Immune response of teleost fish to helminth parasite infection

STAM2 negatively regulates the MyD88-mediated NF-κB signaling pathway in miiuy croaker, Miichthys miiuy

Signal transducing adapter molecule 2 (STAM2), a member of the Signal Transducing Adapter Molecule (STAM) family, is a protein with significant implications in diverse signaling pathways and endocytic membrane trafficking. However, the role of the STAM2, especially in fish, remains largely unknown. In this study, we discovered that STAM2 negatively regulates the NF-κB signaling pathway, and its inhibitory effect is enhanced upon LPS induction. Our study confirmed that STAM2 can enhance the degradation of myeloid differentiation primary-response protein 88 (MyD88), an upstream regulator of NF-κB pathway. Furthermore, the UIM domain of STAM2 is important for the inhibition of MyD88. Mechanistically, STAM2 inhibits the NF-κB signaling pathway by targeting the MyD88 autophagy pathway. In addition, we showed that STAM2 promotes the proliferation of Vibrio harveyi. In summary, our study reveals that STAM2 inhibits NF-κB signaling activation and mediates innate immunity in teleost via the autophagy pathway.

Mucosal immune responses of gut IgM in common carp (Cyprinus carpio) following infection with spring viremia of carp virus (SVCV)

Immunoglobulin M (IgM) specifically recognizes various antigens and can activate complement, mediate cytotoxicity, opsonize and agglutinate pathogens to induce phagocytosis, all of which play an important role in immunity. However, the IgM response of common carp (Cyprinus carpio) in the intestinal mucosa after viral infection has not been thoroughly. Therefore, we successfully produced an anti-carp IgM monoclonal antibody and developed a model of viral infection to study the kinetics of immune responses after viral infection. Our results showed that the expression of IL1-β and Igs were dramatically increased, implying that common carp exhibited a significant innate and adaptive immune response to viral infection. Furthermore, we found that the IgM responses varied between the two infection strategies. At 14 days post-infection (DPI), a significant population of IgM+ B cells were observed in the gut, accompanied by a sharp rise in IgM levels. The immune response to secondary infection started at 7 DPI, suggesting that the IgM response is faster in the gut after re-infection. Importantly, we also explored the variability of different gut compartments to viral infection, and result revealed a stronger immune response in the hindgut than in the foregut and midgut. Overall, our findings indicate that IgM plays an important role in the intestinal immune response following primary and secondary viral infection, in which the hindgut plays a major immune function.

Infection of endemic chub Squalius tenellus with the intestinal tapeworm Caryophyllaeus brachycollis (Cestoda): histopathology and ultrastructural surveys

The endemic chub Squalius tenellus (Heckel, 1843) was introduced more than 100 years ago to Lake Blidinje (Bosnia-Herzegovina). Only 1 species of enteric helminth was found in a sample of 35 chubs, the tapeworm Caryophyllaeus brachycollis (Janiszewska, 1953). The paper includes histopathological investigation with identification of innate immune cells involved in host reaction and molecular data allowed correct designation of the cestode species. Of 35 specimens of chub examined, 21 (60%) harboured individuals of C. brachycollis and a total of 1619 tapeworms were counted, the intensity of infection ranged from 1 to 390 worms per fish (46.2 ± 15.3, mean ± s.e.). Histopathological and ultrastructural investigations showed strict contact between the worm's body and the epithelia and increase in the number of mucous cells, rodlet cells among the epithelial cells. Within the tunica propria-submucosa, beneath the site of scolex attachment, numerous neutrophils and mast cells were noticed. This is the first study of the occurrence of C. brachycollis in chub from Lake Blidinje and on the response of the innate immune cells of S. tenellus to this tapeworm. Interestingly, in 3 very heavily infected chubs, perforation of the intestinal wall was documented; this is uncommon among cestodes which use fish as a definitive host.

