Lymphocyte

Structure

In microscopy, the lymphocytes seem cells ovoid, nucleate, whose core of big size (approximately 7 µm, is the diameter of a red globule) occupies almost all the cellular body. Its Chromatine is laid out in mounds. The lymphocytes B and T are not differentiable on only morphological criteria. They change according to the virus.

Lymphocytes T

Also called thymocytes or cells T , it is a category of lymphocytes which plays a great part in the primary but also secondary Immunizing response. " T" is the Abréviation of thymus, the body in which them development is completed. They are responsible for cellular immunity: the cells (bacteria, cancer cells) recognized as foreign (i.e. others that those which the cells T learned how to tolerate during their maturation) are destroyed by a complex mechanism.

There are several types of cells T:

lymphocytes CD8 evolving/moving in cytotoxic cells T or lymphocytes killers destroy the infected cells. These cells function like tueuses cells (“English killer”) or cytotoxic because they are capable to destroy target cells which express specific antigens that they recognize, by releasing a chemical substance, the perforine, which fits in the plasmic membrane and perforates it, which causes the explosion of the cell by a massive surge of water due to the osmotic pressures.
lymphocytes CD4 evolving/moving in auxiliary lymphocytes T or secreting lymphocytes (in English T-Helper) are intermediaries of the immunizing response which proliferate after contact with the antigen presented by a cell presenter of antigens (CPA) to activate quantity of other types of cells which will act in a more direct way on the answer. The CD₄+ cells control or “help” with the realization of other functions lymphocytaires. It is known that they are a target of HIV (with the Macrophage S); the fall of their population is one of the symptoms of the AIDS.
the suppressors T put a term at the immunizing response as soon as a Antigène was eliminated from the body.
the regulators T help to prevent the activation of the autoimmune lymphocytes which destroy the cells of their own organization.

cellular immunity (the Pathogenic immunizing response with respect to organizations S inside the cells) implies the activation of the cells T.

CD₄ and CD₈ refer to the Antigène S characteristics on the surface of the various sub-types of lymphocytes T. These molecules CD are useful diagnostic markers to identify and quantify these cells by cytometry by means of Anticorps directed against them.

In the past, instead of CD₄ and CD₈, etc, one spoke about OKT ₄ and OKT₈,… and even of T₄ and T₈

Lymphocytes B

Also called bursocytes. " B" comes from " Bone marrow" who means " marrow osseuse" in English who indicates the body where the Lymphocytes B complete their maturation (become " immuno-compétents").

These white globules have as a role to manufacture proteins of the family of the Immunoglobuline S called Anticorps: they are thus responsible for immunity humorale. To be active, other globules white such as Macrophage S, must to present them fragments of Antigen, so that they are transformed into Plasmocyte S. the Plasmocyte S have much more blisters of Golgi, which make it possible to manufacture Anticorps masses some (to 5000 antibodies a second), in order to neutralize the antigens effectively. The plasmocytes are thus lymphocytes B activated and able to produce antibodies directed against the antigen activator.

The lymphocytes B are cells taking part in the specific immunizing response, i.e., that after having recognized an antigen, the lymphocyte B cannot manufacture any more antibodies but against the antigen that one had presented to him.

the cells B are lymphocytes which play a great part in immunity humorale (in opposition to cellular immunity. " B" is the abbreviation of the purse of Fabrice, a body of the birds, in which the cells B become ripe, and not that of osseous English marrow (: bone marrow) in which the cells B are produced at all the other vertebrate ones.

The human body produces hundreds of the types different of cells B, and each type has on its membrane a single receiving protein, which will bind to a particular antigen; at every moment million cells B circulates in blood and the lypmhe, without producing antibody. There are two types of cells b:

the Plasmocyte S secrete Anticorps which take care of the destruction of the Antigène S while binding to those so that they become easier preys for the Phagocyte S.
the cells B with memory are formed specifically against the antigens met at the time of the primary immunizing response; as they can live a long time, these cells can react quickly during one second exposure to their specific antigen.

immunity humorale (the creation of antibody circulating in plasma and the Lymph) implies the Activation cells B. cellular activation can be measured by means of the technique ELISPOT which can determine the percentage of cells B secreting any particular antibody.

The cells B are characterized on the plan immunohistochimic by the presence of CD₂₀ on their cellular membrane.

Susumu Tonegawa obtained the Nobel Prize of Physiology and of Medicine in 1987 to have shown how the cells B create an enormous diversity of antibody at the beginning of a small number of genes.

Case of the AIDS

The virus of the AIDS (HIV) has a tropism for the lymphocytes T of under population CD₄ (i.e. the lymphocytes T expressing on their surface a protein called CD₄), which have a big role in the initiation of the immunizing responses. The HIV penetrates there, multiplies there, then flows in blood when the CD₄ cell dies. The destruction of CD₄ involves the stage AIDS declared of the disease (stage C), where opportunist infections are likely to appear: Disease of Kaposi, Pneumocystose, Candidose, Cryptococcosis, Lymphoma, Toxoplasmose cerebral, etc

See too

Leucocyte

Simple: Lymphocyte

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