Proposed method for agglutinating antibody titer analysis and its use as indicator of acquired immunity in pacu, Piaractus mesopotamicus

Evaluate the potential use of TonB-dependent receptor protein as a subunit vaccine against Aeromonas veronii infection in Nile tilapia (Oreochromis niloticus)

Aeromonas veronii is an emerging bacterial pathogen that causes serious systemic infections in cultured Nile tilapia (Oreochromis niloticus), leading to massive deaths. Therefore, there is an urgent need to identify effective vaccine candidates to control the spread of this emerging disease. TonB-dependent receptor (Tdr) of A. veronii, which plays a role in the virulence factor of the organism, could be useful in terms of protective antigens for vaccine development. This study aims to evaluate the potential use of Tdr protein as a novel subunit vaccine against A. veronii infection in Nile tilapia. The Tdr gene from A. veronii was cloned into the pET28b expression vector, and the recombinant protein was subsequently produced in Escherichia coli strain BL21 (DE3). Tdr was expressed as an insoluble protein and purified by affinity chromatography. Antigenicity test indicated that this protein was recognized by serum from A. veronii infected fish. When Nile tilapia were immunized with the Tdr protein, specific antibody levels increased significantly (p-value <0.05) at 7 days post-immunization (dpi), and peaked at 21 dpi compared to antibody levels at 0 dpi. Furthermore, bacterial agglutination activity was observed in the fish serum immunized with the Tdr protein, indicating that specific antibodies in the serum can detect Tdr on the bacterial cell surface. These results suggest that Tdr protein has potential as a vaccine candidate. However, challenging tests with A.veronii in Nile tilapia needs to be investigated to thoroughly evaluate its protective efficacy for future applications.

Vaccination with bacterial ghosts of Streptococcus iniae and Lactococcus garvieae originated from outbreak of marine fish streptococcosis, induce potential protection against the disease in Nile tilapia, Oreochromis niloticus (Linnaeus, 1758)

Streptococcosis is an important bacterial disease affects fresh, brackish and marine fish. The disease caused annual severe economic losses in Egyptian Mari-culture. S. iniae and L. garvieae usually the main causative agents isolated. The presented study conducted to prepare bacterial ghost vaccine (BGV) candidates from isolated strains of marine streptococcosis outbreaks using NaOH chemical approach. Selected strains confirmed as pathogenic for Nile tilapia, therefore the fish selected as an experimental model. In such respect, the re-isolated S. iniae and L. garvieae were used for ghost preparations, BGVs evaluation and fish challenges. Apart of four, three fish groups namely, A, B, C designated for BGVs evaluations, while the fourth one (D) designated as control. Vaccination experiments performed via intra-peritoneal injection with 0.1 mL (1.5 × 108 CFU/mL/fish) of their corresponding BGVs twice with 2 weeks' interval; however, control fish received 0.1 mL of fish saline instead. Blood, serum, and tissue samples collected from all groups at 2 and 4 weeks post immunization (PI) for estimation of hematological, innate, and specific immune parameters. At the end, all remained fish challenged with appropriated pathogen (s) and the relative percentage of survival (RPS) calculated. Three BGVs generated namely, SiG, in addition to, novel contributions of LgG and SiLgG. Ghosts were corresponding to S. iniae, L. garvieae and their both ghost mixtures, respectively. Fish groups immunized with prepared BGVs revealed variable significant increases in PCV, GLB, PP, SOD, CAT, C5, IL-β1, LZM, specific antibody titers and CD4 expression 2 and 4 weeks PI. MDA decreased in all vaccinated groups that was significantly with group C. Expression of MHC-II showed elevations 2 weeks PI, however, it significantly decreased at 4 weeks. The RPS recorded 90, 88.89 and 95.46% in immunized groups A, B and C, respectively. At all levels tested, obtained results proposed SiG, LgG and SiLgG as innovative vaccine candidates, which can protect cultured fish from being attacked by S. iniae, and/or L. garvieae.

