Question

a. What cellular events are necessary to shift from plasma IgM to IgG production? Explain class switching.

b. What are the major roles of IgM and IgG found in plasma during this type of infection?

Answer 1

a. Class switching occurs after activation of a mature B cell via its membrane-bound antibody molecule to generate the different classes of antibody, all with the same variable domains as the original antibody generated in the immature B cell during the process of V(D)J recombination. After immunization or infection, activated naïve B cells can switch from expressing IgM and IgD on their surface to expressing IgG, IgE or IgA. This isotype/class switch changes the effector function of the antibody and improves its ability to eliminate the pathogen that induced the response.

b. IgM is specialized to activate complement efficiently upon binding antigen. IgG antibodies are usually of higher affinity and are found in blood and in extracellular fluid, where they can neutralize toxins, viruses, and bacteria, opsonize them for phagocytosis, and activate the complement system. IgM is the first antibody to be made by the body to fight a new infection.