4. B cells Flashcards
What is the difference between b cells and t cells?
B cells can recognise antigens in any biological form
Don’t need to communicate with another cell to be active
What stage of B cell development does gene to make a pre-BCR rearrangement occur?
Pre-B cell
What feature of development does the B cell go through while it is an immature B cell?
Gene rearrangement to replace surrogate light chains
Now has an Igm receptor
What receptors are present on a mature B cell?
IgM and IgD
What type of bond attaches the chains of an IgM receptor?
Disulphide
Where are the genes for the heavy chain of the IgM located?
IgH locus on chromosome 14
Which C region is essential to make an IgM BCR?
Cμ
What allows variation within the V region of the IgM receptor?
Random recombination of VDJ segments
What regions code for the light chain of IgM receptors?
Igκ on chromosome 2
or IgI on chromosome 22
What is positive selection?
Expression of a complete BCR
What is negative selection?
Discarded if bind to self-antigen too strongly
Why are checkpoints not as stringent for B cells as T cells?
B cells have a much shorter lifespan
Describe what happens when an antigen binds to the BCR
Triggers phagocytosis
Present antigen on MHC-II
Upregulation of CD40 (co-stim receptor) and cytokine receptors
What happens between Antigen binding to a BCR and activation of the B cell?
B and T cells for the specific antigen meet in the lymph node
How do helper T cells activate B cells?
Activated Th cells recognise antigen presented
T cell increases costimulatory molecules which bind to CD40 on B cells
Release cytokines to cause proliferation and differentiation of B cells
What causes isotype switching?
CD40-CD40L interaction and cytokines released by the Th cells
What is affinity maturation?
Affinity of antibodies produced in response to an antigen increase with prolonged or repeat exposure
What is an epitope?
Any biological molecule
What is the first antibody made by B cells?
IgM
What are the functions of Ig?
Activate complement
Clump microbes for elimination
What is the most common antibody?
IgG
What are the functions of IgG?
Neutralisation
Agglutination
Opsonisation
Complement activation
What antibody can cross the placenta?
IgG
Has implications in grave’s disease
What are the roles of IgE?
Fight helminth disease and cause allergic reactions
What receptors does IgE bind to on eosinophils?
FcεR
What receptors does IgE bind to during an allergic reaction?
Fc receptors on basophils and mast cells
What role does IgA play in immunity?
Mucosal immunity
Where is IgA produced?
Mucosal lymphoid tissues
How is IgA transported across epithelia?
poly-Ig receptors
Which antibody is acquired through breastmilk?
IgA
What vaccine stimulates IgA immunity?
Oral poliovirus vaccine
What is the least common antibody?
IgD
What is the role of IgD?
Bind to mast cells and basophils to cause the production of anti-microbial peptides
What are the regions on an antibody?
Antigen binding site
Complement binding site
Fc portion
What are the functions of antibodies?
Neutralisation Opsonisation and phagocytosis Complement activation Antibody-dependent cellular toxicity Eosinophil/mast-cell mediated reactions
What is neutralisation?
Antibody binds to microbes and toxins and stops them from entering cells
What receptor is IgG recognised by?
FcyR1 on neutrophils, macrophages and DCs
Which increases phagocytosis
What binds to the complement binding site on an antibody?
C1q
What is antibody related cellular toxicity?
NKs bind to antibody coated cells and destroy them
What receptor on NK cells binds to IgG?
FcyRIII
What is CVID?
Common Variable Immune Deficiency
Lack IgG, M and A
What does CVID result in?
Infections of lungs and GIT from age 6
How is CVID treated?
IV Ig
What is selective IgA deficiency?
B cells fail to differentiate into IgA producing plasma cells
Have recurrent sinopulmonary infections
What disease is selective IgA deficiency associated with?
Coeliac’s disease
What is x-linked Agammaglobulinaemia?
Mutation in Bruton’s tyrosine kinase
B cells are absent
Recurrent bacterial infections starting from 3-6 months
