Immune System Overview Flashcards
What’s the first line of defence of the immune system?
Innate immune system (nonspecific)
External barricades: skin, muscous membranes
Internal defences: phagocytes, antimicrobial proteins, attack cells
Chemical defenses
What is the second line of defence of the immune system?
Adaptive immune system (specific/acquired)
What is skin?
An organ of tough keratinised epithelial membrane
What are mucous membranes?
Line any cavity that opens up to the outside world; respiratory, digestive, urinary, reproductive tract
List 5 chemical defenses of the innate immune system
- Acid from skin, stomach, and vaginal secretions
- Mucin that forms mucus in the respiratory and digestive passageways
- Enzymes found in saliva, mucus, and eye fluid that fight bacteria
- Defensins, or antimicrobial proteins
- Chemicals found in sweat that destroy bacteria
3 internal innate defenses
- Fever
- Chemical signals
- Inflammation
The order of arrival of defensive cells
- Phagocytes (neutrophils and macrophages)
- Natural Killer (NK) cells
Neutrophils
Most abundant type of white blood cell
Self-destruct after ingesting a pathogen
Dead neutrophils = pus
Macrophages
Made of monocyte white blood cells that have moved out of the blood stream to occupy tissues
Free type - patrol tissues
Fixed type - attached to fibres in specific organs (ie the Stellate macrophages in the liver)
Attaches to bacterium using cytoplasmic extensions, brings it closer and engulfs it, digesting it, and displays particles on its surface
Natural Killer cells
Patrol blood and lymph looking for abnormal cells
Unique - can kill your own cells if they are infected with viruses or have become cancerous (know because the cell won’t contain MHC1). It then gives the cell an enzyme that triggers apoptosis
What is MHC1?
Major Histocompatibility Complex 1
Normal healthy cells contain this protein on their surface - pieces of endogenous proteins (proteins made within that cell)
If a cell is infected, it stops making this protein
Strategy of the Immune Response
- Inflammatory repsonse
What are symptoms of the inflammatory response?
Redness
Swelling (due to increased blood vessel permeability)
Heat (increases the cell’s metabolic rate)
Pain
What is histamine and what releases it?
Mast cells in connective tissue release histamine
Causes vasodilation
Causes increased permeability of blood vessels - causes nearby capillaries to release protein rich fluids (helps clot blood and build scabs, lymphatic system filters extra fluid, also allows phagocytes to enter inflamed area, and lymphocytes)
What are chemical signalling molecules of the inflammatory response?
Histamine (released by mast cells in connective tissue)
Fatty acid prostoglandins
Kininogen and other plasma proteins
Complement blood proteins
Cytokines
What are lymphoytes?
Destroy pathogens
Clean up dead cell wreckage
Leukocytosis
The release of neutrophils from bone marrow (where they’re made) into the blood stream
Inflamed endothelial cells and capillaries send out chemicals to attract neutrophils
Neutrophils stick to the capillary walls and squeeze through epithelial cells
Monocytes
Arrive at the site of injury and transfrom into macrophages
What are pyrogens?
Chemicals released by immune cells (neutrophils, macrophages, lymhocytes) that travel to the hypothalamus and raise body temperature (systemic fever)
Fever causes increased cell metabolism, and cause liver and spleen to hold on to all iron and zinc so it can’t contribute to bacterial growth
Two types of growth of the adaptive immune system
Organic - touching germs on a doorhandle
Premeditated - vaccines
What are the key differences between the adaptive and the innate immune system?
- Adaptive has the ability to remember specific pathogens
- Adaptive is systemic (innate is more local)
- Adaptive is specific
What are the 2 defenses of the adaptive immune system?
- Humoral immunity
- Cellular defenses
What is your humoral immunity?
Production of antibodies
Made by specialised white blood cells and patrol the body’s humors (fluids - ie blood and lymph)
B Lymphocyte
Originates and matures in bone marrow
Maturing allows it to distinguish self from non-self
Develops immunocompetence and self-tolerance
When mature, displays at least 10,000 special protein receptors on surface (membrane-bound antibodies)
Each B lymphocyte has specific antibodies
Mature B lymphocytes then roam around in secondary lymphoid organs
What is immunocompetence?
How to recognise and bind to a particular antigen
List the secondary lymphoid organs?
Spleen, tonsils, lymph nodes
What happens when a B lymphocyte binds to a pathogen it has an antibody for?
Upon binding the pathogen the cell becomes activated, and quickly starts multiplying
Most activated cells become effector (plasma) cells
Some become memory cells (allows for secondary immune response)
How do effector (plasma) cells work?
Have extra ER
Mass produce the antibodies and release them into the humor at roughly 2000 antibodies per second for 4/5 days until the cells die
What is opsonisation?
Free floating antibodies bind to antigens on pathogens and mark the cells for death
What is neutralisation?
Antibodies bind to all available antigens on a pathogen, thereby blocking the pathogen from attaching to tissues
What is agglutination?
Antibodies have more than one binding site, and can therefore bind to more than one antigen to form clumps which make it easier for macrophages to locate and ingest them
Another function of antibodies
Antibodies call in phagocytes from the innate immune system and special lymphocytes from the adaptive system to destroy the antigen-antibody clumps
Active humoral immunity
B cells bump into antigens and produce antibodies (can occur natrually or artificially)
Passive humoral immunity
Infants get passive humoral immunity (antibodies) from their mother through the placenta and breast milk
Passive antibodies however, don’t live long, and don’t produce effector or memory cells
Can also acquire passive immunity by getting exogenous antibodies from the plasma of an immune donor (not the same as a vaccine, but can buy the patient some time)
Cellular Immune Response
T lympocytes go after infected host cells
What are the functions of T cells?
Causes inflammation
Activates macrophages
Recruits other T cells
Regulate much of the immune response
What are Major Histocompatibility Complexes (class II)?
Bits of a pathogen that the cell has broken down can bind to MHC molecules and are now displayed on its surface
Done by both innate and adaptive immune cells
What are Professional Antigen Presenting Cells?
Cells of the innate and adaptive immune system that present broken pieces of the pathogens that they’ve ingested
Which cells are APC?
Macrophages, dendritic cells and B cells
Where are T cells made and where do they mature?
Made: bone marrow
Mature: thymus (lymphoid gland on top of the heart)
Helper T cells
Naive helper T cell has a receptor specific for an MHC class II protein + a specific antigen on an APC
If this matched, the two cells bind and the helper T cell is activated
T cell divides producing mostly other helper T cells, but also regulatory T cells and memory T cells
T cells release cytokines that when entering other T cells give them the signal to start dividing > some also help activate cytotoxic T cells
Cytotoxic T cells
If cytotoxic T cells meet the correct specific MHC class II + antigen combination they bind
Release perforins (create pores in the cell) and granzymes (a protease) which leads to apoptosis
Immunodeficiencies
AIDS (acquired immudeficiency syndrome) caused by HIV (human immunodeficiency virus) attacks helper T cells
Interaction between B and T cells
When a B cell has engulfed a protein and presented the antigen on its surface, a helper T cell checks if this is indeed a foreign body
If yes, the helper T cell binds and releases cytokines which fully activate the B cell
If not, nothing happens and no immune response is generated
Regulatory T cells
At the end of infection, release inhibitory cytokines that tell other immune cells to stand down
A type of effector cell
Autoimmune disorders
Multiple sclerosis - eats away at the myelin sheaths around neurons
Type 1 diabetes - destroys pancreatic cells that make insulin
