Association of bacterial infection traits with genetic variation at candidate genes for porcine disease resistance

Iowa State University Animal Industry Report 2004. We predict that it may be possible to improve pig disease resistance to Salmonella infection by studying genes that control a piglets initial immune response. The NRAMP1 gene controls susceptibility to multiple pathogens and acts within the macrophage. The BPI gene encodes a neutrophil protein with inhibitory/killing functions against multiple gram-negative bacteria. We investigated NRAMP1 and BPI as candidate genes for contributing to resistance in Salmonella choleraesuis (SC) challenge in pigs. Five NRAMP1 sequence differences (polymorphisms, SNPs) were found, while we cloned and sequenced the full-length BPI gene and identified four polymorphisms at BPI. The effects these polymorphisms have on resistance to infection were tested in two experimental disease studies. In study 1, results showed NRAMP1 and BPI genotypes were associated with decreased fecal bacterial load during infection (P values: < .0006 to < .06). Immune cell numbers were also associated with BPI genotypes. In the second study, many additional immune traits and spleen and liver bacterial counts were collected. The NRAMP1 genotypes were associated with bacterial count in liver (P < .05 and P < .0006) and with polymorphonuclear phagocytes (P values from < .003 to < .05). The BPI genotypes were significantly associated with bacteria uptake by immune cells and with bacterial counts in liver (P<.1) and lymphocyte response post-challenge (P<.0001). These data indicate NRAMP1 and/or BPI gene variation may control, in part, response to Salmonella infection in pigs, and that these differences could be used to identify resistant animals.