Enhanced immune response to inactivated porcine circovirus type 2 (PCV2) vaccine by conjugation of chitosan oligosaccharides

Development a high-sensitivity sandwich ELISA for determining antigen content of porcine circovirus type 2 vaccines

Porcine circovirus type 2 (PCV2) is intensely prevalent in global pig farms. The PCV2 vaccine is an important means of preventing and controlling PCV2. The quality control of PCV2 vaccines is predominantly based on detection techniques such as animal testing and neutralizing antibody titration. Measuring the content of effective proteins in vaccines to measure vaccine efficacy is an excellent alternative to traditional methods, which can greatly accelerate the development speed and testing time of vaccines. In this study, we screened a monoclonal antibody (mAb) that can effectively recognize not only the exogenous expression of PCV2 Cap protein but also PCV2 virus. The double antibody sandwich ELISA (DAS-ELISA) was developed using this mAb that specifically recognize PCV2 Cap. The minimum protein content detected by this method is 3.5 ng/mL. This method can be used for the quality control of PCV2 inactivated vaccine and subunit vaccine, and the detection results are consistent with the results of mice animal experiments. This method has the advantages of simple operation, good sensitivity, high specificity and wide application. It can detect the effective antigen Cap protein content of various types of PCV2 vaccines, which not only shorten the vaccine inspection time but also save costs.

Advances in the preparation, characterization, and biological functions of chitosan oligosaccharide derivatives: A review

Chitosan oligosaccharide (COS), which represent the positively charged basic amino oligosaccharide in nature, is the deacetylated and degraded products of chitin. COS has become the focus of intensive scientific investigation, with a growing body of practical and clinical studies highlighting its remarkable health-enhancing benefits. These effects encompass a wide range of properties, including antibacterial, antioxidant, anti-inflammatory, and anti-tumor activities. With the rapid advancements in chemical modification technology for oligosaccharides, many COS derivatives have been synthesized and investigated. These newly developed derivatives possess more stable chemical structures, improved biological activities, and find applications across a broader spectrum of fields. Given the recent interest in the chemical modification of COS, this comprehensive review seeks to consolidate knowledge regarding the preparation methods for COS derivatives, alongside discussions on their structural characterization. Additionally, various biological activities of COS derivatives have been discussed in detail. Lastly, the potential applications of COS derivatives in biomedicine have been reviewed and presented.

Preparation and adjuvanticity against PCV2 of Viola philippica polysaccharide loaded in Chitosan-Gold nanoparticle

The present Porcine circovirus type 2 virus (PCV2) vaccine adjuvants suffer from numerous limitations, such as adverse effects, deficient cell-mediated immune responses, and inadequate antibody production. In this study, we explored the potential of a novel nanoparticle (CS-Au NPs) based on gold nanoparticles (Au NPs) and chitosan (CS) that modified Viola philippica polysaccharide (VPP) as efficient adjuvants for PCV2 vaccine. The characterization demonstrated that CS-Au-VPP NPs had a mean particle size of 507.42 nm and a zeta potential value of -21.93 mV. CS-Au-VPP NPs also exhibited good dispersion and a stable structure, which did not alter the polysaccharide properties. Additionally, the CS-Au-VPP NPs showed easy absorption and utilization by the organism. To investigate their immune-enhancing potential, mice were immunized with a mixture of CS-Au-VPP NPs and PCV2 vaccine. The evaluation of relevant immunological indicators, including specific IgG antibodies and their subclasses, cytokines, and T cell subpopulations, confirmed their immune-boosting effects. The in vivo experiments revealed that the medium-dose CS-Au-VPP NPs significantly elevated the levels of specific IgG antibodies and their subclasses, cytokines, and T cell subpopulations in PCV2-immunized mice. These findings suggest that CS-Au-VPP NPs can serve as a promising vaccine adjuvant due to their stable structure and immunoenhancement capabilities.

A synthetic Tn-BSA conjugate vaccine bearing chitotriose as built-in adjuvant

Chitotriose (CTS), the hydrolysate of chitosan, is readily soluble in water because of the shorter chain lengths of the oligomers and the free amino groups in the d-glucosamine units. In the current study, we report the synthesis of novel conjugate vaccine Tn-BSA-CTS with chitotriose as built-in adjuvant, along with an evaluation of the effect of adjuvant chitotriose (CTS). Immunological evaluations of the resultant conjugate vaccine revealed that Tn-BSA-CTS could provoke the highest titers of IgG antibodies (102,400). The Tn-BSA-CTS conjugate remarkably enhanced both humoral and cellular immunity. The obtained results demonstrate the potential of CTS as a novel vaccine adjuvant in the development of antitumor vaccine and the covalent linkage of tumor vaccine to CTS might be available strategy to increase the efficacy against cancer.

