Transitional and marginal zone B cells have a high proportion of unmasked CD22: implications for BCR signaling.
CD22, a B cell-specific member of the Siglec family, is an important inhibitor of B cell signaling. The first Ig-like domain of CD22 specifically binds to alpha2,6-linked sialic acids. Through these interactions CD22 can mediate adhesion to other cells in trans, but can also bind endogenous ligands on the B cell surface in cis. Cis binding of CD22 to sialylated ligands enhances the efficiency of inhibition and thereby reduces the BCR signaling strength. In this study we used a newly developed oligomeric streptavidin-based sialylated probe as an artificial CD22 ligand. We found that CD22 is bound to ligands in cis on most B cells. However, there is a proportion of B cells with unbound (unmasked) CD22. The subpopulation with unmasked CD22 is 2-fold increased in transitional and marginal zone B cells in the spleen and on B1 cells in the peritoneum, when compared to mature B cells. Also, B cells with unmasked CD22 have an activated phenotype. Unmasking of CD22 could be functionally involved in lowering the signaling threshold on developmental checkpoints such as transitional B cells and during B cell activation or could be a consequence of such activation processes.
D000818:Animals; D015703:Antigens, CD / Q000032:analysis / Q000378:metabolism*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000032:analysis / Q000378:metabolism*; D016175:B-Lymphocyte Subsets / Q000737:chemistry / Q000276:immunology*; D015815:Cell Adhesion Molecules; D037102:Lectins / Q000032:analysis / Q000378:metabolism*; D008213:Lymphocyte Activation; D051379:Mice; D015335:Molecular Probes / Q000737:chemistry; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D051918:Sialic Acid Binding Ig-like Lectin 2; D015398:Signal Transduction / Q000502:physiology*; D013154:Spleen / Q000166:cytology / Q000276:immunology
D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; C497868:Cd22 protein, mouse; D015815:Cell Adhesion Molecules; D037102:Lectins; D015335:Molecular Probes; D011947:Receptors, Antigen, B-Cell; D051918:Sialic Acid Binding Ig-like Lectin 2