IgG : most abundant in serum, there are 4 types of them. IgG1-4. Differ in heavy region of heavy chains. Major part of secondary response
IgM: a pentamer with ten identical binding sites. It is an isotype predominant in primary response. First Ab secreted in primary response
IgA: predominent in body secretions, including mucus and breast milk. Secreted form is a dimer with 4 antigen binding sites. It is also resistant to proteases. Responsible for passive immunity in breast milk.
IgE: associated with allergic inflammation, can sensitive mast call and basophils.
IgD: not associated with an effector function, but express with IgM on surface of B cell. Can serve as a function in regulation B cell physiology.