Synthesis, Characterization of Low Molecular Weight Chitosan Selenium Nanoparticles and Its Effect on DSS-Induced Ulcerative Colitis in Mice

Selenium nanoparticles have attracted extensive attention due to their good bioavailability and activity. In the present study, a new form of selenium nanoparticle (Low molecular weight chitosan selenium nanoparticles (LCS-SeNPs)) were synthesized in a system of sodium selenite and acetic acid. The size, element state, morphology and elementary composition of LCS-SeNPs were characterized by using various spectroscopic and microscopic measurements. The protection of LCS-SeNPs against dextran sulfate sodium (DSS)-induced intestinal barrier dysfunction and the inherent mechanisms of this process were investigated. The results showed that LCS-SeNPs, with an average diameter of 198 nm, zero-valent and orange-red relatively uniform spherical particles were prepared. LCS-SeNPs were mainly composed of C, N, O and Se elements, of which Se accounted for 39.03% of the four elements C, N, O and Se. LCS-SeNPs reduced colon injury and inflammation symptoms and improved intestinal barrier dysfunction. LCS-SeNPs significantly reduced serum and colonic inflammatory cytokines TNF-α and IL-6 levels. Moreover, LCS-SeNPs remarkably increased antioxidant enzyme GSH-Px levels in serum and colonic tissue. Further studies on inflammatory pathways showed that LCS-SeNPs alleviated DSS-induced colitis through the NF-κB signaling pathway, and relieved inflammatory associated oxidative stress through the Nrf2 signaling pathway. Our findings suggested that LCS-SeNPs are a promising selenium species with potential applications in the treatment of oxidative stress related inflammatory intestinal diseases.

Porcine Circovirus Type 2 Vaccines: Commercial Application and Research Advances

Porcine circovirus type 2 (PCV2) infection can lead to porcine circovirus-associated disease (PCVAD), causing great economic losses to the global swine industry. Conventional vaccination programs are a major measure in the prevention and control of this disease. Currently, there are 5 commercially available PCV2 vaccines in the international market and 10 kinds commercially available PCV2 vaccines in the Chinese market that confer good efficacy against this virus by alleviating clinicopathological manifestations and enhancing growth performance in pigs. In addition, diverse experimental PCV2 vaccines with protective efficiency have been developed, including attenuated chimeric, nucleic acid, subunit, multivalent, and viral-vectored vaccines. These experimental vaccines have been shown to be relatively effective in improving the efficiency of pig production and simplifying prevention procedures. Adjuvants can be used to promote vaccines with higher protective immunity. Herein, we review the application of multiple commercial vaccines over the years and research advances in experimental vaccines, which provide the possibility for the development of superior vaccines to successfully prevent and control PCV2 infection in the future.

Chinese yam polysaccharides PLGA-stabilized Pickering emulsion as an adjuvant system for PCV- 2 vaccine to enhance immune response

Chinese yam polysaccharides (CYP) exhibit superior adjuvant activity and modulate the immune response, but the low bioavailability limits their clinical application. Pickering emulsions have been proven as an efficient vaccine delivery system to enhance the immune response. Here, we used the Chinese yam polysaccharides PLGA-stabilized Pickering emulsion adjuvant system (CYP-PPAS) loaded with Porcine circovirus 2 as a vaccine and focused on investigating its adjuvant activity on humoral and cellular immunity in mice. The CYP-PPAS increased PCV-2 antigen loading efficiency and showed a high antigen uptake efficiency by macrophages in vitro. In vivo, CYP-PPAS significantly facilitated DCs maturation in draining lymph nodes than CYP or PPAS alone group. The CYP-PPAS also induced an increased proliferation index and a CD4⁺/CD8⁺ ratio. Meanwhile, in contrast to the CYP and PPAS groups, CYP-PPAS elicited a stronger anti-PCV-2 IgG and mixed Th1/Th2 immune response. Specifically, the CYP-PPAS group displayed the high expression of CD107a, FasL, and Granzyme B secretion to augment a strong cytotoxic lymphocyte response. Overall, the CYP-PPAS was a successful adjuvant system for promoting humoral and cellular immune responses, which opens up an avenue for the development of effective adjuvants against infectious diseases.

