Do you know how rigid is “quality control” in cells? Extremely rigid, - especially in the making of our T lymphocytes. An estimated 99% of developing T cells do not mature, so only 1% survives and “sees the light of dawn”. Imagine that, only 1% survives the rigid development process! If that is not extremely rigid for you, then I don’t know what is.
T lymphocytes originate from the bone marrow but undergo development and maturation in the thymus. Here (in the thymus) they are well insulated from untimely and extraneous exposure to foreign substances as they undergo development and maturation. The developing lymphocytes are only exposed to foreign elements once it is certain that they can indeed recognize what is foreign and what is self. The thymus has extensive blood-thymus barrier that makes sure this proper environment is maintained.
A mature T cell (the "graduate" of “Thymus University”) must be able to do two important things:
a)recognize self from non-self (foreign) and
b)express receptors that can bind antigen plus self-MHC molecules*
If the T cell during its development untimely develops or does not develop those two attributes, then it undergoes apoptosis or cell suicide, (please see Nov 6 post, cells commit suicide).
So, many cells die on the road to development and maturation and only the elite 1% “graduate” from the “Thymus University”. Can you believe that?
This extremely rigid “weeding out” process is very important for the integrity of our own immune system. Imagine what will happen if the T cell “graduate” cannot recognize foreign from self? Then the T cells will attack our own cells (self)! This by the way is what happens when we suffer from auto immune disorder. What happened to the development of T cells here? This will be the subject of a future post.
So in essence, that is quality control in the cellular world. If the cell does not develop properly, then it is signalled to commit suicide. Only the best survives, no “pwede na” (that’s ok or half-baked) graduates (or end products) here. Is this rigidity at all possible in the human world? What do you think?
*Major Histocompatibility Complex