Suggested mechanism of CCR5Δ32, CCR2-64I and SDF 1-3'A allele frequency change in Polish and Lithuanian gene pools from the perspective of passing time.

The study aimed to determine the frequency of the alleles associated with hereditary immune response in 16 historical populations and assess which evolutionary forces may have contributed to the observed frequency fluctuation. The analysed polymorphic sites are located in three genes - CCR5, CCR2 and SDF 1 (CXCL12). Protein products are involved in the innate immune response and are also involved in various types of infections, autoimmune diseases and tumours. The frequency of the alleles found in the DNA of the studied individuals was determined by the Sanger methodology and was compared with the data obtained for modern populations. To confirm the authenticity of the obtained results, mtDNA HVRI haplotypes of all the studied samples were obtained and compared with the genetic database of the laboratory personnel who came into contact with the studied material. Based on the variability of allele frequency, advanced biostatistical analysis was used to distinguish the effect of natural selection from genetic drift, i.e. the forces operating on the polymorphic sites studied. All procedures were performed according to the guidelines for working with ancient DNA to avoid contamination with modern DNA molecules. 681 samples from 39 archaeological sites in Poland and Lithuania dated to the 40^th century BC and the 19^th century were studied. The biostatistical analysis showed that the fluctuations in the frequency of CCR5Δ32 in the analysed time interval could be mainly the effect of genetic drift. Nevertheless, for CCR2-64I and SDF 1-3'A, the results confirm the suggestion of negative selection as the mechanism involved. Since all the polymorphic sites encode the elements of innate immune response that are indirectly associated with the process of an HPV infection and the development of cervical cancer, the human papillomavirus may be a good candidate for a selection coefficient affecting the frequency of CCR2-64I and SDF 1-3'A. However, for CCR5Δ32, selection was not detected despite its proven role in the molecular mechanism involved in the response to an HPV infection. The presented work seems to be the first in which the problem of the pattern of CCR5Δ32, CCR2-64I and SDF 1-3'A frequency fluctuations in a temporal perspective was discussed, proposing HPV as a factor influencing the occurrence of the CCR2 and SDF1 alleles.