Topic 6 - The Immune System Flashcards
What is a pathogen?
Any organism which can invade the body and cause disease, such as pathogenic bacteria, fungi, viruses and prions
What is an extracellular pathogen?
In which body parts do they proliferate?
- One which invades the body but not its cells
* Skin, gut, lungs, bodily fluids
What is an intracellular pathogen?
One which invades our cells and exploits their functions in order to proliferate
What is the lymphatic system?
The network of tissues and organs which help the body rid itself of toxins, waste and other unwanted material
What are the cells of the innate immune system?
- Granulocytes
- Monocytes
- Lymphoid cells
What is haematopoiesis?
The process which manufactures blood cells
What is the primary function of the lymphatic system?
To transport lymph throughout the body
What is lymph?
A fluid which contains infection-fighting white cells
What are antigens?
Any substance which causes your body to initiate an immune response and produce antibodies against it
What are the primary lymphoid organs?
- Bone marrow
* Thymus
What are the secondary lymphoid organs?
- Lymph nodes
- Spleen
- Tonsils
What are facultative intracellular pathogens?
Pathogens which can either proliferate outside or inside the host cells
What are obligate intracellular pathogens?
Pathogens which can only proliferate inside the host cells
What disease is an example of an obligate intracellular pathogen?
Plasmodium falciparum, aka malaria
What are the two types of intracellular pathogen?
- Facultative
* Obligate
What is meant by the term antigenicity?
The ability of an antigen to trigger an immune response, which depends on the ability of the host animal to recognise the substance/cell as an antigen in the first place
What are the immune system’s two lines of defence?
- Innate immune system
* Adaptive immune system
What are some of the characteristics of the innate immune system?
- Found in all multicellular organisms
- Non-specific
- Exposure quickly leads to response
- No immunological memory
- Components: leukocytes, epithelial and connective tissue
What are some of the characteristics of the adaptive immune system?
- Exclusively found in jawed vertebrates
- Antigen-specific response
- Delayed maximal response
- Exposure leads to immunological memory
- Components: lymphocytes (B and T)
What are the main components of the adaptive immune system?
- B and T lymphocytes
- Antigen-presenting cells (APCs)
- Cytokines (signalling molecules)
What are the components of the innate immune system?
- Antimicrobial substances
- Phagocytosis
- Cytotoxicity
- Inflammation
- Anatomical barriers
What are some examples of antimicrobial substances?
- Lysozyme
- Complement
- Interferons
Where is lysozyme found?
- Tears
- Saliva
- Mucus
What is Complement?
Where is it found?
- A sequence of about 20 proteins
* Bodily fluids, including blood
What are the three elements of the cascade reaction which Complement causes?
- Self amplification
- Feedback control
- Rapidity
What are the three types of immune stem cells?
- Granulocytes
- Monocytes
- Lymphoid cells
What is opsonin?
A soluble molecule which binds to pathogens or antigens to promote their uptake by phagocytosis
What is phagocytosis?
The process by which some white cells engulf and destroy pathogens, cellular debris and toxins
What are eosinophils?
A type of white cell
How do eosinophils work, what antigen are they especially affective against?
- They secrete degradative enzymes and toxic substances on to the target cell
- Parasites
How do NK cells work?
They release proteins in to the space between themselves and the target cell, which perforate the target cell membrane and enable pro-apoptotic substances to enter the target cell
What are the two main types of cytotoxic cells?
- Eosinophils
* NK cells
What antigen are NK cells especially effective against?
Intracellular pathogens/cancerous cells
What is apoptosis?
Programmed cell death
What is the purpose of inflammation?
To isolate, inactivate and remove the causative agent and damaged tissue
What are the hallmarks of inflammation?
- Redness
- Swelling
- Heat
- Pain
Where are leukocytes found (in mammals)?
Bone marrow
How does lysozyme work?
It is an enzyme which splits the chemical bonds (sugars and peptides) that hold together bacterial cell walls, damaging them and so killing the bacterium
Why do bacteria become resistant to antibiotics?
