The role of B cells in the amplification and in the regulation of transplant rejection.

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

Name dc:type.qualificationname

Doctor of Philosophy

Level dc:type.qualificationlevel

Doctoral Thesis

Grantor dc:publisher.institution

King's College London

Year dc:date.issued

2013

Author dc:creator

• Alhabbab, Rowa

Advisors dc:contributor.advisor

• Blair, Paul Anthony
• Lombardi, Giovanna
• Lechler, Robert Ian

Language dc:language

eng

Identifier

oai:kclpure.kcl.ac.uk:studenttheses/c91e6203-4010-497d-8773-9b5c622a1372

OAI identifier oai:identifier

oai:kclpure.kcl.ac.uk:studenttheses/c91e6203-4010-497d-8773-9b5c622a1372