Fish endoparasite metacommunity in environments with different degrees of conservation in the western Brazilian Amazon

Parasite communities correspond to the definition of metacommunity, as species interact and disperse within hosts. The present study evaluated parasite metacommunities in a tropical floodplain. The study was conducted in the Western Amazon around the municipalities of Cruzeiro do Sul, state of Acre, and Guajará, state of Amazonas, Brazil. Six sampling sites were selected and grouped into conserved and degraded environments. Fish were caught between periods of drought and flood, using passive and active sampling methods; in the laboratory, they were measured weighed, and necropsied. Parasites found were fixed, evaluated, and identified. Physical and chemical variables and environmental conservation characteristics were measured in all sites. Diversity index, ANOVA, Tukey, local contribution to beta diversity (LCBD), species contribution to beta diversity by individual species (SCBD), and variance partitioning were summarized. The α species diversity increased in conserved environments and varied between seasonal periods, mainly in detritivorous and omnivorous hosts. Local contributions to beta diversity showed significantly higher values in conserved environments for the endoparasite fauna of piscivorous and omnivorous hosts, indicating that these environments presented unique parasite infracommunities and revealing the conservation status of these environments. Variations in infracommunities were explained mainly by niche-based processes, including environmental conditions, degree of conservation, and host characteristics. Thus, these data will serve as a tool to understand the way parasite communities are structured, which is important information for the management and conservation of aquatic environments.

Revealing the environmental pollution of two estuaries through histopathological biomarkers in five fishes from different trophic guilds of northeastern Brazil

Estuaries in Brazil are mostly anthropically affected due to the discharge of industrial and domestic effluents. In two of them, the Santa Cruz Channel Estuary (ITAP) and Sirinhaém River Estuary (SIR), historically affected by mercury pollution and sugarcane industry in Northeast Brazil, we assessed environmental pollution using liver and gill histopathological biomarkers in fish from different trophic levels. Liver samples exhibited serious damages such as hepatic steatosis, necrosis, and infiltration. The gills showed moderate to severe changes, such as lifting of epithelial cells, lamellar aneurysm, and rupture of lamellar epithelium. Most of the changes in the liver and gills were reported for species Centropomus undecimalis and the Gobionellus stomatus, which were considered as good sentinels of pollution. The combination of biomarker methodologies was efficient in diagnosing the serious damage to the species, reinforcing the need for monitoring the health of the ecosystems evaluated.

A multi-level assessment of biological effects associated with mercury concentrations in smallmouth bass, Micropterus dolomieu

Total mercury (THg) was measured in muscle (fillet) and liver tissue of adult smallmouth bass Micropterus dolomieu collected at multiple sites in the Potomac and Susquehanna River drainages within the Chesapeake Bay watershed. Smallmouth bass in these drainages have experienced episodic mortality events, a high prevalence of skin lesions and reproductive endocrine disruption (intersex or testicular oocytes and plasma vitellogenin in males). A multi-level assessment of general and reproductive health including indicators at the organismal, organ, cellular and molecular levels was conducted on adult smallmouth bass during the spring (prespawn) season. Concentrations of THg were correlated with increased visible abnormalities, increased macrophage aggregates and tissue parasite burdens. In male bass positive correlations of THg were observed with plasma vitellogenin and hepatic transcript abundance of estrogen receptor β1 and androgen receptor α, while there was a negative association with estrogen receptors α and β2 and androgen receptors β. In female bass there was a negative correlation between THg and plasma vitellogenin as well as hepatic transcript abundance of vitellogenin, choriogenin, estrogen receptor β2 and 17β hydroxysteroid dehydrogenase. Associations of THg concentrations with various biological indicators suggest mercury may be an important environmental stressor contributing to the observed adverse effects in smallmouth bass populations.

Endoparasite fauna of freshwater fish from the upper Juruá River in the Western Amazon, Brazil

The Amazon region may present a high diversity of endoparasites with a high degree of endemism. In this sense, this study describes the endoparasite fauna in freshwater fish from the Upper Juruá, in the Western Amazon. The study was carried out around the municipalities of Cruzeiro do Sul, state of Acre, and Guajará, state of Amazonas, Brazil. Fish were caught between periods of droughts and floods, using passive and active sampling methods. In the laboratory, specimens were biometrically analysed and necropsied. As a result, a total of 23,740 endoparasites were recorded, belonging to 62 species, with 91 new host reports and 91 new occurrences for the Western Amazon. Nematoda and Digenea were the most diverse and abundant groups, and the increase in host fish richness and diversity influenced the diversity and richness of endoparasites in the environments. In this sense, the present study expands the number of new reports, and contributes data on the distribution and richness of endoparasites for South America.

