Immunogenetic basis of chicken’s heterophil to lymphocyte ratio revealed by genome-wide indel variants analysis

Abstract

Enhancing host immunity is an effective way to reduce morbidity in chickens. Heterophil to lymphocyte ratio (H/L) is associated with host disease resistance in birds. Chickens with different H/L levels show different disease resistances. However, the utility of the H/L as an indicator of immune function needs to be further analyzed. In this study, a H/L directional breeding chicken line (Jingxing yellow chicken) was constructed, which has been bred for 12 generations. We compared the function of heterophils, and combined statistical analysis to explore the candidate genes and pathways related to H/L. The oxidative burst function of the heterophils isolated from the H/L selection line (G12) was increased (P=0.044) compared to the non-selection line (NS). The 22.44 Mb genomic regions which annotated 300 protein-coding genes were selected in the genome of G9 (n=92) compared to NS (n=92) based on a genome-wide selective sweep. Several selective regions were identified containing genes like interferon induced with helicase C domain 1 (IFIH1) and moesin (MSN) associated with the intracellular receptor signaling pathway, C–C motif chemokine receptor 6 (CCR6), dipeptidyl peptidase 4 (DPP4) and hemolytic complement (HC) associated with the negative regulation of leukocyte chemotaxis and tight junction protein 1 (TJP1) associated with actin cytoskeleton organization. In addition, 45 genome-wide significant indels containing 29 protein-coding genes were also identified as associated with the H/L based on genome-wide association study (GWAS). The expression of protein tyrosine phosphatase non-receptor type 5 (PTPN5) (r=0.75, P=0.033) and oxysterol binding protein like 5 (OSBPL5) (r=0.89, P=0.0027) were positively correlated with H/L. Compared to the high H/L group, the expressions of PTPN5 and OSBPL5 were decreased (P<0.05) in the low H/L group of Beijing you chicken. The A/A allelic frequency of indel 5_13108985 (P=3.85E–06) within OSBPL5 gradually increased from the NS to G5 and G9, and the individuals with A/A exhibited lower H/L than individuals with heterozygote A/ATCT (P=4.28E–04) and homozygous ATCT/ATCT (P=3.40E–05). Above results indicated oxidative burst function of heterophils were enhanced, and 22.44 Mb genomic regions were selected with the directional selection of H/L. In addition, PTPN5 and OSBPL5 genes were identified as H/L-related candidate genes. These findings revealed the complex genetic mechanism of H/L related to immunity and will allow selection for improving chicken immunity based on the H/L.

Keywords

• H/L
• heterophil
• indel
• selective sweep
• GWAS