Campylobacter jejuni is one of the main reasons for gastroenteritis diseases throughout the world, specifically in developing countries[3, 6]. It can be associated with diarrhea (from mild to severe), fever, neurological disorders, reactive arthritis, and weight loss. It is estimated about 14 cases for 100,000 people that were afflicted worldwide every year [4, 23]. In order to handle the disease, the sciences are in urgent to raising their knowledge about C. jejuni. The pathogenicity of C. jejuni is up to the ability to linkage with other organisms and many proteins take part in the adhesion and colonization of bacteria[24]. Among adhesive proteins of the bacteria, many studies approved that the CadF protein could consider as a proper candid for vaccination projects. In this study, we focused on the immunogenic protein of the CadF to design vaccine through bioinformatics tools which can dramatically reduce the number of In vitro tests [20].
In recent years, the bioinformatics knowledge provides easy accession to get information around the design of genomics, proteomics, and new vaccine of the bacteria. With regard to development of recombinant vaccines, predicting this type of vaccines has advantages rather than other methods. In silico vaccines can be considered as time-saving and convenient methods to identify antigens, allergens, and reducing the laboratory errors. In addition, they are cheaper than other traditional methods; while the anticipation of the epitope regions doesn’t always carry out with 100% accuracy and the results of several servers don’t probably present the same results [19, 21, 25, 26].
The past studies have been declared some efforts to suggest an effective vaccine against C. jejuni. For instance, some sciences have used the whole-cell vaccines of the C. jejuni and it had advanced in animal models but has failed at the human cases. Since the results were not able to gotten approved in term of safety for humans [5]. Also, different reports have demonstrated polysaccharide capsule (cps) of the bacteria that could be used for alleviating campylobacteriosis, but this approach was just tested at phase 1 clinical; however there are concerns about being the similarity between bacterial polysaccharides and human gangliosides [10].
Other antigens, e.g. ABC transporter (PEB1), which is known as an immunogenic and protective protein, could be a candidate for vaccination against C. jejuni. Due to the response of the immune system produced by lymphocytes inverse PEB1 protein, it could inhibit the development of the disease. However, this vaccine has been building in pre-clinical trials yet [5, 27]. Beyond a PEB1-vaccine mentioned approach, other pathogenic proteins of C. jejuni have also been analyzed. Kobierecka et al. have found that CjaA, CjaD (binding proteins), FlaA (flagellin), and CmeC (outer-membrane protein) could protect the chickens against C. jejuni in many cases [9]. Neal-McKinney et al. also have asserted the vaccination of chickens with the CadF-FIaA-FIpA fusion protein that could reduce the rate of infection, but there is not any evidence whatever will be able to use in human models [8]. Moreover, some of the peptides related to invasive, virulent, and membrane of the bacteria, which contain FlaA, Cia, CadF, PEB1, PEB3, and MOMP have assessed which could be effective in design a vaccine against C.jejuni by immunoinformatics tools. So, despite many efforts to make the vaccine, there are not any approved the vaccine against C. jejuni to be useful in humans so far [7, 18, 19].
Our findings showed that CadF is a highly conserved protein among Campylobacter spp. and is belonging to the superfamily of outer member proteins (ompA). [28-30].
We collected T-cell and B-cell epitope regions through different servers and the higher epitopes have elicited to make an effective vaccine against C. jejuni. The final common certain epitopes are included LLCLGLASV, RRVDAKFIL, FSADNNVKF, LSDSLALRL, EGHFGFDKTTINPTF, QINFNHANH, ASVLFSADNNVKFEI, QINFNHANHNWVSTL, WVSTLGISFG, LETRDQINFN, VGEKFYFYGL, and NPRSSNDTKEGRADNRRVDA. These epitopes were confirmed to act as humoral- and cell-mediators and induced an immune response and a motivate immune system according to Vaxijen and Allertop data.
In addition, our research also showed the correct topology model based on phyre2 server that predicts CadF is a stable target. This analysis was done with bioinformatics methods and helps to design novel vaccine according to sequence profile and spatial structure and dimension of protein.
In present study used from SYFPEITH, IEDB, NetCTL, NHLAPred, NETMHC I, MHCPred II, Bcepred, ABCpred, and SVMTrip online servers for searching of our study. Finally, common epitopes were identified and the LSDSLALRL epitope was selected as the best potential vaccine candidate. Moreover, the allergenicity of the LSDSLALRL epitope has also confirmed by Allertop server and confirmed that this sequence wasn’t an allergen as well.
The epitope was located in 135-143 regions and can be interacted with HLA-A0101 according to collected results from many above-mentioned servers. In a partial contrary by Yasmin study, who gained its knowledge based on just IEDB and SYFPEITHI servers on CadF protein, suggested that FRLSDSLAL epitope from the protein can be as good chosen for deigning vaccine [19].
It is clear that our epitope has fairly matched with the epitope presented by Yasmin et al. (77.77% of amino acids are matched, LSDSLALRL and FRLSDSLAL, which are marked by underline) and this similarity can be a higher claim for designing an effective vaccine against C. jejuni. Based on Allertop server, the presented epitope by Yasmin et al. was an allergen, while no allergenicity was observed for our epitope "LSDSLALRL" in this study.
In addition, CadF is a significant protein for the colonization and binding the bacteria to host cells and maximum connection can be detected in the regions of the fibronectin-binding domain including phenylalanine-arginine-leucine-serine (FRLS) residues of CadF. Although only fifty percent from the amino acids of our epitope was identified as the binding site to host cells, multiple servers confirmed that this reign has a high score for developing the vaccine.
According to aliphatic index, alanine, valine, isoleucine, and leucine amino acids were detected in structure of the protein, which proposed it as a thermostable protein. These amino acids in thermophilic bacteria, such as C. jejuni, are significantly higher than that of ordinary proteins [31]. This is another advantage of CadF that can be proposed it for the development of the vaccine. Heat stability is an important feature in vaccine production that can simplify the logistics of vaccine distribution and expand the immunization coverage [32]. So, it has been supporting from the most crucial role of this sequence of CadF protein at disease trend and being useful analysis to construct the active vaccine.