{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"IgM forms polymers where multiple immunoglobulins are covalently linked together with disulfide bonds, normally as a pentamer or occasionally as a hexamer. It has a large molecular mass of approximately 900 kDa (in its pentamer form). In germline cells, the gene segment encoding the constant region of the heavy chain is positioned first among other constant region gene segments. For this reason, IgM is the first immunoglobulin expressed by mature B-cells."}]},{"type":"paragraph","children":[{"type":"text","value":"IgM antibody reacts with surface immunoglobulin IgM mu chains. IgM is one of the predominant surface immunoglobulins on B-lymphocytes, and is useful when identifying Leukemias, Plasmacytomas, and B-cell lineage derived Hodgkin’s Lymphomas. Due to the restricted expression of heavy and light chains in these diseases, demonstration of B-cell Lymphomas is possible with clonal gene-rearrangement studies."}]}]}