In addition, the importance of the GC response in health and disease will be highlighted. This review will cover recent progress in understanding the cellular and molecular mechanisms controlling the GC response and recent evidence that innate immune pathways can substantially impact the quality of the GC response. IgA and IgE have somewhat distinct biology, but nonetheless these isotypes also may provide a more long-lasting protection than the more rapidly turning over IgM. These long-lived plasma cells are responsible for more than half of the IgG in blood and provide a continual protection against re-infection with viruses and microbes. Moreover, whereas the plasma cells generated prior to the GC are almost all programmed to die after a few days, many of the plasma cells generated from the GC can migrate to the bone marrow, where they access survival niches that allow them to live for yearsĢ. While somatic mutation and antibody class switch occur to some extent outside of GCs, these processes occur to a much greater extent in the GC. At the same time, there is a change in the type of antibodies being produced, from IgM to IgG, IgA, or IgE, which have more specialized properties with respect to their localization and effector functions. The output of the GC is both memory B cells and antibody-secreting cells (called “plasma cells”), and the affinity of both increases for weeks to months, as long as the GC persists, resulting in “affinity maturation” of the antibodies in the bloodġ. The germinal center (GC) reaction is a critical part of the antibody response in which antigen-specific B lymphocytes undergo a sustained period of rapid cellular proliferation, high-level mutagenesis of their antibody genes, and stringent Darwinian selection for those B cells within the GC that make higher-affinity antibodies.
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