A CD22-Shp1 phosphatase axis controls integrin β7 display and B cell function in mucosal immunity.

Abstract

The integrin α4β7 selectively regulates lymphocyte trafficking and adhesion in the gut and gut-associated lymphoid tissues (GALT). Here we describe unexpected involvement of tyrosine phosphatase Shp1 and the B cell lectin CD22 (Siglec 2) in regulation of α4β7 surface expression and gut immunity. Shp1 selectively inhibited β7 endocytosis, enhancing surface α4β7 display and lymphocyte homing to GALT. In B cells, CD22 associated in a sialic acid-dependent manner with integrin β7 on the cell surface to target intracellular Shp1 to β7. Shp1 restrained plasma membrane β7 phosphorylation and inhibited β7 endocytosis without affecting β1 integrin. B cells with reduced Shp1 activity, B cells lacking CD22, or B cells expressing CD22 with mutated Shp1-binding or carbohydrate-binding domains displayed parallel reductions in surface α4β7 and in homing to GALT. Consistent with the specialized role of α4β7 in intestinal immunity, CD22 deficiency selectively inhibited intestinal antibody and pathogen responses.