Foundations in Immunology 2 Flashcards
What are the functions of the lymphatic system?
- Drainage of tissue
- Absorption and transport of fatty acids and fats
- Immunity
- Removal of ISF from tissues
What direction does the lymphatic system carry fluid?
Away from the tissues
What are the 3 phases of immune defence?
- Recognition of danger
- Production of specific weapons
- Transport of weapons to site of attack
Where does the recognition stage take place?
Secondary lymphoid tissues (lymph nodes, spleen and mucosal associated lymphoid tissues)
What are primary lymphoid tissues?
- Where the lymphocytes (B and T cells) originate and receiver their early training
- Bone marrow and thymus
How does haematopoiesis vary with age?
Where it takes place
What is the thymus?
Site of T cell maturation
What can be found in the thymus?
- Macrophages
- Dendritic cells
- Thymocytes
What are secondary lymphoid organs?
Site of lymphocyte activation by antigens
What is the spleen made up of?
Red and white pulp
What is the primary function of the red pulp of the spleen?
Filter the blood of antigens, microorganisms and defective or worn-out red blood cells
What is red and white pulp made of?
- Red pulp: several different types of blood cell
- White pulp: mainly lymphocytes
Where do B and T cells gather in the spleen?
- B cells: Region between PALS and the marginal sinuses
- T cells: PALS
What happens when T cells are activated?
They migrate into the lymphoid follicles to give the B cells that life-saving secondary signal
What activates T cells?
APCs
What is a feature of secondary lymphoid tissue (excluding the spleen)?
High endothelial venules which allow lymphocytes to escape from the blood vessels
What are Peyer’s patches?
- Patches of smooth cells embedded in the villi-covered cells that line the small intestine
- MALT
What do Peyer’s patches lack?
Incoming lymphatic system
How do antigens gain entry to Peyer’s patches?
- M cells transport Ag from the lumen of the intestine to the Peyer’s patch.
- They enclose Ag in vesicles called endosomes which are then transported across the M cells
- Ag are spat out and then carried by the lymph to the lymph nodes
What can asymmetric tonsils in adults indicate?
- Viral infection
- Lymphoma
- Squamous cell carcinoma
What kind of cancers can develop in areas of the lymphatic system?
- Lymphoma
- Thymus cancer
- Multiple myeloma
- Leukaemia
- Tonsillar cancer
- Adenoidal cancer
What materials are most commonly spread via the lymph vessels?
- Fragments of tumours
- Infected material
What is lymphangitis?
Infection of lymph vessel walls
Describe adaptive immunity.
- very specific
- Immunological memory
How do secondary responses differ to primary responses ?
- More rapid
- Larger
- Qualitatively different
Why does immunological memory occur?
- Each exposure to a particular antigen causes and expansion in the clone of lymphocytes which react to that antigen
- Stimulation of naïve lymphocytes by exposure to antigen causes some lymphocytes to become memory cells
How do memory B ad T cells differ to their naïve counterparts?
- Memory B cells produce antibodies that bind to the antigen with a much higher affinity than naïve B cells
- Memory T cells react much more quickly than naïve T cells
How is active immunity conferred?
By a host response to a microbe or microbial antigen
How is passive immunity conferred?
By adoptive transfer of antibodies or T lymphocytes specific for the microbe
What do both active and passive immunity provide?
Resistance to infection and are specific for microbial antigens, but only active immune responses generate immunological memory
What are 2 examples of passive immunity?
-Maternal Abs transferred to foetus
Natural active immunity
Occurs during infection. It is active because lymphocytes are activated by antigens on pathogens surface
Artificial active
Injecting or taking antigens by mouth. Takes time for T and B cells to be activated but gives long lasting immunity
Natural passive
Mother to child through placenta or milk
Artificial passive
Used during potentially fatal diseases. provides an instant response but only temporary as Abs are not the body’s own so memory cells are not created.
Where are B cells produced?
-Bone marrow
What do B cells mature into?
Plasma cells
What are plasma cells responsible for?
Antibody production
What do B cells express?
Surface immunoglobulin (sIg) which is the antigen receptor for the B cell
Why is it more important to tolerize T cells?
Both B and T cells can be made tolerant but B cells cannot make Ab to most antigens without the help of T cells
What is an antigen?
Any substance capable of triggering an immune response
How does an antigen announce its foreignness?
By means of intricate and characteristic shapes called epitopes which protrude from its surface.
Describe the structure of an antibody.
- Y shaped
- Contains heavy chains and light chains
- Split into Fc region (tail) and Ag binding region (Fab) (arms)
- Contains disulphide bonds
What are the 2 types of light chains that exist in mammals?
- lamda
- kappa
- in each Ab, only 1 type is present and the 2 chains are identical
What defines Ig class of Ab?
The heavy chain
What are the 2 regions of heavy chains/
- A constant region (same for all Ig classes)
- A variable region that differs between different B cells
What are the 5 types of mammalian Ig heavy chains?
- alpha
- gamma
- delta
- mu
- epsilon
What are the 5 different classes of Abs?
- IgM
- IgG
- IgA
- IgE
- IgD
IgA
Protects mucosal surfaces, resistant to stomach acid
IgD
No known Ab function
IgE
Defends against parasites, causes anaphylactic shock
IgM
Good at fixing compliment and opsonization
IgG
Good optimizer
How can B cells be activated?
- T cell dependent activation
- T cell independent activation
What is T cell dependent activation?
Requires a signal from the clustered BCR along with signal from a T cell in which a protein on the surface of a T cell which recognises the same antigen as the B cell binds to a receptor on the B cell
What is T cell independent activation?
It can happen when huge numbers of BCR are clustered together by an antigen with a very large number of repeated epitopes- a mitogen
What is the first Ab that B cell produce when activated?
IgM
What is transcytosis?
Process by which IgA binds to the poly Ig receptor at the base of an epithelial cell and is transported across the cell and released into the lumen by proteolytic cleavage
What can enhance B cells response to Ag?
Binding of CR2 on B cells