Matrix metalloproteinase-25 from Japanese sea bass (Lateolabrax japonicus) is involved in pro-inflammatory responses

Matrix metalloproteinases (MMPs) are highly expressed in leukocytes and macrophages, which play a role in the innate immune response. Here, the cDNA sequence of MMP25 from Japanese sea bass (Lateolabrax japonicus) (LjMMP25) was identified. Phylogenetic analysis revealed that LjMMP25 was most closely related to large yellow croaker MMP25. Multiple sequence alignment of LjMMP25 with MMP25 sequences from other teleosts revealed that regions of known functional importance were highly conserved. Expression analysis revealed that LjMMP25 was highly expressed in the head kidney and widely expressed in other tissues including gill, spleen, and liver. LjMMP25 was found to regulate inflammatory cytokine production and promote phagocytosis and bacterial killing in monocytes/macrophages (MO/MФ). Furthermore, LjMMP25 regulated the inflammatory response by modulating NF-κB signaling. These findings reveal new information about the role of LjMMP25 in regulating pro-inflammatory responses in this species.

Severe Natural Outbreak of Cryptocaryon irritans in Gilthead Seabream Produces Leukocyte Mobilization and Innate Immunity at the Gill Tissue

The protozoan parasite Cryptocaryon irritans causes marine white spot disease in a wide range of fish hosts, including gilthead seabream, a very sensitive species with great economic importance in the Mediterranean area. Thus, we aimed to evaluate the immunity of gilthead seabream after a severe natural outbreak of C. irritans. Morphological alterations and immune cell appearance in the gills were studied by light microscopy and immunohistochemical staining. The expression of several immune-related genes in the gills and head kidney were studied by qPCR, including inflammatory and immune cell markers, antimicrobial peptides (AMP), and cell-mediated cytotoxicity (CMC) molecules. Serum humoral innate immune activities were also assayed. Fish mortality reached 100% 8 days after the appearance of the C. irritans episode. Gill filaments were engrossed and packed without any space between filaments and included parasites and large numbers of undifferentiated and immune cells, namely acidophilic granulocytes. Our data suggest leukocyte mobilization from the head kidney, while the gills show the up-regulated transcription of inflammatory, AMPs, and CMC-related molecules. Meanwhile, only serum bactericidal activity was increased upon infection. A potent local innate immune response in the gills, probably orchestrated by AMPs and CMC, is triggered by a severe natural outbreak of C. irritans.

Effects of Different Temperatures on the Antibacterial, Immune and Growth Performance of Crucian Carp Epidermal Mucus

Fish is one of the important sources of energy and protein, and proper water temperature is key to successful fish breeding. The authors of this study evaluated crucian carp growth, mucus antibacterial properties, and immune indicators at 17, 21, 24, 27, and 31 °C. The results indicated that in the range of 17–31 °C, the resistance of epidermal mucus to Vibrio harveyi decreased with temperature rising. At 24 and 27 °C, the activities of lysozyme and catalase significantly increased; alkaline phosphatase activity, superoxide dismutase activity, and total protein concentration first increased and then decreased with rising temperature; the highest values were observed at 24 °C, with increases of 56.55%, 26.64%, and 44.52%, respectively, compared to those under the 17 °C treatment. When the treatment reached 27 °C, the temperature had an effect on the growth and antibacterial properties of crucian carp, and the activities of alkaline phosphatase and superoxide dismutase were significantly reduced. At temperatures of 17–24 °C, the survival rate of crucian carp could reach more than 93%, and at the temperature of 24 °C, the specific growth rate reached the highest value of 43.29%. Therefore, the most favorable temperature for the long-term breeding of crucian carp was found to be 24 °C. This study provides a favorable experimental basis for the establishment of intelligent aquaculture systems and the setting of water environment parameters.

