Bovine mammary interleukin-8 receptor expression and genetic association with Streptococcus uberis based mastitis.

Mastitis is an economically distressing disease in the dairy industry. Bacterial pathogens enter the gland and encounter cell types that release immune mediators including interleukin (IL)-8. IL-8 has two membrane bound receptors: CXCR1 and CXCR2. CXCR1 and CXCR2 are expressed on neutrophils and other cell types in other species but their expression is unknown in the bovine mammary gland. To test this, mammary tissue samples from six Holstein dairy cows were subject to dual immunofluorescence with bovine specific CXCR1 and CXCR2 antibodies and cell type markers. CXCR1 was expressed on alveolar epithelial cells, fibroblasts, and leukocytes. CXCR2 expression was identified on alveolar epithelial cells and leukocytes. Within the bovine CXCR1 sequence, key amino acids 122, 207, 245, 327, and 332 have the potential to influence receptor efficiency in ligand binding and/or downstream signaling effects. Previous studies have linked some of these SNPs with mastitic phenotypes. The three SNPs (VWHRR, VWHKH, and AWQRR) were representative of 99% of the population. To test the haplotype effect, forty Holstein dairy cows were haplotyped and experimentally challenged with Streptococcus uberis. Various infection responses were monitored until 28 days post challenge. All cows with the VWHRR x VWHRR (n=5) and AWQRR x VWHRR (n=6) haplotype combinations required antibiotic treatment to clear infection whereas only 33.33% of VWHRR x VWHKH cows (n=7) required antibiotic therapy (p=0.0153). Cows with a VWHRR homozygous haplotype displayed significantly higher milk (1.05 ± [plus or minus] 0.21) and mammary (1.23 ± [plus or minus] 0.17) scores and AWQRR x VWHRR cows had significantly lower milk (0.17 ± [plus or minus] 0.18) and mammary (0.41 ± [plus or minus] 0.14) scores then cows of all other haplotype combinations (p=0.0263 and p=0.0161 respectively) indicating levels of inflammation differed among haplotype combinations. VWHRR homozygous cows also displayed significantly higher S. uberis bacteria counts (981.99 ± [plus or minus] 1947.05) then cows of any other haplotype combination (p=0.0348). Somatic cell counts (p=0.1399) and milk yield (p=0.6126) were not influenced by haplotype. Coupling this knowledge together indicates the critical role this receptor-ligand complex plays in a cow’s ability to resist mastitis.