Scientists examining the remains of 36 bubonic plague victims from a 16th century mass grave in Germany have found the first evidence that evolutionary adaptive processes, driven by the disease, may have conferred immunity on later generations of people from the region. "We found that innate immune markers increased in frequency in modern people from the town compared to plague victims," said the study's joint-senior author Paul Norman, PhD, Associate Professor in the Division of Personalized Medicine at the University of Colorado School of Medicine. "This suggests these markers might have evolved to resist the plague." The results of the study, carried out in conjunction with the Max Planck Institute in Germany, were published online on May 6, 2021 in Molecular Biology and Evolution. The open-access article is titled “Analysis of Genomic DNA From Medieval Plague Victims Suggests Long-Term Effect of Yersinia Pestis on Human Immunity Genes.” The researchers collected DNA samples from the inner ear bones of individuals in a mass grave in the southern German city of Ellwangen which experienced bubonic plague outbreaks in the 16th and 17th centuries. The scientists then took DNA samples from 50 current residents of the town. They compared their frequency spectra--the distribution of gene variants in a given sample--for a large panel of immunity-related genes. Among the current inhabitants, the team found evidence that a pathogen, likely Yersinia pestis which causes bubonic plague, prompted changes in the allele distribution for two innate pattern-recognition receptors and four human leukocyte antigen (HLA) molecules, which help initiate and direct immune response to infection. An allele is a variant form of a gene. "We propose that these frequency changes could have resulted from Y. pestis plague exposure during the 16th century," Dr. Norman said. The findings are the first evidence that evolutionary processes, prompted by Y. pestis, may have been shaping certain human immunity-relevant genes in Ellwangen, and possibly throughout Europe for generations.
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