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T and B Cell.swf

Monday, August 8, 2011


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Lymphocytes are one of the five kinds of white blood cells or leukocytes), circulating in the blood. [More]

Although mature lymphocytes all look pretty much alike, they are extraordinarily diverse in their functions. The most abundant lymphocytes are:
  •     B lymphocytes (often simply called B cells) and
  •     T lymphocytes (likewise called T cells).

Each B cell and T cell is specific for a particular antigen. What this means is that each is able to bind to a particular molecular structure.

The specificity of binding resides in a receptor for antigen:
  •     the B cell receptor (BCR) for antigen and
  •     the T cell receptor (TCR) respectively.


Both BCRs and TCRs share these properties:
  •     They are integral membrane proteins.
  •     They are present in thousands of identical copies exposed at the cell surface.
  •     They are made before the cell ever encounters an antigen.
  •     They are encoded by genes assembled by the recombination of segments of DNA.
  •     How antigen receptor diversity is generated.
  •     They have a unique binding site.
  •     This site binds to a portion of the antigen called an antigenic determinant or epitope.
  •     The binding, like that between an enzyme and its substrate depends on complementarity of the surface of the receptor and the surface of the epitope.
  •     The binding occurs by non-covalent forces (again, like an enzyme binding to its substrate).
  •     Successful binding of the antigen receptor to the epitope, if accompanied by additional signals, results in:
  •         stimulation of the cell to leave G0 and enter the cell cycle.
  •         Repeated mitosis leads to the development of a clone of cells bearing the same antigen receptor; that is, a clone of cells of the identical specificity.

BCRs and TCRs differ in:
  •     their structure;
  •     the genes that encode them;
  •     the type of epitope to which they bind.

Monoclonal Antibody Production.swf / Produksi Antibodi Monoklonal


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Process by which large quantities of antibodies (targeted against a particular antigen X) can be produced.

A mouse is immunized by injection of an antigen X to stimulate the production of antibodies targeted against X. The antibody forming cells are isolated from the mouse's spleen.

Monoclonal antibodies are produced by fusing single antibody-forming cells to tumor cells grown in culture. The resulting cell is called a hybridoma.

Each hybridoma produces relatively large quantities of identical antibody molecules. By allowing the hybridoma to multiply in culture, it is possible to produce a population of cells, each of which produces identical antibody molecules. These antibodies are called "monoclonal antibodies" because they are produced by the identical offspring of a single, cloned antibody producing cell.

Once a monoclonal antibody is made, it can be used as a specific probe to track down and purify the specific protein that induced its formation.

Leukocyt.swf / Sel darah Putih.swf


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Leukocytes, or white cells, are responsible for the defense of the organism. In the blood, they are much less numerous than red cells. The density of the leukocytes in the blood is 5000-7000 /mm3. Leukocytes divide in two categories: granulocytes and lymphoid cells or agranulocytes. The term granulocyte is due to the presence of granules in the cytoplasm of these cells. In the different types of granulocytes, the granules are different and help us to distinguish them. In fact, these granules have a different affinity towards neutral, acid or basic stains and give the cytoplasm different colors. So, granulocytes distinguish themselves in neutrophil, eosinophil (or acidophil) and basophil. The lymphoid cells, instead, distinguish themselves in lymphocytes and monocytes. As we will see later, even the shape of the nucleus helps us in the recognition of the leukocytes.

Each type of leukocyte is present in the blood in different proportions:

neutrophil 50 - 70 %
eosinophil 2 - 4 %
basophil 0,5 - 1 %
lymphocyte 20 - 40 %
monocyte 3 - 8 %

Neutrophils are very active in phagocyting bacteria and are present in large amount in the pus of wounds. Unfortunately, these cells are not able to renew the lysosomes used in digesting microbes and dead after having phagocyted a few of them.

Eosinophils attack parasites and phagocyte antigen-antibody complexes.

Basophil secrete anti-coagulant and vasodilatory substances as histamines and serotonin. Even if they have a phagocytory capability, their main function is secreting substances which mediate the hypersensitivity reaction.

Lymphocytes are cells which, besides being present in the blood, populate the lymphoid tissues and organs too, as well as the lymph circulating in the lymphatic vessel. The lymphoid organs include thymus, bone marrow (in birds bursa), spleen, lymphoid nodules, palatine tonsils, Peyer's patches and lymphoid tissue of respiratory and gastrointestinal tracts.

Cytotoxic.swf

Wednesday, July 27, 2011


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Cytotoxicity is the quality of being toxic to cells. Examples of toxic agents are a chemical substance, an immune cell or some types of venom (e.g. from the puff adder or brown recluse spider).
 
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