• Adaptive immunity is the third line of defence.
• It happens after the physical barriers such as tears, skin mucous and stomach acid.
• This is followed by innate immunity which is the immune system that is present from birth, this includes soluble mediators such as complement and cytokin...
Adaptive immunity is the third line of defence.
It happens after the physical barriers such as tears, skin mucous and stomach acid.
This is followed by innate immunity which is the immune system that is present from
birth, this includes soluble mediators such as complement and cytokines in the
blood. And also includes a number of cell types that it can immediately recognise
and attack pathogens after they have infected our body.
Adaptive immunity
Requires different types of cells specifically the lymphocytes such as B and T cells.
They have similar effective mechanisms to innate immunity but they have a unique
system of recognition that leads to a very specific response.
These cells also have the capacity to develop memory.
They stick around and are in place to protect us if we are infected with the same
pathogen again.
Pathogen recognition-innate immunity
Pathogen recognition in innate immunity is the fixed repertoire of cells and soluble
molecules.
So these are pathogen recognition receptors, such as TLR-4 (This is the PRR that
recognises LPS)
All of these components are inherited, they are in place at birth, and new variants
very rarely arise.
The overall strategy is to recognise broad non-differentiating pathogenic structures
or to detect alterations in infected or damaged cells.
Pathogen recognition- adaptive immunity
Pathogen recognition in adaptive immunity is very specific.
Each lymphocyte (T-cells and B-cells) expresses just one type of molecular receptor
with a single specificity.
B-cells express the B cell receptor (AKA BCR or membrane bound immunoglobulin)
T cells express the T cell receptor
These receptors are made by gene rearrangements so they get jumbled up so we
have millions of different specificities.
Each cell is a clone that expresses a unique and specific receptor. That only
recognises one epitope of a pathogen.
Advantages of adaptive immunity:
Precise targeting- immune system is only going after the main thing that has infected
you.
Memory cells- it is able to generate memory cells
It is also able to recognise new pathogens- pathogens do change what they look like
over time to evade the immune system and the adaptive immune system is capable
of responding to this.
Receptors of adaptive immunity
, Receptors of adaptive immunity are antibody
When it is expressed on the surface of a B cell it is called a B cell receptor.
Every B cell only produces one of these antibodies.
A B cell expresses surface immunoglobulin.
The immunoglobulin have a transmembrane region
whereas Plasma cells which are a more matured form of B cells, they just produce
antibody for secretion into the extracellular space.
Plasma cells produce a secreted antibody and no longer express the antibody on the
cell surface.
T cells
They express a T cell receptor with an alpha and beta chain.
This is always on the cell surface receptor and is ready to recognise antigen.
The T cell receptor has a constant region towards the cell membrane and the distal
site at the very end of the molecule, that is where the very specific antigen binding
site is.
The antigen binding site recognises a specific epitope or protein fragment from a
specific pathogen and each one of these T cells or B cells produces one kind of this
receptor.
In the antibody B cell molecule, we have a constant region, this stays the same
depending on which class of antibody you are talking about.
The antigen binding site is at the ends of the Y shaped arms of this molecule and that
is the specific region of that molecule that can detect a particular epitope of a
pathogen.
Receptor diversity is generated by gene rearrangement
this receptor diversity is generated by gene rearrangements.
There is a germline configuration of genes that encodes for the B cell and T cell
receptors that cannot be transcribed.
These need to undergo a nucleotide insertion and rearrangement to allow
transcription to happen.
And whilst this happens certain segments are chosen.
Gene rearrangement happens differently in every clone.
Every different lymphocyte undergoes its own unique type of rearrangements of
these genes to produce a unique T cell or B cell receptor.
Receptors of adaptive immunity are highly specific
1. During development, progenitor cells give rise to large numbers of circulating
lymphocytes, each having a different form of cell-surface receptor.
2. The receptors of only a few circulating lymphocytes interact with any given
pathogen.
3. Pathogen reactive lymphocytes are triggered to divide and proliferate.
4. Pathogen-activated lymphocytes differentiate into effector cells that eliminate the
pathogen.
During development the progenitor cells give rise to a large numbers of circulating T
cells.
You have many different types of T cells and B cells. So lots of different circulating
lymphocytes and each of these has a different cell surface receptor.
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