43 Immune System Flashcards
What is the immune system functionally divided into?
The innate immune system and the adaptive immune system.
How do the innate and adaptive immune systems differ in terms of their response?
The innate system recognises traits shared by a broad rang of pathogens using a few receptors.
The adaptive system is different in that it can learn and recognise individual pathogens.
Despite this the innate system is quicker as the adaptive system needs time to adapt to the specific threat.
In what organisms are the innate and adaptive immunity systems seen?
All animals (and to some degree plants) have innate immunity whereas only vertebrates have adaptive immunity.
What is the innate immune system divided into?
Barrier defences and internal defences.
What are innate barrier defences?
Skin, mucus membranes, secretions i.e. basic to make skin inhospitable to bacteria
What are the innate internal defences?
Phagocytic cells, “natural killer cells”, anitmicrobial proteins and the inflammatory response.
What is adaptive immunity divided into?
Humoral response and cell-mediated response.
What is the adaptive humoral response?
Antibodies that defend against infection in body cells.
What is the adaptive cell-mediate response?
Cytotoxic cell that defend against infection of body cells.
What is an insect’s exoskeleton composed of?
Chitin.
Where besides the exoskeleton is chitin found in an insect?
In the intestines where it prevents bacterial invasion while still allowing nutrient absorption.
What are the innate internal responses seen in insects?
They have immune cells called ‘hemocytes’ that travel round the hemolymph and attack bacteria etc. through phagocytosis.
Hemocytes also secrete chemicals that trap Plasmodium, the parasite carried by mosquitos that causes malaria.
Hemocytes and other insect immune cells can also secrete “antimicrobial peptides” that circulate and kill fungi and bacteria by disrupting their plasma membrane.
Besides chitin, how is an insects digestive tract protected from bacteria?
Their intestines secrete Lysozyme, an enzyme that breaks down bacterial cells walls
What organism causes malaria?
The par aside Plasmodium which is carried by mosquitos.
How are fungal and bacteria cell walls distinguished by the innate immune system of insects?
Fungal cell walls contain certain unique polysaccharides, whereas bacterial cell walls have polymers containing combinations of sugars and amino acids not found in animal cells.
How specific is the insect innate internl defence system?
Quite, it can recognise fungal cells walls using the protein-receptor “Toll” which is found on the plasma membranes of hemocysts, leading to specific anti-fungal antimicrobial peptides
Bacterial infection leads to the triggering of different responses and thus antibacterial peptides.
What is an example of a fungus that infects flies?
Neurospora crassa
What is an example of a bacterium that infects flies?
Micrococcus luteus,
What does the innate barrier defences of vertebrates include?
Epithelial cells and mucus membranes that line the digestive, reproductive and respiratory tracts.
Tears, saliva and mucus also include Lysozymes, which are enzymes that break down the cell walls of bacteria etc.
Stomach acid also breaks down bacteria etc. in food.
Secretions from oil and sweat glands give human skin a pH ranging of 3 to 5, acidic enough to stop bacterial growth
How does mucus act as a barrier defence?
It traps bacteria which are then swept away by cilia.
How are the innate cellular response of vertebrate regulated?
With receptors named “Toll-like receptors” (TLR) that bind to common component of bacteria.
What are some examples of specific toll-like receptors in vertebrates?
TL3 is in the inside membrane of vesicles to detect double-stranded RNA characteristic of viruses.
TR4 on the plasma membranes of immune cells recognises lipopolysaccharide which are found on many bacteria.
TLR5 detects “flagellin”, the main component of bacterial flagella.
What happens after a toll-like receptor detects a microbe?
Endocytosis occurs, trapping the microbe in a vacuole. The vacuole fuses with a lysosome. The lysosome contains gasses that poison the bacteria and enzymes that break it down.
The debris format the bacteria is then released through endocytosis.`
What are main phagocytic cells of the vertebrate innate immune system?
Neutrophils and Macrophages.
How do neutrophils and macrophages differ?
Neutrophils are smaller an circulate the blood,
Macrophages are much large so some circulate the blood while others reside permanently in organs where they are likely to encounter pathogens.
Where do many macrophages reside and why?
In the spleen as this is where many blood pathogens are trapped.
What are the less common phagocytic cells of the vertebrate immune system?
Dendritic cells and eosinophils.
What are dendritic cells?
