Anergy

Anergy is a theory in immunobiologyin which there is a lack of reaction by the body's defence mechanisms when foreign substances come into contact with the body. Often this term is used to indicate that the immune systemis unable to mount a normal immune response.

At the cellular level, the term "anergy" defines the inability of an immune cell to mount a complete response against its target. In the immune system circulating cells called lymphocytes form an primary army that defends the body against pathogenic viruses, bacteria and parasites. There are two major kinds of lymphocytes - the T-lymphocyte and the B-lymphocyte. Among the millions of lymphocytes in the human body, only a few actually are specific for any particular infectious agent. At the time of that infection, these few cell must be recruited and allowed to multiply rapidly. This process called "clonal expansion", allows the body to quickly mobilise an army (of clones) as and when required. This clonal army then combats the pathogen until the body is free of the infection. Subsquently the clones (that are no longer needed) die away naturally.

However, some of the body's army of lymphocytes are often able to react with proteins that are normally present in a healthy body. The clonal expansion of those cells can lead to "autoimmune" diseases where the body attacks itself. In order to prevent this process, lymphocytes possess an intrinsic quality control mechanism. This machinery shuts down their ability to expand, if the trigger for the expansion turns out to be the body's own protein. This phenomenon was first described in B lymphocytes by Gustav Nossal and termed "Clonal Anergy". The clones of B lymphocytes in this case can still be found alive in the circulation, but are poor at mounting effective responses. Later Ronald Schwartz and Marc Jenkins described a similar process operating in the T lymphocyte as well. Interestingly many viruses (notably HIV) seem to exploit this phenomenon to evade the immune system.

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Anergy Wikipedia article Anergy.