B cell Tolerance Mechanisms Following ABO-incompatible Infant Heart Transplant: A Potential Role for CD22

  • Author / Creator
    Biffis, Kimberly M
  • Due to presumed immune immaturity, infants are able to accept heart transplants across the ABO barrier, a procedure that would result in catastrophic consequences if performed in adults. Our group has demonstrated that following ABO-incompatible heart transplantation (ABOi HTx), infants develop specific B cell tolerance to the A/B antigens of their new graft. (1) A precise understanding of ABO-immunobiology in this setting, including elucidating mechanisms of B cell tolerance to donor A/B antigens, is essential to efforts to expand ABOi HTx beyond the immature immune period and thus reduce organ transplant waitlists, as well as to explore human neonatal tolerance to non-ABO antigens. One of many potential mechanisms of B cell tolerance may involve the B cell surface molecule CD22. CD22 has been recognized as an inhibitory molecule of the B cell. (2-4) Interaction of CD22 with its ligand has been reported to play a role in down-regulation of B cell responses and subsequent B cell tolerance in vivo in animal studies. (2) In this thesis we began to investigate the role of CD22 in B cell tolerance in human infants. We examined expression levels of CD22 on human B cell subsets across the lifespan and found increased expression of CD22 on the splenic CD27+IgM+ B cell subset in infants. To further study the role of CD22 in B cell tolerance, we then developed a FACS protocol to isolate the CD27+IgM+ and CD27-IgM+ B cell subsets. Isolated B cells were then analyzed by ELISPOT to assess whether this fraction contained ABO antibody-secreting B cells (ASC), the cells presumably tolerized in the setting of infant ABOi HTx. Results indicated that the majority of the ABO ASC were derived from the CD27+IgM+ B cell subset from infant and adult samples. Lastly, we optimized a Phospho-specific flow cytometry assay using Ramos cells to measure B cell signaling upon engagement of the B cell receptor (BCR) and CD22. Future plans are to use this assay to investigate isolated primary B cells of infants and older individuals and compare signaling profiles upon engagement of BCR and CD22. Understanding inhibitory signaling pathways in B cells from infants and those beyond infancy may allow us to manipulate the immune system and expand the timeframe in which ABOi HTx can be safely performed.

  • Subjects / Keywords
  • Graduation date
    Spring 2015
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • 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.