Session 7: Adaptive Immunity 2 Flashcards
Where are B and T lymphocytes produced?
+ mature
T = produced in bone marrow and mature in thymus B = produced in bone marrow and mature in tissues following contact with antigen
When does lymphadenopathy occur?
When B and T cells are activated by antigens
Where do T and B lymphocytes accumulate?
In key lymphoid tissues:
MALT (mucosa associated lymphoid tissue)
Lymph nodes
Spleen
What are the antigen recognition receptors found on T-lymphocytes?
T cell receptors (TCR) with alpha and beta chains
What forms of antigens are recognised?
Peptides displayed by MHC molecules
There are different subtypes of antigen recognition.
What do helper T cells recognise?
What do Cytotoxic T cells recognise?
Helper T (CD4+) recognise peptide presented by MHC class II molecules Cytotoxic T cells (CD8+) recognise peptide presented by MHC class I molecules.
Binding by antigen to a TCR does not activate the T cell. What else is needed?
CD3 complex
Explain the costimulation of T-helper cells.
There are three signals needed to fully activate T cells.
Signal 1 which is the presentation of the peptide by the antigen presenting cells on the MHC class I or class II.
Signal 2 which is the activation of CD28 by B7
Signal 3 which is the activation of T cell by cytokines.
What different T helper cells can Th0 differentiate into?
Th1
Th2
Th17
Treg
Explain how Th0 (naive CD4+ T cell) turns into Th1.
Explain the role of Th1
This depends on the cytokine environment.
IL-12 (cytokine) will turn Th0 into Th1.
Th1 is a part of the cell mediated immunity response and excels at defence against intracellular and extracellular pathogens like bacteria, viruses and fungi.
Th1 stimulates activation and differentiation of CD8+ T cells, recruits and activates macrophages. Stimulates B cells to produce IgG or IgA.
Explain how Th0 turns into Th2.
Explain the role of Th2.
IL-4 will turn Th0 into Th2.
Th2 is a part of the humoral immunity which excels at defence against extracellular pathogens like parasites and worms.
Th2 stimulates B cells to produce IgE.
Stimulates Eosinophils and Mast cells.
Explain how Th0 turns into Th17.
Explain the role of Th17.
IL-1 and IL-6 which will recruit and activate Neutrophils.
Explain how Th0 turns into Treg.
Explain the role of Treg.
IL-10 and TGFbeta will turn Th0 into Treg.
Treg is important in tolerance and immune suppression.
Explain the differentiation of CD8+ T cells.
Naive CD8+ T cells goes to become Memory CD8+ T cells or Effector CD8+ T cells.
Effector CD8+ T cells can then become cytotoxic T cells and kill pathogens.
What does effector CD8+ T cells need in order to become cytotoxic T cells?
They need Th1 to stimulate the differentiation.
What is the antigen recognition receptor on B cells?
B cell receptor or BCR which are found on the membrane and bound to antibodies.
What’s unique for BCRs?
Every B cell has its unique specificity/combination of the antigen binding site.
What forms of antigens are recognised by BCR?
Macromolecules like proteins, polysaccharides, lipids and nucleic acids.
Small chemicals.
It’s important to note that BCR and therefore B cells do not need processed antigens presented by MHCs.
Explain activation of B lymphocytes.
It requires multiple signals.
Signal 1: An antigen can bind to BCR and cause processing of the antigen. This phagocytose the antigen.
There is also increased B7 costimulator numbers.
Signal 2: An already activated T helper cell (Th1 or Th2 depending on the antibody needed to be produced). This is TCR engagement and CD40L will switch IgM to a different isotype (IgA, IgG or IgE).
Signal 3: Cytokines and CD40 activation.
This causes proliferation of B cells and antibody production.
How does production of IgM differ to production of IgG, IgE and IgA?
IgM production is T helper independent.
The rest of the antibodies need T helper cells to isotype switch IgM into them.
How does affinity maturation occur?
By prolonged or repeated exposure of an antigen.
What are memory B cells?
B cells produced after exposure to an antigen. Upon re-challenger the memory B cells will give a faster, stronger and longer antibody response.
Explain how antigen stimulated B cells produce IgM.
They turn into plasma cells and then the plasma cells produce IgM.
Explain how antigen stimulated B cells produce IgG.
Needs stimulation by effector T helper cells (Th1) by the presence of IFNgamma.
Explain how antigen stimulated B cells produce IgE.
Needs stimulation by effector T helper cells (Th2) by the presence of IL-4.
Explain how antigen stimulated B cells produce IgA.
Needs stimulation by effector T helper cells (Th1) by the presence of TGFbeta.
What are the fates of B cells?
Plasma cells
IgG, IgE or IgA producing B cells.
Memory B cells
Why is the ratio of IgG to IgM important?
Because it will tell us whether an infection is acute or chronic?
How can you tell if an infection is chronic vs acute?
In a chronic infection IgG will be high.
In an acute infection IgM will be high.
Effector functions of IgG.
Fc-dependent phagocytosis
Complement activation
Neonatal immunity
Toxin/virus neutralisation
Effector functions of IgA.
Mucosal immunity
Effector functions of IgE.
Immunity against helminths and mast cell degranulation in allergies.
Effector functions of IgM.
Complement activation.
