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After the process of affinity maturation in germinal centers, plasma cells have an indeterminate lifespan, ranging from days to months. Recently they have been shown to reside for much longer periods in the bone marrow as long lived plasma cells (LLPC). They secrete high levels of antibodies, ranging from hundreds to thousands of antibodies per second per cell. Unlike their precursors, they cannot switch antibody classes, cannot act as antigen-presenting cells because they no longer display MHC-II, and do not take up antigen because they no longer display significant quantities of immunoglobulin on the cell surface. However, continued exposure to antigen through those low levels of immunoglobulin is important, as it partly determines the cell's lifespan. The lifespan, class of antibodies produced, and the location that the plasma cell moves to also depends on signals, such as cytokines, received from the T cell during differentiation. Differentiation through a T cell-independent antigen stimulation (stimulation of a B cell that does not require the involvement of a T cell) can happen anywhere in the body and results in short-lived cells that secrete IgM antibodies. The T cell-dependent processes are subdivided into primary and secondary responses: a primary response (meaning that the T cell is present at the time of initial contact by the B cell with the antigen) produces short-lived cells that remain in the extramedullary regions of lymph nodes; a secondary response produces longer-lived cells that produce IgG and IgA, and frequently travel to the bone marrow. For example, plasma cells will likely secrete IgG3 antibodies if they matured in the presence of the cytokine interferon-gamma. Since B cell maturation also involves somatic hypermutation (a process completed before differentiation into a plasma cell), these antibodies frequently have a very high affinity for their antigen.
Plasma cells can only produce a single kind of antibody in a single class of immunoglobulin. In other words, every B cell is specific to a single antigen, but each cell can produce several thousand matching antibodies per second. This prolific production of antibodies is an integral part of the humoral immune response.
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