Immune System 15 Flashcards
What is the immune system?
A versatile defence system that protects us from pathogenic microbes
Facts about the first line of defence
Innate immunity
Physical barrier created by the skin and mucous membranes
Facts about the second line of defence
Innate immunity
Non-specific immune response that includes immune cells, proteins, fever and inflammation
Facts about the third line of defence
Specific / adaptive immunity
Activated by innate immune system
Specific response to a specific pathogen
What is a pathogen
An infectious agent that can cause disease in a host
How can pathogens enter the body?
Breaks in the skin
The respiratory system
The digestive system
Reproductive system
Eyes
What is an antigen
A substance that can be recognised by leukocytes
What are the two types of antigen
Foreign antigens
Self-antigens
What are antigens normally made from
Proteins
What are antibodies
Proteins that are produced in response to a specific antigen. They combine with these specific antigens
What are the two main first lines of defence?
- the skin
- mucus membranes
How is the skin a first line of defence?
It’s a physical barrier with layers of tightly-packed epithelial cells.
What accessory structures does the dermis contain that have an immenue function
Sweat glands
Sebaceous glands
What is the immune function of sweat
Removes microbes from skin
Contains IgA
What is the immune function of sebum?
Contains fatty acids that inhibit microbial growth
Where do you find mucus membranes?
In the digestive, respiratory and urogenital tracts plus the conjunctive in the eyes
What washes away secretions in the mucus membranes?
Saliva, tears and mucus secretions
What is the mucociliary escalator and where is in found?
In the respiratory tract
Cilia propel foreign substances towards the pharynx where they are swallowed
How does the nose defend against pathogens?
Hairs filter air
How does the vagina protect against pathogens
It’s acidic
How does the gastric tract protect against pathogens
Acidity
Microflora outcompete pathogens
Excretion of urine and faeces expels microbes
Vomiting and diarrhoea are rapid means of expelling pathogens
When pathogens penetrate the physical and chemical barriers what do they encounter next?
The second line of defence
List some elements of the second line of defence?
Complement system
Transferrins
Phagocytes
Natural killer cells
Inflammation
Cytokines - eg interferons
Fever
What are transferrins and how do they work?
Iron-binding proteins in the blood - inhibit the growth of certain bacteria by reducing the amount of available iron.
What is the complement system and where is it made?
A defense system of over 30 proteins made by the liver
What happens when complement proteins are activated?
They act in a cascade (they are amplified)
What is the most common mechanism that complement proteins are activated?
‘Classical pathway’ where antigen-antibody complexes are formed
What are the three stages for complement proteins to destroy microbes?
- promote phagocytosis - coat microbes in a process called opsonisation which promotes the attachment of a phagocyte to a microbe
- promote inflammation - bind to mast cells to release histamine
- cause cytolysis by destroying microbes
What is opsonisation
In the complement system when a fragrame coats a microbe to promote the attachment of a phagocyte to the microbe
What are cytokines?
Small protein hormones that stimulate or inhibit normal cell function
What are cytokines secreted by?
Leukocytes
Name three types of cytokines
Interleukins
Interferons
Tumour necrosis factor
What do interleukins do?
Mediators between leukocytes - mostly produced by T-helper cells
What do interferons do?
Involved in anti-viral responses
What does tumour necrosis factor do?
Promotes accumulation of neutrophils and macrophages to cause cell death
How do interferons work?
They interfere with viral replication
Attach and penetrate a cost cell to prevent it replicating
What is phagocytosis
Cell digestion
What attracts phagocytic cells to sites of inflammation
Chemotaxis
2 major types of phagocytes?
Macrophages (monocytes in blodd) and neutrophils
Are phagocytes selective
no
What type of phagocyte is also an antigen presenting cell?
Macrophages
Two types of macrophages
Wandering and fixed
Where can you find fixed macrophages?
Histiocytes
Kupffer cells
Alveolar
Microglia - nervous tissue
Langerhands - skin
Tissue macrophages - spleen, bone marrow and lymph nodes
5 stages of phogocytosis
- chemotaxis - release chemicals to activate complement and attract phagocytes
- Adherence - of phagocyte to target
- Ingestion - engulf microbe
- Digestion - lysozymes and digestive enzymes
- Excretion - of indigestible material
What are natural killer cells
Non-specific lymphocytes
The account for 5-10% of lymphocytes
Where do you find natural killer cells
Blood, lymph nodes, spleen and bone marrow
What do natural killer cells do?
They attack anything they don’t recognise
How do natural killer cells perform phagocytosis?
Realease granules called perforin
Perforin inserts into the cell membrane and create a channel for tissue fluid which causes
cytolysis
What is inflammation
A non-specific defensive response to tissue damage
What can cause inflammation?
