Genetic mechanisms of antigenic variation in infectious bursal disease virus: Analysis of a naturally occurring variant virus

Abstract

The major immunogenic protein VP2 from a pathogenic field isolate (variant A virus) of infectious bursal disease virus (IBDV) was cloned and sequenced to examine antigenic variations. The VP2 open reading frame consists of 1509 nucleotides and codes for a 503 amino acid protein. Overall, the VP2 amino acid sequence of the variant A virus shares 98.6% identity with VP2 genes from other published IBDV strains. However, within the central region of VP2 (amino acids 222-334) lies a highly divergent area that we have termed the variable domain. Relative to five other IBDV isolates, a total of six amino acid changes occur within the variable domain of the variant A virus. At positions 284-288, a substitution of isoleucine to threonine, a decrease in the number of Chou and Fasman beta turns, and a switch from a hydrophilic to a hydrophobic region are found only in the variant A virus. Together these changes predict a decrease in antigenicity as determined by calculation of potential antigenic sites. This suggests that only minor changes within VP2 contributed to the emergence of a variant virus that can cause disease in immunized birds.

Restriction fragment length polymorphism analysis of the VP2 gene of Australian strains of infectious bursal disease virus

“…Very virulent (vv) IBDV strains can cause high mortalities and have spread from Europe to the Middle East, Asia, Africa and South America (Lin et al, 1993;Etterradossi et al, 1999;Kwon et al, 2000;Zierenberg et al, 2000;Ikuta et al, 2001;Islam et al, 2001;Meir et al, 2001). Antigenic variants are predominantly confined to the US, and are highly immunosuppressiv e but do not induce specific mortalities (Lana et al, 1992;Lasher & Shane, 1994).…”

Sequence Comparison of the VP2 Variable Region of Infectious Bursal Disease Virus Isolates from Vietnam.

“…The average mortality was about 3 in flocks from which four bursa samples (16,17,18 and 17a) were collected, and about 15% in flocks from which other 19 bursa samples (1f, 10, 11, 26, 21, 1u73, 12, 15, 19, 20, 2r, 13, 14, 22, 24, 27, 28, 23, and 25) were collected.…”

“…The remaining 9 Vietnamese vv strains 2r, 13, 14, 22, 23, 24, 25, 27, and 28 had one or two amino acid substitutions with respect to DV86, all of which occurred in the first hydrophilic region. There was only one amino acid change in the first hydrophilic region between the 4 Vietnamese virulent strains (16,17,18 and 17a) and the classical strains 52/70 and STC. It is interesting to note that the amino acid sequences of 3 Vietnamese virulent strains (16, 17 and 18) and vaccine strain (18a) had only one amino acid change and this was located in the hydrophobic matrix (residue 302 from threonine to alanine).…”

“…Field strains: Twenty-three field bursa samples were collected from outbreaks of IBD occurred in Vietnam in D00869 [3]; STC, accession D00499 [15]; Cu-1, accession D00867 [3]; PBG98, accession D00868 [3]; Variant A, accession M64285 [18]; Variant E, accession D10065 [10]; 849VB, accession X95883 [28]; UK661, accession X92760 [6]; OKYM, accession D49706 [31]; DV86, accession D16675; HK46, accession AF051838; OH, accession M66722 [16]; 23/82, accession Z21971 [26].…”

“…Previous findings indicate that the molecular basis of antigenic variation between strains is clustered in a variable domain of VP2 which is highly hydrophobic and flanked by two hydrophilic regions, the first hydrophilic region being from amino acids 212 to 224 and the other from 314 to 324 [3,18,25,27]. The first region has been speculated to be responsible for stabilizing the conformation epitope and the second region for recognition by the virus-neutralizing MAbs [10].…”