64 High Expression of the B-Cell Inhibitory Molecule CD22 on Memory B-Cells in Early Life May Contribute to Better Transplant Outcomes

Abstract

Purpose: ABO-incompatible heart transplantation (ABOi HTx) can be performed safely in infants and is generally followed by B-cell tolerance to donor ABO antigens (ags). ABO antibodies are thought to arise in a T-independent (TI) manner. TI B-cell activation can be inhibited by the interaction of CD22, an inhibitory B-cell co-receptor, with sialic acids on cells/tissues, leading to B-cell tolerance. Since immune responses to TI-ags are limited in early childhood, we hypothesize that the role of CD22 may be elevated during infancy compared to later in life. In this study, we determined CD22 expression on B-cell subsets from infancy to adulthood. Methods and Materials: We analyzed splenocytes from organ donors of various age (n 41; age 4 d 74 yr) by flow cytometry to quantify CD22 expression on the surface of CD19 B-cell subsets including CD27IgM IgD CD38high (previously defined as recent bone marrow emigrants), CD27-IgM IgD , CD27-IgM-IgD , CD27-IgM-IgD-, and the memory-like phenotypes CD27 IgMand CD27 IgM . Results: CD22 Median Fluorescence Intensity (MFI) differed amongst various B-cell subsets (p 0.0001; Kruskal Wallis test). Post testing with Dunn’s multiple comparison test showed that CD27-IgM-IgDcells had lower CD22 expression (p 0.001) and CD27 IgM cells had higher expression (p 0.001) compared to other subsets. Furthermore, CD22 on CD27 IgM cells was inversely correlated with age (p 0.001): infant samples had the highest CD22 expression, which decreased with increasing age. Conclusions: Based on previous studies showing the inhibitory role of CD22 on B-cell activation, our findings suggest that higher CD22 expression on the memory subset may cause infant B-cells to be more susceptible to down-regulation of B-cell signaling leading to subsequent inactivation. CD22 may thus play a role in the restricted TI responses to ABO ags after ABOi HTx. Functional assays are underway to determine its role in B-cell signalling during infancy and in regulation.