In resting B cells, CD22 is a prominent cis ligand for itself, forming CD22 homo-oligomers. Cross-linking experiments showed that CD22 primarily recognizes alpha2,6-linked sialic acid (2,6Sia or N-acetylneuraminic acid (NAc)) on neighboring CD22 molecules present on the same B-cell (Han et al. 2005). NH2-terminal immuno globulin (Ig) domains, Ig1 and Ig2, mediate 2,6Sia binding (Law et al. 1998, Jin et al. 2002). Thus, CD22 recognizes self structures and triggers inhibitory signals, which may be relevant for suppression of autoimmune B-cell responses.