A 14 bp indel polymorphism in the promoter region is associated with different responses to porcine circovirus type 2 infection by regulating MRC1 transcription

Abstract

Mannose receptor, C type 1 (MRC1) is a key factor in regulating the body's immune response to resist pathogen invasions. In this study, mRNA expressions of MRC1 gene in nine porcine organs/tissues were compared between Laiwu (LW) and Yorkshire × Landrace crossbred (YL) pigs prior to and post PCV2 infection. We found that, for pigs uninfected with PCV2, MRC1 mRNA expressions in the lung, spleen, large intestine, small intestine and mesenteric lymph node tissues of LW were significantly higher than those of YL pigs (P < 0.05). After PCV2 infection, MRC1 mRNA levels in the liver, kidney and mesenteric lymph node were significantly increased in LW pigs (P < 0.05); while, significantly decreased in the heart and lung tissues of YL pigs (P < 0.05). The transcriptional activity of porcine MRC1 promoter was further analyzed to investigate the molecular mechanism underlying these expressional differences in response to PCV2 infection. Luciferase assay indicated that a 14 bp indel polymorphism “GTTTTTTTTTTTTT” at the site −864 of MRC1 promoter contributed to the transcriptional activity. The frequency of 14 bp insertion in LW and Dapulian pigs, generally resistant to PCV2 infection, was higher than that in Duroc, Landrace and Yorkshire pigs, which were sensitive to PCV2 infection. The promoter with 14 bp insertion displayed higher MRC1 transcription level both prior to and post PCV2 infection compared with that carrying no insertion in PK15 cells (P < 0.01). The results suggest that this 14 bp indel polymorphism is associated with different responses to PCV2 infection by regulating MRC1 transcription.