Susceptibility to paratuberculosis infection in cattle is associated with single nucleotide polymorphisms in Toll-like receptor 2 which modulate immune responses against Mycobacterium avium subspecies paratuberculosis

摘要

Paratuberculosis is a chronic intestinal infection in ruminants, caused by Mycobacteriumavium subspecies paratuberculosis (Map). To study the role of host genetics in diseasesusceptibility, the Toll-like receptor 2 (TLR2) gene, selected based on its potential role inimmunity to mycobacterial infections, was analyzed for single nucleotide polymorphisms(SNP) and their potential association with disease.For SNP discovery and to study SNP association with disease, a case–control studyincluding 24 cows from farms with paratuberculosis was conducted. Sequence analysisof the TLR2 genes from 12 paratuberculosis-infected animals and 12 age-matchedhealthy herd mates revealed 21 different SNP. The TLR2-1903 T/C SNP was significantlyassociated with resistance to Map. This and four additional TLR2 SNP were studied in asubsequent observational field study with 553 cows from farms with paratuberculosis.The allelic distribution of the TLR2-1903 T/C SNP was confirmed to be significantlydifferent between the infected and non-infected animals. For the TLR2-1903 T/C SNPthe odds ratio was calculated, and similar to the dominance model in the associationstudy, the CT and CC genotypes were compared to the TT genotype. Cows with theTLR2-1903 T/C mutation (i.e., the CT and CC genotypes) were at 1.7 (95% CI: 1.2, 2.8)times the odds of being Map-infected compared to cows with the TT genotype. In invitro functional assays, monocyte-derived macrophages from animals with a TLR2-1903 TT genotype produced more IL12p40 and IL1b when stimulated with Mapcompared to cells derived from TLR2-1903 CT and CC genotypes. Also, T cellproliferative responses to mycobacterial antigens were higher in animals with a TLR2-1903 TT genotype.