Swine Influenza Virus Infection Decreases the Protective Immune Responses of Subunit Vaccine Against Porcine Circovirus Type 2

Porcine circovirus type 2 (PCV2) is the primary pathogen of porcine circovirus diseases and porcine circovirus associated diseases. Immunization with a vaccine is considered an effective measure to control these diseases. However, it is still unknown whether PCV2 vaccines have protective immune responses on the animals infected with swine influenza virus (SIV), a pandemic virus in swine herds. In this study, we first compared the effects of 2 different PCV2 vaccines on normal mice and SIV-infected mice, respectively. The results showed that these two vaccines had protective immune responses in normal mice, and the subunit vaccine (vaccine S) had better effects. However, the inactivated vaccine (vaccine I) instead of vaccine S exhibited more immune responses in the SIV-infected mice. SIV infection significantly decreased the immune responses of vaccine S in varying aspects including decreased PCV2 antibody levels and increased PCV2 replication. Mechanistically, further studies showed that SIV infection increased IL-10 expression and M2 macrophage percentage, but decreased TNF-α expression and M1 macrophage percentage in the mice immunized with vaccine S; on the contrary, macrophage depleting by using clodronate-containing liposomes significantly alleviated the SIV infection-induced decrease in the protective immune responses of vaccine S against PCV2. This study indicates that SIV infection decreases the protective immune responses of vaccine S against PCV2. The macrophage polarization induced by SIV infection might facilitate decreased immune responses to vaccine S, which provides new insight into vaccine evaluation and a reference for the analysis of immunization failure.

Chitooligosaccharides alleviate hepatic fibrosis by regulating the polarization of M1 and M2 macrophages

Regulating immune homeostasis by targeting liver macrophage polarization is a potential therapeutic strategy for hepatic fibrosis. Chitooligosaccharide (COS) is a bioactive oligosaccharide possessing potent immunomodulatory and hepatoprotective effects. In this study the hepatoprotective effect of COS on hepatic fibrosis was examined in mice and the underlying mechanisms were investigated. Herein, mice were induced to hepatic fibrosis using carbon tetrachloride (CCl₄) and concurrently treated with COS orally. Kupffer cells (KCs) were skewed towards M1 macrophage polarization by lipopolysaccharide (LPS) and towards M2 macrophage polarization by interleukin-4 (IL-4) in vitro, which were utilized for COS treatment. The results showed that mice were rescued from hepatic fibrosis by COS, marked by a reduction in the deposition of the extracellular matrix (ECM) and histological lesions. COS had an inhibitory effect on the polarization of M1 and M2 macrophages both in vivo and in vitro, characterized by the raised biomarker of the M1 and M2 macrophages slipping towards the basal levels. Furthermore, COS inhibited the JAK2/STAT1 pathways on M1 macrophages and the JAK1/STAT6 pathways on M2 macrophages in KCs. In summary, this study revealed a molecular mechanism for the impact of COS effectiveness on the polarization of liver macrophages, suggesting that is could be a possible intervention for hepatic fibrosis.

Multi-walled carbon nanotube polysaccharide modified Hericium erinaceus polysaccharide as an adjuvant to extend immune responses

In recent years, the utilization of CS-MWCNT as targeted drug carriers has attracted considerable attention. Hericium erinaceus polysaccharide (HEP) has been reported as an immunostimulant to improve immune responses. This study was focussed on developing CS-MWCNT encapsulating HEP (CS-MWCNT-HEP). Using in mice peritoneal macrophages, we found the immune response could be effectively regulated by CS-MWCNT-HEP, promoted the expression of the MHCII, CD86, F4/80 and gp38. Moreover, the mice immunized with CS-MWCNT-HEP nanoparticles significantly extended PCV₂-specific IgG immune response and the levels of cytokines. The results demonstrated that CS-MWCNT-HEP may be a promising drug delivery system for immuno-enhancement.

Polysaccharides obtained from natural edible sources and their role in modulating the immune system: Biologically active potential that can be exploited against COVID-19

BACKGROUND

The global crisis caused by the outbreak of severe acute respiratory syndrome caused by the SARS-CoV-2 virus, better known as COVID-19, brought the need to improve the population's immunity. The foods rich in polysaccharides with immunomodulation properties are among the most highly rated to be used as immune response modulators. Thus, the use of polysaccharides obtained from food offers an innovative strategy to prevent serious side effects of viral infections.

SCOPE AND APPROACH

This review revisits the current studies on the pathophysiology of SARS-CoV-2, its characteristics, target cell interactions, and the possibility of using polysaccharides from functional foods as activators of the immune response. Several natural foods are explored for the possibility of being used to obtain polysaccharides with immunomodulatory potential. And finally, we address expectations for the use of polysaccharides in the development of potential therapies and vaccines.

KEY FINDINGS AND CONCLUSIONS

The negative consequences of the SARS-CoV-2 pandemic across the world are unprecedented, thousands of lives lost, increasing inequalities, and incalculable economic losses. On the other hand, great scientific advances have been made regarding the understanding of the disease and forms of treatment. Polysaccharides, due to their characteristics, have the potential to be used as potential drugs with the ability to modulate the immune response. In addition, they can be used safely, as they have no toxic effects, are biocompatible and biodegradable. Finally, these biopolymers can still be used in the development of new therapies and vaccines.

