Lecture 3 - Effector Immune functions Flashcards
What are the 5 different types of constant regions (Fc) of the heavy chain?
IgM IgD IgE IgG IgA
What is the purpose of having different types of constant region of the heavy chain?
- lead to different antibody structure and function
- different types found in different areas of the body as have different function
What is the structure and function of the IgG Fc region?
- occurs as a dimer of 2 heavy chains and 2 light chains
- high affinity antibody with a key role in memory immune responses (protect against viruses and toxins)
- most common immunoglobulin in serum
What is the concentration of different types of antibody following vaccination?
1) IgM peaks at low levels with affinity not changing much over time
2) As immune system continues response, IgG affinity increases -> increasingly higher levels of IgG with increasing affinity
What is the structure of IgM?
pentameric structure with 5 antibody dimers held together by J chain protein
What is the features of IgM?
- low affinity antibody with role in protection during immune response
- first antibody made during an immune response
- makes up for low affinity by having 10 binding sites
- becomes an IgG molecule as a result of AID in somatic hypermutation
What is the structure of IgA?
dimeric structure with 2 antibody dimers held together by J chain protein
What are the features of IgA?
- found in mucosal secretions as can cross mucosal surfaces e.g. into intestine
- lymph node and pyrus patch produce B cells producing IgA -> transported into gut lumen through epithelial cells at base of crypts -> dimeric IgA binds to layer of gut mucus overlaying epithelium -> binds to pathogens + neutralises
- found in breastmilk -> into baby gut and intestines when born and suddenly into contact with bacteria mother already encountered has some protection, into bloodstream
What is the structure of IgE?
similar to IgG, a dimer of two heavy chains and light chains but with a difference in the ‘tail’
What are the features of IgE?
- crosslinks to special receptors on mast cells and eosinophils, when bound, release histodine
- role in allergic responses
Why is IgM made first?
normally transcription will through through, after VJD rearrangments, into Cu (IgM) and THEN C& (IgG)
How does class switching occur to produce IgG instead of IgM?
1) AID is only expressed in cells undergoing somatic hypermutation
2) AID induces breaks above Cu (Su and S&1 switch regions)
3) Body goes in to repair DNA, causing reciprocal breaks to occur
4) dsbreak system going in to repair DNA
5) during the process of repair is a looping out of the switch region -> removes piece of DNA, deleting IgM and only make IgG
Why are IgM low affinity?
Because AID doesn’t have an oppurtunity to make somatic hyper mutations
What are the symbols for IgG IgM, IgA, IgE?
IgG (y)
IgM (u)
IgA (o<)
IgE (E)
What three things do antibodies do?
1) Neutralise toxins
2) Aid phagocytosis of bacteria
3) Destroy bacteria
How do antibodies neutralise toxins?
1) Antibodies released and bind to bacterial toxin and neutralise
2) Toxin molecules bound by antibodies are digested by macrophage
3) Toxins and antibodies are digested by enzymes
How do antibodies aid phagocytosis of bacteria?
1) bacteria are present in extracellular space
2) Antibodies targeting bacteria are present in previously infected host
3) Antibodies bind antigens on bacteria
4) Antibodies and bacteria injested by macrophage and digested by enzxymes
How do antibodies directly destroy bacteria?
1) Bacteria present in extracellular space
2) Antibodies targeting bacteria are present in previously infected host
3) Antibodies bind to recognised sites on bacteria
4) A complement protein binds to the antibodies forming a complement protein complex on bacterial membrane
5) Complex forms a hole on bacterial membrane leading to bacteria losing osmotic control and being destroyed
What is tetanus caused by?
a neurotoxin produced by soil bacterium clostridium tetani under anaeobic conditions
What does the tetanus toxin do?
inhibits GABA or glyceine release (pre-synaptic activity) and in the absense of inhibitory neurotransmitters leads to unrestraineed excitation of neuroaxon leading to muscle spasm
How do antibodies protect against tetanus toxin? (vaccines)
1) Tetanus toxin treated with formaldehyde (so it retains it’s structure) which prevent activity to inactivate it, but allowing immune system 3D shape to bind to
2) injected with an adjuvant which induces a high affinity antibody response by anti-tetanus toxin specifc antibody producing B cell, to tetanus toxin
3) antibodies bind to tetanus protein and neutralise toxin
4) antibody prevents toxin having an effect but need high titre to protect against effects
What is the influenza virus?
rapidly evolving set of viruses which affects birds and mammals and is transmitted through aerosols
How do antibodies protect against influenza?
