Clonal selection is an important process in adaptive immunity, picking the most specific B cell for antibody production. High specificity is desirable for an antibody, ensuring the target is bound efficiently to allow for a maximal immune response.
Selecting for more specific binding as the immune response continues is an important part of clonal selection. Somatic recombination occurs during B cell division to plasma cells, giving variation in the variable domains of antibody.
Memory cells are formed from some plasma cells during the adaptive immune response. These remain in circulation for long periods of time (>years), allowing a rapid adaptive response to be mounted on subsequent exposure to the same antigen. As these cells produce highly specific antigen, the secondary immune response is much stronger and faster.
During the primary immune response, on the first exposure to a pathogen, IgM is produced in high levels first. This helps expel the pathogen more effectively if it is a parasite. During the primary immune response, class switching occurs, changing the constant region of the antibody to give a more effective response that can reach more parts of the body – IgG begins to synthesised. In secondary exposure to same antigen, IgG is synthesised in high quantities soon after infection, while IgM is expressed in low concentrations.