Implications of genetic diversity on expression of LILRB1 in Natural Killer cells and susceptibility to HCMV infection in transplant patients

• Author / Creator

  Davidson, Chelsea L

• Leukocyte Ig-like Receptor 1 (LILRB1) is an inhibitory receptor expressed on a number of immune cells. The expression profile on NK cells is variable between people, with a range of 25-80% of NK cells expressing LILRB1. We previously uncovered a correlation between genotype within the 5’ end of the LILRB1 gene and frequency of expression on NK cells. This thesis research expands on our previous work in elucidating the regulatory mechanisms involved in LILRB1 gene expression as well as the role of the expression correlated SNPs. We first set out to characterize the distal promoter of LILRB1 used by NK cells, a distal region not yet characterized at the time this research began. We identified JunD as an activator of this promoter and thus a regulator of LILRB1 gene expression. Next we focused on the role of the SNPs within the previously identified expression-correlated haplotypes. We discovered that the haplotypes extended to the distal promoter and correlated with expression in the distal promoter region, indicating that SNPs in either promoter region could be responsible for the expression level. Interestingly, the expression of LILRB1 on B cells appears to be unchanged regardless of donor genotype, which led us to investigate the potential reason. We found that there are differences in both the factors in the nuclear environment that are able to bind the core promoter and also in methylation of the DNA in the regulatory regions. Upon further examination, we found that the two haplotypes of the distal promoter show no difference in activity by reporter assay while the proximal promoter haplotypes differ. This led us to focus on identification of a role for the proximal promoter in NK cells. We found that the proximal promoter is active in NK cells under activating conditions. Finally, we examined some of the potential implications of the genetic diversity of LILRB1 observed within the population. We focused on the role of LILRB1 diversity in the context of Human Cytomegalovirus (HCMV) infection, as LILRB1 is targeted by this virus by the production of a mimic of LILRB1’s endogenous ligand, MHC-I, called UL18. We found that one LILRB1 protein variant, associated with the low expressing haplotype, binds UL18 with a higher affinity than the high expressing haplotype. Additionally, we found a trend wherein the low expressing promoter haplotype as well as the rare allele at position 927 in the gene, which produces a non-synonymous change from Isoleucine to Threonine, are correlated with increased susceptibility to CMV disease post-organ transplant. This is the first research examining LILRB1 genetic regulation in NK cells in any detail. With this research, we have begun to uncover the role of LILRB1 genetic diversity in the context of a specific disease, HCMV infection. Understanding the regulation of the observed variable LILRB1 expression on NK cells will help to further uncover the role of this variability in the context of both health and disease.

• Subjects / Keywords

  • HCMV
  • LILRB1
  • JunD
  • Polymorphisms
  • Haplotypes
  • Nk cells
  • LIR-1

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3TQ5RK3M

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.