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Functional analysis of MICA polymorphism : with an emphasis on Behcet's disease

Behcet’s disease (BD) is a multi-organ inflammatory pathology. A main factor of genetic predisposition locates to HLA-B*51, but MIC A* 009 is also reported to be strongly associated with BD. The aim of the thesis is to undertake a functional analysis of MICA polymorphism, and determine the functional effects of the HLA-B*51-MICA* 009 combination. Isogenic stable cell lines expressing MICA*009,*008,*009v and ULBP2 were separately created. These were used in killing assays to compare the cell biology of the different MICA isoforms and to assess whether that encoded by MICA*009 varies from other isoforms in its capacity to promote killing by NKG2D positive cells from healthy controls and BD patients. Similarly, double transfectants: HLA-B*51-MICA*009 and HLA-B52*MICA*009 (control) were created and used in similar assays to determine the inhibitory effect, if any, of HLA-B*51 on the targeting of MICA+ cells by patients’ lymphocytes. Data from killing assays show a most unanticipated, donor-to-donor variation in the hierarchy with which different transfectants are targeted by lymphocytes from healthy controls and from patients. These hierarchies seem stable longitudinally and are validated by the CD107a assay. Differential killing cannot easily be explained by an affinity hierarchy because people’s cells kill different targets with different hierarchies. Variation among patients is even greater: Approximately 25% of patients preferentially target cells expressing MIC A* 009 versus cells expressing other MICA isoforms. HLA-B*51 and HLA-B*52 comparably inhibit the targeting of MICA*009+ cells by lymphocytes from healthy controls but for 45% of patients, HLA-B*51 shows distinctively stronger inhibition of the targeting of MICA*009+ cells. The variation is killing is not explained by either the number of NKG2D+ or KIR3DL1* cytotoxic cells nor the expression level of these molecules. In conclusion, this thesis advances the current understanding of human MICA biology by presenting novel data detailing the expression and function of MICA proteins. The data in this study provide insight into the "tuning" of the lymphocyte stress surveillance response and the impact upon this of HLA-B*51, with implications for the pathogenesis of Behcet’s disease.
Date January 2013
CreatorsShafi, Seema
PublisherKing's College London (University of London)
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation

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