<prompt> First immunoglobulin to appear following infection -IgGIgMIgAIgE  <response>: IgM is a heavy molecule. - IgM molecules are polymers of five four-peptide subunits. IgM is relatively sho-lived - hence their demonstration in serum indicates recent infection. ReReference:nathanarayan panikers 9th edition, pg no: 98 p 