Which one of the following statements about primary and secondary antibody responses is NOT true?

Question

A. Antibodies in primary responses generally have lower affinity for antigen than those produced in secondary responses.
B. Secondary responses reach peak levels more quickly than primary responses.
C. Primary responses require higher concentrations of antigen for initiation than secondary responses.
D. Primary responses occur to all types of antigens, but secondary responses mostly occur only to protein antigens.
E. Primary responses are characterized by IgG antibodies, whereas secondary responses are dominated by IgM antibodies.

Answer 1

ANS: E. In a primary immune response, IgM antibodies are initially produced against antigens. IgG production requires T cell-dependent isotype switching and is seen predominantly in secondary responses. Primary antibody responses can be mounted to any type of antigen, but secondary responses usually require CD4+ T cell help, and therefore the antigen must be a protein. Primary responses do require higher concentrations of antigen for initiation. The affinity of membrane Ig for antigen is lower on naive B cells, which are responsible for primary responses, compared with memory B cells, which are responsible for secondary responses. Secondary responses develop more quickly and produce higher peak levels of antibody as compared with primary responses.