Immunology 4- Acquired immune response and antibodies Flashcards
What two signals do B cells need to become fully activated and clonal proliferate?
- The antigen
- ‘helping’ signals
What do activated B cells differentiate into?
Plasma cells.
What are plasma cells?
Antibody secreting cells which are much larger than B cells and have many RER, meaning they can produce many antibodies.
In what ways can B cells mutate and produce better antibodies?
Switch from low to high affinity antibody production.
Switch the class of antibody they produce (e.g. IgM> IgG).
Differentiate into long-lived plasma cells and long-lived memory B cells.
Are IgM antibodies high or low affinity molecules?
Low affinity.
Which type of antibody do plasma cells first produce?
IgM antibodies.
What are the two signals needed from non-protein antigens for B cell activation?
1- BCR + antigen
2- PRR + PAMP
why do B cells not need a second signal for antigens with multiple antigenic epitopes?
There is enough interaction to activate the B cell without a secondary signal.
What do non-protein antigens and antigens with repetitive antigenic epitopes lead to?
- low affinity antibodies
- short lived plasma cells
- no memory cells
What are the two signals needed from protein antigens for B cell activation?
1- BCR binding to antigen
2- Help from Th cells
Through what process do B cells internalise protein antigens?
Endocytosis
What do B cells do to receive help from Tfh cells?
The peptides derived from chopping up protein antigens are presented on the B cell surface as an MHC-II peptide signal. The Tfh cell can then bind to this signal. Tfh helps by secreting co-stimulatory molecules to help the B cell.
How do Tfh cells help B cells?
They release co-stimulatory molecules. (help B cells produce antibodies)
What is the germinal centre reaction?
Rapid proliferation
What are the two parts of an antibody?
- The ‘recognition function’ at the top, mediates binding to antigen by variable region sites
- The ‘effector function’ at bottom, mediates clearance mechanisms by interaction of its heavy chain constant region and the effector molecules (complement or Fc receptors)
Describe IgM.
- In its membrane-bound monomeric form, IgM serves as the B cell antigen receptor (mediates B cell activation)
- In its secreted (from plasma cells) pentameric form, IgM is the first Ig type produced during a humoral immune response, it is present in plasma and secretory fluids, its involved in agglutination and complement system activation
What is agglutination?
The action of an antibody when it cross-links multiple antigens producing clumps of antigens.
Agglutination increases the efficacy of pathogen elimination by enhancing phagocytosis. It prevents viruses from binding and infecting host cells
What two antibodies mediate agglutination?
IgM and IgG.
Which pathway in the complement system is activated by the Fc region on IgM and IgG?
the classical pathway
Describe IgG.
- Most abundant antibody in normal human serum
- Present in serum in a monomeric form (IgA)
Functions:
• Neutralisation
• Agglutination
• Complement system activation through classical pathway
• Foetal immune protection (transported across the placenta, directly into the foetal blood circulation)
• Opsonisation
•NK cells activation
What is neutralisation?
A process mediated by specific antigen binding to high affinity IgG and secretory IgA antibodies which is blocking viral entry
What does IgE do?
Triggers allergic responses, involves mast cells.
Describe IgA.
- Second most abundant Ig type
- Present in serum in a monomeric form
- Does neutralisation
- Present in secretory fluids in dimeric form (secretory IgA, sIgA) which is good for neonatal defence (protects GI tract) and neutralisation at mucosal sites
Describe IgD.
In membrane-bound monomeric form, IgD serves as a B cell antigen receptor (mediates B cell activation)