Evaluation of three alum-precipitated Aeromonas hydrophila vaccines administered to Labeo rohita, Cirrhinus mrigala and Ctenopharyngodon idella: immunokinetics, immersion challenge and histopathology

Aeromonas hydrophila is a cause of infectious disease outbreaks in carp species cultured in South Asian countries including Pakistan. This bacterium has gained resistance to a wide range of antibiotics and robust preventive measures are necessary to control its spread. No prior use of fish vaccines has been reported in Pakistan. The present study aims to develop and evaluate inactivated vaccines against local strain of A. hydrophila in Pakistan with alum-precipitate as adjuvant. The immunogenic potential of vaccine was evaluated in two Indian major carps (Rohu: Labeo rohita, Mori: Cirrhinus mrigala) and a Chinese carp (Grass carp: Ctenopharyngodon idella). Fish were vaccinated intraperitoneally followed by a challenge through immersion. Fish with an average age of 4-5 months were randomly distributed in three vaccinated groups with three vaccine concentrations of 108, 109 and 1010 colony forming unit (CFU)/ml and a control group. Fixed dose of 0.1ml was applied to each fish on 1st day and a booster dose at 15 days post-vaccination (DPV). Blood samples were collected on 14, 28, 35, 48 and 60 DPV to determine antibody titers in blood serum using compliment fixation test (CFT). Fish were challenged at 60 DPV with infectious A. hydrophila with 108 CFU/ml through immersion. Significantly higher levels of antibody titers were observed from 28 DPV in all vaccinated groups as compared to those in the control group. In challenge experiment the average RPS (relative percent survivability) was 71% for groups vaccinated with 109 and 1010 CFU/ml and 86% for 108 CFU/ml. Vaccine with 108 CFU/ml induced highest immune response followed by 109 and 1010 CFU/ml. The immune response of L. rohita and C. idella was better than that of C. mrigala. In general, normal histopathology was observed in different organs of vaccinated fish whereas minor deteriorative changes were found in fish vaccinated with higher concentrations of the vaccine.

Ubiquitous convalescent plasma: An artificial universal plasma for COVID-19 patients

Objectives and background

In December 2019, the first case of COVID-19 was reported in Wuhan, China. Its causative virus, is a novel strain of RNA viruses with high mortality rate. There is no definitive treatment, but among available approaches the use of recovered patients’ plasma containing specific antibodies can enhance the immune response against coronavirus. However, the dearth of eligible donors and also ABO incompatibility in plasma transfusion, have limited this therapeutic method. Therefore, it is highly desirable to introduce a simple procedure that allows efficient reduction or even removal of natural ABO antibodies. Accordingly, we aimed to evaluate a RBC-mediated adsorption technique that reduces the titer of the mentioned antibodies in plasma.

Methods/materials

This experimental study was conducted in Kerman University of Medical Sciences, Kerman, Iran. The pre- and post-incubation antibody titers of 168 plasma samples were determined. For incubation, each plasma sample was exposed (60 min) to different percentages of RBCs at room temperature or 4 °C.

Results

The results evidenced that both the concentration of RBCs and temperature had significant decreasing effects on antibody titer (P < 0.001) and all concentrations significantly reduced titer. Compared to RT, 4 °C further reduced the antibody titer. Overall, the best incubation condition for reducing antibody titer in all blood groups was 4 °C and 2% RBCs concentration.

Conclusion

The presented adsorption procedure is able to produce universal plasma (we call it Ubiquitous Convalescent Plasma) with a non-immunogenic level of ABO mismatch antibodies which can be used for COVID-19 patients with any type of blood group with desirable simplicity, feasibility, and efficacy.

Elucidating the Efficacy of Vaccination against Vibriosis in Lates calcarifer Using Two Recombinant Protein Vaccines Containing the Outer Membrane Protein K (r-OmpK) of Vibrio alginolyticus and the DNA Chaperone J (r-DnaJ) of Vibrio harveyi

