METHODS AND RESULTS: In this study, recombinant TYMVcHis6 expressed in Escherichia coli self-assembled into VLPs of approximately 30-32 nm. SDS-PAGE and Western blot analysis of protein fractions from the immobilized metal affinity chromatography (IMAC) showed that TYMVcHis6 VLPs interacted strongly with nickel ligands in IMAC column, suggesting that the fusion peptide is protruding out from the surface of VLPs. These VLPs are highly stable over a wide pH range from 3·0 to 11·0 at different temperatures. At pH 11·0, specifically, the VLPs remained intact up to 75°C. Additionally, the disassembly and reassembly of TYMVcHis6 VLPs were studied in vitro. Dynamic light scattering and transmission electron microscopy analysis revealed that TYMVcHis6 VLPs were dissociated by 7 mol l-1 urea and 2 mol l-1 guanidine hydrochloride (GdnHCl) without impairing their reassembly property.
CONCLUSIONS: A 10-residue peptide was successfully displayed on the surface of TYMVcHis6 VLPs. This chimera demonstrated high stability under extreme thermal conditions with varying pH and was able to dissociate and reassociate into VLPs by chemical denaturants.
SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first C-terminally modified TYMVc produced in E. coli. The C-terminal tail which is exposed on the surface can be exploited as a useful site to display multiple copies of functional ligands. The ability of the chimeric VLPs to self-assemble after undergo chemical denaturation indicates its potential role to serve as a nanocarrier for use in targeted drug delivery.
RESULTS: The depletion of IgM+ cells and infiltration of macrophages were observed to be higher in bursa infected with AF2240 as compared to IBS002. In line with the increment of the macrophage population, higher nitric oxide (NO) and malondialdehyde (MDA) contents which indicated higher oxidative stress were also detected in bursa infected with NDV AF2240. In addition, higher pro-inflammatory cytokines and chemokine gene expression such as chicken CXCLi2, IL-18 and IFN-γ were observed in AF2240 infected bursa. Depletion of IgM+ cells was further confirmed with increased cell death and apoptosis of the cells in AF2240 infected bursa as compared to IBS002. However, it was found that the viral load for NDV strain IBS002 was comparatively higher than AF2240 although the magnitude of the pro- inflammatory cytokines expression and cell apoptosis was lower than AF2240.
CONCLUSION: The results of our study demonstrated that infection of NDV strains AF2240 and IBS002 caused apoptosis in bursa IgM+ cells and its severity was associated with increased expression of pro-inflammatory cytokines/chemokine, macrophage infiltration and oxidative stress as the infection duration was prolonged. However, of the two viruses, we observed that NDV AF2240 induced a greater magnitude of apoptosis in chicken bursa IgM+ cells in comparison to IBS002. This might be due to the high level of oxidative stress and inflammatory cytokines/chemokine as well as lower IL10 expression which subsequently led to a high rate of apoptosis in the chicken bursa of Fabricius although the detected viral load of AF2240 was lower than IBS002.