Chitosan Oligosaccharides Coupling Inhibits Bacterial Biofilm-Related Antibiotic Resistance against Florfenicol

The formation of bacterial biofilms has increased the resistance of bacteria to various environmental factors and is tightly associated with many persistent and chronic bacterial infections. Herein we design a strategy conjugating florfenicol, an antibiotic commonly used in the treatment of streptococcus, with the antimicrobial biomaterial, chitosan oligosaccharides. The results demonstrated that the florfenicol-COS conjugate (F-COS) efficiently eradicated the mature Streptococcus hyovaginalis biofilm, apparently inhibiting drug resistance to florfenicol. A quantity of 250 μg/mL F-COS showed effective inhibitory activity against planktonic cells and biofilm of the bacteria, and a 4-fold improvement of the F-COS compared to unmodified florfenicol was observed. Furthermore, the conjugate showed a broad-spectrum activity against both Gram-positive and Gram-negative bacteria. It suggested that F-COS might have a potential for application in the treatment of biofilm-related infections.

Research Advances in Chitosan Oligosaccharides: From Multiple Biological Activities to Clinical Applications

Chitosan oligosaccharides (COS), hydrolysed products of chitosan, are low-molecular weight polymers with a positive charge and good biocompatibility. COS have recently been reported to possess various biological activities, including hypoglycaemic, hypolipidaemic, antioxidantantioxidant, immune regulation, anti-inflammatory, antitumour, antibacterial, and tissue engineering activities, exhibiting extensive application prospects. Currently, the biological processes and mechanisms of COS are attractive topics of study, ranging from the genetic, molecular and protein levels. This article reviews the recent discoveries about COS, especially in metabolic regulation, immune function and tissue repair, providing important insights into their multiple biological activities, medical benefits, and therapeutic mechanisms.

The Immunoenhancement Effects of Polyethylenimine-Modified Chinese Yam Polysaccharide-Encapsulated PLGA Nanoparticles as an Adjuvant

Background

Poly(lactic-co-glycolic acid) (PLGA) has been extensively applied for sustained drug delivery and vaccine delivery system. However, vaccines delivered by PLGA nanoparticles alone could not effectively activate antigen-presenting cells (APCs) to induce strong immune responses.

Purpose

The aim of the present study was to design polyethylenimine (PEI)-modified Chinese yam polysaccharide (CYP)-encapsulated PLGA nanoparticles (CYPP-PEI) as a vaccine delivery system and evaluate the adjuvant activities in vitro and in vivo.

Materials and Methods

Cationic-modified nanoparticles exhibited high antigen absorption and could be efficiently taken by APCs to enhance the immune responses. Therefore, PEI-modified CYP-encapsulated PLGA nanoparticles (CYPP-PEI) were prepared. The storage stability and effective adsorption capacity for porcine circovirus-2 (PCV-2) antigen of these antigen-absorbed nanoparticles were measured for one month. Furthermore, the adjuvant activity of CYPP-PEI nanoparticles was evaluated on macrophages in vitro and through immune responses triggered by PCV-2 antigen in vivo.

Results

The PCV-2 absorbed CYPP-PEI nanoparticles showed excellent storage stability and high absorption efficiency of PCV-2 antigen. In vitro, CYPP-PEI nanoparticles promoted antigen uptake, enhanced surface molecular expressions of CD80 and CD86, and improved cytokine secretion of TNF-α, IFN-γ, and IL-12p70 in macrophages. After immunization with CYPP-PEI/PCV-2 formulation in mice, the expressions of surface activation markers on dendritic cells which located in draining lymph nodes were increased, such as MHCI, MHCII, and CD80. In addition, CYPP-PEI nanoparticles induced dramatically high PCV-2-specific IgG levels which could last for a long time and stimulated the secretion of subtype antibodies and cytokines. The results showed that CYPP-PEI could induce Th1/Th2 mixed but Th1-biased type immune responses.

