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Immunology – Lecture 1 + 2 Overview, The Innate Immune System, B Cells andAntibodies (H1, H2, H3)
The main functions of the immune system:
Protection against infections microbes “non-self”
- Intracellular: viruses, some bacteria and parasites
- Extracellular: most bacteria and parasites, fungi
Protection against modified “self”
- Cancer/tumour cells or transformed cells
The skin is a physical barrier. The
skin itself is 2 m2. The mucous
membrane contains 400 m2. The
digestive, respiratory and
reproductive tract (mucous
membranes) has 200 m2.
Innate immunity = non-specific defence mechanism
constantly scanning cells that can be dangerous for us. Also
penetrate from within to the outside, to send out signals. This
innate immunity is the second defence mechanism.
LET OP! This is a rapid response, they are always there.
The innate immunity makes use of macrophages. These are
important, big, cells. They send the bacterium to their
receptors and eat the bacterium.
Lysosomes are filled with enzymes with a low pH. The
lysosome fuses with the phagosome with acidic environment, so it will break down the
bacterium.
When the cells that can mature into macrophages first exit the bone marrow and enter the
blood stream, they are called monocytes.
During their battle with bacteria, macrophages produce and give off (secrete) proteins called
cytokines hormone-like messengers which facilitate communication between cells of the
immune system.
From dendritic cell – red blood cell Innate Cells
Neutrophil, Eosinophil, Mast Cell Granulocytes
1
,Macrophage, Neutrophil Professional Phagocytes
From B cell – Killer T cell Adaptive Cells
B cell Professional Antigen presenting cells (APCs)
Dendritic Cell, Macrophage Professional Antigen presenting cells (APCs)
Adaptive immunity = is activated by exposure to pathogens, adapts to defend against specific
invaders. This is the third defence mechanism.
- B cell antibodies are produced by plasma B cells
- Helper T cell
- Killer T cell
Antibodies molecules can prevent infectious diseases. They usually contain light chains and
heavy chains. These are made against specific pathogens.
Fc region constant region (determines its class)
Fab region antigen binding region
IgG makes up about 75% of the antibodies in the blood,
but there are four other classes: IgA, IgD, IgE and IgM.
Each kind of antibody is produced by B cells.
In order to protect from every possible invader we
would need 100 million specificities. So we would need 10.000 heavy chains and 10.000 light
chains to combine.
LET OP! But our entire genome is 25.000 genes, so that is not possible!
In every B cell, on the chromosomes that encode the antibody heavy chain there are
multiple copies of four types of DNA molecules = gene
segments (V, D, J and C)
Light chain is also assembled by picking gene segments.
After this, additional DNA bases are added ore deleted =
junctional diversity.
So these are the only cells that doesn’t contain a constant
DNA combination; can re-arrange and cut out their own DNA. They have different segments.
But then, there won’t be enough B cells available with one specific binding site. So that’s
why there made on demand. If they recognize their epitope (=part of virus or bacterium),
they can make more of themselves.
2
, Antibodies can optimize. When antibodies opsonize
bacteria or viruses, they do so by binding to the invader
with their Fab regions, leaving their Fc tails available to
bind to Fc receptors on the surface of cells such as
macrophages. Using this strategy, antibodies can form a
bridge between the invader and the phagocyte, bringing
the invader in close, and preparing it for phagocytosis.
There are different types of T-cells.
- T cell receptor (TCR)
- Needs antigen presentation to be activated
o Can be done by Professional Antigen
presenting cells (APCs)
Dendritic cell
Macrophages
B cells
- Cytotoxic T cells (CTLs) destroys virus-infected
cells by making contact with its target and then triggering the cell to commit suicide
(LET OP! When a virus-infected cell dies, the viruses within the cell die also)
- T helper cells (Th cells) secretes cytokines (interleukin 2, IL-2, en interferon
gamma, INF-γ)
- Regulatory T cell (Treg) keep the immune system from overreacting or from
reacting inappropriately and maintain homeostasis.
There are two types of antigen presentation, done by 2 types of molecules = major
histocompatibility complex:
• Class I MHC all nucleated cells in the body,
represents and shows what’s inside the cell (peptide
only fits within the cell)
• Class II MHC mainly immune cells, represents and
shows what they have eaten; antigen presenting cells
(peptide can also be outside the cell, open on both
sides)
LET OP! Every part of your body is drained by lymph, will go into lymph nodes. Here the cells
are concentrated and close to each other to communicate.
After the invader is clean-up, a few B and T cells become long-lived memory cells. Once the
invader infects again, they are ready for combat.
What if B and T cells recognize our bodies own cells?
- Autoimmune disease
3
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