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Title: The role of B cells in the amplification and in the regulation of transplant rejection
Author: Alhabbab, Rowa
Awarding Body: King's College London (University of London)
Current Institution: King's College London (University of London)
Date of Award: 2013
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B cells are known to contribute to and/or influence immune response trough a variety of mechanisms. Regulatory B cells (Bregs) have recently discovered and their role in regulating autoimmune diseases has been demonstrated in different murine models. In the context of transplantation B cells are generally thought to promote graft rejection through the production of alloantibody and their capacity to efficiently present alloantigens. However, recent clinical trials with B cell depletion have suggested that B cells contribute to the regulation of immune responses to grafts. In addition the evidence that renal transplant patients that are tolerant to the graft have an expansion of B cells with a regulatory phenotype further confirm this idea. The hypothesis tested during this PhD is that murine regulatory B cells, defined as transitional-2 marginal zone precursor (T2-MZP), are contributing to transplantation tolerance. The aims of this project are: i) to investigate whether T2-MZP can transfer transplantation tolerance; ii) to analyse whether the expression of Galectin-1 (Gal-1), known to be a functional molecule for Tregs, is necessary for T2-MZP to suppress; iii) to study whether an increase in T2-MZP is observed in tolerant mice like what has been shown in tolerant transplant patients. The results obtained during this PhD have demonstrated that T2-MZP purified from naïve mice were unable to regulate the immune responses to graft antigens both in vitro and in vivo. However, their regulatory capacity was observed when T2-MZP were purified from mice kept in the conventional (CV) area of the animal house although IL-10 was not involved in their regulatory 4 capacity. A difference in the gut flora between mice kept in the Specificpathogen- Free (SPF) and CV areas was observed and maybe responsible for the differences in the T2-MZP functions. Moreover, Gal-1 was confirmed to be expressed by B cells and T2-MZP isolated from Gal-1-/- mice kept in the CV area lost the ability to suppress in vitro CD4+ T cell activation and to prolong skin graft survivals, suggesting that Gal-1 has a functional role in B cell suppressive function. One of the hypotheses was that the absence of Gal-1 influences the response of B cells to gut. Gal-1-/- B cells showed reduced IL-10 production and increased up-regulation of activation markers in response to a variety of Toll-like receptor ligands in comparison to wild-type B cells, and showed differences in the percentage of P38, ERK phosphorylation and NF-κB translocation. Finally, in trying to mimic the findings with renal transplant patients, mice were rendered tolerant to skin transplants using in vivo anti- CD40L (MR1) and donor splenocyte transfusion (DST). The number of T2-MZP increased in these mice and these cells were suppressive in vitro and, as before, their regulatory capacity did not appear to correlate with IL-10 production. Once transferred in vivo T2-MZP isolated from tolerant mice, and not animal rejecting an allograft, induced prolongation of skin transplants onto naïve recipients. These observations indicate that T2-MZP play a role in transplant tolerance, they need to be “primed” either during tolerance induction protocol or by interaction with gut flora and that Gal-1 is a functional molecule for B cells and T2-MZP B cells.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available