ICS Immunology Flashcards
What must the immune system do in order to be effective?
The immune system has to discriminate self from non-self.
Describe innate immunity.
Non-specific, instinctive, present from birth, first line of defence. It is focused around physical and chemical barriers and phagocytosis. No lymphocyte involvement.
Give examples of physical and chemical barriers used in innate immunity?
Skin, mucociliary escalator, gastric acid, hairs, lysozymes etc.
What is the function of lysozyme?
It destroys bacterial cell walls.
Describe adaptive immunity.
Specific, requires lymphocytes. Memory and quicker response.
Draw the haematopoesis flowchart
Give examples of 3 polymorphonuclear leukocytes.
- Neutrophils.
- Basophils.
- Eosinophils.
Give examples of 3 mononuclear leukocytes.
- Monocytes.
- B lymphocytes.
- T lymphocytes.
In which primary lymphoid tissue do T cells mature?
Thymus.
In which primary lymphoid tissue do B cells mature?
Bone marrow.
How do T cells recognise antigens?
For T cells to recognise antigens they must be displayed by an antigen presenting cell and bound to MHC1/2. T cells can’t recognise soluble antigens.
What is the function of T helper 1 (CD4)?
It helps the immune response against intracellular pathogens. Secretes cytokines.
What is the function of T helper 2 (CD4)?
It helps produce antibodies against extracellular pathogens. Secretes cytokines.
What is the function of Cytotoxic T cell (CD8)?
It can kill cells directly by binding to antigens; they induce apoptosis.
What is the function of T reg (FoxP3)?
They regulate the immune response.
Which cells express MHC1?
All nucleated cells express MHC1. e.g. a virus infected or cancer cell would express MHC1.
Which cells express MHC2?
Antigen presenting cells ONLY e.g. macrophages, B cells, dendritic cells.
Which MHC would an intracellular antigen (endogenous) lead to the expression of?
MHC1.
Which MHC would an extracellular antigen (exogenous) lead to the expression of?
MHC2.
What type of T cell binds to MCH1?
Cytotoxic T cells (CD8).
What type of T cells binds to MCH2?
Helper T cells (CD4).
What do B cells differentiate into?
Plasma cells. The plasma cells then produce antibodies.
What does a helper T cell bind to?
A T cell receptor which is bound to an antigen epitope which is bound to MHC2 on an APC.
Which interleukin is secreted when a helper T cell is bound to a T cell receptor?
IL-2. This then binds to an IL-2 receptor on the T cell and produces a positive feedback mechanism leading to division and differentiation.
How many antibodies can each B cell make?
Each B cell can only make 1 antibody. This 1 antibody can only bind to 1 epitope.
What happens to B cells that recognise ‘self’?
They are killed in bone marrow.
Describe the process of a T helper cell binding to a B cell.
A B-cell antibody binds an antigen -> phagocytosis -> epitope is displayed on the surface of the B-cell bound to an MHC2 -> TH2 binds to B-cells -> cytokine secretion induces B-cell clonal expansion -> differentiation into plasma cells and memory B cells.
Give 3 functions of antibodies.
- Neutralise toxins.
- Opsonisation.
- Activate classical complement system.
Which immunoglobulin is found in breast milk and other secretions?
IgA.
What are the 2 most common immunoglobulins?
IgG and IgM.
Which region of an antibody binds antigens?
The fab region.
Which region of an antibody binds to B cells?
The Fc region.
Name 4 types of cytokines.
- Interferons.
- Interleukins.
- Colony stimulating factors.
- Tumour necrosis factors.
What is the function of interferons?
Interferons produce antiviral proteins.
What is the function of interleukins?
Interleukins cause cell division and differentiation.
What is the function of colony stimulating factor (CSF)?
CSF causes division and differentiation of bone marrow stem cells.
What is the function of tumour necrosis factor (TNF)?
TNF mediates inflammation and cytotoxic reactions.
What is the function of chemokines?
Chemokines attract leukocytes to sites of infection.
Give examples of secondary lymphoid tissue.
The spleen, lymph nodes, mucosa associated lymphoid tissue - MALT.
Describe the process of phagocytosis.
- Pathogen binds to neutrophil/macrophage.
- Engulfment of pathogen.
- Phagosome formation.
