Germinal center 3625299 219693233 2008-06-16T13:10:26Z 81.98.163.161 {{Infobox Anatomy | Name = Germinal centre | Latin = | GraySubject = 175 | GrayPage = 689 | Image = Keimzentrum.jpg | Caption = Image labeled in German, but "Keimzentrum" visible in upper right. | Image2 = | Caption2 = | Precursor = | System = | Artery = | Vein = | Nerve = | Lymph = | MeshName = | MeshNumber = | DorlandsPre = c_20 | DorlandsSuf = 12226657 | }} '''Germinal centres''' (GC) are areas within [[lymph nodes]] where [[B lymphocytes]] rapidly divide, and are an important part of the [[humoral immunity|humoral immune response]]. They develop dynamically after the activation of [[B-cell]]s by T-dependent [[antigen]]. [[Histology|Histologically]], the GCs describe microscopically distinguishable parts in [[lymphoid]] tissues. ==Process== 1. Activated B-cells migrate into the [[follicular system]] and begin [[monoclonal]] expansion in the environment of [[follicular dendritic cell]]s (FDC). 2. After three days of expansion the B cells mutate their [[antibody]]-[[encode|encoding]] [[DNA]] and thus generate a diversity of [[Clone (genetics)|clone]]s in the germinal centre. This also involves deletions, insertions and [[recombination]] of the [[V(D)J_recombination|V, D, J]] genes. 3. Upon some unidentified stimulus from the FDC, the B cells start to expose their antibody to their surface and in this stage are referred to as [[centrocyte]]s. The centrocytes are in a state of [[activation|activated]] [[apoptosis]] and compete for survival signals from FDCs that present the antigen. This rescue process is believed to be dependent on the [[affinity]] of the antibody to the antigen. 4. The functional B-cells have then to interact with helper T cells to get final differentiation signals. This also involves [[isotype switching]] for example from [[IgM]] to [[IgG]]. The interaction with T cells is believed to prevent the generation of autoreactive antibodies.<ref>{{cite journal | author=Thorbecke GJ, Amin AR, Tsiagbe VK| title=Biology of germinal centers in lymphoid tissue| journal=FASEB | volume=8 | year=1994 | pages=832–840 | pmid=8070632}}</ref> 5. The B cells become either a [[plasma cell]] spreading antibodies or a [[memory B cell]] that will be activated in subsequent contacts with the same antigen. They may also restart the whole process of [[proliferation]], [[mutation]] and [[selection]] according to the recycling hypothesis. ==Morphology at different stages== The [[morphology (biology)|morphology]] of GCs is very specific and shows properties which are characteristic for different stages of the reaction. * In an early state of the reaction a network of FDCs is fully filled with proliferating B cells. * Later at day 4 of the reaction GCs show a separation of two zones, the dark and the light zone.<ref>{{cite journal | author=Meyer-Hermann ME|title=A Mathematical Model for the Germinal Center Morphology and Affinity Maturation |journal=J. theor. Biol. |volume=216|year=2002|pages=273–300 | pmid=12183119|doi=10.1006/jtbi.2002.2550}}</ref> The former still contains dominantly proliferating cells while the latter one is the area of B cells selection. * These zones dissolve after 10 days of GC development which ends after about 3 weeks. ==References== <references/> ==See also== * [[Lymph node]] ==External links== * {{UIUCHistologySubject|563}} * {{BUHistology|07103loa}} - "Lymphoid Tissues and Organs: lymph node, germinal center" *[http://www.bio.davidson.edu/courses/immunology/hyperhuman/Lymphnode/medula/node40_0.html Hyperlinked Human Histology] *[http://www.owlnet.rice.edu/~bios423/Lecture%20outlines/BCELLSH.htm Summary of lecture on B-cell development] with Q'n'A collection * {{LoyolaMedEd|Histo/practical/lymph/hp12-42.html}} * [http://www.cvm.okstate.edu/instruction/mm_curr/histology/HistologyReference/HRLym.htm Overview at okstate.edu] {{Lymphatic system}} [[Category:Lymphatic system]] [[de:Keimzentrum]]