MSH: Multi-subunit proteins which function in IMMUNITY. They are produced by B LYMPHOCYTES from the IMMUNOGLOBULIN GENES. They are comprised of two heavy (IMMUNOGLOBULIN HEAVY CHAINS) and two light chains (IMMUNOGLOBULIN LIGHT CHAINS) with additional ancillary polypeptide chains depending on their isoforms. The variety of isoforms include monomeric or polymeric forms, and transmembrane forms (B-CELL ANTIGEN RECEPTORS) or secreted forms (ANTIBODIES). They are divided by the amino acid sequence of their heavy chains into five classes (IMMUNOGLOBULIN A; IMMUNOGLOBULIN D; IMMUNOGLOBULIN E; IMMUNOGLOBULIN G; IMMUNOGLOBULIN M) and various subclasses.,CSP: glycoproteins found in the blood that function as antibodies; the basic structure is a y shaped molecule consisting of two light polypeptide chains and two heavy polypeptide chains linked by disulfide bonds.,NCI: A protein that acts as an antibody. Immunoglobulins are made by B cells and plasma cells. An Ig is a type of glycoprotein with two heavy chains and two l