Functional anatomy Flashcards
What are leukocytes?
Cells of the immune response
Do most immune responses take place in tissues or blood?
Tissues
Blood is simply a transmit system
What are the two types of lymphoid tissue that are involved in the activation and production of IR?
Primary lymphoid organ - where lymphocytes are produced at all times
Secondary lymphoid organ - active when IR is triggered
What are the primary lymphoid tissues?
Bone marrow
Thymus
What cells give rise to cells T and B cells?
Haematopoietic stem cells
What happens in the bone marrow and thymus?
T and B cells undergo education by maturation
Antigen-specific
Can recognise antigens from pathogens and damaged cells
Educated to only recognise pathogenic cells - prevent autoimmunity
What are the secondary lymphoid organs?
Spleen - deals with antigens in the blood
MALT - deals with antigens on mucosal surfaces
Lymph nodes - deals with antigens present on tissues draining into local lymph nodes
Which of the lymphoid organs are encapsulated?
Spleen
Lymph nodes
What does MALT stand for?
Mucosa-associated lymphoid tissues
In which state do T cells enter the thymus?
As double-negative
Don’t express CD4 nor CD8
Following which process do T cells become double positive?
Thymic education
What is a double positive T cell?
Express both CD4 and CD8 genes on their surface
How is the large variety of TCRs produced?
Through random recombination of genes
Millions of possible combinations
What are the two stages of thymic education?
Positive selection
Negative selection
Explain the process of positive selection of T cells in the thymus
Positive selection selects working TCRs
Happens in the cortex of the thymus
T cells have default system of apoptosis so they are destined to die
If the T cells react weakly or do not bind to MHC - don’t receive survival signals
If interacts with MHC I = CD8
If interacts with MHC II = CD4
Explain the process of negative selection of T cells in the thymus
Prevents autoimmunity
Happens in the medulla of the thymus
CD4 or CD8 cells have default system of survival
If the TCRs bind to self-MHCs or self-peptides too stronly they receive apoptotic signal
What is the main goal of positive selection?
Select working TCRs
Where does positive selection take place?
In the cortex of the thymus
What is the main goal of negative selection?
Prevent autoimmunity
Where does negative selection take place?
In the medulla of the thymus
What percentage of T cells arriving from the thymus are allowed to recirculate lymphoid tissues?
2%
Where do antigen specific lymphocytes circulate?
Circulatory system
Lymphatic system
Describe the process of lymphocyte recirculation
During absence of infection -> antigen specific lymphocytes exist in small numbers
Constant recirculation to seek out their antigen
Lymphocytes enter the lymph nodes to see if antigen is present to which they are specific to
How do lymphocytes enter the lymph nodes?
Via the afferent lymphatic vessels
Directly from the circulatory system -> via high endothelial venule
What is the high endothelial venule (HEV)?
Specialised type of blood vessel endothelium that allows lymohocytes to enter lymph nodes
What happens if antigens lymphocytes are specific to are in the lymph nodes?
Lymphocytes stay in the lymph nodes
Proliferate
Differentiate into effector and memory cells
What happens if antigens lymphocytes are specific to are not in the lymph nodes?
Lymphocytes leave the lymph via the efferent lymphatic vessel
Drain into the circulatory system via the thoracic duct
How do antigens enter lymph nodes?
Soluble antigens -> drain into nodes via afferent lymphatics
Actively transported -> via dendritic cells
What is a type of dendritic cell found on the skin?
Langerhans cells
Process by which dendritic cells present antigens in lymph nodes
Dendritic cells wait for infection
If they recognise PAMPs or DAMPs via PRRs -> become activated
Phagocytose pathogens and become motile
Dendritic cells change properties
Begin to express MHC II and costimulatory molecules (CD80/86)
Drain into local lymph nodes via afferent lymphatics
Where do antigens in the tissues go?
To the lymph nodes
Where do antigens in the blood go?
To the spleen
What is the structure of the spleen?
Split into white and red pulp
What is the function of the white pulp of the spleen?
Deals with antigens
Contains periarteriolar lymphoid sheaths (PALS)
Marginal zone - follicles next to PALS
What is the structure of PALS in the white pulp of the spleen?
Sheath of lymphoid tissues around the arterioles of the spleen
Consists of T lymphocytes mainly
What is the marginal zone of the white pulp of the spleen made of?
Mainly B cells
Where in the spleen do T and B cells interact?
Mantel
What is the B-cell zone of the spleen called?
Marginal zone
What is the T-cell zone of the spleen called?
PALS
What happens at the mantel?
Interaction of B and T cells to generate an immune response against blood-borne pathogens
Where do most infectious agents enter the body?
Through the sub-mucosal tissues
What is the MALT in the gut called?
GALT
Containes Peyer’s patches - specialised, induce immune responses
What type of immune responses are induced in the GALT?
Adaptive immune response
What is the process by which MALT produces an immune response?
M cells transport antigen from the lumen of the gut to the underlying cells of the immune response (dendritic cells)
Partly acticated lymphocytes upon presentation to antigens move up to the lymph nodes where they become superactivated
Superactivated lymphocytes travel back to the gut at site of infection via efferent lymphatic vessels
What important function do T regulatory cells do in GALT?
Lymphocytes in the gut also meet commensal organisms and food antigens
T regulatory cells mediate tolerance to prevent overactivation of the antibodies
Why are the germinal centers of secondary lymphoid tissues important?
They are the powerhouses of the adaptive immune response
Critical events are tiggered upon infection
What processes happen in the germinal center?
Class switching
Clonal expansion
Generation of memory cells
Somatic hypermutation
Precursors to plasma cells mature into plasma cells
Formation of memory cells
What is class switching?
Non-specific antibodies IgM and IgD produced by B cells switch to specific IgA, IgG and IgE
What is clonal expansion?
Proliferation of T cells to expand lymphocyte number
What is somatic hypermutation?
Antibodies develop mutations to the variable parts
Antibodies bind better to the antigen
What are the three parts of the germinal center?
Dark zone
Basal light zone
Apical light zone
What mechanisms happen in the dark zone of the germinal center?
Clonal expansion
Somatic hypermutation
What mechanisms happen in the basal light zone of the germinal center?
Affinity selection for antigen on follicular dendritic cells
What mechanisms happen in the apical light zone of the germinal center?
Generation of memory cells
Generation of plasma cell precursors
Class switching
Describes what happens in the process of forming specific lymphocytes
APCs go to the T cell zone
Complement, soluble antigen and T cells go to the B cell zone
T cells are triggered to become follicular helper cells
B cells become centroblasts and then mature further into centrocytes
In the mantle zone - symbiotic activation
Move to the germinal center to undergo specialised processes
