecting polystyrene beads into the body cavity. This treatment does not in itself make a fly susceptible to Escherichia coli infection. However, when performed on flies carrying the mutation immune deficiency (imd), which affects the humoral immune response [3], the treatment results in a striking decrease in resistance to infection. We therefore carried out a sensitized genetic screen to identify immunocompromised mutants by co-injecting beads and E. coli. From this screen, we identified a new gene we have named red shirt and identified the caspase Dredd as a regulator of the Drosophila immune response. The observation that mutants with defects in the humoral immune response are further immunocompromised by blocking phagocytosis, and thus inhibiting the cellular immune response, shows that the Drosophila cellular and humoral immune responses act in concert to fight infection.  相似文献   

11.
The immune interactions occurring between parasitoids and their host insects, especially in Drosophila–wasp models, have long been the research focus of insect immunology and parasitology. Parasitoid infestation in Drosophila is counteracted by its multiple natural immune defense systems, which include cellular and humoral immunity. Occurring in the hemocoel, cellular immune responses involve the proliferation, differentiation, migration and spreading of host hemocytes and parasitoid encapsulation by them. Contrastingly, humoral immune responses rely more heavily on melanization and on the Toll, Imd and Jak/Stat immune pathways associated with antimicrobial peptides along with stress factors. On the wasps’ side, successful development is achieved by introducing various virulence factors to counteract immune responses of Drosophila. Some or all of these factors manipulate the host's immunity for successful parasitism. Here we review current knowledge of the cellular and humoral immune interactions between Drosophila and its parasitoids, focusing on the defense mechanisms used by Drosophila and the strategies evolved by parasitic wasps to outwit it.  相似文献   

12.
Eicosanoid actions in insect cellular immune functions   总被引:1,自引:0,他引:1  
Insects are more or less constantly challenged with a daunting array of pathogenic organisms, including viruses, bacteria, fungi, protozoans as well as various metazoan parasites and parasitoids. At the first level of defense, the pathogens are rebuffed by physical barriers, including the cuticle and peritrophic membrane. Upon breaching these barriers, pathogens meet with an arsenal of robust and efficacious immune defense mechanisms. Two general categories of defenses are typically recognized, humoral defenses and hemocytic or cellular defenses. The former involves induced synthesis of various antibacterial proteins and peptides, such as cecropins and lysozyme. Cellular defense mechanisms are characterized by direct interactions between circulating hemocytes and the invaders. These include phagocytosis, microaggregation, nodulation, and encapsulation. Microaggregation is a step in the nodulation process, which is responsible for clearing the bulk of bacterial infections from circulation. Coordinated cellular actions lead to encapsulation of invaders, such as parasitoid eggs, that are very much larger than individual hemocytes. While the defense mechanisms are broadly appreciated, less is known about the biochemical signals responsible for mediating and coordinating the cellular actions. We now know eicosanoids mediate phagocytosis, microaggregation, and nodulation reactions to immune challenge, as well as cell spreading, a specific step in nodulation. We have several goals in this mini review. We provide a brief background on cellular immunity, outline eicosanoid biosynthesis, and review eicosanoid actions in cellular immunity in insects. Recent work indicates some pathogens have usurped eicosanoid‐mediated immunity; they disable insect immunity by inhibiting eicosanoid biosynthesis. We interpret these findings and their significance with respect to the biological control of insects. We also present preliminary work designed to test hypotheses on how eicosanoids exert their actions. We address shortcomings in our knowledge on eicosanoids in insect biology.  相似文献   

13.
14.
The braconid wasp Microplitis demolitor carries Microplitis demolitor bracovirus (MdBV) and parasitizes the larval stage of several noctuid moths. A key function of MdBV in parasitism is suppression of the host's cellular immune response. Prior studies in the host Pseudoplusia includens indicated that MdBV blocks encapsulation by preventing two types of hemocytes, plasmatocytes and granulocytes, from adhering to foreign targets. The other main immune response mediated by insect hemocytes is phagocytosis. The goal of this study was to determine which hemocyte types were phagocytic in P. includens and to assess whether MdBV infection affects this defense response. Using the bacterium Escherichia coli and inert polystyrene beads as targets, our results indicated that the professional phagocyte in P. includens is granulocytes. The phagocytic responses of granulocytes were very similar to those of High Five cells that prior studies have suggested are a granulocyte-like cell line. MdBV infection dose-dependently disrupted phagocytosis in both cell types by inhibiting adhesion of targets to the cell surface. The MdBV glc1.8 gene encodes a cell surface glycoprotein that had previously been implicated in disruption of adhesion and encapsulation responses by immune cells. Knockdown of glc1.8 expression by RNA interference (RNAi) during the current study rescued the ability of MdBV-infected High Five cells to phagocytize targets. Collectively, these results indicate that glc1.8 is a key virulence determinant in disruption of both adhesion and phagocytosis by insect immune cells.  相似文献   