1) Virus haemagglutanin (HA) binds to epithelial surface on lung and mediates infection, allows virus to replicate
2) Antibodies mediate/neutralize HA prevent host cell infection
PROBLEM flu virus undergoes rapid recombination, new HA can dodge immune system, H1 strains nasty
How many people died of smallpox in the 20th centuary?
300-500 million deaths
Why did infection with cow pox protect against small pox?
cowpox virus had some of same proteins on surface, leading to production of high affinity antibodies to protect against small pox
Why was global immunisation possible for smallpox in the 1980s?
world was communist/capatialist
What is the process of antibody induced phagocytosis? (Antibody opinization)
1) bacterium coated with complement and IgG antibodies
2) C3b binds to CRI, antibody bind to Fc receptor on macrophage, bacteria are phagocytised
3) Macrophage membranes fuse creating a phagosome = membrane enclosed vesicle
4) lysosomes fuse with vesicles, delivering enzymes that degrade bacteria
How do antibodies mediate the release of inflammatory mediators from mast cells?
1) resting inactivated mast cells contains preformed granules containing histamine and other inflammatory mediators, also on surface Fc e RI receptors that the IgE antibody binds to
2) Multivalent antigen cross links IgE antibody on mast cell surface, causing activation of mast cells and release of granule contents (cytokines, histodenes, and active substances)
Where do the effects of mast cell activation act?
1) gastrointestinal tract
2) eyes, nasal passages and airways
3) blood vessel
What effects does mast cell activation have in gastrointestinal tract?
increased fluid secretion and increased peristalsis -> expulsion of gastrointestinal tract content = diarrhea and vomiting
What effects does mast cell activation have in the eyes, nasal passages and airways?
decrease diameter and increase mucus secretion -> congestion and blockage of airways, swelling and mucus secretion in nasal passageways
What effects do mast cells activation have in the blood vessels?
-increased blood flow
-increased permeability
Leads to
-increased fluid in tissues including flow to lymph nodes
-increased cells and protein in tissues
-increased effector response in tissues
-hypertension potentially leading to anaphylactic shock
What is the process of Antibody dependent cell-mediated cytotoxicity?
1) Antibody binds to antigens on surface of target cells
2) Fc receptors on Natural killer cells recognise bound antibody
3) Cross linking of Fc receptors signal NK cell to release killing secretion adn kill target cell
4) target cell dies by apoptosis
What is complement mediated cell lysis?
an enzymatic pathway involving many different proteins that lead to the formation of cellular destruction
What does complement mediated cell lysis have role in?
helping to recruit cells
process of phagocytosis
direct formation of pores in cells/bacteria
What protein complex initates complement mediated cell destruction and how?
The CI protein complex and though binding to an (or multiple antibodies)
How many IgM antibodies are required to bind to a complement protein to iniate the destruct of bacteria?
1 IgM molecule, bound to antigens on bacterial surface, needs to be bound by a complement protein to initiate destruction
How many IgG antibodies are required to bind to a complement protein to iniate the destruct of bacteria?
2 IgG molecule, bound to antigens on bacterial surface, needs to be bound by a complement protein to initiate destruction
What occurs when the CIq binds to an Ig molecule on a bacterium?
1) Binding of CIq to Ig molecules activates C1r
2) C1r cleaves and activates serine protease C1s
3) Leads to series of biochemical reaction (to amplify response and for regulation)
4) produces a porelike structure inserted into the membrane of a bacteria
5) bacteria loses osmostic control and dies
How have polyclonal antibodies been used to protect against toxins?
1) snake venom isolated
2) sheep/horse immunised with small amounts toxinf
3) Higher titre antibody isolated and used to treat patients
Who discovered monoclonal antibodies and when?
MILSTEIN, KOHLER and JERNO 1984
What is an advantage of monoclonal antibodies?
Allow scientists to produce large quantites of antibody with the same predefined specificity
How are monoclonal antibodies produced?
1) immunisation of mice with antigen to induce primary antibody response
2) mice immunised a second time to induce somatic hyper mutation
3) leads to production of IgG and a lot of antibody with high affinity
4) take plasma cells (B cells) and Myeloma cells and fuse two cell types using polyethylene glycol
5) but under drug selection to produce monoclonal hybridoma which are immortal antibody producing cells
What are the differences between a resting B lymphocyte and an activated antibody secreting plasma B cell?
Resting B lymphocyte
-mostly nucleus
Activated B cell
-lots of ER to produce protein (antibody) and secrete
What are some of the applications of monoclonal antibodies?
1) Monoclonal antibody therapy e.g. Truztuzumab (Herceptin) - used for treatment of breast cancer, NK cells kill off tumour
2) Diagnostics
3) ELISAs
4) Flow cytrometry (cell purification)
5) Protein analysis
6) immunocytochemistry