Conclusion

Polyethylenimine-modified Chinese yam polysaccharide-encapsulated PLGA nanoparticle was a potential vaccine delivery system to trigger strong and persistent immune responses.

pH-sensitive PEG-coated hyper-branched β-d-glucan derivative as carrier for CpG oligodeoxynucleotide delivery

β-d-glucan is a natural non-digestible polysaccharide that can be selectively recognized by recognition receptors such as Dectin-1 receptors, resulting in an emerging interest on exploring its capacity for carrying biological information to desired organs or cells. CpG oligodeoxynucleotide (ODN) has the potentiality to initiate an immune-stimulatory cascade via activating B cells inducing proinflammatory cytokines, which is conducive to immunotherapy and nucleic acid vaccine. Herein, we developed a pH-sensitive delivery system loading with CpG ODN by introducing poly-ethylenimine (PEI) to a hyperbranched β-d-glucan (HBB) and coating with poly-ethylene glycol (PEG) shell via acidic liable Schiff bond. This delivery system exhibited a favorable biocompatibility and facilitated the cellular uptake of CpG ODN at pH 6.8 with the possibility of having higher accumulation in acidic cancer microenvironment. Furthermore, this carrier together with class B CpG ODN could enhance the secretion of cytokines including interleukin-6 and interferon-α as well as capable of interferon-α induction.

Cloning and Expression of the Tibetan Pig Interleukin-23 Gene and Its Promotion of Immunity of Pigs to PCV2 Vaccine

Vaccines against Porcine circovirus type 2 (PCV2) have been studied intensely and found to be effective in decreasing mortality and improving growth in swine populations. In this study, interleukin-23 (IL-23) gene was cloned from peripheral blood mononuclear cells (PBMCs) of Tibetan pigs and inserted into a eukaryotic VR1020 expression vector-VRIL23. Coated with chitosan (CS), the VRIL23-CS was intramuscularly injected into 3-week-old piglets with PCV2 vaccine. The blood was collected after vaccination at 0, 1, 2, 4, 8, and 12 weeks, respectively, to detect the immunological changes. The IgG2a and specific PCV2 antibodies were detected using ELISA, and blood CD4+ and CD8+ T cells were quantified by flow cytometry. Quantitative fluorescence PCR was used to evaluate the expression of immune genes. The results indicate that leukocytes, erythrocytes, and CD4+ and CD8+ T cells increased significantly in the blood of VRIL23-CS inoculated piglets in comparison with the control (p < 0.05) and so did the IgG2a and PCV2 antibodies. In addition, the expressions of Toll-like receptor (TLR) 2, TLR7, cluster of differentiation (CD) 45, IL-15, IL-12, signal transducer and activator of transcription (STAT)1, STAT2, STAT3, STAT4, and B-cell lymphoma (Bcl)-2 genes were also obviously higher in the VRIL23-CS inoculated pigs at different time points (p < 0.05). Overall, the results demonstrated that VRIL23-CS can enhance the comprehensive immune responses to PCV2 vaccine in vivo and has the promising potential to be developed into a safe and effective adjuvant to promote the immunity of pig against PCV disease.

Sophorasubprosrate polysaccharide suppress the inflammatory reaction of RAW264.7 cells infected with PCV2 via regulation NF-κB/MAPKs/c-Jun signal pathway and histone acetylation modification

The purpose of this study was to investigate the regulation of Sophorasubprosrate polysaccharide (SSP) on inflammatory response and histone acetylation modification of RAW264.7 cells (mouse mononuclear macrophage cell line) infected with porcine circovirus type 2 (PCV2). We further explored the role of inflammatory response and histone acetylation modification on the basis of the original study. The results showed that SSP decreased the secretion levels of TNF-α and IL-6 and the intracellular iNOS, COX-2 enzyme activities and their mRNA expression levels in PCV2 infected RAW264.7 cells, but increased the level of IL-10 secretion and its mRNA expression. SSP inhibited the phosphorylation levels of proteins of p65, ERK1/2, p38 and c-Jun in RAW264.7 cells infected with PCV2. The activities of HAT and HDAC enzymes and the mRNA expression levels of HAT1 and HDAC1 were increased when the PCV2-infected RAW264.7 cells were treated by SSP. Meanwhile, the expression of acetylation modification of histones both H3 and H4 was obviously inhibited. In conclusion, SSP may reduce the acetylation levels of both H3 and H4 and activate NF-κB/MAPKs/c-Jun signaling pathway by increasing the activity of HADC enzyme and the expression of HDAC mRNA, further inhibiting inflammatory response by regulating the gene expression levels of inflammatory factors. The findings indicated that the molecular mechanism of how traditional Chinese medicine polysaccharide regulates inflammatory signal pathways and inflammatory factors by regulating histone acetylation.

Effect of Chitosan oligosaccharides on ischemic symptom and gut microbiota disbalance in mice with hindlimb ischemia

This study was designed to explore the effect of Chitosan oligosaccharides (COS) on mouse hindlimb ischemia by femoral artery ligation. Here, we demonstrated that COS treatment statistically promoted the blood perfusion and neovascularization in ischemic hindlimb of mice, accompanied by the suppression of inflammation and oxidative stress. By 16S rDNA gene sequencing, the disbalanced gut microbiota was observed in ischemic mice, while COS treatment, at least in part, restored the abundance changes of some intestinal bacteria at either phylum or genus levels. Based on metabolomics analysis on mouse plasma by UPLC-QTOF-MS, we screened 20 metabolites with the largest responses to ischemia, several of which were markedly reversed by COS. By Spearman's correlation analysis, the changed metabolites might act as a bridge between improved intestinal bacterial structure and alleviated hindlimb ischemia of mice treated by COS. Our studies point towards a potential role of COS in treatment of peripheral ischemia diseases.