As a result of DNA mutations
What is beta-lactamase?
An enzyme produced by antibiotic-resistant bacteria
How do beta-lactamases work?
By breaking the structure of the antibiotic
What are the characteristics of granulocytes?
- They have secretory granules in their cytoplasm
- They make up 50-70% of circulating white cells
- They are sub-divided in to 3 categories
What are the three sub-categories granulocytes are divided in to?
- Neutrophils
- Basophils
- Mast cells
What is a macrophage?
A type of cell responsible for detecting, engulfing and destroying pathogens and apoptotic cells
What is a phagocyte?
A type of cell capable of engulfing and absorbing bacteria and other small cells and particles
What is a macrophage?
A type of cell responsible for detecting, engulfing and destroying pathogens and apoptotic cells which also act as a link between the innate and adaptive immune systems by acting as “antigenpresenting cells” to T cells, and secreting Complement components and cytokines
What do dendritic cells do?
Patrol the outer surface of the body to identify possible pathogens
What are the characteristics of lymphocytes?
- They make up 25-35% of circulating white cells
- They’re involved in the innate immune system through cytotoxicity
- They can attack cancer cells
What are neutrophils?
The most abundant subtype of circulating white cell
What do basophils and mast cells do?
Contribute to inflammatory response by producing histamine
What can trigger inflammation?
- Histamine
- Serotonin
- Prostaglandins
- Heparin
- Bradykinin
What do NK cells target?
Cells which have become infected with intracellular pathogens, especially cancer cells
What are examples of anatomical barriers?
- Skin
- Mucous membranes of respiratory, GU and GI tracts
- Saliva, tears, nasal secretions
- Stomach acid
What is an effector cell?
A cell of various types which actively responds to a stimulus and effects some change
What is an MHC molecule?
A cell which is on the outside of immune cells and whose purpose is to sense foreign antigens
What are major histocompatibility complexes (MHCs)?
Cell surface molecules which present antigenic peptides to T cells
What are the main components of the adaptive immune system?
- B and T lymphocytes
- Antigen-presenting cells
- Cytokines
What are cytokines?
Signalling molecules, how the cells of the immune system communicate
What are antigen-presenting cells (APCs)?
An immune cell which detects, engulfs and informs the adaptive immune response about an infection
What are cytokines?
Signalling molecules; the chemical signals through which immune system cells comunicate
What are some of the functions of cytokines?
- Activate/inactivate immune reactions
- Help maturation of lymphocytes
- Recruit immune cells to sites of infection
Where do T cell precursors migrate to?
The thymus
What type of cell do both T and B cells start out as?
Progenitor cells
What are granzymes?
Enzymes which trigger apoptosis
What type of cells can T cells and B cells differentiate in to?
- Effector cells
* Memory cells
What is an epitope?
The part of an antigen molecule which the antibody attaches itself to
How is isotype switching achieved?
By changing the expression of the non-variable portion of the H chain
What is tolerance?
The process by which the body recognises self-antigens and healthy tissues
What mechanism ensures the elimination of self-reactive T cells?
Negative selection
What is immunological tolerance?
The process by which the body recognises self-antigens and healthy tissues
What would be the effect of a defect in negative selection?
It could potentially cause autoimmune dise
What does idiopathic mean?
A disease which arises from internal dysfunctions with no known cause
What is HLA?
A group of proteins which are resonsible for the regulation of the immune system
In people who have the high risk HLA variant, what are the factors which could trigger autoimmune disease?
Exposure to certain infections or toxins (including tobacco smoke)
Define an allergen
Any non-self protein which is tolerant to most people’s immune systems but in certain susceptible individuals, triggers a prologned inflammatory response
Which of the divisions of the peripheral nervous system could counteract the dangerous reduction in heart activity caused by anaphylaxis?
The sympathetic system as it increases heart rate and blood pressure
What is immune system evasion?
