Plasma cell

Plasma cells, also called plasma B cells or effector B cells, are

Plasma cells are large

Unlike their precursors, plasma cells 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.^[12] However, continued exposure to antigen through those low levels of immunoglobulin is important, as it partly determines the cell's lifespan.^[12]

The lifespan, class of antibodies produced, and the location that the plasma cell moves to also depends on signals, such as

The current findings suggest that after the process of affinity maturation in germinal centers, plasma cells develop into one of two types of cells: short-lived plasma cells (SLPC) or

The long-term survival of LLPC are dependent on a specific environment in the bone marrow, the plasma cell survival niche.[18] Removal of an LLPC from its survival niche results in its rapid death. A survival niche can only support limited number of LLPC, thus the niche’s environment must protect its LLPC cells but be able to accept new arrivals.^[19][20] The plasma cell survival niche is defined by a combination of cellular and molecular factors and though it has yet to be properly defined, molecules such as IL-5, IL-6, TNF-α, stromal cell-derived factor-1α and signalling via CD44 have been shown to play a role in the survival of LLPC.^[21] LLPC can also be found, to a lesser degree, in gut-associated lymphoid tissue (GALT), where they produce IgA antibodies and contribute to mucosal immunity. Recent findings suggest that plasma cells in the gut do not necessarily need to be generated de novo from active B cells but there are also long-lived PC, suggesting the existence of a similar survival niche.^[22] Tissue specific niches that allow for the survival of LLPC have been also described in nasal-associated lymphoid tissues (NALT), human tonsillar lymphoid tissues and human mucosa or mucosa-associated lymphoid tissues (MALT).^{[23][24][25][26]}

Originally it was thought that the continuous production of antibodies is a result of constant replenishment of short-lived plasma cells by memory B cell re-stimulation. Recent findings, however, show that some PC are truly long-lived. The absence of antigens and the depletion of B cells does not appear to have an effect on the production of high-affinity antibodies by the LLPC. Prolonged depletion of B cells (with anti-CD20 monoclonal antibody treatment that affects B cells but not PC) also did not affect antibody titres.^[27][28][29] LLPC secrete high levels of IgG independently of B cells. LLPC in bone marrow are the main source of circulating IgG in humans.^[30] Even though IgA production is traditionally associated with mucosal sites, some plasma cells in bone marrow also produce IgA.^[31] LLPC in bone marrow have been observed producing IgM.^[32]

Clinical significance

Common variable immunodeficiency is thought to be due to a problem in the differentiation from lymphocytes to plasma cells. The result is a low serum antibody level and risk of infections.

Primary amyloidosis (AL) is caused by the deposition of excess immunoglobulin light chains which are secreted from plasma cells.

See also

• Leukocyte
• Plasma cell dyscrasia
• List of distinct cell types in the adult human body

References