Immune effect of Vibrio harveyi formalin-killed cells vaccine combined with chitosan oligosaccharide and astragalus polysaccharides in ♀Epinephelus fuscoguttatus×♂Epinephelus lanceolatus

Vibrio harveyi is the pathogen causing vibriosis in marine-cultured animals, leading to massive deaths in farmed grouper around the world. It is urgent to develop an effective vaccine to prevent vibriosis. In the previous study, we developed a V. harveyi formalin-killed cells vaccine (FKC), and sought an effective adjuvant for enhancing the immune efficacy of vaccine. In this study, we aimed to evaluate the immune responses and protective effect of FKC combined with chitosan oligosaccharide (COS) or Astragalus polysaccharides (APS) in the pearl gentian grouper♀Epinephelus fuscoguttatus × ♂E. lanceolatus. The results indicated the vaccine triggered a remarkably higher expression levels of IL-1β, IL-16, TNF-α, MHC-Iα and IgM in the kidney and spleen of groupers post-vaccination. Antibody titers, lysozyme, catalase, superoxide dismutase and total protein were significantly elevated in the vaccinated fish compared with those in the control. The experimental groupers were challenged intraperitoneally by V. harveyi at 35 d post-vaccination, and the relative percentage of survival (RPS) of group FKC + COS, FKC + APS, COS, APS and FKC were 80%, 72%, 52%, 47% and 55%, respectively. These results demonstrated COS and APS was the potential adjuvants for FKC against V. harveyi in aquaculture.

Immunoenhancement of Recombinant Neisseria meningitides PorB Protein on Porcine Circovirus Type 2 and Mycoplasma hyopneumoniae Genetically Engineered Vaccines

BACKGROUND

Porcine circovirus and Mycoplasma hyopneumoniae can cause respiratory diseases in pigs, which cause serious economic loss in the worldwide pig industry. Currently, these infections are mainly prevented and controlled by vaccination. The new vaccines on the market are mainly composed of subunits and inactivated vaccines but usually have lower antigenicity than traditional live vaccines. Thus, there is an increasing need to develop new adjuvants that can cause rapid and long-lasting immunity to enhance the antigenic efficacy for vaccines. Studies have shown that meningococcal porin PorB can act as a ligand to combine with Toll-like receptors to activate the production of immunological projections and act as a vaccine immunological adjuvant.

OBJECTIVE

In this article, we expressed and purified the recombinant PorB protein and verified its immunogenicity against porcine circovirus type 2 and Mycoplasma hyopneumoniae genetically engineered vaccine.

METHODS

In this article, we used prokaryotic expression to express and purify recombinant PorB protein, four different concentrations of PorB protein, Freund's adjuvant with two genetically engineered vaccines were combined with subcutaneous immunization of mice.

RESULTS

Our study shows that the appropriate dose of the recombinant protein PorB can enhance the levels of humoral and cellular responses induced by two genetically engineered vaccines in a short period of time in mice. The PorB adjuvant group may cause statistically higher antibody titers for both genetically engineered vaccines compared to Freund's commercial adjuvant (P<0.001).

CONCLUSION

The recombinant protein PorB may be a good candidate adjuvant for improving the protective effect of vaccines against porcine circovirus type 2 and Mycoplasma hyopneumoniae, and the protein can be used for future practical applications.

Implantable microneedles with an immune-boosting function for effective intradermal influenza vaccination

