Tunicate cytokine-like molecules and their involvement in host defense responses

The effect of infection with the entomopathogenic fungus Conidiobolus coronatus (Entomopthorales) on eighteen cytokine-like proteins in Galleria mellonella (Lepidoptera) larvae

Background

In response to the replace mammal research models with insects in preliminary immunological studies, interest has grown in invertebrate defense systems. The immunological response is regulated by cytokines; however, while their role in mammals is well understood, little is known of their function in insects. A suitable target for studies into insect immunology is Galleria mellonella (Lepidoptera), the wax moth: a common host for human fungal and bacterial pathogens. G. mellonella is also a perfect subject for studies into the presence of cytokine-like proteins.

Specific objectives

The main goal of present research was detection in insect immunocompetent cells the 18 mammalian cytokines (IL-1α, IL-1β, IL-2, IL-3, IL-6, IL-7, IL-8, IL-12, IL-13, IL-15, IL-17, IL-19, IFN-γ, TNF-α, TNF-β, GM-CSF, M-CSF, G-CSF), which play important role in immunological response and indication how their level change after fungal infection.

Methodology

The changes of cytokine-like proteins level were detected in hemocytes taken from G. mellonella larvae infected with entomopathogenic fungus, C. coronatus. The presence of cytokine-proteins was confirmed with using fluorescence microscopy (in cultured hemocytes) and flow cytometry (in freshly collected hemolymph). The ELISA test was used to detect changes in concentration of examined cytokine-like proteins.

Results

Our findings indicated the presence of eighteen cytokine-like molecules in G. mellonella hemocytes during infection with C. coronatus. The hemocytes taken from infected larvae demonstrated higher fluorescence intensity for six cytokine-like proteins (GM-CSF, M-CSF, IL-3, IL-15, IL-1β and IL-19) compared to untreated controls. ELISA test indicated significantly higher IL-3 and IL-15. M-CSF, IL-1α and IL-19 concentration in the hemolymph after fungal infection, and significantly lower TNF-β and G-CSF.

Conclusions

Our findings confirm that the selected cytokine-like molecules are present in insect hemocytes and that their concentrations change after fungal infection, which might suggest that they play a role in the anti-fungal immunological response.

Two macrophage migration inhibitory factors (MIFs) from the clam Ruditapes philippinarum: Molecular characterization, localization and enzymatic activities

Macrophage migration inhibitory factor (MIF) is an evolutionarily ancient cytokine-like factor and plays a critical role in both innate and adaptive immunity. In the present study, two MIFs (designed as RpMIF-1 and RpMIF-2, respectively) were identified and characterized from the clam Ruditapes philippinarum by rapid amplification of cDNA ends (RACE) approaches. The full-length cDNA of RpMIF-1 and RpMFI-2 consisted of 531 and 722 nucleotides, encoding a polypeptide of 113 and 114 amino acid residues, respectively. Multiple alignments and phylogenetic analysis revealed that both RpMIF-1 and RpMIF-2 belonged to the MIF family. The conserved catalytic-site Pro² for tautomerase activity was identified in the deduced amino acid sequences of RpMIFs. Both RpMIF-1 and RpMIF-2 transcripts were constitutively expressed in examined tissues of R. philippinarum with dominant expression in hepatopancreas, gills and hemocytes. Immunolocalization analysis showed that RpMIF-1 and RpMIF-2 proteins were expressed in examined tissues with the exception of adductor muscle and foot. After Vibrio anguillarum and Micrococcus luteus challenge, the mRNA expression of RpMIFs was significantly modulated in hemocytes, gills and hepatopancreas. Recombinant RpMIF-1 and RpMIF-2 proteins possessed significant tautomerase activity and oxidoreductase activity, indicating that these two proteins was perhaps involved in inflammatory responses. In summary, our results suggested that RpMIF-1 and RpMIF-2 played an important role in the innate immunity of R. philippinarum.

