11 Adaptive immune responses bring specificity Flashcards
B/ T cells provide specific immune response. They look very similar, but can be distinguished by their surface antigens
CD number (cluster of differentiation). A designation to allow antibodies to recognise different epitopes on the same molecule to be grouped together
What are primary lymphoid organs?
Primary where lympocytes develop
Bone marrow, thymus (T cells)
Secondary where immune responses initatied
Secondary lymphoid organs are where immune response is initiated.
Which areas respond to each antigen:
Antigens in tissue
Antigens in blood
Antigens at mucosal surfaces
Antigens in tissue - lymph node
Antigens in blood - spleen
Antigens at mucosal surfaces - MALT/ GALT
Each B cell expresses antibody of one specificity on its surface. How does this happen?
formed by splicing different variable and constant region genes together. This takes place in bone marrow
Usually B cells which would recognise self are terminated at the point, to prevent AI disease
What is role of the thymus
What CD antigens do they being to express?
Thymus does not develop in Digeorge syndrome.
Thymus decreases in size as we age, but still functions even in adults
mature T cells develop here from immature T cells
Outer cortex they receive maturation signals from IL7.
T cells rearrange gene segments to create unique T-cell receptor
All T cells aleadly have CD3, but they now start to express both CD4 and CD8. They will eventually pick either CD4 or CD8 to be positive (continue CD3 positive)
If T-cell can recognise individual MHC then they are released into circulation. T-cells which bind too strongly to MHC are terminated at the point, to prevent AI disease
What is life cycle of B/T cell
Start in bone marrow
Move into blood stream
T cell move to thymus
- Circulate in blood, and pass through spleen
- Move into tissues - circulate in lymphatics, back through thoracic duct which empties in left subclavian vein to rejoin circulation
- Move from lymphatics to lymph node
Both can move anywhere when required, if correct signal comes
Which cell types have these CD markers
CD3
CD4
CD8
CD3 All T cells
CD4 - CD4 T cells (T helper cell). HIV binds to CD4 molecule
CD8 - CD8 T cells
Which cell types have these CD markers
CD 14
CD19
CD20
CD 14 - monocytes/ macrophages
CD19 - B cells
CD20 - B cells
Why are T cells immature when they leave thymus?
Express CD3 and CD4 or CD8, with functional T-cell receptor
Still immunologically naive as not been activated by signals they receive when they recognise antigen presented by self-MHC
Lymphoid organs are compartmentalized into T-cell and B-cell areas
What is structure of lymph node
B cells in B cell follicles. They can become activated here following antigen stimulation, and proliferate into plasma cells which produce antibodies.
These follicles are surrounded by T cell zones
T cells respond to antigens brought by dendritic cells
What is structure of spleen?
B cells found in B cell follicles termed white pulp
T cells found in area called periareriolar lymphoid sheath
Where is MALT found?
Lymphocytes can respond to antigens from environment, by producing IgA and antibodies for mucosal secretions
There is also fat associated lymphoid clusters in the pleural, pericardial and peritoneal cavities
Small intestine in Peyer’s patches
Bronchi
Antibodies expressed on surface of B cells where they can bind to antigen directly, or be secreted by B cells as soluble antibodies
What is general structure of an antibody
four chain structure - 2x heavy chain, 2 x light chain
Held together by disulphide bridge
Specificity determined by sequences of three hypervariable regions on both heavy and light chain which together form Fab (fragment antigen binding) region
Static region termed Fc region
Flexible hinge joint where fab joins Fc region
How are different antibodies produced, which have different variable regions
Similar to T-cell receptor unique formation
DNA within B cell which codes for antibodies has two regions
VDJC genes code for heavy chain
VJC genes code for light chain
Variable splicing of genes, and random recombinisation creates new antibodies with new variable regions
Antibodies have different binding affinity depending on which Ig it is
What is function of each type of Ig
IgG (IgG1, IgG2, IgG3, IgG4) IgA IgM IgD IgE
IgG - most common (80% total), agglutinates batceria, fixes complement
IgA - (13% total) protects mucosal surfaces
IgM - (6% total) agglutinating bacteria, fixes complement
IgD - unknown function
IgE - helminths/ allergies
What is structure of each Ig and how many antigen binding sites
IgG IgA IgM IgD IgE
IgG - two heavy/ light chains (monomer) - 2 antigen binding sites
IgM - five monomers together (pentamer) - 10 antigen binding sites
IgA - two momomenrs together (dimer) - 4 antigen binding sites
IgD - two heavy/ light chains (monomer) - 2 antigen binding sites
IgE - two heavy/ light chains (monomer) - 2 antigen binding sites
