which antibody is called the millionaire molecule

IgM: Immunoglobulin M (IgM), the largest pentameric immunoglobulin is used as a marker of recent primary infection for some diseases. IgM constitutes 5-10% of serum immunoglobulins in adults. IgM has a half life of 5 days. Because of its high molecular weight (900,000- 1000,000), it is often called macroglobulin and the 'millionaire molecule Ref : Ananthanarayana textbook of Microbiology 9th edition Pgno : 98