- Lysosome fusion - phagolysosome.
- Pathogen is destroyed.
Give 3 examples of O2 dependent mechanisms of killing.
- Killing using reactive oxygen intermediates.
- Superoxides can be converted to H2O2 and then to hydroxyl free radicals.
- NO leads to vasodilation and increased extravasation and so more neutrophils etc are in the tissues to destroy pathogens.
What is the role of NO in killing pathogens?
NO leads to vasodilation and increased extravasation. This means more neutrophils etc pass into the tissues to destroy pathogens.
Why can superoxides be used to destroy pathogens?
Superoxides can be converted to H2O2 and then to hydroxyl free radicals. Hydroxyl free radicals are highly reactive and can destroy pathogens.
What mechanisms or cells are involved in O2 independent killing?
Defensins, lysozyme, pH, TNF.
Where are complement system plasma proteins derived from?
The liver.
What are the 3 main outcomes of complement system activation?
- Direct lysis- MAC formation.
- Opsonisation- increased phagocytosis (C3b)
- Inflammation- macrophage chemotaxis (C3a and C5a).
What activates the classical complement pathway?
Antibodies.
What compound prevents excessive activation of the classical complement pathway?
C1 inhibitor.
- C1 inhibitor leads to a negative feedback loop.
What activates the lectin pathway?
Mannose binding protein.
What activates the alternative pathway?
Bacterial cell walls and endotoxin.
What are the 3 different pathways that make up the complement system?
- Classical.
- Lectin.
- Alternative.
Which complement plasma proteins have opsonic properties when bound to a pathogen?
C3b and C4b.
What is the function of MAC in a pathogens’ membrane?
MAC is a leaky pore like channel. Ions and water pass through the channel and disrupt the intracellular microbe environment -> microbe lysis.
Which complement plasma proteins are pro-inflammatory and cause chemotaxis and activation of neutrophils and monocytes etc?
C3a and C5a.
What kind of immunity are PRR’s and PAMP’s associated with?
Innate immunity.
What are PRR’s a receptor for?
PAMP’s.
Name 3 receptors that make up the PRR family.
- Toll-like receptors (TLR).
- Nod-like receptors (NLR).
- Rig-like receptors (RLR).
What is the main function of TLR’s?
TLR’s send signals to the nucleus to secrete cytokines and interferons. These signals initiate tissue repair. Enhanced TLR signalling = improved immune response.
What is the main function of NLR’s?
NLR’s detect intracellular microbial pathogens. They release cytokines and can cause apoptosis if the cell is infected.
What disease could be caused by a non-functioning mutation in NOD2?
Crohn’s disease.
What is the main function of RLR’s?
RLR’s detect intracellular double stranded RNA. This triggers interferon production and so an antiviral response.
TLR’s are adapted to recognise damaged molecules. What characteristic do these damaged molecules often have in common?
They are often hydrophobic.
What kind of TLR’s can be used in vaccine adjuvants?
TLR4 agonists.
Give examples of diseases that can be causes by PRR’s failing to recognise pathogens.
- Atherosclerosis.
- COPD.
- Arthritis.
Give examples of 3 extracellular PRR.
- Mannose receptors.
- Scavenger receptors.
- TLR’s.
What is the function of mannose and scavenger extracellular receptors?
The induce pathogen engulfment.
Give an example of an intracellular PRR.
NLR.
Where are circulating PRR secreted from?
Epithelia, phagocytes and the liver. They can activate the complement cascade and induce phagocytosis.
What happens when a PAMP binds to a PRR?
The innate immune response and inflammatory response is triggered.
What is extravasation?
Leukocyte (WBC) migration across the endothelium.
What do macrophages at the tissues secrete to initiate extravasation?
TNF alpha.
Describe the process of extravasation.
- Macrophages at tissues release TNF alpha.
- The endothelium is stimulated to express adhesion molecules and to stimulate chemokines.
- Neutrophils bind to adhesion molecules; they roll, slow down and become stuck to the endothelium.
- Neutrophils are activated by chemokines.
- Neutrophils pass through the endothelium to the tissue to help fight infection.
What 2 compounds can act as C3 convertase?
- C4b2b - produced in the classical and lectin pathways.
2. C3(H2O)Bb - produced in the alternative pathway.