Plasma cells are cells of the immune system and are used for the production and secretion of antibodies . They are effector cells and correspond to the last stage of the differentiation of the B cell series and appear under the light microscope as large oval cells with an eccentrically located nucleus . The importance of plasma cells for the formation of antibodies was described in 1948 by the Swedish immunologist Astrid Fagraeus as part of her doctoral thesis.
The lifespan of plasma cells varies from a few days or weeks to extremely long-lived plasma cells. B cells are activated by antigen contact and differentiate into plasma cells via the stage of the so-called plasmablasts. While plasmablasts are still able to divide but are already secreting antibodies, terminally differentiated plasma cells no longer divide.
When antigen-presenting B cells in the T-cell zone of the lymph nodes encounter specific T helper cells that recognize the presented antigen, they are activated. They then form a primary focus and differentiate into antibody-producing plasma cells. Some of the B cells that have been activated in this way by T cell help migrate to primary lymph follicles and form what is known as a germinal center . B cells that have been activated by T cell-independent antigens, on the other hand, are prevented from forming germinal centers. Affinity maturation does not occur in these T-cell-independently activated B-cells, and the isotype change is not carried out either. The antibodies produced are always of the IgM type. There is no memory formation.
In the germinal center, the B cells undergo affinity maturation and the isotype change in order to produce high-affinity antibodies of various immunoglobulin classes as plasma cells . Some of the B cells do not develop into plasma cells, but rather into memory B cells . The memory cells in turn mediate the immunological memory for this antigen . The formation of such memory cells is, for example, the necessary prerequisite for a successful vaccination . Memory cells can be activated more quickly when they meet the antigen again and differentiate into plasma cells, which leads to an accelerated and stronger second immune response. In addition, due to their mutations in the membrane-bound antibody, they are already very affine for the antigen. In addition to the memory cells, plasma cells with high-affinity antibodies of various classes are also formed in the germinal center. Most of these migrate into the bone marrow , where they receive survival signals for a long time from the stromal cells of the bone marrow and can secrete antibodies. The maturation of the plasma cells can be inhibited with Atacicept .
In humans, plasma cells can be characterized by the expression of surface markers such as CD19 , CD38 and CD138 as well as TACI . Earlier it was believed that the expression of CD19 to walk is lost to the bone marrow, but this evidence comes from experiments with multiple myeloma , so cancer plasma cells. However, recent studies indicate CD19 expression also on terminally differentiated plasma cells.
Plasma cells have a large amount of cytoplasm and many layers of the endoplasmic reticulum in order to be able to synthesize large amounts of antibodies. They no longer express MHC-II and can therefore no longer present a signal to the T helper cells. Surface immunoglobulins are still expressed in small amounts.