Dose-dependent co-infection of Argulus sp. and Aeromonas hydrophila in goldfish (Carassius auratus) modulates innate immune response and antioxidative stress enzymes

Co-infection with parasites and bacteria is of frequent occurrence in aquaculture, leads to growth impedance otherwise mortality in fish depending on the varying degree of a load of primary pathogen either parasite or bacteria. The mechanistic regulation of immune response during co-infection in fish has merely documented. The aim of this study was to determine the impact of co-infection with Aeromonas hydrophila at three exposure doses of Argulus sp. on the innate immune responses and antioxidative stress enzymes of goldfish (Carassius auratus). The experimental fish were randomly distributed into eight treatment groups viz. T1 (control group without Argulus and A. hydrophila infection), T2 (fish exposed to a sub-lethal dose of A. hydrophila), T3 (low Argulus-infested fish), T4 (T3 + sub-lethal dose of A. hydrophila), T5 (moderate Argulus-infested fish), T6 (T5 + sub-lethal dose of A. hydrophila), T7 (high Argulus-infested fish) and T8 (T7+ sub-lethal dose of A. hydrophila) in duplicates. After distributing experimental fish into their respective treatment group, A. hydrophila was injected to T2, T4, T6 and T8. After the bacterial challenge, four fish from each experimental group were randomly sampled on 24, 72, and 168 h and subjected to the hematological, innate immune parameters and enzymatic analysis. In the co-infection group T8, a high degree of enhanced pathogenicity of A. hydrophila was noticed with increased mortalities (84.2%) in comparison to other groups. The current study shows a declining pattern in RBC, PCV and Hb values with the degree of parasite infestation without co-infection groups. Moreover, in the T8 group, exposure of a sub-lethal dose of bacteria resulted in a drastic reduction of the recorded parameters. Furthermore, a decreased value for WBC, monocyte and neutrophil was found in higher parasite group co-infected with a sub-lethal dose of bacteria relative to other co-infected groups during the experimental period. Also, a decrease in innate immune parameters and antioxidative stress enzymes were observed in the T8 group compared to T7 and T2 groups throughout the trial period. These findings indicate that a rise in the dose of Argulus infection improves A. hydrophila colonization in goldfish and contributes to suppression of the innate immune system and increased mortality.

Role of temperature and co-infection in mediating the immune response of goldfish

Aquatic Pathogens are expected to encounter tremendous levels of variation in their environment - both abiotic and biotic. Here we examined the change in innate immune parameters and mortality pattern of Carassius auratus during the interaction of co-infection due to an ectoparasite, Argulus and bacteria Aeromonas hydrophila, along with a temperature gradient. Experimental fish were assigned randomly to six treatment groups (T1-T6). Fish of groups T1, T3 and T5 are assigned for healthy fishes kept at 23, 28 and 33°c temperature and served as control. T2, T4 and T6 groups are the co-infected groups kept at temperature gradient. For the haematological and enzyme parameter analysis, sampling was done at 24 h, 72 h and 168 h post challenge from 4 fish in all experimental groups. A temperature dependent increase in intensity of Argulus was observed in the experimental group. Both in control group and co-infected group a temperature dependent mortality pattern was observed, showing an increased mortality of 60% in T6 and 20% in T5 group. A significant decrease of RBC, Hb, and PCV values was observed in co-infected group when compared with control fish in each of the experimental group. Also a temperature dependent increase in WBC, neutrophil and monocyte value was observed in control fish. Whereas, a significant reduction in WBC, neutrophil and monocyte was observed in co-infected fish exposed to 33 °C during the progression of infection. Furthermore, T4 group showed a significantly higher Nitroblue tetrazolium test, Myelo peroxidase and lyzozyme activity compared to other co-infection group. A significantly increased activity of Superoxide dismutase, Glutathione peroxidise and catalase activity was recorded in control fish exposed to 33 °C (T5) whereas, there was no significant difference observed in the activity of catalase and Glutathione peroxidise in the other control fish (T1 and T3 group). This result implies that increase in temperature not only accelerates the intensity of co-infection but also imbalance the health status of the fish by hampering the immunological and physiological parameters towards more detrimental side.