Flow cytometric characterization of hemocytes of the solitary ascidian, Halocynthia roretzi

Internal defense of ascidians relies, at least partially, on cells circulating in body fluids and infiltrating in tissues, referred to as hemocytes, although structure and composition of ascidian hemocytes still remain unclear. In the present study, we investigated hemocyte types and their functions of the solitary ascidian Halocynthia roretzi using flow cytometry. Based on morphology, cellular activities and intracellular parameters from the flow cytometry, we identified eight hemocyte types including, three granulocytes (Gr-1, Gr-2, and Gr-3), 4 hyalinocytes (Hy-1, Hy-1', Hy-2, and Hy-3) and lymphocyte-like (Ly-like) cells. The granulocyte Gr-1 accounted for 30% of the total circulating hemocytes and exhibited highest density of lysosomes and oxidative activity. Gr-1 was deeply involved in phagocytosis and degradation of foreign material. Hyalinocytes consist of two main populations, Hy-1 and Hy-2, and each accounted for 30% of the circulating hemocyte. Hy-1 displayed lysosomal content, an inducible oxidative activity, and no proteases, while Hy-2 expressed highest density of intracellular proteases, no lysosomes and a low oxidative activity. It was believed that Hy-2 may represent an important link between cellular and humoral immune reactions. Hy-1 did not show phagocytosis activity. Hy-3 and the Ly-like cells presented a similar profile except for their size and complexity, and Hy-3 may represent an intermediate differentiation/maturation step between Ly-like cells and other hemocyte populations. This first characterization of the hemocyte populations of H. roretzi provides a solid basis to investigate further their respective roles and functions in physiological and pathological contexts.

IL-17 signaling components in bivalves: Comparative sequence analysis and involvement in the immune responses

The recent discovery of soluble immune-regulatory molecules in invertebrates takes advantage of the rapid growth of next generation sequencing datasets. Following protein domain searches in the transcriptomes of 31 bivalve spp. and in few available mollusk genomes, we retrieved 59 domains uniquely identifying interleukin 17 (IL-17) and 96 SEFIR domains typical of IL-17 receptors and CIKS/ACT1 proteins acting downstream in the IL-17 signaling pathway. Compared to the Chordata IL-17 family members, we confirm a separate clustering of the bivalve domain sequences and a consistent conservation pattern of amino acid residues. Analysis performed at transcript and genome level allowed us to propose an updated view of the components outlining the IL-17 signaling pathway in Mytilus galloprovincialis and Crassostrea gigas (in both species, homology modeling reduced the variety of IL-17 domains to only two 3D structures). Digital expression analysis indicated more heterogeneous expression levels for the mussel and oyster IL-17 ligands than for IL-17 receptors and CIKS/CIKSL proteins. Besides, new qPCR analyses confirmed such gene expression trends in hemocytes and gills of mussels challenged with heat-killed bacteria. These results uphold the involvement of an ancient IL-17 signaling pathway in the bivalve immune responses and, likewise in humans, suggest the possibility of distinctive modulatory roles of individual IL-17s/IL-17 receptors. Overall, the common evidence of pro-inflammatory cytokines and inter-related intracellular signaling pathways in bivalves definitely adds complexity to the invertebrate immunity.

Analysis of genes isolated from plated hemocytes of the Pacific oyster, Crassostreas gigas

A complementary deoxyribonucleic acid library was constructed from hemocytes of Crassostrea gigas that had been plated on poly-lysine plates for 24 h. From this library, 2,198 expressed sequence tags (ESTs) of greater than or equal to 100 bp were generated and analyzed. A large number of genes that potentially could be involved in the physiology of the oyster hemocyte were uncovered. They included proteins involved in cytoskeleton rearrangement, proteases and antiproteases, regulators of transcription and translation, cell death regulators, receptors and their associated protein factors, lectins, signal transduction proteins, and enzymes involved in eicosanoid and steroid synthesis and xenobiotic metabolism. Based on their relationship with innate immunity, the expression of selected genes was analyzed by quantitative polymerase chain reaction in gills from bacterial-challenged oysters. Several genes observed in the library were significantly upregulated by bacterial challenge including interleukin 17, astacin, cystatin B, the EP4 receptor for prostaglandin E, the ectodysplasin receptor, c-jun, and the p100 subunit of nuclear factor-kB. Using a similar approach, we have been analyzing the genes expressed in trout macrophages. While there are significant differences between the types of genes present in vertebrate macrophages compared with oyster hemocytes, there are some striking similarities including proteins involved in cytoskeletal rearrangement, proteases and antiproteases, and genes involved in certain signal transduction pathways underlying immune processes such as phagocytosis. Finally, C. virginica homologs of some of the C. gigas genes uncovered in the ESTs were obtained by aligning the ESTs reported here, against the assembled C. virginica ESTs at the National Center for Biotechnology Information.

