The ligand-binding domain of siglec-g is crucial for its selective inhibitory function on b1 cells
30.04.2014
Hutzler S, Ozgör L, Naito-Matsui Y, Kläsener K, Winkler TH, Reth M, Nitschke L
J Immunol. 2014;192(11):5406-14
Siglec-G is an inhibitory receptor on B1 B cells. Siglec-G–deficient mice show a large B1 cell expansion, owing to higher BCR-induced Ca2+ signaling and enhanced cellular survival. It was unknown why Siglec-G shows a B1 cell–restricted inhibitory function. We found that Siglec-G has a different ligand sialic acid–binding pattern on peritoneal B1 cells than on splenic B cells, and its sialic acid ligands are expressed differentially on these two B cell populations, suggesting that cis-ligand binding plays a crucial role on B1 cells. A mutation of the ligand-binding domain of Siglec-G strongly reduces the Siglec-G–IgM association on the B cell surface. Thus, Siglec-G sialic acid–dependent binding to the BCR is crucial for the B1 cell–restricted inhibitory function of Siglec-G and is regulated in an opposite way to that of the related protein CD22 (Siglec-2) on B cells.
