<prompt> True about IgMFix ComplementIncreased in primary responseFab region is composed of variable regionFc is antibody - binding option  <response>: IgM Produced in the primary response to an antigen Fixes complement.Does not cross the placentaAntigen receptors are on the surface of B cells.IgG is also involved in complement fixationReference: Harper biochemistry 30th edition page no 681 