Association of SNP in the CCL2, IL8, CCR2, and CXCR1 genes with health and production traits in Canadian Holsteins

Chemokines and their receptors contribute to leukocyte trafficking to the mammary gland, and may play an important role in the host immune response during acute and chronic intramammary infections. Therefore, identification of SNP in coding and regulatory sequences from chemokine genes is fundamental for understanding chemokine function and gene expression in response to infectious diseases. The aim of this study was to identify the presence of SNP in chemokine and chemokine receptor genes and their 5' regulatory regions, to assess their potential contribution to variation in estimated breeding values (EBV) for somatic cell score (SCS) and production traits of Holstein bulls. A DNA pool was constructed for SNP detection by sequencing using equal amounts of DNA from bulls with high (H) and low (L) EBV for SCS. Using this approach, we were able to detect SNP with a frequency as low as 1%, and 16 SNP in various chemokines and chemokines receptor genes. The SNP in CCL2 (n = 2), CXCL8 (n = 5), CXCR1 (n = 4) and CCR2 (n = 1) were genotyped in Canadian Holstein bulls (n = 338) using Tetra Primer ARMS-PCR. Average allele substitution effects were estimated to investigate associations between the 12 SNP and EBV for SCS and production traits. The SNP CXCR1c.-1768T>A was found the most significantly associated with EBV for SCS in the first (P = 0.019) and second (P = 0.035) lactations at comparison-wise level, and across all lactations (P = 0.007) at experimental-wise level. Given the location of SNP CXCR1c.-1768T>A, it may be implicated in gene regulation. To test this hypothesis, we evaluated the impact of CXCR1c.-1768T>A SNP on CXCR1 expression by quantitative real-time PCR. Neutrophils were isolated from whole blood challenged with lipopolysaccharide (LPS) from cows with genotypes (AA n = 4, AT n = 5, and TT n = 5) at 0, 3 and 5h post in vitro challenge. CXCR1 expression was significantly different in cows with the AA genotype, when compared to the AT and TT genotypes. Further analysis of the associtation between CXCR1c.-1768T>A SNP and SCS is warranted before this genetic marker can be implemented in a selective breeding program.