Recombinant cell vaccines expressing the OmpK and DnaJ of Vibrio were developed and subsequently, a vaccination efficacy trial was carried out on juvenile seabass (~5 cm; ~20 g). The fish were divided into 5 groups of 50 fish per group, kept in triplicate. Groups 1 and 2 were injected with 10⁷ CFU/mL of the inactivated recombinant cells vaccines, the pET-32/LIC-OmpK and pET-32/LIC-DnaJ, respectively. Group 3 was similarly injected with 10⁷ CFU/mL of inactivated E. coli BL21 (DE3), Group 4 with 10⁷ CFU/mL of formalin killed whole cells V. harveyi, and Group 5 with PBS solution. Serum, mucus, and gut lavage were used to determine the antibody levels before all fish were challenged with V. harveyi, V. alginolyticus, and V. parahemolyticus, respectively on day 15 post-vaccination. There was significant increase in the serum and gut lavage antibody titers in the juvenile seabass vaccinated with r-OmpK vaccine. In addition, there was an up-regulation for TLR2, MyD88, and MHCI genes in the kidney and intestinal tissues of r-OmpK vaccinated fish. At the same time, r-OmpK triggered higher expression level of interleukin IL-10, IL-8, IL-1ß in the spleen, intestine, and kidney compared to r-DnaJ. Overall, r-OmpK and r-DnaJ triggered protection by curbing inflammation and strengthening the adaptive immune response. Vaccinated fish also demonstrated strong cross protection against heterologous of Vibrio isolates, the V. harveyi, V. alginolyticus, and V. parahaemolyticus. The fish vaccinated with r-OmpK protein were completely protected with a relative per cent of survival (RPS) of 90 percent against V. harveyi and 100 percent against V. alginolyticus and V. parahaemolyticus. A semi-quantitative PCR detection of Vibrio spp. from the seawater containing the seabass also revealed that vaccination resulted in reduction of pathogen shedding. In conclusion, our results suggest r-OmpK as a candidate vaccine molecule against multiple Vibrio strain to prevent vibriosis in marine fish.

Hematological and immune changes in Piaractus mesopotamicus in the sepsis induced by Aeromonas hydrophila

The pathogenesis of sepsis involves complex systems and multiple interrelationships between the host and pathogen producing high mortality rates in various animal species. In this study, hematological disturbances, innate immunity and survival during the septic process in Piaractus mesopotamicus inoculated with Aeromonas hydrophila were studied. For this aim, fish blood samples were taken from control and infected groups 1, 3, 6, and 9 h post-inoculation (HPI). Leukogram showed reduction in the number of leukocytes and thrombocytes, followed by cessation of leukocyte chemotaxis 6 HPI and severe morphological changes in leukocytes and erythrocytes. At 3 HPI production of reactive oxygen species increased and at 6 HPI decreased. There was no change in serum lysozyme concentration and lytic activity of the complement system, despite the progressive increase in serum lytic activity and bacterial agglutination. Finally, the changes in clinical signs due to aeromonosis and increasing septicemia resulted in a reduction in survival to 57.14% after 36 HPI. It was possible concluded that these hematological and immune are crucial event in the worsening of sepsis in P. mesopotamicus, and these findings are utility for diagnosing and understanding the pathophysiology sepsis in pacu induced by A. hydrophila.

Potential and safety tests of egg drop syndrome candidate vaccine from Medan isolate, Indonesia

Aim:

The study was aimed to prepare and examine the potential and safety concerns of egg drop syndrome (EDS) vaccine candidate seed. The potential and safety trials of EDS Medan isolate vaccine need to be done before commercial scale of EDS vaccines are made.

Materials and Methods:

The safety test of EDS candidate vaccine was tested on 4-week-old specified pathogen-free chickens in an experimentally isolated enclosure.

Results:

The result of the safety test obtained 2^7.3 hemagglutination inhibition (HI) unit of geometric mean titer antibody post-vaccination. However, the potency test of the EDS candidate vaccine was conducted on 17-week-old laying hens. Test results of the EDS potency vaccine in layer obtained antibody titer increased in every week of blood taking with average titer of antibody: Before vaccinated was 2^2.9 HI unit, 1 week after vaccination was 2^3.7 HI unit, 2 weeks post-vaccination was 2⁵ HI unit, and 3 weeks after vaccination was 2^7.3 HI units. In contrast, decreasing trend was observed in control group (unvaccinated chicken).

Conclusion:

Serologically, the seed vaccine of EDS virus isolates from Medan was able to produce protective antibody titers starting in the 2^nd and 3^rd weeks post-vaccination.

Asparagus racemosus aqueous root extract induced effects on cellular immune reaction of Labeo rohita (Hamilton)

