Figure 2.
Schematic diagram depicting the potential role of CD22 in mediating homing of B-cell subsets to the bone marrow. Mature recirculating immunoglobulin D+ (IgD+) B cells enter the bone marrow sinus via the bloodstream. Unmasked CD22 on subsets of these cells (as demonstrated in the present study) may engage sialylated ligands expressed on bone marrow sinusoidal endothelial cells.34 This could lead to transmigration into the haemopoietic spaces and subsequent enrichment of B cells with unmasked CD22 in the bone marrow. In contrast, B cells expressing CD22, whose binding site is masked by endogenous α2,6-linked sialic acid (α2,6 Sia) (the majority in peripheral organs), do not interact with sialylated ligands on bone marrow endothelium and hence remain in the circulation.