This study details effective influenza vaccination via sustained intradermal (ID) release of vaccines using implantable and patch-free chitosan microneedles (MNs). The microneedle (MN) patch is composed of vaccine-loaded chitosan MNs with a dissolvable supporting array that gives extra length for complete insertion of MNs and is dissolved within the skin during insertion. Chitosan MNs can be quickly and entirely implanted into the dermis to function as a depot and an immune-boosting agent for the extended release of vaccines and simultaneous activation of the immune system. We found the influenza virus-specific antibody levels induced by chitosan MN vaccination were significantly higher than those elicited by intramuscular (IM) immunization with influenza vaccine alone. The MN induced immune-enhancing effect was obvious 4 week after the vaccination and lasted for at least 16 weeks. Most importantly, MN-immunized mice were completely protected from H1N1 viral challenge without major weight loss, whereas mice receiving IM injection at the same dose had a mortality rate of 60% and experienced notable weight loss after challenge. Our results suggest that the chitosan MNs cannot only be a viable tool for precise ID vaccine delivery but also exert strong adjuvanticity to enhance vaccine potency and induce protective immunity against influenza virus infections. STATEMENT OF SIGNIFICANCE: There is an urgent need for generating a new vaccination strategy to address the threat of global pandemic influenza. This study presents implantable chitosan microneedles (MNs) with immune-boosting function for effective influenza vaccination. We demonstrate that the chitosan MN can not only be an efficient tool for sustained intradermal delivery but also serve as an immunological adjuvant to boost vaccine efficacy. Continuous antigen exposure and immune stimulation provided by the implanted MNs may enhance the immunogenicity of influenza vaccines and evoke long-lasting immune responses to completely protect mice from lethal influenza challenge. The proposed MN system has great potential to be used as a new adjuvanted vaccine formulation and make influenza vaccination more effective and more accessible.

Polyethylenimine-coated PLGA nanoparticles-encapsulated Angelica sinensis polysaccharide as an adjuvant to enhance immune responses

Nanoparticle delivery systems have been widely investigated as new vaccines strategy to enhance the immune responses to antigens against infectious diseases. The positively charged nanoparticles could efficiently improve the immune responses due to targeting and activating the antigen-presenting cells. In this study, the immunopotentiator Angelica sinensis polysaccharide (ASP) was encapsulated into Poly (lactic-co-glycolic acid) (PLGA) nanoparticles, and the polyethylenimine, one of the cationic polymers, was used to coat nanoparticles to develop a new nanoparticle delivery system (ASP-PLGA-PEI) with positively charged. The ASP-PLGA-PEI nanoparticles significantly activated macrophages, and promoted the expression of the MHCII and CD86 and the production of IL-1β and IL-12p70 cytokines of macrophages. Furthermore, the antigen adsorbed on the surface of the ASP-PLGA-PEI nanoparticles enhanced the antigen uptake by macrophages. Moreover, the mice immunized with PCV2 antigen adsorbed ASP-PLGA-PEI nanoparticles significantly enhanced PCV2-specific IgG immune response and the levels of cytokines, induced a mixed Th1/Th2 immune response with Th1 bias compared with other groups. These findings demonstrate that the positively charged nanoparticles (ASP-PLGA-PEI) have the potential to serve as an effective vaccine delivery and adjuvant system to induce vigorous and long-term immune responses.

A review on the preparation of chitosan oligosaccharides and application to human health, animal husbandry and agricultural production

Chitosan oligosaccharides (COS) are the degraded products of chitin or chitosan prepared by chemical or enzymatic hydrolysis. As compared to chitosan, COS not only exhibit some specific physicochemical properties such as excellent water solubility, biodegradability and biocompatibility, but also have a variety of functionally biological activities including anti-inflammation, anti-bacteria, immunomodulation, neuroprotection and so on. This review aims to summarize the preparation and structural characterization methods of COS, and will discuss the application of COS or their derivatives to human health, animal husbandry and agricultural production. COS have been demonstrated to prevent the occurrence of human health-related diseases, enhance the resistance to diseases of livestock and poultry, and improve the growth and quality of crops in plant cultivation. Overall, COS have presented a broad developmental potential and application prospect in the healthy field that deserves further exploration.

Conjugation of chitosan oligosaccharides via a carrier protein markedly improves immunogenicity of porcine circovirus vaccine

Porcine circovirus type 2 (PCV2)-associated diseases have led to huge economic losses in pig industry. Our laboratory previously found that conjugation of chitosan oligosaccharides (COS) enhanced the immunogenicity of PCV2 vaccine against infectious pathogens. In this study, an effective adjuvant system was developed by covalent conjugation of COS via a carrier protein (Ovalbumin, OVA) to further increase the immunogenicity of vaccine. Its effect on dendritic cells maturation was assessed in vitro and its immunogenicity was investigated in mice. The results indicated that, as compared to the PCV2 and COS-PCV2, COS-OVA-PCV2 stimulated dendritic cells to express higher maturation markers (CD80, CD86, CD40 and MHC class II) and remarkably promoted both humoral and cellular immunity against PCV2 by enhancing the lymphocyte proliferation and inducing a mixed Th1/Th2 response, including the increased production of PCV2-specific antibodies and raised levels of inflammatory cytokines. Furthermore, it displayed better immune-stimulating effects than the physical mixture of vaccine and ISA206 (a commercialized adjuvant). In conclusion, conjugation of COS via a carrier protein might be a promising strategy to enhance the immunogenicity of vaccines.

