B-cell epitope of beta toxin of Clostridium perfringens genetically conjugated to a carrier protein: Expression, purification and characterization of the chimeric protein

Immunogenicity assessment of Clostridium perfringens type D epsilon toxin epitope-based chimeric construct in mice and rabbit

Epsilon toxin (Etx) belongs to family of pore-forming toxin and is produced by Clostridium perfringens type D. The Etx toxin is responsible for the pathogenesis of enterotoxaemia in sheep and goats, and occasionally in other livestock animals. The present study aimed to develop a Clostridium perfringens epsilon toxin-based chimeric epitope construct having immunodominant B-cell epitope and universal T-cell epitope and its immunogenicity was evaluated in mice and rabbit. An artificial chimeric epitope construct (CEC) was prepared by joining tandem repeats of a peptide containing amino acids (aa) 134–145 of epsilon toxin B-cell epitope and universal T-cell epitopes. The CEC was expressed in the Escherichia coli following codon optimization for efficient translational efficiency and purified by affinity chromatography. The antigenic reactivity of r-CEC proteins was confirmed by western blot with rabbit anti-r-Etox hyperimmune sera. The immunogenicity of the recombinant single CEC was examined in mice and rabbit by indirect ELISA. It was found that r-CEC yielded high titers of neutralizing antibodies (≥ 1.035 IU/ml) in immunized mice and rabbit. The potency of chimeric protein immunized serum was observed to be higher than the recommended level (0.1–0.3 IU/ml) for protection in sheep and goats. This indicated the potential ability of the chimeric protein as a vaccine candidate. This further requires studying the immune response in targeted host species (sheep and goat).

Immunization of mice against alpha, beta, and epsilon toxins of Clostridium perfringens using recombinant rCpa-b-x expressed by Bacillus subtilis

The anaerobic pathogen Clostridium perfringens is the most potent cause of intestinal diseases, such as enterotoxemia, hemorrhagic enteritis, and lamb dysentery, in sheep. Three toxinotypes (B, C, and D) are usually the cause of these diseases and are mainly mediated via three important exotoxins: alpha toxin (CPA), beta toxin (CPB), and epsilon toxin (ETX). We have designed a chimeric protein, rCpa-b-x, that contains the C-terminal binding region of CPA, partial sequence of CPB, and ETX (Cpa^247-370, Cpb^108-305, and Etx^H118P, respectively) according to the principle of structural vaccinology. The rCpa-b-x protein was then expressed by pHT43 plasmid in vivo using Bacillus subtilis as a delivery vector (Bs-pHT43-Cpa-b-x). The immunological activity of the rCpa-b-x protein was verified by western blot and its immunological efficacy was evaluated in a murine model. Oral administration with a recombinant agent caused local mucosal and systemic immune responses, and serum lgG and intestinal mucosal secretory IgA (sIgA) antibody titers were significantly increased. Levels of IL-2, IL-4, and IFN-γ were significantly higher in lymphocytes isolated from the Bs-pHT43-Cpa-b-x group compared with levels from the control groups. The percentages of CD4⁺ and CD8⁺ T lymphocytes in the Bs-pHT43-Cpa-b-x and inactivated vaccine (IV) groups were in the normal range. Mice of vaccine groups and control groups were challenged with 1x LD₁₀₀ unit filtrate containing alpha, beta, and epsilon toxins. Mice in the Bs-pHT43-Cpa-b-x group were found to have lower rates of morbidity. The active immunization of mice with Bs-pHT43-Cpa-b-x still maintained 85% to 90% survival at the end of the 10-day observation period, whereas mice of control groups died within two to five days. The results of this study demonstrate the effectiveness of Bs-pHT43-Cpa-b-x in preventing C. perfringens infection in mice, and that Bs-pHT43-Cpa-b-x could be considered a potential vaccine against C. perfringens.

Immunization with recombinant fusion of LTB and linear epitope (40-62) of epsilon toxin elicits protective immune response against the epsilon toxin of Clostridium perfringens type D

Epsilon toxin (Etx) produced by Clostridium perfringens types B and D, a major causative agent of enterotoxaemia causes significant economic losses to animal industry. Conventional vaccines against these pathogens generally employ formalin-inactivated culture supernatants. However, immunization with the culture supernatant and full length toxin subjects the animal to antigenic load and often have adverse effect due to incomplete inactivation of the toxins. In the present study, an epitope-based vaccine against Clostridium perfringens Etx, comprising 40-62 amino acid residues of the toxin in translational fusion with heat labile enterotoxin B subunit (LTB) of E. coli, was evaluated for its protective potential. The ability of the fusion protein rLTB.Etx_40-62 to form pentamers and biologically active holotoxin with LTA of E. coli indicated that the LTB present in the fusion protein retained its biological activity. Antigenicity of both the components in the fusion protein was retained as anti-fusion protein antisera detected both the wild type Etx and LTB in Western blot analysis. Immunization of BALB/c mice with the fusion protein resulted in a significant increase in all isotypes, predominantly IgG1, IgG2a and IgG2b. Anti-fusion protein antisera neutralized the cytotoxicity of epsilon toxin both in vitro and in vivo. Thus, the results demonstrate the potential of rLTB.Etx_40-62 as a candidate vaccine against C. perfringens.