Cytotoxic activity of a dichloromethane extract and fractions obtained from Eudistoma vannamei (Tunicata: Ascidiacea)

This study consists of the bioassay-guided fractionation of the dichloromethane extract from Eudistoma vannamei and the pharmacological characterization of the active fractions. The dried hydromethanolic extract dissolved in aqueous methanol was partitioned with dichloromethane and chromatographed on a silica gel flash column. The anti-proliferative effect was monitored by the MTT assay. Four of the latest fractions, numbered 14 to 17, which held many chemical similarities amongst each other, were found to be the most active. The selected fractions were tested for viability, proliferation and death induction on cultures of HL-60 promyeloblastic leukemia cells. The results suggested that the observed cytotoxicity is related to apoptosis induction.

Rapid accumulation of an interleukin 17 homolog transcript in Crassostrea gigas hemocytes following bacterial exposure

Interleukin-17 (IL-17) gene models have been found in the sequenced genomes of Strongylocentrotus purpuratus and Caenorhabditis elegans. However, there have been no published reports on the empirical cloning and characterization of any interleukin cDNAs in invertebrates. From a Pacific oyster (Crassostrea gigas) hemocyte cDNA library, two clones were obtained that encoded a protein similar to vertebrate IL-17s. The putative oyster IL-17 homolog (CgIL-17) was 27% identical to rainbow trout IL-17D, 21% to human IL-17D and 24% to an IL-17D-like gene model obtained from the annotation of the sea urchin genome. IL-17s from the oyster, sea urchin, trout and human, contained conserved cysteine residues found in all forms of IL-17 in mammals. Injection of bacteria into C. gigas oysters produced a large and rapid elevation in CgIL-17 transcript abundance in hemocytes, suggesting that this is a very early response gene to pathogens that may be responsible for the stimulation of other immune genes in the oyster.

Inducible lectins with galectin properties and human IL1α epitopes opsonize yeast during the inflammatory response of the ascidian Ciona intestinalis

Studies on inducible ascidian lectins may shed light on the evolutionary emergence of cytokine functions. Here, we show that the levels of opsonins, with IL1alpha-epitopes, increase in Ciona intestinalis hemolymph as a response to an inflammatory stimulus and, in particular, to intratunic injection of lipopolysaccharide (LPS). The inflammatory agent promptly (within 4 h) enhances Ca(2+)-independent serum hemagglutinating and opsonizing activities, which are both inhibited by D-galactose and D-galactosides (alpha-lactose, N-acetyl-D-lactosamine, thio-digalactoside), suggesting that anti-rabbit erythrocyte lectins with galectin properties are involved as opsonins. Inducible galectin molecules contain interleukin-1alpha (IL1alpha) epitopes, and their activities are specifically inhibited by anti-human recombinant IL1alpha antibody. Analysis by SDS-polyacrylamide gel electrophoresis has revealed that the density of the bands of several serum proteins increases within 4 h after LPS injection, correlated with the enhanced serum activity. Moreover, Western blot patterns demonstrate that several serum proteins (59, 37, 30, 23, 15 kDa) cross-react with the antibody as early as 4 h post-injection. Although we have not been able to establish whether, in adition to galectins, various types of D-galactose-specific lectins are contained in the serum, we show, for the first time in invertebrates, that galectin molecules with opsonic properties can be enhanced in response to a non-specific inflammatory stimulus, and that their release can be further stimulated by LPS. Finally, we reveal that multiple galectins share human IL1alpha epitopes, probably because of steric configuration and the oligomerization process.

Proteases and protease inhibitors: a balance of activities in host-pathogen interaction

The immune system is the collection of effector molecules and cells of the host that act against invading parasites and their products. Secreted proteases serve important roles in parasitic metabolism and virulence and the several families of protein protease inhibitors of the plasma and blood cells play an important role in immunity by inactivating and clearing the protease virulence factors of parasites. The protease inhibitors are of two classes, the active-site inhibitors and the alpha2-macroglobulins. Inhibitors for the first class bind and inactivate the active site of the target protease. Proteins of the second class bind proteases by a unique molecular trap mechanism and deliver the bound protease to a receptor-mediated endocytic system for degradation in secondary lysosomes. Proteins of the alpha2-macroglobulin family are present in a variety of animal phyla, including the nematodes, arthropods, mollusks, echinoderms, urochordates, and vertebrates. A shared suite of unique functional characteristics have been documented for the alpha2-macroglobulins of vertebrates, arthropods, and mollusks. The alpha2-macroglobulins of nematodes, arthropods, mollusks, and vertebrates show significant sequence identity in key functional domains. Thus, the alpha2-macroglobulins comprise an evolutionarily conserved arm of the innate immune system with similar structure and function in animal phyla separated by 0.6 billion years of evolution.