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

[摘要] 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.

[发布机构] University of Alberta

[效力级别] ABO-incompatible transplantation