Analysis of ligands for CD83, a marker of activated immune cells

CD83, a member of the immunoglobulin superfamily, is a type‐1 transmembrane glycoprotein and expressed on various activated immune cells. The soluble form of CD83 strongly suppresses mixed lymphocyte reaction (MLR) and experimental autoimmune encephalomyelitis (EAE), however, the mechanism of CD83‐mediated immune regulation including ligands for CD83 (CD83L) has not been elucidated. By flow cytometry using the CD83‐Fc fusion protein, we screened immune cells from mouse lymphoid organs to identify CD83L + cells and found that CD83‐Fc bound to B220 int IgM hi CD11b + peritoneal B‐1 B cells, but not to cells from spleen, bone marrow, or thymus. When we tested the binding of CD83‐Fc to various B lymphocytic cell lines, the fusion protein bound to BCL1‐B20 cells which are known to be derived from B‐1 B cells. The pull‐down assay using CD83‐Fc revealed that a part of glycosylated IgM heavy chain was precipitated from the crude membrane fraction of BCL1‐B20 cells. Furthermore, anti‐mouse IgM antibodies blocked binding of CD83‐Fc to B‐1 B cells and BCL1‐B20 cells. These results suggest that CD83 + cells might recognize surface IgM with unique glycosylation expressed on B‐1 B cells during immune responses.