We can learn from cells about ... quality control

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?

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*Major Histocompatibility Complex

cells commit suicide

Some cells die because of cell injury but other cells die because they commit suicide. Yes, they do! And why would cells do that? There are various reasons.

One reason is, to remove severely damaged cells and prevent them from being duplicated. Cells generally repair some damages that may develop in them. If the damage is too extensive however, they receive signals to commit suicide rather than pass on their defect to the next generation of cells.

Another reason is to maintain the number of cells in the body. We cannot have too many or too little number of cells. So “old, worn-out cells” that have reached their “expiry date” are told to commit suicide. They are then replaced by new cells through the process of mitosis. In the cell world, there is no such thing as extension of retirement. Any extension is always detrimental to the whole organism. Some cancerous cells for example ignore this “expiry date” so the organism develops cancer.

Still another reason is “body sculpting” during development. In the formation of our fingers and toes for example, the starting form is a whole solid mass. During development, the “in-between” cells in the mass commit suicide and this leads to the formation of separate fingers and toes. Sometimes some cells may not commit suicide so the separation of fingers can be incomplete. Thus, we sometimes see people with partially fused fingers or toes.

The disappearance of the tadpole’s tail as it is transformed to an adult frog is an example of “body sculpting” produced by cell suicide.

There are other reasons for cell suicide but those three are the most important ones.

By the way, the scientific term for cell suicide is – “apoptosis” or programmed cell death.