The mechanisms by which cancer and other pathogens are able to elude the immune system
What are granzymes?
Serine proteases which induce apoptosis in target cells
What are serine proteases?
A class of enzyme - one which cleaves peptide bonds in proteins
What are the functions of T cells?
To directly attack cells infected with viruses
To regulate the immune system
Where do T cells mature?
The thymus
What are CD8+ T cells?
Killer, or cytotoxic, T cells
Where do T cells migrate to once they are matured?
- Spleen
- Lymph nodes
- Bone marrow
- Blood
What are CD4+ T cells?
Helper T cells
How many classes of antibodies are there?
Five
What do helper T cells do?
- Assist B cells to produce antibodies
* Assist killer T cells in attacking foreign substances
What are the five classes of antibody?
- IgA
- IgD
- IgE
- IgG
- IgM
What is IgA’s main function?
To help prevent colonisation by pathogens
Where is IgA mainly found?
- B cell membranes
* Mucus membranes
Where is IgD mostly found?
B cell membranes
What is IgD’s main function?
Antigen internalisation (helps activate B cells, binds to basophils and mast cells to activate them)
What is IgE’s main function?
- Prevents parasitic infections
* Mediates allergic reactions
What is special about IgG?
It is the only antibody which can cross the placenta
What is IgG’s main function?
- Neutralises pathogens such as viruses and bacteria
* Immunological memory
Where is IgG mainly found?
Blood
Where is IgE mainly found?
- B cell membranes
* Biological fluids
Where is IgM mainly found?
- B cell membranes
* Blood
What is IgM’s main function?
Early immune reaction
Which types of pathogens are extracellular pathogens?
- Bacteria
- Fungi
- Parasites
Which types of pathogens are intracellular pathogens?
- Viruses
- Some bacteria
- Some parasites
What type of stem cells are precursors to immune system cells?
Haematopoeitic stem cells
What is special about haematopoeitic stem cells?
They can differentiate into one of three types of immune system cells
What are the immune system cells which haematopoeitic stem cells can differentiate into?
- Granulocytes
- Monocytes
- Leukocytes
What are the three main components of the immune system?
- Primary lymphoid organs (bone marrow, thymus)
- Seconary lymphoid organs (lymph nodes, spleen, tonsils)
- Lymphatic vessels
Cancer cells can trigger an immune response. How is this possible given that they are “self” cells?
Their expressed proteins are different from the “normal” proteins expressed by the body so therefore not antigenic
With regards to the immune system, what do the terms “cell dependent” or “cell independent” mean?
- Cell independent mechanisms do not require any cells of the immune system to be present
- Cell dependent mechanisms are directly mediated by cells of the immune system
Which components of the innate immune system are “cell independent” (not mediated by cells of the immune system)?
- Anatomical barriers
* Antimicrobial substances
Which components of the innate immune system are “cell dependent” (are mediated by cells of the immune system)?
- Phagocytes
- Cytotoxicity
- Inflammation
Why is lysozyme toxic for bacteria but not for human cells?
Because human cells do not have bacterial sugar molecules
What is a cascade reaction?
A reaction which relies on the presence of a series of molecules that exist in an inactive state. They remain inactive until a specific trigger activates the first member of the series, which then activates the second, and so on
What is Complement’s effect on a cell?
It attacks many sites on the cell surface, punching a large number of tiny holes through the membrane, which can cause cell death
How do interferons work?
They are a chemical barrier which can interfere with the life cycle of a virus
What type of cell is the main kind of phagocyte in the bloodstream?
Neutrophils
What substances does inflammation trigger the release of?
- Histamine
- Serotonin
- Prostaglandins
- Heparin
- Bradykinin
What is bradykinin?
A peptide which promotes inflammation by causing arterioles to dilate and making veins constrict
Which naturali antimicrobial substance has a similar mechanism of action to that of antibiotics?
Lysozyme - it splits the chemical bonds which hold together the molecular components of bacterial cell walls
What are antigen-presenting cells (APCs)?
