Lymph nodes are the control centres where the body starts immune responses
Inside lymph nodes
many different types of immune cells meet.
Dendritic cells arrive from nearby parts of the body
bringing with them antigens from external invaders
that the body needs to eliminate.
The dendritic cells search for a responsive T-cell
to present these antigens to.
These T-cells become activated
and start to rapidly divide until they form
a clone army that will scour the body
to find the source of the invasion and get rid of it.
But with all those growing T-cells, the lymph node can quickly fill up,
which is a big problem.
If there isn't enough space to build a sufficiently large army of T-cells
the immune response is weakened.
Luckily, the dendritic cells have a trick up their sleeve.
As they search for T-cells, they crawl across a meshwork of fibroblast cells.
These fibroblasts form the structural scaffolding
that keeps the lymph node's shape intact.
On their way to activating the T-cells
dendritic cells warn the fibroblast network
that it's going to get crowded soon.
In response to these warning signals
the fibroblasts relax, and become more stretchy.
This gives the lymph nodes enough flexibility
to quickly expand when the clone army of T-cells begins to grow.
As the lymph node continues to expand, the fibroblast network grows as well
This makes sure there are enough fibroblasts to support
the large number of T-cells in the expanding lymph node.
But when those activated T-cells have left to fight the infected parts of the body
the fibroblast network regains tension
and begins to shrink the lymph node back to normal size.
Ready and waiting to build the next immune response
to keep us safe from subsequent invaders.
