Construction of a Lactobacillus plantarum Strain Expressing the Capsid Protein of Porcine Circovirus Type 2d (PCV2d) as an Oral Vaccine

A porcine circovirus type 2d-based virus-like particle vaccine induces humoral and cellular immune responses and effectively protects pigs against PCV2d challenge

The pathogenic porcine circovirus type 2 (PCV2) leads to significant economic losses in pig production. PCV2d is currently the dominant genotype causing porcine circovirus-associated disease (PCVAD) worldwide. Therefore, development of a recombinant PCV2d-based vaccine is required to elicit complete protection against PCV2d infection. In this study, we generated virus-like particles of PCV2d-based capsid protein (Bac-2dCP) using a baculovirus expression system and evaluated its protective efficacy against PCV2d infection in specific pathogen-free (SPF) pigs. Three-week-old SPF miniature pigs were intramuscularly immunized with purified Bac-2dCP and intranasally challenged with PCV2d at 4 weeks post-vaccination. The Bac-2dCP group showed significantly higher IgG levels and neutralizing antibodies against PCV2b and PCV2d genotypes, as well as increased interferon-γ levels, and increased body weight and average daily weight gain compared with positive (challenged) and negative (unchallenged) controls. In particular, the Bac-2dCP group showed almost complete absence of PCV2d DNA in serum, nasal, and rectal swabs and in lung, lymph node, and kidney tissue samples. However, the positive control group exhibited low levels of neutralizing antibody, and high levels of PCV2 DNA in serum, swab, and tissue samples, resulting in PCV2-associated pathological lesions. The results of this study demonstrated that a recombinant Bac-2dCP vaccine conferred complete protection against a PCV2d challenge in SPF miniature pigs.

An updated review on oral protein-based antigen vaccines efficiency and delivery approaches: a special attention to infectious diseases

Various infectious agents affect human health via the oral entrance. The majority of pathogens lack approved vaccines. Oral vaccination is a convenient, safe and cost-effective approach with the potential of provoking mucosal and systemic immunity and maintaining individual satisfaction. However, vaccines should overcome the intricate environment of the gastrointestinal tract (GIT). Oral protein-based antigen vaccines (OPAVs) are easier to administer than injectable vaccines and do not require trained healthcare professionals. Additionally, the risk of needle-related injuries, pain, and discomfort is eliminated. However, OPAVs stability at environmental and GIT conditions should be considered to enhance their stability and facilitate their transport and storage. These vaccines elicit the local immunity, protecting GIT, genital tract and respiratory epithelial surfaces, where numerous pathogens penetrate the body. OPAVs can also be manipulated (such as using specific incorporated ligand and receptors) to elicit targeted immune response. However, low bioavailability of OPAVs necessitates development of proper protein carriers and formulations to enhance their stability and efficacy. There are several strategies to improve their efficacy or protective effects, such as incorporation of adjuvants, enzyme inhibitors, mucoadhesive or penetrating devices and permeation enhancers. Hence, efficient delivery of OPAVs into GIT require proper delivery systems mainly including smart target systems, probiotics, muco-adhesive carriers, lipid- and plant-based delivery systems and nano- and microparticles.

Development of ELISA Using Recombinant Proteins for the Diagnosis of Mycoplasma hyopneumoniae Infection

In order to develop a more sensitive and reliable method for detection of serum antibodies against Mycoplasma hyopneumoniae infection in pigs, six recombinant proteins of M. hyopneumoniae (P102, P95, P46, P97 like, Lppt, and hypothetical P987) were used for the standardization of an indirect enzyme-linked immunosorbent assay (ELISA). The proteins were evaluated against 50 sera of the specific pathogen-free and 50 sera of pigs with lesions suggestive of infection. The sensitivity was 88%, 86%, 78%, 74%, 66%, and 60% for the proteins P102, P95, P46, P97 like, Lppt, and hypothetical protein P987, respectively. Moreover, the proteins were used to establish the seroprevalence in two different commercial herds (254 sera pigs from farm considered free of M. hyopneumoniae and 246 from farm with clinical signs of enzootic pneumonia and positive serology for M. hyopneumoniae) and the positive rate was 65.2% for P95, 54.6% for P102, 40.2% for P46, 37.2% for P97 like, 17.4% for the hypothetical P987, and 14% for Lppt protein. In addition, the ELISA with six recombinant proteins was compared to commercial HerdCheck kit using 118 random pig sera samples and the results showed that ELISA with recombinant proteins were more sensitive than the commercial test. These data show that the recombinant proteins P95 and P102 are potential targets to be used in diagnostic tests to detect antibodies against M. hyopneumoniae. Although more studies are necessary, this study provides insights that these recombinant proteins can be useful in epidemiological investigations and as potential biomarkers in differentiating infected animals from those vaccinated.

Improving the Acid Resistance of Tannase TanBLp (AB379685) from Lactobacillus plantarum ATCC14917T by Site-Specific Mutagenesis

Tannin acyl hydrolase referred commonly as tannase catalyzes the hydrolysis of the galloyl ester bond of tannin to release gallic acid. The tannase TanBLp which cloned from Lactobacillus plantarum ATCC14917^T has high activity in the pH range (7.0-9.0) at 40 °C, it would be detrimental to the utilization at acidic environment. The catalytic sites and stability of TanBLp were analyzed using bioinformatics and site-specific mutagenesis. The results reiterated that the amino acid residues Ala164, Lys343, Glu357, Asp421 and His451 had played an important role in maintaining the activity. The optimum pH of mutants V75A, G77A, N94A, A164S and F243A were shifted from 8.0 to 6.0, and mutant V75A has the highest pH stability and activity at acidic conditions than other mutants, which was more suitable for industrial application to manufacture gallic acid. This study was of great significance to promote the industrialization and efficient utilization of tannase TanBLp.

Evaluation of novel recombinant porcine circovirus type 2d (PCV2d) vaccine in pigs naturally infected with PCV2d

INTRODUCTION

The pathogenic porcine circovirus type 2 (PCV2) causes significant economic losses in pig production. Emergence of the PCV2d genotype has been linked with PCV2-associated disease (PCVAD) outbreaks. However, no study has been conducted efficacy of an experimental PCV2d-based subunit vaccine in pigs. Therefore, PCV2b- and PCV2d-based capsid (CP) proteins were generated using a baculovirus (Bac) expression system, and we evaluated the protective immune responses in a commercial pig farm where predominant PCV2d is circulating.

METHODS

Eighteen 3-week-old pigs with maternal antibodies were randomly divided into four groups, and were immunized with purified Bac-2dCP, mixed 1:1 ratio with purified Bac-2bCP and Bac-2dCP (Bac-mCP), a commercial PCV2a-based subunit vaccine (VAC) or phosphate-buffered saline (PBS) as controls.

RESULTS

The Bac-2dCP and Bac-mCP groups had significantly higher PCV2b- or PCV2d- specific IgG and neutralizing antibody without interference by maternal antibody compared to control group in pigs naturally infected with PCV2d. Interestingly, not only serum IL-4 level was significantly increased in the Bac-2dCP group, but also PCV2d viremia level was significantly reduced than the control group.

CONCLUSIONS

The recombinant Bac-2dCP subunit vaccine is a good candidate for the effective reduction against PCV2d infection.