The Molecules of HIV
helper T cell
www.mcld.co.uk/hiv
The helper T lymphocyte has been termed "the leader of the immunological orchestra". Helper T cells circulate throughout the body and check for antigens (substances that might be signs of invading virus/bacteria/etc). (The mechanism of checking is actually that they interface with HLA class II protein on other cells, checking what kind of substance HLA class II is presenting.)
If the helper T cell is stimulated by contact with antigen, it responds by cell division, as well as producing lymphokines and chemokines. Lymphokines and chemokines are chemical messages which alert other cells that there is an antigen to be dealt with; cell division means that there are more and more activated helper T cells around to sound the alarm.
In the following diagram you can see the helper T cells (marked TH) at the centre of the immune response:
The helper T cell is normally the main cell which carries the CD4 surface protein. This means that it's the main type of cell targeted by HIV. (Not all helper T cells are CD4+ cells - a small minority of them carry CD8 instead.) The above description of the helper T cell's role should tell you the reason that HIV is so crippling to the immune system: it can destroy the majority of CD4+ cells in the human immune system - and the orchestra, having no leader, can't do very much. The body becomes immunocompromised.
Written by
Dan Stowell
(©2002-2006)