Clostridium perfringens beta toxin DNA prime-protein boost elicits enhanced protective immune response in mice

Clostridium perfringens beta toxin (CPB) is the primary pathogenic factor responsible for necrotic enteritis in sheep, cattle and humans. Owing to rapid progression of the disease, vaccination is the only possible recourse to avoid high mortality in animal farms and huge economic losses. The present study reports evaluation of a cpb gene-based DNA vaccine encoding the beta toxin of C. perfringens with homologous as well as heterologous booster strategy. Immunization strategy employing heterologous booster with heat-inactivated rCPB mounted stronger immune response when compared to that generated by homologous booster. Antibody isotyping and cytokine ELISA demonstrated the immune response to be Th1-biased mixed immune response. While moderate protection of immunized BALB/c and C57BL/6 mice against rCPB challenge was observed with homologous booster strategy, heterologous booster strategy led to complete protection. Thus, beta toxin-based DNA vaccine using the heterologous prime-boosting strategy was able to generate better immune response and conferred greater degree of protection against high of dose rCPB challenge than homologous booster regimen, making it an effective vaccination approach against C. perfringens beta toxin.

Recombinant Alpha, Beta, and Epsilon Toxins of Clostridium perfringens: Production Strategies and Applications as Veterinary Vaccines

Clostridium perfringens is a spore-forming, commensal, ubiquitous bacterium that is present in the gastrointestinal tract of healthy humans and animals. This bacterium produces up to 18 toxins. The species is classified into five toxinotypes (A-E) according to the toxins that the bacterium produces: alpha, beta, epsilon, or iota. Each of these toxinotypes is associated with myriad different, frequently fatal, illnesses that affect a range of farm animals and humans. Alpha, beta, and epsilon toxins are the main causes of disease. Vaccinations that generate neutralizing antibodies are the most common prophylactic measures that are currently in use. These vaccines consist of toxoids that are obtained from C. perfringens cultures. Recombinant vaccines offer several advantages over conventional toxoids, especially in terms of the production process. As such, they are steadily gaining ground as a promising vaccination solution. This review discusses the main strategies that are currently used to produce recombinant vaccines containing alpha, beta, and epsilon toxins of C. perfringens, as well as the potential application of these molecules as vaccines for mammalian livestock animals.

A novel linear neutralizing epitope of hepatitis E virus

Hepatitis E virus (HEV) is a serious public health problem that causes acute hepatitis in humans and is primarily transmitted through fecal and oral routes. The major anti-HEV antibody responses are against conformational epitopes located in a.a. 459-606 of HEV pORF2. All reported neutralization epitopes are present on the dimer domain constructed by this peptide. While looking for a neutralizing monoclonal antibody (MAb)-recognized linear epitope, we found a novel neutralizing linear epitope (L2) located in a.a. 423-437 of pORF2. Moreover, epitope L2 is proved non-immunodominant in the HEV-infection process. Using the hepatitis B virus core protein (HBc) as a carrier to display this novel linear epitope, we show herein that this epitope could induce a neutralizing antibody response against HEV in mice and could protect rhesus monkeys from HEV infection. Collectively, our results showed a novel non-immunodominant linear neutralizing epitope of hepatitis E virus, which provided additional insight of HEV vaccine.

Recent insights into Clostridium perfringens beta-toxin

Clostridium perfringens beta-toxin is a key mediator of necrotizing enterocolitis and enterotoxemia. It is a pore-forming toxin (PFT) that exerts cytotoxic effect. Experimental investigation using piglet and rabbit intestinal loop models and a mouse infection model apparently showed that beta-toxin is the important pathogenic factor of the organisms. The toxin caused the swelling and disruption of HL-60 cells and formed a functional pore in the lipid raft microdomains of sensitive cells. These findings represent significant progress in the characterization of the toxin with knowledge on its biological features, mechanism of action and structure-function having been accumulated. Our aims here are to review the current progresses in our comprehension of the virulence of C. perfringens type C and the character, biological feature and structure-function of beta-toxin.