B cells and antigen recognition Flashcards
Where do B lymphocytes differentiate?
Bone marrow
What is the major function of B lymphocytes?
To produce antibodies
What can antibodies bind to?
- proteins
- polysaccharides
- small molecules such as toxins
How many different constant regions are there?
5
What does papain cleave antibodies into?
Fc and Fab
What are the 5 different isotypes of Ig?
- IgM
- IgG
- IgA
- IgE
- IgD
Which Ig isotype is never secreted?
IgD
Which Ig isotypes are found in the plasma?
IgG and IgM
Which Ig isotype is found in extracellular fluid and crosses the placenta?
IgG
Which Ig is mainly found in secretions?
IgA
What are the characteristics of IgM?
- Produced 1st in response
- Pentamer
- Effective first defence against bacteria
- Fairly low affinity
What are the characteristics of IgG?
- Produced late in the immune response
- Most abundant
- Crosses the placenta
How many subtypes of IgG are there?
4
What are the characteristics of IgA?
- Produced late in the immune response
- Can exist as monomers or dimers
- Major Ig in secretions
Which Ig is involved in the response to parasitic infections?
What does IgE do?
Induces degranulation of mast cella and basophils
What are the characteristics of IgD?
- Found as a receptor on the surface of naive lymphocytes
- Not secreted
- Function unknown
Which type of BCRs are found on naive B cells?
IgM and IgD
What happens when B cells encounter an antigen for the 1st time?
It proliferates massively
How are effector cells different to naive cells?
They are already class switched and quicker at reaching pathogens
What does isotype switching involve?
Changing the C domain of the heavy chain at DNA level
What are the 3 major functions of antibodies?
- Neutralization
- Opsonization
- Complement fixation
What are the 2 ways antibodies complete neutralisation?
- Prevents bacteria and viruses from adhering to and infecting cells
- Binding to toxins prevents cell damage
Why is neutralisation specifically important in response to viruses/intracellular bacteria?
Blocks internalisation
What is opsonization?
Where antibodies coat a bacteria to promote phagocytosis
How does opsonization demonstrate a link between the adaptive and innate immune systems?
The coating of anitbodies enhances the action of the innate immune system (and phagocytosis) by extending recognition repetoir
How does opsonization enhance the immune response?
- Promotes phagocytosis
- Activates natural killer cells
What is complement?
A blood-borne group of proteins that form a proteolytic cascade in response to pathogen recognition
Is complement part of the innate or adaptive immune response?
Innate
What triggers the complement pathway?
Antibody-antigen complexes
What are the 2 ways innate immune cells can be activated?
- Activation of pattern recognition receptors as part of innate function
- Activation of receptorsfor antibodies that are produced as part of the adaptive immune response
How does complement kills pathogens?
It forms pores in the membranes to premealise the cell
What is isotype switching?
The process by which the C domain of the heavy chain of an antibody is changed at the DNA level in order to change the class of immunoglobulin a particular antibody is
Where does isotype switching occur?
In germinal centres in lymph nodes
What do C3a and C5a do?
Powerful initiators of effector function
What does C3b do?
It can label bacteria (provides an alternative to opsonisation
What are the 2 effector functions of complement?
- Can label bacteria
- Forms a membrane attack complex
Outline the general principles of how complement works
- Complement proteins are activated by microbial surfaces or antibody-antigen complexes
- This leads to the formation of proteases
- Soluble factors are released
- Membrane attack complex is formed
