How much higher is the avidity of IgM compared to IgG assuming that both isotypes have the same affinity?

A) 2-fold

B) 5-fold

C) IgG had the same avidity as IgM

D) 10-fold

B) 5-fold

Explanation:

Affinity is the measure of the strength of a single bond between an antibody and an antigen. Avidity is the measure of the strength of the overall connection between antibody and antigen. Avidity depends on affinity and also on the number of antigen binding sites present on the antibody.

Here, it is assumed that both IgG and IgM antibodies have same affinity. Hence, avidity will depend on the number of binding sites. IgG is bivalent which means it has two binding sites. IgM is theoretically decavalent which means it has ten binding sites. So avidity of IgM will be 5 times more (2 * 5 = 10) than IgG isotype.