A group of functionally defined cells which are capable of taking antigens and presenting them to lymphocytes in a form they can recognise
Which molecules are capable of secreting cytokines?
- Lymphocytes
- Macrophages
- Fibroblasts
What type of cells are formed when a mature lymphocyte encounters its antigen?
- Memory cells
* Effector cells
What can occur if negative selection does not eliminate lymphocytes that react with self-antigens?
Autoimmune reactions
In order to function properly, T cell receptors also need to be co-activated with what other molecules?
CD4 and CD8 molecules
What are CD8+ T cells?
A class of T lymphocyte that triggers the destruction of cancer cells and self-cells infected by intracellular pathogens
What are CD4+ T cells?
A class of T lymphocyte involved in the activation of the innate and adaptive immune system through the production of cytokines
What are the main stages of lymphocyte maturation and differentiation?
- During early differentiation, B and T cells are exposed to endogenous ligands (molecules derived from host tissues/cells) which bind to their receptors
- Only cells with functional receptors survive (+ve selection)
- The selected cells are then exposed to self-antigens in order to establish immunological tolerance (-ve feedback) - only cells that can recognise non-self antigens survive
- At first encounter with their antigen, mature cells differentiate into either effector or memory cells
Where do B cell precursors mature?
Entirely in the bone marrow
Where do mature B cells migrate to?
- Lymph nodes
* Spleen
Helper T cells are characterised by the expression of which co-receptor?
CD4
Cytotoxic T cells are characterised by the expression of which co-receptor?
CD8
All T cells are activated by the binding of a T cell receptor with what?
The antigen in a complex with the MHC
What are B cells’ main functions?
- The production of antibodies
- The presentation of antigens to helper (CD4+) T cells
- The development of memory B cells
What are the two main differences between a B cell receptor and a T cell receptor?
B cell receptors:
- Do not need an MHC molecule, instead bind directly to their antigen
- Can be secreted and circulate in the bloodstream/bodily fluids in the form of a soluble immunoglobulin (antibody)
What are somatic mutations?
Genetic mutations which occur in the soma (any cell not involved with reproduction)
What is isotype switching?
The molecular mechanism by which B cells change the type of immunoglobulin they express (e.g. from IgM to IgG)
How are B cells activated?
When their receptor binds to either soluble or membrane bound antigens
In the lymphoid organs, B cells are activated by which cells?
CD4+ T cells
Which type of mutations change the affinity of the B cell receptor for the antigen?
Somatic mutations
B cells with the highest or lowest affinity for the antigen will survive?
The highest
What mechanism enables the immune system to recognise healthy tissues and self-antigens
Tolerance. All autoimmune diseases are caused by a defect in self-tolerance
What mechanism ensures the elimination of self-reactive T cells?
Negative selection
What would be the effect of a defect in negative selection?
It could cause autoimmune disease
What substance does IgE trigger the release of?
Pro-inflammatory molecules such as histamine
Which part of the peripheral nervous system could counteract the dangerous reduction in heart activity caused by anaphylaxis?
The sympathetic nervous system as it can increase heart rate and blood pressure
What type of lymphocyte and Ig isotype are involved in immunological memory?
- Memory B and T cells
- IgM
- IgG
What is meant by the term “active immunity”?
Resistance to infection with a specific pathogen, acquired as a result of antibody production by the immune system
What is meant by the term “passive immunity”?
Resistance to infection with a specific pathogen, acquired as a result of receiving the products of someone else’s active immune response (e.g. maternal antibodies passed on through breast milk)
Blood group A can receive blood from which other groups?
- O
* A
Blood group B can receive blood from which other groups?
- O
* B
Blood group AB can receive blood from which other groups?
- O
- A
- B
- AB
Blood group O can receive blood from which other groups?
- O
Which blood group is the “universal recipient”?
AB
Which blood group is the “universal donor”?
O
What is meant by the term “immune evasion”?
Mechanisms by which cancer cells and pathogens elude the immune system