The present study was undertaken to evaluate the effect of Asparagus racemosus aqueous root extract on cellular immune reaction of Labeo rohita (Hamilton) fingerlings with response to bacterial infection caused by Aeromonas hydrophila at cool hilly mid altitude region of Meghalaya. Four concentrates mixtures of pelleted diet were formulated viz. without A. racemosus aqueous root extract (control); with 50 mg A. racemosus aqueous root extract/kg of diet (AR1); with 100 mg A. racemosus aqueous root extract/kg of diet (AR2); and with 150 mg A. racemosus aqueous root extract/kg of diet (AR3). Feeding trial was conducted for 60 days. Immune reactions, viz. NBT level, phagocytic activity, total immunoglobulin level, lysozyme activity, antiprotease activity and myeloperoxidase activity of fish were determined at 0, 15, 30, 45 and 60 days of feeding. Fish were infected with A. hydrophila 60 days post feeding, mortalities (%) and agglutination antibody titre were recorded over 14 days post infection. The results showed that in the treatment group AR2, AR3, there was significantly enhanced NBT level, phagocytic activity, lysozyme activity, immunoglobulin level, antiprotease activity and myeloperoxidase activity compared to control. The treatment group AR1 NBT level, phagocytic activity, lysozyme activity, myeloperoxidase activity were significantly enhanced whereas immunoglobulin level and antiprotease activity were nonsignificant compared to control. The highest survival was recorded in the AR2 (43.36±0.65) group, followed by AR3 (24.32±0.14), AR1 (17.26±0.45) and lowest were recorded in the control (3.42±0.02). The highest agglutination antibody titre was recorded in the AR2 (87.36±0.65) group followed by AR3 (49.32±0.14) and AR1 (38.26±0.45) group and lowest in control (17.42±0.02) against A. hydrophila infection. Thus, from the present study it can be deduced that feed containing A. racemosus aqueous root extracts/kg diet can influence immune reaction in L. rohita; however, AR2 group showed better result in terms of immune reaction and protection against pathogenic A. hydrophila at cool hilly mid altitude region of Meghalaya.

A formalin-inactivated vaccine provides good protection against Vibrio harveyi infection in orange-spotted grouper (Epinephelus coioides)

Vibrio harveyi is one of the most common threats to farmed grouper, so considerable efforts are in practice to control the pathogen. This study presents a highly effective vaccine against V. harveyi in the orange-spotted grouper with the help of a single intraperitoneal immunization. The vaccine candidate was in form of whole, formalin-inactivated V. harveyi cells combined with a metabolizable ISA763 AVG adjuvant. Our results indicated that the vaccine triggered a remarkably higher expression level of interleukin (IL)-1β, IL-6, IL-8, and IL-10 in the groupers' kidneys and spleens, as recorded after 1 and 3 days of immunization. Antibody titers were significantly elevated in the vaccinated fish. A pivotal observation was that the vaccine highly protected the grouper from a homologous V. harveyi strain challenge with relative percentage survival values of 100% and 91.7% at 6 and 12 weeks post-immunization, respectively. Vaccinated fish also demonstrated strong cross-protection against a heterologous bacterial isolate challenge. Therefore, the inactivated V. harveyi vaccine is a promising candidate that could stimulate good immune responses and confer remarkable protection in farmed groupers.

Disease resistance of pacu Piaractus mesopotamicus (Holmberg, 1887) fed with β-glucan

Effects of β-glucan on innate immune responses and survival were studied in pacu experimentally infected with Aeromonas hydrophila. Fish fed diets containing 0, 0.1% and 1% β-glucan were injected with A. hydrophila. β-glucan enhanced fish survival in both treated groups (26.7% and 21.2% of the control, respectively). Leukocyte respiratory burst and alternative complement pathway activities were elevated after bacterial challenge regardless the β-glucan concentration. Lysozyme activity was higher after infection and showed a gradual increase as β-glucan concentration increased. A significant elevation in WBC count was observed either after bacterial challenge or by influence of β-glucan separately. The same response was observed in the number of thrombocytes, lymphocytes, eosinophils, LG-PAS positive cell and monocytes. It can be concluded that feeding pacu with β-glucan can increase protection against A. hydrophila, due to changes in non-specific immune responses.

Serum bactericidal activity as indicator of innate immunity in pacu Piaractus mesopotamicus (Holmberg, 1887)

The immune system of teleost fish has mechanisms responsible for the defense against bacteria through protective proteins in several tissues. The protein action can be evaluated by serum bactericidal activity and this is an important tool to analyze the immune system. Pacu, Piaractus mesopotamicus, is one of the most important fish in national aquaculture. However there is a lack of studies on its immune responses. In order to standardize and assess the accuracy of the serum bactericidal activity assay, fish were briefly challenged with Aeromonas hydrophila and sampled one week after the challenge. The bacterial infection increased the concentration of protective proteins, resulting in a decrease of colony-forming unit values expressed as well as an enhanced serum bactericidal activity. The protocol showed a reliable assay, appropriate to determine the serum bactericidal activity of pacu in the present experimental conditions.