Which of the following concerning IgG is correct?
It comprises the majority of circulating antibody in serum This is the correct answer
It differs from other isotypes in not being able to cross the placental barrier
It has a molecular weight of 50,000 kd
It is monovalent
It is the major antibody produced during the primary response
Normal range 8-19 g/L. Next is IgA, 1-5 g/L, followed by IgM 0.5-2 g/L. It is, in fact, the only antibody capable of crossing the placental barrier, which it does through gaining attachment via its Fc portion. Each light chain has a molecular weight (MW) of 25,000 and each H chain a MW of 50,000. Therefore, since the whole molecule consists of 2 L and 2 H chains, the MW is 150,000 kd. It exists as a monomer with 2 F portions, each of which can interact with an antigenic determinant. Therefore it is divalent. It is the major antibody produced in the secondary immune response. IgM is the major antibody produced during the primary response.