Local selection of human populations shapes complex evolution patterns of CXCL10 gene.

CXC motif chemokine 10 (CXCL10) is a small cytokine belonging to the CXC chemokine family, and it is secreted by several cell types in response to IFN-γ and regulates immune responses through the recruitment and activation of lymphocytes. As CXCL10 is very important in T-cell immunity and infectious diseases, we studied the effect of natural selection on the CXCL10 locus. By sequencing 74 individuals from three human populations, we found a complex pattern of natural selection acting on the CXCL10 locus. We discovered a signature of balancing selection in the European population with a significant positive Tajima's D value (2.57, P=0.005) and an excess of intermediate frequency alleles. However, we observed an excess of high frequency-derived alleles and a significant Fay and Wu's test statistics (P=0.015) in the Chinese population, which suggests that recent selective sweeps under positive selection had occurred. Also, there are a lot of alleles showing great frequency difference among populations. These results demonstrate that local selection has shaped CXCL10 evolution and indicates that there exist different actions of natural selection on the CXCL10 locus in different populations. This study provides insights into the likely relative roles of natural selection and population history in shaping today's genetic variation at the CXCL10 locus, indicates the relationship between adaptation to past infection and predisposition to autoimmunity in modern populations, improves our understanding of CXCL10 evolution, and motivates further investigations of the role of CXCL10 in infectious diseases and autoimmune diseases.