Retrospective evidence that the MHC (B haplotype) of chickens influences genetic resistance to attenuated infectious bronchitis vaccine strains in chickens

Abstract

Infectious bronchitis is a respiratory disease of chickens that is caused by the coronavirus infectious bronchitis virus (IBV). Virtually all broiler and layer breeder flocks are routinely vaccinated against IBV. Two hatches of 1-day-old chicks from four lines were mistakenly vaccinated for infectious bronchitis using a moderately attenuated vaccine designed for chicks of an older age. The vaccination resulted in high mortality, and chicks from three of four lines died with signs typical of infectious bronchitis. The mortality that occurred using this less-attenuated vaccine was significantly influenced by the genetic line, and the MHC (B) haplotype in chickens of three B congenic lines. B congenic chickens possessing the B*15 haplotype were resistant in contrast to chickens possessing the B*13 or B*21 haplotypes. Chicks from two further hatches of the four lines were vaccinated appropriately with a more attenuated IBV vaccine, and only limited chick mortality was seen. These retrospective data from two repeated hatches confirm earlier data indicating chicken genes influence resistance to IBV, and indicate for the first time that genes tightly linked to the B haplotype are relevant in resistance to IBV. Due to extenuating circumstances it was not possible to verify results with chicks from F 2 matings. Factors that may enhance definition of the role of the B haplotype in immune response to IBV, and the desirability for further analysis of a B haplotype-linked influence on immunity to IBV are discussed.

Dramatic differences in the response of macrophages from B2 and B19 MHC-defined haplotypes to interferon gamma and polyinosinic:polycytidylic acid stimulation

“…Monocytes derived from additional homozygous MHC haplotypes were also differentially activated by IFNγ. The cells purified from B15/B15 birds, which were shown by Bacon et al (2004) to be more resistant to IBV infection also demonstrated greater macrophage stimulation. It is possible that genes lying outside this region could also affect macrophage activation as demonstrated in other lines.…”

Coronavirus avian infectious bronchitis virus

“…It is suspected that the underlying cause of the difference is immunological. There is evidence for the MHC haplotype of chickens influencing genetic resistance to IBV [2].…”

Coronaviruses in poultry and other birds

“…The capacity of the virus to replicate in so many tissues may contribute to the sequence diversity of its proteins, especially that of the S protein. Strains of IBV differ in their virulence, and the genetic background of the host can influence the outcome of infection (see Bacon et al ., 2004, and references cited therein). Thus, IBV is not a simple pathogen and its heterogeneity with respect to its protein sequences, broad tissue tropism and pathogenicity should be borne in mind in the context of the host range of the virus, which, as described later, may be wide.…”