Phagocytic cells typically found on the skin. They are port of the adaptive immune system
What are eosinophils?
Immune cells that are found under mucus surface and that are not as active at phagocytosis.
They primarily defend against large invaders such as parasitic worms which they kill by secreting enzymes.
Besides phagocytic cells, what type of cells are part of the vertebrate innate cell-mediated immune system?
Natural killer cells.
What are natural killer cells?
Cells that detect microbes by analysing key component and then release chemicals that kill the bacterium etc.
What immune defences are seen in the lymph vessels?
Some macrophages reside in the lymph nodes.
Dendritic cells reside outside the lymph system but migrate to the lymph nodes when they interact with bacteria.Within the lymph nodes, dendritic cells interact with other immune cells, stimulating adaptive immunity.
Besides cells, what is secreted as part of the innate immune system of vertebrates?
Antimicrobial peptides and proteins.
What is an example of an innate-defence antimicrobial protein?
Interferons which provide innate defences against viruses.
What causes the release of interferons?
Virus-infected body cells secrete it to trigger nearby uninfected cells to secrete substances to protect themselves.
Some white blood cells secrete a different type of interferon that activates macrophages to enhancing their phagocytic ability.
Besides interferons, which antimicrobial proteins are released?
The “complement system”, which consist of roughly 30 blood plasma proteins with immune properties.
How does the “complement system” work?
The antimicrobial proteins circulate the blood in their inactive forms. They are activated by substance on the surface of the microbes.
When they identify a microbe they destroy it by catalysing a cascade of reaction that results in lysis (bursting) of the cell.
What is an important innate response to infection
The inflammatory response.
What causes the inflammatory response?
The signalling molecule histamine is store in the granules (vesicles) of “mast cells” which are located in connective tissue.
Damage to this tissue causes the release of this histamine which triggers nearby blood vessels to dilate causing more antimicrobial peptides to arrive. Activated macrophages and neutrophils release cytokines which signal good flow to increase.
Complement proteins are also attracted and after being activated trigger more histamine release.
Why is the inflammatory response important?
It attracts macrophages and neutrophils etc. to consume bacteria and digest the cell debris. Increased blood flow also ‘recruits’ more antimicrobial peptides.
What is an immune response across the body called?
A “systemic” response as opposed to inflammation, which is local.
What are some example of systemic responses?
Injured/infected cells send signals to the bone marrow stimulating more neutrophils and other white blood cells to be released.
Also fever.
What is fever?
A systemic response in which the body raises its own “thermostat” i..e intentionally becomes hotter.
What is the advantage of raising the temperature during fever?
It is believed to improve phagocytosis and by speeding up chemical reaction accelerate tissue repair.
What is an excessive systemic inflammatory response?
Septic shock, often the result of bacterial infection, leads to a very high fever, low blood pressure and poor blood flow through capillaries.
What does “chronic” refer to with regard to a disease?
Ongoing even when the cause is gone i.e. pain after injury has healed?
What disease are caused by chronic inflammation?
Crohn’s disease and ulcerative colitis, both of which occur when unregulated inflammatory respond disrupts intestinal function.
How have bacteria adapted to avoid phagocytic destruction?
Some have an outer capsule that disrupts molecular recognition.
Some bacteria, such as those that cause TB, can survive in lysosomes and thus are essentially hidden from the immune system.
What are the basic cells of the adaptive immune system?
B cells and T cells.
How are B and T cells produced?
In the bone marrow they both develop from stem cels. Some migrate the “thymus”, an organ above the heart, and develop into T Cells.
Those that remain in the bone marrow develop into B Cells.
What is a substance that elicits an adaptive-immune response called?
An antigen
How are antigens detected?
By “antigen receptors” of the plasma membranes of B and T cells.
How does antigen reception differ from “Toll-like receptors”?
They are extremely specific to the point they respond to specific bacteria species.
How many types of antigen receptors are there and how many different kinds does one B/T cell have?
There are millions of different antigen receptors but each B/T cell only has one type.
Note:
Antigens are often proteins or polysaccharides
Where are the antigens located?
Many are on the plasma membrane of the bacteria etc. or are a particular part of the first
Some are products secreted by microbes.
How does the antigen bind to the antigen receptor?
A specific region of the antigen, known as the “epitope” binds to a specific region of the antigen receptor.
What is an epitope also called?
An “antigenic determinant”
