Evaluation of cellular and humoral immune response in chickens immunized with flagellin-adjuvanted inactivated newcastle disease virus.

The aim of the present study was to evaluate the potential effect of flagellin as adjuvant in Newcastle disease virus (NDV) vaccine on the cellular and humoral immunity in chickens. Fifty-six specific pathogen-free chickens were assigned to seven groups of eight chickens and immunized twice with a two-week interval, intramuscularly. Group 1, received phosphate buffered saline as control (C), groups 2, 3, 4, 5, 6 and 7 were immunized with inactivated NDV [Ag], Ag + full FliC protein [AgF], Ag + truncated Flic protein [AgT], Ag + native Flic protein [AgN], commercial NDV vaccine [Vac] and Vac + N [VacN], respectively. After 45 days, spleen and bursa of Fabricius samples were collected and analyzed by flow cytometry and responses in control/vaccinated chickens were studied by immunophenotyping. Humoral response was also, evaluated by ELISA during the experiment. Results showed that immunized chickens with Ag + flagellin proteins had significantly higher frequency of circulating CD3+, CD4+ and CD8+ T cells in bursa of Fabricius in AgF, AgT and AgN, respectively, compared with other groups. Similar results were observed for spleen; however, the highest frequency of circulating CD3+, CD4+ and CD8+ T cells belonged to AgT and AgF, respectively. ELISA results showed that all flagellin-adjuvanted groups had higher antibody titers than other groups with the highest antibody response in VacN. It can be concluded that flagellin may induce both humoral and cellular immune responses against ND and is suggested for use as an efficient adjuvant.

Comparison of flagellin and an oil-emulsion adjuvant in inactivated Newcastle disease vaccine in stimulation of immunogenic parameters.

The present study was designed to investigate the potential application of native (N) and recombinant (truncated modified [tmFliC] and full-length [flFliC]) flagellin proteins along with inactivated Newcastle disease virus (NDV). Fifty six SPF chickens were immunized twice with PBS (control), inactivated NDV (Ag), inactivated NDV/flFliC (AgF), inactivated NDV/tmFliC (AgT), inactivated NDV/N (AgN), commercial vaccine containing Montanide (Vac) and Vac/N (VacN), with a two-week interval. Blood was collected weekly and spleens were harvested after chickens were sacrificed. Interleukin-6 (IL-6) and tumor necrotic factor-α (TNF-α) gene expression in peripheral blood mononuclear cells were analyzed by Real-Time PCR. Antibody response was assessed by haemagglutination inhibition (HI). Cellular activity was quantified by MTT assay. Results showed that the most IL-6 and TNF-α gene expression was observed in AgF group (P < 0.01). The lowest gene expression among vaccinated groups was observed in Ag group for IL-6 and Ag and Vac group for TNF-α. The highest HI titer was observed in Vac, VacN, AgF and AgT groups. The AgF group showed the highest cellular activity (P < 0.01). In conclusion, flagellin-adjuvanted groups showed a pro-inflammatory effect and acted similarly to or better than the Vac group. Hence, flagellin can be proposed as a potential adjuvant for ND vaccine.

Effect of flagellin on inhibition of infectious mechanisms by activating opsonization and salmonella flagellum disruption.

Some serovars of salmonella cause huge global diseases such as enteric fever and invasive non typhoidal Salmonella disease. Flagellin as a key antigenic component of salmonella, can induce humoral and cellular immunity responses. In this research, we performed an opsonophagocytic killing assay (OPKA) as an important mechanism of the host-defense system, for salmonella to study the activity of anti-sera of native FliC, truncated modified recombinant FliC (tmFliC) and full length recombinant FliC proteins (flFliC). Also, the potency of antibodies for inhibiting bacterial movement was evaluated by traditional and newly-designed motility inhibition assay methods. Results showed both recombinant FliC anti-sera and native FliC (nFliC) anti-serum had the ability to opsonize Salmonella typhimurim, which led to bacterial clearance by mice macrophages. Also, inhibition of bacterial motility was observed for all anti-sera. Anti-nFliC and anti-flFliC sera showed higher effects on Salmonella typhimurim motility than that of tmFliC. In traditional method, about 88%, 86% and 80% inhibition were observed by using 5% nFliC, anti-flFliC and anti-tmFliC sera, respectively. In the newly-designed method using SIM (Sulfide indole motility) medium, results confirmed the traditional method for motility inhibition. Our findings suggest that salmonella fliC as a protective antigen may disrupt the flagellum apparatus activity.

Skimmed milk as an alternative for IPTG in induction of recombinant protein expression.

Cost-effectiveness is an important issue in biotechnological manufacturing industry and using alternative cheap materials with the same benefits has been noticed in most literatures. Isopropyl ß-d-1-thiogalactopyranoside (IPTG), a well-known chemical element for induction of protein expression, has several disadvantages such as high expense and toxicity. In this study, we aimed to introduce skimmed milk as an alternative material for protein expression by induction of lac operon. In this way, Escherichia coli BL21 (DE3) bacteria were induced using 1 mM IPTG or 1.0% (w/v) skimmed milk. Protein purification was performed using Ni-NTA (nickel-nitrilotriacetic acid) for His-tagged recombinant proteins and protein purity was evaluated by SDS-PAGE. Results showed high level of recombinant protein expression using skimmed milk, and interestingly, the growth rate of bacteria improved. Our findings suggested that skimmed milk can be a suitable alternative for induction of recombinant protein expression, which has advantages such as more availability and affordability, in comparison to IPTG supplementation.

