[Inside the thymus]
Our immune system fights
infections and cancer cells,
with a type of white blood cell,
the T cell.
T cells are made in an organ
called the thymus.
Immature blood cells are made
from blood stem cells in the bone marrow,
travel through the bloodstream
to the thymus.
Inside the thymus, over the course
of approximately 2 weeks,
a network of different cells
impart chemical signals
that affect the fate
of the immature T cells.
They're guided through
a process of development,
selection,
and also elimination
to become mature T cells.
Firstly, the immature T cells
are instructed to develop receptors.
At the next stage,
those cells with receptors
that can respond to the type of proteins,
the ones useful to our immune system,
are signaled to survive.
The rest are eliminated.
After this stage,
some of the developing T cells,
they recognize proteins
from the healthy cells of our own body
which can be dangerous
and cause auto-immunity,
where they may target
those cells and tissues.
In the final stage,
these cells are eliminated.
The remaining now matured T cells,
which have passed
through the selection process,
enter the bloodstream
and become part of our immune system.
In fact, as little as one percent
reach this stage
and are now ready to protect
against harmful infection and disease -
but not the healthy cells of our own body.
From a young age our thymus
degenerates, getting smaller.
Throughout our lives,
fewer and fewer T cells are made,
reducing our protection against
new infections and cancer,
especially, in old age.
Finding ways to regenerate the thymus
could help to boost the immune system
when this happens
and could also lead to treatments
for a number of conditions
affecting both the thymus
and the immune system.