We’re going to explore
Cell-mediated immunity is immunity
that is provided by cytotoxic
T-cells and by T-helper cell-mediated activation of macrophages.
It’s required to defeat intracellular pathogens which
are hidden from the effects of antibody and complement.
So if you have an organism outside of a cell,
such as a bacterium or even a virus before it
enters a cell, antibody and complement are great
at dealing with that particular infection.
However, once organisms enter into cells as all viruses
do for some of their life cycle, and also some parasites
and some bacteria also spend at least some time inside
cells; antibody and complement just can’t get at them.
And that’s where we need
So at the core of cell-mediated
immunity is the helper T-cell.
And these act predominantly by producing
soluble molecules called cytokines.
And these cytokines can help activate cytotoxic T-cells
or cytotoxic T-lymphocytes (CTL) as we often call them.
And they can also help
Let’s compare the two types of T-cell
that have different T-cell receptors;
in other words, the alpha-beta (αβ)
T-cell and the gamma-delta (γδ) T-cell.
So here you can see the αβ T-cell
with the T-cell receptor on its cell
surface composed of a T-cell receptor
α-chain and a T-cell receptor β-chain.
And then on the right hand side, you can see a γδ T-cell
with its T-cell receptor composed of a γ-chain and a δ-chain.
Diversity for both of these types of receptors is called--
is created by recombination of T-cell receptor genes.
The T-cell receptor genes for the α-chain
and the β-chain in the case of the
αβ T-cell receptor, and the γ-chain and
δ-chain in the case of the γδ T-cells.
And both of these recombination processes occur within the
thymus; αβ T-cells recognize
peptides presented by MHC molecules.
In contrast, γδ T-cells can either recognize antigens
directly, entirely on their own just like antibodies
do, or they can recognize lipoprotein and glycolipids
that are presented by the MHC-like molecule CD1.