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Germinal centres (GC) are areas within lymph nodes where B lymphocytes rapidly divide, and are an important part of the humoral immune response
Humoral immunity

The Humoral Immune Response is the aspect of immunity that is mediated by secreted antibodies produced in the cells of the B lymphocyte lineage ....
. They develop dynamically after the activation of B-cells by T-dependent antigen
Antigen

An antigen is a substance that prompts the generation of antibodies and can cause an immune response. The word originated from the notion that they can stimulate antibody generation....
. Histologically
Histology

Histology is the study of the anatomy of cell and tissue of plants and animals. It is performed by examining a thin slice of tissue under a light microscope or electron microscope....
, the GCs describe microscopically distinguishable parts in lymphoid tissues.

ctivated B-cells migrate into the follicular system and begin monoclonal
Monoclonal

Monoclonal cells are defined as a group of cells produced from a single ancestral cell by repeated cellular replication. Thus they can be said to form a single "cloning#Cellular cloning"....
 expansion in the environment of follicular dendritic cells (FDC).

2.






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Germinal centres (GC) are areas within lymph nodes where B lymphocytes rapidly divide, and are an important part of the humoral immune response
Humoral immunity

The Humoral Immune Response is the aspect of immunity that is mediated by secreted antibodies produced in the cells of the B lymphocyte lineage ....
. They develop dynamically after the activation of B-cells by T-dependent antigen
Antigen

An antigen is a substance that prompts the generation of antibodies and can cause an immune response. The word originated from the notion that they can stimulate antibody generation....
. Histologically
Histology

Histology is the study of the anatomy of cell and tissue of plants and animals. It is performed by examining a thin slice of tissue under a light microscope or electron microscope....
, the GCs describe microscopically distinguishable parts in lymphoid tissues.

Process

1. Activated B-cells migrate into the follicular system and begin monoclonal
Monoclonal

Monoclonal cells are defined as a group of cells produced from a single ancestral cell by repeated cellular replication. Thus they can be said to form a single "cloning#Cellular cloning"....
 expansion in the environment of follicular dendritic cells (FDC).

2. After three days of expansion the B cells mutate their antibody
Antibody

Antibodies are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacterium and viruses....
-encoding
Encode

Encode may refer to:* Can be related to "Code"* Encode ApS, a Danish software company* ENCODE, the ENCyclopedia Of DNA Elements...
 DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 and thus generate a diversity of clones in the germinal centre. This involves random substitutions, deletions and insertions due to somatic hypermutation
Somatic hypermutation

Somatic hypermutation is a mechanism inside Cell that is part of the way the adaptive immune system to the new foreign elements which confront it ....
.

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 centrocytes. The centrocytes are in a state of activated
Activation

Chemistry In chemistry, activation of molecules is required for a chemical reaction to occur. The phrase activation energy refers to the Energy the reactants must acquire before they can successfully react with each other to produce the Product , that is, to reach the transition state....
 apoptosis
Apoptosis

Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Programmed Cell death involves a series of biochemical events leading to a characteristic cell Morphology and death, in more specific terms, a series of biochemical events that lead to a variety of morphological changes, including Bleb , changes...
 and compete for survival signals from FDCs that present the antigen. This rescue process is believed to be dependent on the affinity
Affinity

Affinity, in etymology affinity is the opposite of infinity . These two words have the same root coming from the Latin: finis = end....
 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
IGM

IGM might be an acronym or abbreviation for:* The polymeric Antibody, Immunoglobulin M* Grandmaster , a chess ranking* intergalactic medium...
 to IgG. The interaction with T cells is believed to prevent the generation of autoreactive antibodies.

5. The B cells become either a plasma cell
Plasma cell

Plasma cells, also called plasma B cells or plasmocytes, are White blood cells of the immune system transported by the blood plasma and the lymphatic system....
 spreading antibodies or a memory B cell
Memory B cell

Memory B cells are a B cell sub-type that are formed following primary infection....
 that will be activated in subsequent contacts with the same antigen. They may also restart the whole process of proliferation
Proliferation

The word proliferation can refer to:*Nuclear proliferation*Chemical weapon proliferation*Cell growth* The proliferative phase of wound healing...
, mutation
Mutation

In biology, mutations are changes to the nucleotide sequence of the genetic material of an organism. Mutations can be caused by copying errors in the genetic material during cell division, by exposure to ultraviolet or ionizing radiation, chemical mutagens, or virus , or can be induced by the organism, itself, by cellular processes such as s...
 and selection
Selection

In the context of evolution, certain traits or alleles of a species may be subject to selection depending on the Pragmatics the user has with the word....
 according to the recycling hypothesis.

The above process involves TNF-alpha.

Morphology at different stages

The morphology
Morphology (biology)

The term morphology in biology refers to form, structure and configuration of an organism. This includes aspects of the outward appearance as well as the form and structure of the internal parts like bones and organs....
 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. 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.


Medical relevance

Germinal centres survive in rheumatoid arthritis
Rheumatoid arthritis

Rheumatoid arthritis is a chronic, systemic disease inflammation that may affect many tissues and organs, but principally attacks the joints producing a inflammatory synovitis that often progresses to destruction of the articular cartilage and ankylosis of the joints....
 and other autoimmune diseases. The GC can be disrupted by TNF inhibitor
TNF inhibitor

Tumor necrosis factor promotes the inflammatory response, which in turn causes many of the clinical problems associated with autoimmune disorders such as rheumatoid arthritis, ankylosing spondylitis, Crohn's disease, psoriasis and refractory asthma....
 drugs to reduce excessive B cells.

See also

  • Lymph node
    Lymph node

    A Lymph node is an organ consisting of many types of cells, and is a part of the lymphatic system. Lymph nodes are found all through the body, and act as filters or traps for foreign particles....


External links

- "Lymphoid Tissues and Organs: lymph node, germinal center"
  • with Q'n'A collection