Cytotoxic T cells.
Virus-infected cells
are killed by cytotoxic T cells.
Cytotoxic T cells contain toxic granules.
Their contents are transferred into a
sick cell, causing death.
The majority of T cells circulate in the
blood and lymph.
Most are not cytotoxic
and are considered naive.
High concentrations of naive T cells can be
found in lymph nodes which are scattered
throughout the body.
Shown here are naive CD8 positive T
cells inside a lymph node.
These T cells have the potential to become cytotoxic
when activated.
The body creates millions
of variant T cells each with the unique
ability to recognise different pathogens.
But T cells cannot recognise pathogens
on their own.
They first encounter the
pathogen via another immune cell called
an antigen-presenting cell.
Antigen-presenting cells are one of the first
cells to detect infections in our bodies.
Their role is surveillance
inspecting their environment and taking samples
back to nearby lymph nodes.
Once in the lymph node
the antigen-presenting cells
search for a T cell that will recognise
their cargo.
By chance this T cell
recognises the cargo carried by this
antigen- presenting cell.
The recognition is controlled by molecular interactions
between the cells.
The antigen-presenting
cell produces proteins called MHC on its
cell surface.
The MHC contains a virus fragment.
The virus fragment is also known as a virus peptide.
Each naive T cell produces a
unique receptor that can recognise
different virus peptide MHC combinations.
The presence of the CD8 molecule defines
this subclass of T cells.
The receptors
on this particular T cell bind to the
virus peptide MHC complex.
Co-receptor CD8 binds the complex.
The receptors cluster.
Eventually leading to T cell activation.
The activated T cell divides and
produces clones of itself.
The cells gain
cytotoxic capabilities as they grow.
Chemical cues attract the cytotoxic T cells
to the infection.
The cytotoxic T cells
specifically recognise the
infected cells.
The recognition is
controlled by molecular interactions
between the cells.
The infected cell displays
the same virus peptide MHC complex.
T cell receptor binding and clusterings
trigger the killing process.
Cytotoxic granules are transferred and
kill the infected cell.
Only infected cells
display the virus fragment on
their cell surface ensuring that only
infected cells are killed.