Date Published: May 29, 2009
Publisher: Taylor & Francis
Author(s): L. B. Liu, C. M. Wu, J. Wen, J. L. Chen, M. Q. Zheng, G. P. Zhao.
Antibody titers raised for vaccinations against avian influenza (AI) and Newcastle disease (ND) were higher in Chinese Beijing-You (BJY) than in White Leghorn (WL) (P < 0.001), but there was no breed difference in titers for sheep red blood cells (SRBC). Genotyping by PCR-SSCP identified seven haplotypes in WL and 17 in BJY. After sequencing PCR products (35 and 85, respectively), 43 (WL) and 47 (BJY) single nucleotide polymorphisms (SNPs) were found in the 264 bp of exon 2. In WL chickens, significant associations were found with antibody responses to AI (two SNPs), ND (six SNPs), and SRBC (one SNP), while in BJY there was association with responses to ND (two SNPs) and SRBC (two SNPs), but none with AI. These results indicate that the genomic region bearing exon 2 of the major histocompatibility complex B-F gene has significant effects on antibody responses to SRBC and vaccination against AI and ND. Different SNPs affected antibody titers for each of the antigens and they differed between these very distinct breeds.
The major histocompatibility complex (MHC) molecules play important roles in the regulation of the immune response by communicating among different cellular components of the immune system: T cells, B cells, and antigen-presenting cells (Lamont, 1998a,b,c). The MHC in chickens is known to have a significant association to disease resistance and susceptibility to numerous pathogens including Marek’s disease virus (Bacon et al., 2001), Rous sarcoma tumor virus (Taylor, 2004), and Salmonella (Cotter et al., 1998). The association between MHC and disease outcome is found in laboratory strains of chickens and commercially important flocks (Hansen et al., 1967; Bacon et al., 1981). The crucial function of the MHC in the immune response therefore makes it a promising candidate region for genetic selection to improve avian disease resistance.
In conclusion, this study has clearly shown that genomic variation in exon 2 of the MHC B-F gene in chickens had significant effects on antibody responses to vaccination against SRBC, AIV, and NDV. Different SNPs were shown to be associated with responses to AIV, NDV, and SRBC and some linkage was demonstrated between nucleotide loci. The SNPs detected here, which differed between WL and BJY, have the potential for changing the antigen binding pocket in MHC Class I molecules, possibly accounting for differences in immune re-activity. It is noteworthy that SNPs 180 and 182 generate the non-synonymous mutations Arg, ser, or gly for AA61, the critical amino acid emphasized by Koch et al. (2007). The a/t SNP at 182 was relatively frequent and in WL was significantly associated with antibody response to SRBC. Additional work is needed, with immune traits for other important disease vectors, to confirm and extend the array of polymorphisms within the chicken gene encoding Class I MHC. Such investigation may provide the rationale for future application of Marker-Assisted Selection (MAS) for enhancing immunocompetence in chickens.