Associations Between Immune Traits And SNPs Of MHC B-F Gene In Two Genetic Types Of Chickens

Major histocompatibility complex (MHC) plays a key role in disease resistance. In the present study, associations between immune traits and SNPs of MHC B-F gene Exon 2 were tested in two genetic type chickens: one was Beijing-you(BJY, n=250), a Chinese local breed, the other one was White leghorns (WL, n=250), a standard egg-type breed. The birds were reared under the same farming system and 5 immune traits were investigated. PCR-SSCP analysis combined with DNA sequencing was used to detect the SNPs within Exon 2. The results showed:1. Diversity of immune function traits between two populations:①There were significant differences in the heterophil/lymphocyte(H/L) ratio between two breeds (P<0.001). Mean of H/L ratios were 0.36±0.21 and 0.52±0.51 for BJYs and WLs, respectively.②The total number of Blood White Cells of BJYs were higher than the one of WLs distinctly (P<0.001).③No differences were found in sheep blood red cell(SRBC)antibody titers between two breeds (P>0.05);④H5N1 Avian Influenza (AI) antibody titers were measured at 50, 71,100,134 days of age. There were significant differences between these two breeds. Titers of 50,71,100,134 days of age for BJYs are higher than them of WLs, respectively(P<0.001); at the same age as AI antibody tested, La Sota Newcastle Disease ( ND) antibody titer were measured. Titers of 50,71, 100 ,134 days of age of BJYs is significantly higher than WLs, respectively (P<0.001, P<0.05, P<0.001). These results demonstrated that there were significant differences in immune function traits between the two genetic type chickens.2. Comparison of sequence polymorphisms for MHC-B-F Gene Exon 2 between the two breeds:The results of sequencing indicated that the sequences were highly polymorphic in Exon 2 gene (264 bp) of MHC B-F region in both breeds. Total 50 nucleotide mutation sites and 31 sites lead to amino acid mutation among them were found in Exon 2 sequence, for BJYs(n= 67); while 42 nucleotide mutation sites and 25 sites lead to amino acid mutation were found in WLs (n=134). The homology of nucleotide (213/264,223/264) was both higher than the one of amino acid (57/88,63/88) between the two populations. Of these, 36 SNP sites were shared in both breeds. There were 12 sense mutations among 14 nucleotide mutation sites only appeared in BJYs and 2 sense mutations among 6 nucleotide mutation sites only appeared in WLs. The results demonstrated that the polymorphisms of Exon 2 gene of BJYs were more than that of WLs, not only in DNA molecular level but also in amino acid level.3.Association of the MHC B-F Exon 2 (MHC class Iα1 domains) with immune traits contained antibody response, H/L and white cell count :Based on seven haplotypes analysis from 134 individuals of WLs, there were significant effects of 11 SNPs in the MHC B-F Exon 2 region on partial immune traits(P<0.05). The results showed: the SNP on the 64th site were found association with H/L; the SNP on the 182nd site were found association with antibody response to SRBC; Six SNPs on the 69th, 218th,220th, 221st, 223rd and 235th locus had significant(P<0.05, P<0.01)main effects on antibody response to ND; three SNPs on the 214th ,217th and 232nd were significant effects on antibody response to A I.In addition, based on 67 individuals of BJYs, there were significant effects of 5 SNPs in the MHC B-F Exon 2 region on partial immune trait(P<0.05). The results showed: Four SNPs on the 158th, 194th, 192nd, and 221st locus had significant(P<0.05, P<0.01)main effects on antibody response to ND; only one SNP on the 214th were significant effects on antibody response to A I.Both breeds shared the SNP on the 214th locus in MHC B-F Exon 2 region and were found association with antibody response to A(IP<0.05). There were the same trends of allele frequencies and genotype frequencies about this SNP (on the 214th locus) between two genetic types of chickens.