Effect of C-Terminus Modification in Salmonella typhimurium FliC on Protein Purification Efficacy and Bioactivity.

Recombinant flagellin (FliC) has shown low efficacy in purification because of inclusion bodies formation and aggregation. We hypothesized preserving TLR5 binding site of FliC and removing some amino acids could be responsible for aggregation and solubility improvement. Hence, a bioinformatics study was performed to find hotspots in aggregate formation. Protein modeling was carried out by SWISS-MODEL and I-TASSER servers and models were compared by MATRAS server and Chimera 1.11.2. Gene modification was carried out based on bioinformatics studies. Genes, (truncated modified fliC (tmFliC) and full-length fliC (flFliC)), were cloned and expressed in pET-21a vector. Protein purification was carried out using HIS-Tag method. Proliferation assay and also induction of IL-8 in HEK293 cells were performed to confirm bioactivity function of tmFliC. Bioinformatics results showed that partial deletion of C-terminus may increase solubility without unfavorable effect on TLR5 recognition. Also, model comparison showed that this protein may preserve 3D structure. In addition, GlobPlot server demonstrated that tmFliC formed its globular domains which were important in TLR5 recognition. As we expected, high purification efficacy for tmFliC compared with flFliC was also obtained in experimental studies and a proper function for tmFliC was observed. The tmFliC enhanced cell proliferation in HEK293 cells compare with control after 24 h. Also, IL-8 level was increased with stimulation by tmFliC after 24 h. In conclusion, reducing hydrophobicity in C-terminus and deleting necessary amino acids for filament formation may increase protein solubility.

Introducing a cost-effective method for purification of bioactive flagellin from several flagellated gram-negative bacteria.

The objective of this study was to introduce a simple and cheap method for purification of flagellin. So, flagellin proteins of Salmonella typhimurium (S. typhimurium), Escherichia coli (E. coli), Citrobacter freundii (C. freundii) and Salmonella typhi (S. typhi) were purified by a modified simple method. Bacterial cultures were precipitated by centrifugation. Precipitates were washed twice and flagellin proteins were detached by shaking vigorously (in PBS pH = 2), and then flagellin proteins were precipitated by ammonium sulfate saturation. Evaluation of purification efficiency and concentration were examined by SDS-PAGE and Bradford assay. Polyclonal antibodies were produced against S. typhimurium FliC and cross-reactivity of anti-S. typhimurium was assessed against other flagellins. Bioactivity of flagellins was evaluated by cell proliferation and IL-8 protein expression assay in HEK293 cells, and also, IL-6 and TNF-α genes expression in chicken cells. Results showed a single band for flagellin proteins of all bacteria on %10 SDS-PAGE, which concentration ranged from 150 to 400 µg/mL. All flagellin proteins increased cell proliferation, and IL-8 levels were increased after treatment by flagellins and levels of IL-6 and TNF-α were increased after treatment with S. typhimurium FliC. All flagellin proteins showed cross-reactivity with antibodies. Findings showed that application of our method, not only reduced time and cost, but also, the purified flagellin proteins had acceptable bioactivity.

Immunostimulatory effects of truncated and full-length flagellin recombinant proteins.

Problems regarding purification efficacy in recombinant technologies is due to the protein structure. Experimental manipulation of genes and the subsequent proteins may overcome this issue. In order to improve production efficacy and maintain immunestimulatory effect of flagellin, the Toll-like Receptor 5 (TLR5) ligand and a potent adjuvant, we performed a bioinformatic study to find the best model for FliC manipulation. Truncated modified FliC (tmFliC) and full length FliC (flFliC) genes were cloned and expressed in pET-21a vector and protein purification was carried out using an improved His-Tag method. Polyclonal antibodies were generated against flFliC and tmFliC in New Zealand white rabbits. IgG response to the recombinant proteins was determined by ELISA. Cross-reactivity assay was performed by ELISA for all proteins and bacteria. Immunogenicity of tmFliC and flFliC was evaluated in chicken cells, and expression level of tumor necrotic factor-α (TNF-α) and interleukin-6 (IL-6) were relatively analyzed by Real-Time-PCR. Results showed high purification efficacy for tmFliC. Antibody titer of tmFliC was significantly higher than that of flFliC. In addition, the cross-reactivity assay for both proteins and Salmonella was positive which indicates similar epitopic regions. Stimulation of both FliCs significantly increased TNF-α and IL-6 expression in peripheral blood mononuclear cells (PBMCs) and splenocytes, with higher effect observed with flFliC. IL-8 protein level increased after 6 and 24 h stimulation with different concentrations of tmFliC and flFliC. These results suggest that the aimed gene modification in fliC gene produces a bioactive immunostimulant type of flagellin which upregulates TLR5 downstream genes as well as in flFliC.