Genetic resistance to Infectious Bronchitis Virus infection

Abstract

An IBV infectivity study was conducted using inbred lines of White Leghorn chickens homozygous at the B-complex, or MHC genes. One heterozygous haplotype was also included. Of the groups examined, based on clinical illness, the B5/B5 haplotype was the most resistant, followed by B2/B12, B2/B2, B19/B19, and B12/B12. Low levels of virus were recovered in the lungs of only the infected B2/B2 and B12/B12 haplotypes. Virus was easily detected in infected kidneys of all groups examined and levels detected correlated with severity of clinical illness. Lymphocyte infiltration was seen in the lungs of both uninfected and infected birds, with the most seen in the B2/B2 chicks. Mucus production was noted in both the uninfected and infected lungs for all three groups, with the B12/B12 haplotype having the highest production in both control and infected tissue. Heterophils were seen only in the lungs of infected birds, and while all groups developed heterophilia by day 8 post infection, heterophilia in the heterozygous B2/B12 lungs appeared early in infection. In kidney tissues, lymphocyte infiltration was seen in the uninfected B2/B2 and heterozygous B2/B12 kidneys, however, none were noted in uninfected B12/B12 tissues. Of all the kidneys examined for heterophilia, the B2/B2 uninfected kidneys contained the highest amount, and this was the only group having large numbers both before as well as throughout the course of infection. The heterozygous B2/B12 haplotype clinical illness was not as severe as the homozygous B2/B2 haplotype, suggesting that having only one B2 allele was enough to protect against IBV challenge. The B12/B12 and B19/B19 haplotypes, which have almost identical Class I genes, showed similar kinetics of illness, therefore, the differences seen between these two haplotypes is, at least in part, due to differences in the Class I genes.