Differential expression of CXCR1 and commonly used reference genes in bovine milk somatic cells following experimental intramammary challenge

Background: Chemokine (C-X-C motif) receptor 1 (CXCR1 or IL-8RA) plays an important role in the bovine mammary gland immunity. Previous research indicated polymorphism c.980A > G in the CXCR1 gene to influence milk neutrophils and mastitis resistance. In the present study, four c.980AG heifers and four c.980GG heifers were experimentally infected with Staphylococcus chromogenes. RNA was isolated from milk somatic cells one hour before and 12 hours after the experimental intramammary challenge. Expression of CXCR1 and eight candidate reference genes (ACTB, B2M, H2A, HPRT1, RPS15A, SDHA, UBC and YWHAZ) was measured by reverse transcription quantitative real-time PCR (RT-qPCR). Differences in relative CXCR1 expression between c.980AG heifers and c.980GG heifers were studied and the effect of the experimental intramammary challenge on relative expression of CXCR1 and the candidate reference genes was analyzed. Results: Relative expression of CXCR1 was not associated with polymorphism c.980A > G but was significantly upregulated following the experimental intramammary challenge. Additionally, differential expression was detected for B2M, H2A, HPRT1, SDHA and YWHAZ. Conclusions: This study reinforces the importance of CXCR1 in mammary gland immunity and demonstrates the potential effect of experimental intramammary challenge on expression of candidate reference genes in milk somatic cells.