Pathogens, abrasions, chemicals, cell distortion, extreme temperature
Is inflammation specific
No - it’s non-specific so the response to different insults is the same
What are the five cardinal signs of inflammation
Redness
heat
pain
swelling
loss of function
What are the first stage of inflammation
- vasodilation and increased permeability - allows additional blood to the area
Increased permeability permits movement of immune cells
Together these create redness, swelling and heat.
Why does inflammation create pain
Pain is the result of injury from neurons and toxic chemicals
What is the second stage of inflammation
Emigration of phagocytes (via chemotaxis)
Neutrophils squeeze through vessal wall
Monocytes follow
Dead phagocytes accumulate as puss
What is stage three of inflammation
Tissue repair
What do inflammatory mediators do?
Coordinate the inflammatory response
4 inflammatory mediators
Histamine
Leukotrienes
Kinins
Prostaglandins
Where does histamine come from and what does it do?
Released by mast cells and basphils - causes vasodilation and increased permeability
Where do leukotrienes come from and what do they do?
Released by basophils and mast cells.
Attract phagocytes and increase vessel permeability
What are kinins and what do they do?
Proteins that induce vasodilation and increased permeability
What are prostaglandins and what do they do?
Lipids from damaged cells
Enhance effects of histamine and kinins - intensify pain
What are the benefits of inflammation x 4
Promotes phagocytosis
Promotes immune response
Dilutes toxins
Fibrin formation - helps bind wounds
Harmful effects of inflammation x 4
Swelling
Pain
Adhesions and scar tissue
Atherosclerosis
4 possible outcomes of inflammation
- resolutions
- chronic inflammation
- granuloma - cellular attempt to contain foreign body
- fibrosis - scar tissue formation
What is a fever
Abnormally high body temperature
Why happens in the body when you get a fever
Hypothalamus thermostat is reset
Many bacterial toxins elevate body temperature - release fever causing cytokines such as interleukin-1
Interleukin-1 induces a fever
What does an elevated body temperature do?
Makes interferons more effective
Inhibits growth of some microbes
Speeds up reactions that aid repair
6 leukocytes
- Basophils and mast cells
- eosinophils
- neutrophils
- monocytes and macrophages
- natural killer cells
- B and T lymphocytes
Facts about basophils and mast cells
In blood basophils
in blood mast cells
Release histamine - vasodilates and heparin
Receptors for IgE
Facts about Eosinophils
Destroy parasitic worms via phagocytosis
Facts about Neutrophils
60% of leukocytes
Phagocytic
Granules release lysozymes that digest debris
Facts about monocytes and macrophages
Blood monocytes
Tissue - macrophages
Phyagocytic and secrete cytokines e.g interleukin-1 and TNF
Facts about natural killer cells
Target foreign cells, secrete perforin to induce cytolysis
B and T lymphocytes
Adaptive (specific) immunity and immunological memory
What can B and T lymphocytes do as part of the third line of defence?
Possess specificity for antigen - recognise self from non-self
Produce immune memory
Allows quicker and more effective attack with next encounter
What are cytokines?
Messenger molecules that mediate the connection between innate immune system and adaptive immune system
What are the effector cells of the adaptive immune system?
T and B lymphocytes
What does MHC stand for?
Major histocompatibility complex
What are major histocompatibility complexes?
Group of cell-surface proteins that allow the immune system to differentiate healthy body cells from non-self
What is the structure of major histocompatibility complex
4 polypeptide chains
Display a protein produced by the cell
What is major histocompatibility complex I
Located in all body cells except erythrocytes
Abnormal proteins mix with MHC-I to display flags on the cell surface
What is major histocompatibility complex II
Located only on the cell membrane of antigen presenting cells - macrophages and B-lymphocytes
What does major histocompatibility complex II present antigens to?
T-helper cells
What do T lymphocytes do?
Each t-lymphocyte has a unique t-cell receptor that only recognises a specific antigen
Where are T lymphocytes produced and where do they mature?
Produced in bone marrow
Mature in thymus
What are the two types of T-cell?
T-helper cells
Cytotoxic t-cells
What are t-helper cells also known as?
CD4 cells
What are cytotoxic t-cells also known as
CD8 cells
What to traits must t-cells have?
Self-recognition and self-tolerance
What does loss of self-tolerance lead to?
Autoimmunity
What is adaptive immunity
Body’s ability to defend itself against specific agents
What are the two types of adaptive immunity
cell-mediated and anti-body mediated
Facts about cell-mediated immunity
By t-lymphocytes
Cytotoxic t-cells attack antigens
Mostly against intra-cellular pathogens
Facts about anitbody-mediated immunity
By B-lymphocytes
Secrete specific antibodies
Mostly defend against extra-cellular pathogens