Conjugation of chitosan oligosaccharides enhances immune response to porcine circovirus vaccine by activating macrophages

Porcine circovirus type 2 (PCV2)-associated diseases have led to great economic losses to the pig industry. Our lab previously found that conjugation of chitosan oligosaccharides (COS) or via a carrier protein enhanced the immunogenicity of PCV2 vaccine against infectious pathogens. However, precise mechanisms and signal transduction pathways underlying the efficacy of COS conjugation remains poorly defined. In this study, to better understand the effects and mechanism of COS conjugates maintain the adjuvant potential in vivo, we investigated its augmentation of macrophage function, including cell activation, NO production, cytokine production and phagocytosis. Additionally, the role of Toll-like receptors (TLR) proteins in this process was also assessed. The results indicate that, as compared to the PCV and PCV/COS, conjugation of COS effectively enhanced the NO production, cytokines generation and phagocytosis activity of macrophages. Noticeably, the generation of NO and proinflammatory cytokines was closely related to the TLR2/4 signaling pathways, strongly suggesting that conjugation of COS regulates innate and adaptive immunity by activation of macrophages, resulting in immune enhancement. In summary, the present study provides a potential mechanism of COS conjugation as a novel adjuvant to improve immune responses against various diseases.

Immunogenicity evaluation of inactivated virus and purified proteins of porcine circovirus type 2 in mice

Background

Vaccination is considered as an effective and economical way to against PCV2 infection. However, some of commercial available vaccines are based on inactivated viruses, while the others are based on purified protein of PCV2. In the present study, we aimed to compare the immunogenicity of inactivated virus and purified proteins of porcine circovirus type 2 in mice.

Results

The results showed that positive antiserum titers were significantly increased after second, third and fourth immunization using inactivated PCV2 or purified proteins as coating antigen. Moreover, the inactivated PCV2 induced significantly higher levels of PCV2-specific antibodies than that of PCV2 subunit proteins. After PCV2 wild strain challenged, the average daily gain was comparable with that of mice in the mock group, and the sera from both inactivated PCV2-immunized animals and subunit protein Cap+ORF3 + Rep immunized animals had significantly higher neutralizing antibody titers than that of the PBS group. As expected, the neutralizing antibody in the inactivated PCV2 group was significantly higher than that of the subunit protein group. These results indicated that positive antiserum induced by the inactivated PCV2 had a better reactivity and specificity than that of the positive antiserum induced by the purified proteins.

Conclusions

The results in the present study demonstrated inactivated PCV2 is more effective than PCV2 subunit proteins in stimulating immune response to against PCV2 infection.

Mouse models of porcine circovirus 2 infection

PCV2 is considered the main pathogen of porcine circovirus diseases and porcine circovirus-associated diseases (PCVD/PCVAD). However, the exact mechanism underlying PCVD/PCVAD is currently unknown. Mouse models of PCV2 are valuable experimental tools that can shed light on the pathogenesis of infection and will enable the evaluation of antiviral agents and vaccine candidates. In this review, we discuss the current state of knowledge of mouse models used in PCV2 research that has been performed to date, highlighting their strengths and limitations, as well as prospects for future PCV2 studies.

The Positive Correlation of the Enhanced Immune Response to PCV2 Subunit Vaccine by Conjugation of Chitosan Oligosaccharide with the Deacetylation Degree

Chitosan oligosaccharides (COS), the degraded products of chitosan, have been demonstrated to have versatile biological functions. In primary studies, it has displayed significant adjuvant effects when mixed with other vaccines. In this study, chitosan oligosaccharides with different deacetylation degrees were prepared and conjugated to porcine circovirus type 2 (PCV2) subunit vaccine to enhance its immunogenicity. The vaccine conjugates were designed by the covalent linkage of COSs to PCV2 molecules and administered to BALB/c mice three times at two-week intervals. The results indicate that, as compared to the PCV2 group, COS-PCV2 conjugates remarkably enhanced both humoral and cellular immunity against PCV2 by promoting lymphocyte proliferation and initiating a mixed T-helper 1 (Th1)/T-helper 2 (Th2) response, including raised levels of PCV2-specific antibodies and an increased production of inflammatory cytokines. Noticeably, with the increasing deacetylation degree, the stronger immune responses to PCV2 were observed in the groups with COS-PCV2 vaccination. In comparison with NACOS (chitin oligosaccharides)-PCV2 and LCOS (chitosan oligosaccharides with low deacetylation degree)-PCV2, HCOS (chitosan oligosaccharides with high deacetylation degree)-PCV2 showed the highest adjuvant effect, even comparable to that of PCV2/ISA206 (a commercialized adjuvant) group. In summary, COS conjugation might be a viable strategy to enhance the immune response to PCV2 subunit vaccine, and the adjuvant effect was positively correlated with the deacetylation degree of COS.