IMMUNOLOGY

Detailed explanation-1: -IgG is said to be divalent, i.e., it has two identical antigen-binding sites that comprise 2 L chains and 2 H chains joined by disulfide bonds.

Detailed explanation-2: -Two consensus binding sites exist on the Fc portion of IgG, the hinge proximal region of the CH2 domain for FcRs binding and the junction of the CH2 and CH3 domains where Protein A, Protein G, neonatal Fc receptor (FcRn), and some rheumatoid factors are retained (Nezlin and Ghetie, 2004).

Detailed explanation-3: -A pentameric IgM molecule has 10-antigen combining sites and can bind 10 small antigens (haptens). However, due to steric restrictions, only five large antigen molecules can be bound by one IgM molecule. The antibody activity of IgM is destroyed upon reduction of the intersubunit disulfide linkages.

Detailed explanation-4: -Each Ig monomer contains two antigen-binding sites and is said to be bivalent. The hinge region is the area of the H chains between the first and second C region domains and is held together by disulfide bonds.

Detailed explanation-5: -Antibody-antigen interactions. Because antibodies have two identical antigen-binding sites, they can cross-link antigens. The types of antibody-antigen complexes that form depend on the number of antigenic determinants on the antigen.

Detailed explanation-6: -However, due to its pentameric conformation, secreted IgM has higher avidity, or overall strength of binding to antigen, due to the presence of ten antigen-binding sites per pentameric IgM molecule.

Detailed explanation-7: -Due to its large size, IgM is mostly intravascular and has a lower affinity for antigens. However, since pentameric IgM has 10 antigen binding sites, it has higher avidity (overall binding strength) for antigens than IgG and acts as an excellent activator of the complement system and agglutination.