Identification of CD14 transcript in blood polymorphonuclear neutrophil leukocytes and functional variation in Holsteins.

Polymorphonuclear neutrophil (PMN) leukocytes are primary phagocytic cells of the bovine mammary gland and a first line of defense against invading pathogens during bovine mastitis infection. Cluster of differentiation 14 (CD14) is mainly expressed in macrophages and neutrophils and acts as a co-receptor that binds bacterial lipopolysaccharide (LPS) and recruits PMNs to CD14-LPS complexes in mammary epithelial cells. In this study, we identified a novel splice variant in PMNs, named CD14-SV, characterized by a deleted region from c.143-579 nt compared to the CD14 reference mRNA sequence. Moreover, a single nucleotide polymorphism (c.523 A>G) in exon 2 of CD14 was identified and found to modify the secondary structure and hydrophilicity of the CD14 protein. Association analysis also showed that the milk somatic cell score, an indicator of mastitis, of cows with the GG genotype was lower than that of cows with the AA and AG genotypes. Our findings suggest that the expression of CD14 in bovine blood PMNs is regulated by alternative splicing, and that CD14-SV is a candidate functional marker that may influence mastitis-resistance in dairy cows.