Cell-adhesive immunoglobulin M in human plasma

Human plasma contains a cell-adhesive protein that has a structure related to immunoglobulins. This protein was purified by affinity chromatography on an elastin-Sepharose column and by Mono Q anion-exchange chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis under non-reducing and reducing conditions revealed that this protein is a kind of immunoglobulin M (IgM). Antibodies against the mu chain and against the Fc region of IgM inhibited the adhesion of cells to this protein. Addition of the peptide GRGDS into media inhibited the adhesion, too. These results suggest that this protein is a special subset of IgM having a cell-binding sequence in the Fc region. We propose the name "cell-adhesive immunoglobulin M (CA-IgM)" for this protein. CA-IgM binds to alpha-elastin and laminin suggesting that it may play a role in the interaction between cells and the extracellular matrix.