IMMUNOLOGY Flashcards
What must the immune system do in order to be effective?
Must discriminate self from non-self
Describe innate immunity
Non-specific Instinctive Present from birth First line of defence Based on physical and chemical barrier and phagocytosis (No lymphocyte involvement)
Give examples of physical and chemical barriers used in innate immunity
Skin, mucociliary escalator, gastric acid, hairs, lysozymes
What is the function of a lysozyme?
To destroy bacterial cell walls
Describe adaptive immunity
Specific Acquired/learned immunity Requires lymphocytes Antibodies Memory and quicker response
Name 3 polymorphonuclear leukocytes
- Neutrophil
- Eosinophil
- Basophil
Name 3 mononuclear leukocytes
- Monocytes
- T lymphocytes
- B 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?
Antigens 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 a T helper 1 (CD4)?
Helps immune response against intracellular pathogens
Secretes cytokines
What is the function of a T helper 2 (CD4)?
Helps produce antibodies against extracellular pathogens
Secretes cytokines
What is the function of cytotoxic T cell (CD8)?
Kills cells directly by binding to antigens - they induce apoptosis
What is the function of T reg?
They regulate the immune response
Which cells express MHC 1?
All nucleated cells
Which cells express MHC 2?
Antigen presenting cells - macrophages, B cells and dendritic cells
Which MHC would an intracellular antigen (endogenous) lead to the expression of?
MHC 1
Which MHC would an extracellular antigen (exogenous) lead to the expression of?
MHC 2
What type of T cell binds to MCH 1?
Cytotoxic T cells (CD8)
What type of T cell binds to MCH 2?
Helper T cells (CD4)
What do B cells differentiate into?
Plasma cells
What do plasma cells 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 MHC 2 on an APC
Which interleukin is secreted when a helper T cell is bound to a T cell receptor?
IL-2
IL-2 binds to an IL-2 receptor on the T cell and produces positive feedback mechanism leading to division and differentiation
How many antibodies can each B cell make?
Only 1 antibody which 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 to an antigen
Phagocytosis
Epitope is displayed on the surface of the B cell bound to an MHC 2
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
Name 5 immunoglobulins
IgG IgA IgM IgD IgE
What are the 2 most common immunoglobulins?
IgG (70-75%) and IgA (15%)
What is an IgE response associated with?
Hypersensitivity allergic response and defence against parasitic infections
What is the predominant Ig in mucous secretions?
IgA
Which region of an antibody binds to antigens?
The Fab region
Which region of an antibody binds to B cells?
The Fc region
Name 4 types of cytokines
- Interferons (IFN)
- Interleukins (IL)
- Colony Stimulating factors
- Tumour necrosis factors (TNFa &b)
What is the function of interferons?
Produce antiviral proteins
IFNy - released by activated Th1 cells
What is the function of interleukins?
Interleukins causes cell division and differentiation
What is the function of colony stimulating factors?
CSF causes division and differentiation of bone marrow stem cells
What is the function of tumour necrosis factors?
TNF mediates inflammation and cytotoxic reactions
What is the function of chemokines?
Chemokines attract leukocytes to the site of infection
Give examples of secondary lymphoid tissue
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 mechanism 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 that more neutrophils etc are in 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 radical are highly reactive and can destroy pathogens
What mechanisms or cells are involved in O2 independent killing of microbes?
Lysozyme, defensives, TNF, pH
What are the complement system plasma proteins derived from?
Liver
What are the 3 main outcomes of complement system activation?
- Pathogen lysis
- Activation of leukocytes
- Increased phagocytosis
Name the 3 complement activation pathways
- Classical
- Lectin
- Alternative
What activates the classical complement pathway?
Antibodies
What activates the Lectin complement pathway?
Mannose binding protein
What activates the alternative pathway?
Bacterial cell walls and endotoxin
Describe Th1 (CD4) activation
Antigen presenting cell presents antigen with MHC II to a naïve CD4 T-cell
Stimulation with high levels of IL-12 activate naïve cells to CD4 T helper 1 cells
Th1 cells travel to secondary lymphoid tissue
Proliferate (clonal expansion)
Recognise antigen on infected cells with MHC II via T cell receptor (CD4)
Th1 secretes INFy causing apoptosis
Describe cytotoxic (CD8) T cell activation
Antigen presenting cell presents antigen with MHC 1 to a naive CD8 T cell
Activation to a cytotoxic T cell
Chemokines released –> inflammatory cell recruitment
Proteolytic granules release perforins and granulysin –> apoptosis and killing of pathogen
IFN release –> macrophage activation –> intracellular killing
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
Name things Th 1 cells do
Produce IL-2, IFNy and TNFb
Activate macrophages –> inflammation
Promotes production of cytotoxic T cells
Induce B cells to make IgG antibodies
Name things Th 2 cells do
Produce IL-4,5,6,10
Activate eosinophils and mast cells
Important in secondary infections and allergy
Induce B cells to make IgE - promotes release of inflammatory mediators
Why is innate immunity needed?
To handle pathogens we need a rapid response to
What are pattern recognition receptors (PRRs) a receptor for?
Pathogen-associated molecular pattern molecules (PAMPs)
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?
Send signals to the nucleus to secrete cytokines and interferons –> initiate tissue repair
Enhanced TLR signalling = improved immune response
What is the main function of NLR’s?
Detect intracellular microbial pathogens
Release cytokines and can cause apoptosis if the cell is infected
What disease could be caused by a non-functioning mutation of NOD2?
Crohn’s disease