Polymorphism of TLR2 in bank vole populations in North Eastern Poland is not associated with Borrelia afzelii infection prevalence

Polymorphism in innate immune genes in host populations can structure spatial variation in the prevalence of infectious diseases. In Europe, Borrelia afzelii is an important tick-borne pathogen of small mammals including the bank voles ( Myodes glareolus ). The Toll-like receptor 2 (TLR2) is an innate immune receptor that is important for detecting Borrelia burgdorferi sensu lato pathogens. The TLR2 gene is polymorphic in bank vole populations and is classified into four distinct clusters: C1, C2, C3, and C4. The C2 and C4 clusters versus the C1 and C3 clusters are associated with lower versus higher infection prevalence, respectively. We detected three TLR2 clusters in 487 bank voles from 30 populations in NE Poland: 84.2% of the obtained sequences belonged to the C1 variant, 7.2% to C2, and 8.6% to C3. However, no clear spatial structure of TLR2 clusters among the populations was detected. B. afzelii infection prevalence across all studied individuals was 12.1% and varied from 0 to 37.5% among populations. There were no significant differences in B. afzelii prevalence among voles carrying alleles of different TLR2 clusters, or between individuals belonging to two mtDNA lineages. Most infected individuals were adults, and males were infected more often than females. There was no significant relationship between the prevalence of TLR2 clusters in the vole populations and climatic and environmental factors within the study area. We therefore could not confirm an adaptive role of the TLR2 C2 alleles in reducing B. afzelii infection prevalence in bank voles.