Class switching and affinity maturation are two key processes that occur during the germinal center reaction and contribute to the production of high-affinity antibodies.
Class Switching: Class switching is the process by which B cells change the class of antibody that they produce while retaining the same antigen specificity. This occurs through a process called class switch recombination (CSR), which involves the recombination of switch regions that are located upstream of the constant region genes. By switching the class of antibody that they produce, B cells can change the effector functions of the antibody, such as its ability to activate complement or bind to specific Fc receptors on immune cells.
Affinity Maturation: Affinity maturation is the process by which B cells that have undergone somatic hypermutation in the germinal center are selected for higher affinity BCRs. During the affinity maturation process, high-affinity B cells are preferentially selected for survival and proliferation within the germinal center, while low-affinity B cells are eliminated by apoptosis. The selection process is driven by interactions between B cells and Tfh cells, as well as interactions between B cells and antigen-presenting cells. These interactions provide signals that promote the survival and proliferation of high-affinity B cells, while inducing apoptosis in low-affinity B cells. Over time, this process leads to the production of a pool of B cells with BCRs that have higher affinity for the antigen.
Both class switching and affinity maturation are tightly regulated processes that are critical for the production of high-affinity antibodies during the adaptive immune response. Dysregulation of these processes can lead to the production of low-affinity antibodies, which may not provide effective protection against pathogens or high-affinity antibodies that are directed against self-antigens, leading to autoimmune disease.