Ig domains 1 and 2 of murine CD22 constitute the ligand-binding domain and bind multiple sialylated ligands expressed on B and T cells.
Baby hamster kidney cells transfected with murine CD22 (mCD22) mediate adhesion to B- and T-lineage cells. To further characterize mCD22-mediated cell adhesion, we generated a panel of recombinant globulins (Rg) consisting of different extracellular Ig-like (Ig) domains of mCD22. FACS analysis using these mCD22.Rgs revealed that ligands for mCD22 are expressed on both B and T cell lines and also normal B and T cells. In B-lineage cells, the expression of mCD22 ligands began on sIgM- pre-B cells in bone marrow. The ligand-binding site of mCD22 for ligands was mapped to Ig domains 1 and 2: mCD22.Rgs containing Ig domains 1 and 2 bound target cells and immunoprecipitated sets of glycoproteins similar to Rgs containing Ig domains 1 to 3 or all 7 CD22 Ig domains, whereas Rgs containing Ig domains 2 to 3 or 3 to 7 did not bind either B or T cells. Furthermore, B cells apparently expressed higher levels of mCD22 ligands than that of T cells, suggesting a potential competition for CD22 binding between ligands expressed on the same B cell and those expressed on another B cell or T cells. Immunoprecipitation experiments using the mCD22.Rgs identified mCD22 itself and the B cell-specific isoform of mCD45RA (B220) as two of the mCD22 ligands expressed on B cells. Thus, mCD22 may potentially regulate B cell activation through interactions with itself or mCD45RA/B220.
Law
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CL
Department of Microbiology, University of Washington, Seattle 98195, USA.
Aruffo
A
A
Chandran
K A
KA
Doty
R T
RT
Clark
E A
EA
D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics / Q000276:immunology; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D002478:Cells, Cultured; D006224:Cricetinae; D017931:DNA Primers; D018014:Gene Transfer Techniques; D007136:Immunoglobulins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D037102:Lectins; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D017421:Sequence Analysis; D051918:Sialic Acid Binding Ig-like Lectin 2; D013601:T-Lymphocytes / Q000276:immunology*
D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; C497868:Cd22 protein, mouse; D015815:Cell Adhesion Molecules; D017931:DNA Primers; D007136:Immunoglobulins; D037102:Lectins; D008024:Ligands; D011994:Recombinant Proteins; D051918:Sialic Acid Binding Ig-like Lectin 2