15.
Galleria mellonella and Pieris brassicae larvae were injected with a standardized dose of killed Bacillus cereus and other bacteria and the reactions of hemocytes followed in the first 24 hr by dissection and histology. Nodules formed in all insects injected with nonpathogens, but a pathogen, Staphylococcus aureus, failed to provoke this reaction. Within 5 min, clumps consisting of granular hemocytes, plasmatocytes, and bacteria were found attached to the internal surfaces of the insects. In the following hours, the cells comprising the clumps broke down and merged with a melanizing acellular substance, and the necrosing masses became encapsulated by plasmatocytes to form mature nodules. The role of granular hemocytes in the formation of the initial cell/bacteria aggregates is discussed along with the possible importance of nodules to the cellular defense reactions of insects.  相似文献   

16.
In this study, we examined cellular immune responses in the flesh fly, Sarcophaga bullata, when parasitized by the ectoparasitoid Nasonia vitripennis. In unparasitized, young pharate adults and third instar, wandering larvae of S. bullata, four main hemocyte types were identified by light microscopy: plasmatocytes, granular cells, oenocytoids, and pro-hemocytes. Parasitism of young pharate adults had a differential effect on host hemocytes; oenocytoids and pro-hemocytes appeared to be unaltered by parasitism, whereas adhesion and spreading behavior were completely inhibited in plasmatocytes and granular cells by 60 min after oviposition. The suppression of spreading behavior in granular cells lasted the duration of parasitism. Plasmatocytes were found to decline significantly during the first hour after parasitism and this drop was attributed to cell death. Melanization and clotting of host hemolymph did not occur in parasitized flies, or the onset of both events was retarded by several hours in comparison to unparasitized pharate adults. Hemocytes from envenomated flies were altered in nearly identical fashion to that observed for natural parasitism; the total number of circulating hemocytes declined sharply by 60 min post-envenomation, the number of plasmatocytes declined but not granular cells, and the ability of plasmatocytes and granular cells to spread when cultured in vitro was abolished within 1 h. As with parasitized hosts, the decrease in plasmatocytes was due to cell death, and inhibition of spreading lasted until the host died. Isolated crude venom also blocked adhesion and spreading of these hemocyte types in vitro. Thus, it appears that maternally derived venom disrupts host immune responses almost immediately following oviposition and the inhibition is permanent. The possibility that this ectoparasite disables host defenses to afford protection to feeding larvae and adult females is discussed.  相似文献   

17.
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19.
Hemocytes collected from larvae of Pseudoplusia includens (Lepidoptera: Noctuidae) were separated by centrifugation on Percoll cushions. The procedure resulted in 95% purity of plasmatocytes and greater than 99% purity of granular and spherule cells. Medium supplemented with chicken serum enhanced cell viability and promoted spreading of plasmatocytes. Cell-free plasma and medium preconditioned by plasmatocytes or granular cells stabilized cells in vitro and also accelerated spreading of plasmatocytes relative to medium supplemented with chicken serum. Oenocytoids were the only morphotype that exhibited endogenous phenoloxidase activity, while granular cells and plasmatocytes were the only cells that endocytosed fluorescent beads in vitro. Granular cells and plasmatocytes ingested fluorescently labelled beads, both in mixed populations of hemocytes and after separation. Plasmatocytes were the only morphotype that encapsulated large foreign targets in vitro following separation. Separated granular cells attached and spread on the surface of foreign targets but never formed a multilayered capsule.  相似文献   

20.
In Drosophila melanogaster larvae, three classes of circulating cellular immune surveillance cells (hemocytes) can be identified: plasmatocytes, crystal cells, and lamellocytes. Plasmatocytes are professional phagocytes most similar to the mammalian monocyte/macrophage lineage and make up approximately 95% of circulating hemocytes. The other approximately 5% of circulating hemocytes consists of crystal cells, which secrete components necessary for the melanization of invading organisms, as well as for wound repair. A third cell type known as lamellocytes are rarely seen in healthy larvae and are involved in the encapsulation of invading pathogens. There are no obvious mammalian counterparts for crystal cells or lamellocytes, and there is no equivalent to the lymphoid lineage in insects. In this review, I will discuss what is currently known about Drosophila hemopoiesis and the cellular immune response and where possible compare it to vertebrate mechanisms.  相似文献   

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