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Title: Features of rearrangements of human immunoglobulin light chains
Author: Tahir, Romeeza
ISNI:       0000 0004 5372 0888
Awarding Body: King's College London
Current Institution: King's College London (University of London)
Date of Award: 2015
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B cells recognize a wide range of antigens by their specific surface B cell receptor. BCRs are immunoglobulin polypeptides and made up of heavy chain (IGH) and light chain. Light chains are of two types: kappa (IGK) or lambda (IGL). The variable regions of immunoglobulin chains are generated by somatic rearrangement of V, D and J segments to generate a diverse repertoire of BCRs. The aim of this thesis is to analyze features of immunoglobulin gene rearrangements in the context of heavy and light chain pairings and light chain gene expression. Mature naïve B cells generated in blood or tissues have a ratio of IGK:IGL expression of approximately 2:1. In contrast IgA plasma cells exhibit IGK:IGL ratio of approximately 1:1. Such a bias could be acquired by antigen selection or by changes in light chain gene rearrangements such as light chain revision. In order to better understand this, IGL genes were PCR amplified, cloned and sequenced from the DNA of transitional, naïve and IgA expressing B cells. Unusual biases in genetic reading frame were observed in the IgA expressing cells of the most commonly used IGL families. This was further investigated using a high throughput sequencing method that identified biases in the IGL genes of IgA with preferential selection of IGLV2-14 in IgA subsets (Chapter 3). In the bone marrow, IGL gene rearrangement starts only if the rearrangement at IGK locus is non-functional. However, approximately 25% to 30% of IGL expressing cells have previously undergone apparently functional IGK gene rearrangement, but for some reasons these productive rearrangements were not expressed. In order to better understand the regulation of the IGK locus, IGK gene rearrangements were sequenced from naïve B cells expressing either IGK or IGL. Sequences were divided into productive and non-productive according to the characteristics of the junction. The actual expressed genes in cDNA were also amplified from IGK expressing B cells. Overall results identified selection and expression biases operating at the time of establishment of IGK repertoire (Chapter 4). During B cell development, IGH rearrangements that pair better with surrogate light chains are selected at the pro-B cell stage. Therefore, it was decided to investigate if there is any possibility that later during B cell development, rearranged light chains could show preferences for particular IGH gene segments. If so, this will help in identifying additional factors shaping the IGH repertoire of naïve B cells. Rearranged IGH were sequenced from naïve B cells expressing either IGK or IGL. The relative usage of IGHV, IGHD and IGHJ and CDR-3 characteristics were compared. It was found that there is no preference of IGH to be associated with either IGK or IGL (Chapter 5). This thesis has identified some unusual features of light chain gene rearrangements. The relevance this data to B cell immunology will be discussed.
Supervisor: Spencer, Jo Michele Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available