Somatic hypermutation (SHM) is a biological process that occurs in the adaptive immune system, specifically in B cells. It involves the introduction of point mutations into the variable regions of immunoglobulin (antibody) genes, resulting in a pool of antibodies with slightly different antigen-binding affinities. This process primarily occurs after B cells have been activated by an antigen, and the goal is to improve the binding affinity of antibodies for their specific antigens. The mutations introduced through SHM allow the immune system to fine-tune its response to pathogens and produce antibodies that are more effective at neutralizing them.

Class switching, also known as class switch recombination (CSR), is a distinct process that occurs in activated B cells. It enables a B cell to change the type, or class, of antibody it produces while retaining the same antigen specificity. Initially, B cells produce immunoglobulin M (IgM) antibodies, but through class switching, they can produce other types of antibodies, such as IgG, IgA, or IgE, which have different functions and properties. This allows the immune system to tailor its response to different pathogens or phases of infection, with each antibody class playing a unique role in defense.