Goat polyclonal antibody to human IgM. IgM is a monomeric immunoglobulin, with two heavy chains and two light chains. IgM can be found in blood and it is one of several isotypes of antibody (also known as immunoglobulin) that are produced by vertebrates. It binds to many types of pathogens, protecting the body against them by complement activation, opsonization for phagocytosis and neutralisation of their toxins.