Immunogenicity in Swine of Orally Administered Recombinant Lactobacillus plantarum Expressing Classical Swine Fever Virus E2 Protein in Conjunction with Thymosin α-1 as an Adjuvant

Abstract

e Classical swine fever, caused by classical swine fever virus (CSFV), is a highly contagious disease that results in enormous economic losses in pig industries. The E2 protein is one of the main structural proteins of CSFV and is capable of inducing CSFVneutralizing antibodies and cytotoxic T lymphocyte (CTL) activities in vivo. Thymosin ␣-1 (T␣1), an immune-modifier peptide, plays a very important role in the cellular immune response. In this study, genetically engineered Lactobacillus plantarum bacteria expressing CSFV E2 protein alone (L. plantarum/pYG-E2) and in combination with T␣1 (L. plantarum/pYG-E2-T␣1) were developed, and the immunogenicity of each as an oral vaccine to induce protective immunity against CSFV in pigs was evaluated. The results showed that recombinant L. plantarum/pYG-E2 and L. plantarum/pYG-E2-T␣1 were both able to effectively induce protective immune responses in pigs against CSFV infection by eliciting immunoglobulin A (IgA)-based mucosal, immunoglobulin G (IgG)-based humoral, and CTL-based cellular immune responses via oral vaccination. Significant differences (P < 0.05) in the levels of immune responses were observed between L. plantarum/pYG-E2-T␣1 and L. plantarum/pYG-E2, suggesting a better immunogenicity of L. plantarum/pYG-E2-T␣1 as a result of the T␣1 molecular adjuvant that can enhance immune responsiveness and augment specific lymphocyte functions. Our data suggest that the recombinant Lactobacillus microecological agent expressing CSFV E2 protein combined with T␣1 as an adjuvant provides a promising strategy for vaccine development against CSFV. C lassical swine fever virus (CSFV), a member of the Pestivirus genus of the Flaviviridae family, is a small, enveloped, singlestranded RNA virus. The genome of CSFV consists of a positivestranded RNA molecule of about 12.3 kb, encoding a single open reading frame that is translated into a 3,898-amino-acid polyprotein, giving rise to different CSFV proteins after coprocessing and after translational processing (1, 2). Of these, the E2 structural protein encompasses major antigenic domains and cytotoxic T lymphocyte (CTL) epitopes, suggesting a promising candidate for an immunogen with the capacity to induce neutralizing antibodies and CTL activities against CSFV (3-10). CSFV often causes severe and lethal disease in pigs, resulting in enormous economic losses in pig industries (11,12). Therefore, the development of effective vaccines against CSFV infection is an issue of growing importance.For the development of CSFV vaccines, the roles of neutralizing antibody-based humoral immune responses (13, 14) and CTL-based cellular immune responses (15-20) have been both highlighted. Furthermore, the invasion of CSFV often initiates at mucosal surfaces, particularly intestinal tissues, and thus, vaccination inducing IgA-based protective mucosal immunity via the mucosal approach could effectively prevent the virus from entering the body via mucosa and its further spread to the systemic circulation. Taken together, the design of new vaccines ...

Oral recombinant Lactobacillus vaccine targeting the intestinal microfold cells and dendritic cells for delivering the core neutralizing epitope of porcine epidemic diarrhea virus

“…Samples of the intestinal tract were stored at − 40 °C until analysis. In addition, fecal samples were collected on days 0, 4, 6,8,10,12,14,16,20,22,24,26,28,30,32,34, and 36 after immunization, and treated according to a previously described method [26]. Briefly, 0.1 g of fecal pellets were suspended in 400 μL of PBS containing 1 mmol L −1 phenylmethylsulfonyl fluoride (Sigma, USA) and 1% bovine serum albumin (BSA), and then incubated at 4 °C for 16 h. After centrifugation, the supernatants were stored at − 40 °C until use.…”

“…Cell wall associated or secreted factors from some Lactobacillus strains can enhance innate immune responses and epithelial barrier function, modulate the intestinal micro-environment, regulate immune cell behavior, and elicit release of cytokines [11]. In addition to natural immune-stimulating adjuvants with weak immunogenicity [12] and capacity to survive the gastric acid and digestive enzymes, several Lactobacillus strains have been applied for the delivery of heterologous antigens to trigger mucosal immune responses against pathogens [13][14][15].…”

Immunogenic Properties of Lactobacillus plantarum Producing Surface-Displayed Mycobacterium tuberculosis Antigens

“…Recent studies in animal models have found that antigen delivery by orally administered L. plantarum may elicit secretion of specific IgA antibodies against antigens related to influenza (61), cancer (44), foot-and-mouth disease virus (FMDV) (62), and classical swine fever virus (63). In this regard, we investigated whether orally administered AgE6-displaying L. plantarum induced production of AgE6-specific IgA antibodies at intestinal mucosa.…”

Adjuvant Strategies for Lactic Acid Bacterial Mucosal Vaccines

“…There were three LAB adjuvant studies that did not fit into the above categories: Japanese herbal medicines (Juzen-taiho-to (JTT) and Hochi-ekki-to (HEY)), receptor activator of nuclear factor kappa-B ligand (RANKL), and thymosin α-1 [116][117][118]. They are briefly reviewed in Table 5 and their mechanisms of action described here.…”