LEI0258 microsatellite variability and its association with humoral and cell mediated immune responses in broiler chickens

MHC-linked microsatellite LEI0258 variability and population structure of chicken ecotypes in Iran

Background

Investigation of chicken major histocompatibility complex (MHC) genes along with their diversity across native regions and populations, as a genetic resource, can be used in the breeding programs. Important characteristics of MHC genes, such as the association with immunological and production traits, make them exceptional candidates for marker assisted selection.

Aims

The aim of this study was to characterize MHC based on the LEI0258 microsatellite marker to evaluate the genetic variability and diversity within and between Iranian chicken populations.

Methods

Blood samples were collected from six indigenous ecotypes (n=633) and Ross 308 (n=216) as a commercial breed. The MHC variability was determined based on a microsatellite marker located within MHC, LEI0258. Polymerase chain reaction and fragment analysis was used for microsatellite polymorphism detection.

Results

Based on the fragment analysis, 7 alleles were found in Ross 308 and 25 alleles across all 6 populations. The population with the maximum genetic diversity was Mazandaran (0.939), while the population with the minimum genetic diversity was Ross 308 (0.794). Out of the 6 Iranian chicken ecotypes, all except Arian and Khorasan, were in Hardy-Weinberg equilibrium (P<0.05). The genetic variations within (84.92%) and between (15.08%) populations were statistically significant (P<0.001).

Conclusion

A significant genetic structure that is not completely homogeneous among the Iranian chicken populations can be considered as distinct genetic resources. This study highlights the value of using markers such as LEI0258 to investigate the diversity of genes that play dual roles in immunity and production.

Association of Major Histocompatibility Complex Polymorphism With Acute Phase Response in Broiler Chicken

BACKGROUND

Stress associated with changes in host immunity occurs in response to altered environmental conditions, endogenous imbalances, infectious agents and harmful stimuli. The importance of genetic diversity in chickens has increased due to individual immune differences towards resistance and susceptibility to various stimuli.

OBJECTIVES

This study aimed to investigate the association of major histocompatibility complex (MHC) polymorphism with acute phase response (APR) in Ross 308 broiler chickens.

METHODS

The allelic diversity of the LEI0258 microsatellite marker was determined in 120 Ross broilers. In addition, acute phase proteins (APPs), including serum amyloid A (SAA) and alpha-1-acid glycoprotein (AGP), were analysed as markers of the APR. Furthermore, leukocyte count and the heterophil/lymphocyte ratio (H/L ratio) were examined. The antibody response to the Newcastle disease vaccine (NDV) was also measured to assess humoral mediated immunity. Lastly, the correlation between immune responses and MHC alleles was investigated to identify the most effective alleles in a stress-related situation.

RESULTS

A total of six alleles, ranging from 195 to 448 bp, were identified. Association study revealed a significant influence of MHC alleles on APPs in Ross population (p < 0.05). Notably, Allele 448 had a significant correlation with SAA concentration and the H/L ratio. Allele 207 displayed a positive association with AGP concentration, whereas Allele 195 showed a negative association. Furthermore, a significant association was observed between Allele 448 and basopenia, as well as between Allele 195 and monocytosis.

CONCLUSIONS

Results confirmed the significance of MHC as a candidate gene marker for immune responses, which supports its use for vaccine design, genetic improvement of disease-resistant traits and resource conservation in commercial broiler chickens.

Genetic Diversity of MHC B-F/B-L Region in 21 Chicken Populations

The chicken major histocompatibility complex (MHC) on chromosome 16 is the most polymorphic region across the whole genome, and also an ideal model for genetic diversity investigation. The MHC B-F/B-L region is 92 kb in length with high GC content consisting of 18 genes and one pseudogene (Blec4), which plays important roles in immune response. To evaluate polymorphism of the Chinese indigenous chickens as well as to analyze the effect of selection to genetic diversity, we used WaferGen platform to identify sequence variants of the B-F/B-L region in 21 chicken populations, including the Red Jungle Fowl (RJF), Cornish (CS), White Leghorns (WLs), 16 Chinese domestic breeds, and two well-known inbred lines 63 and 72. A total of 3,319 single nucleotide polymorphism (SNPs) and 181 INDELs in the B-F/B-L region were identified among 21 populations, of which 2,057 SNPs (62%) and 159 INDELs (88%) were novel. Most of the variants were within the intron and the flanking regions. The average variation density was 36 SNPs and 2 INDELs per kb, indicating dramatical high diversity of this region. Furthermore, BF2 was identified as the hypervariable genes with 67 SNPs per kb. Chinese domestic populations showed higher diversity than the WLs and CS. The indigenous breeds, Nandan Yao (NY), Xishuangbanna Game (XG), Gushi (GS), and Xiayan (XY) chickens, were the top four with the highest density of SNPs and INDELs. The highly inbred lines 63 and 72 have the lowest diversity, which might be resulted from a long-term intense selection for decades. Collectively, we refined the genetic map of chicken MHC B-F/B-L region, and illustrated genetic diversity of 21 chicken populations. Abundant genetic variants were identified, which not only strikingly expanded the current Ensembl SNP database, but also provided comprehensive data for researchers to further investigate association between variants in MHC and immune traits.

Genetic diversity at major histocompatibility complex and its effect on production and immune traits in indigenous chicken breeds of India

The genetic diversity at major histocompatibility complex (MHC) in indigenous chicken breeds of India (Ghagus and Nicobari) in comparison with the White Leghorn (WLH) breed was investigated by genotyping the MHC-linked LEI0258 marker. Altogether 38 alleles and 96 genotypes were observed among three breeds. The observed and effective alleles were highest in Ghagus (23, 8.3) followed by Nicobari (14, 3.2) and WLH (10 and 2.2) breeds. The size of alleles ranged from 193 to 489 bp in Ghagus, 193 to 552 bp in Nicobari and 241 to 565 bp in the WLH breed. The number of private alleles was also highest in Ghagus (18) followed by Nicobari (8) and WLH (5) breeds. The most frequent allele was 261 bp in WLH (66 %), 343 bp in Nicobari (50.4 %) and 309 bp in the Ghagus (28.15 %) breed. Observed and expected heterozygosities were highest in Ghagus (0.83, 0.88) followed by Nicobari (0.58, 0.68) and WLH (0.53, 0.54). The genetic distance (Nei) between Ghagus and Nicobari breeds (2.24) was higher as compared to that of Ghagus and WLH (1.23) and that between Nicobari and WLH breeds (0.89). Association analysis revealed significant influence of MHC alleles on body weight, egg production in Ghagus and WLH breeds and antibody titres to Newcastle disease vaccine in the Nicobari breed.