Characterization of the chicken antibody response against infectious bursal disease virus (IBDV), IBDV impact on B-cells and full-length genomic sequencing followed by antigenic and phylogenetic analysis of IBDV strains with different pathogenicities
Petkov, Daniel Iordanov
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The aim of the first project was to elucidate the effect of infectious bursal disease virus (IBDV) on the serum immunoglobulin levels and B-lymphocyte subpopulations using flow cytometric analysis. In the bursa, two B-cell subpopulations designated as A and B were identified based on cell size and granularity. The IgM+, B-cell subpopulation B was reduced following IBDV vaccination and challenge. Both subpopulations were phenotyped using B-cell surface expressed antigens. Age-related changes were demonstrated such as a decrease in the proportion of subpopulation A and an increase of subpopulation B when compared with the total analyzed bursal cells. In addition, they express Lewisx, IgM, Bu1b, MUI36, and 78 differentially but not MHCII surface antigens. The reduction of subpopulation B did not reduce the total serum immunoglobulins nor did it affect IgG+ and IgA+, B-cells in the spleen. The IBDV resistant subpopulation A most likely consists of immature cells which act to repopulate the bursa following IBDV infection. The second project was designed to sequence and characterize the full-length genomes of four IBDV strains with different pathogenicities. Only previously described hydrophilic, major A and minor 1 peaks are located within the newly predicted VP2 antigenic regions. At the VP2 processing site the Edgar cell culture adapted (CCA) and chicken embryo adapted (CEA) were more similar to the very virulent (vvIBDV) strains. Lukert, Edgar CCA, and Edgar CEA have overall sequence characteristics of the classical strains and were closely related to each other. Analysis of the VP1, VP3, and VP4 proteins revealed 9109 has characteristics of classical type virus but within the same proteins shares unique amino acids with vvIBDV strains. At the 3’ and 5’ noncoding regions of segment A 9109 has similarities to the vvIBDV strains. Within the VP2 protein several predicted antigenic regions and deduced amino acids were conserved between this isolate and variant E. The amino acid (aa) sequences of VPX protein aa 202-451 and 210-473 but not the VP2 protein are the best representatives of the entire IBDV genome.