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.

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