Adaptive Immunity 2 Flashcards
Where do B cells mature?
bone marrow
Where do B cells circulate and where are they found in large amounts
circulate in blood and lymph
found in lymphoid organs
How do B cells identify antigens?
B cell receptor (BCR)
What are BCRs usually?
antibodies
IgM and IgD
What quality in BCR allows identification of multiple antigens?
diversity
What are the 5 classes of immunoglobulins/antibodies?
IgG, IgE, IgD, IgM and IgA
What is the most prominent antibody in the body, where is it found and what is its role?
IgG
blood and bodily fluids
responsible for resistance against viruses, bacteria and bacterial toxins
IgG triggers phagocytosis to initiate opsonization reaction (complement cascade)
What is the role of IgE?
attaches to mast cells and basophils causing them to release histamine
What is the role of IgD?
on the surface of B cells where it binds to antigens
What is the role of IgM?
capable of binding multiple antigens
first class of antibody secreted after antigen is encountered
primary barrier against pathogens
declines as IgG accelerates
What is the role of IgA and where is it found?
attack pathogens before they enter internal tissues
found in secretions of saliva, sweat, mucus, urinary tract, semen, digestive tract
What differs in B cell receptor structure to T cells?
B cell receptors do not have alpha and beta chains
instead light and heavy chains
What is each developmental B cell stage defined by?
rearrangement of light and heavy chains
What genes does heavy chain rearrange?
Variable
Diversity
Joining
What genes does light chain rearrange?
Variable
Joining
What is the usual receptor for immature B cells?
IgM
What are the receptors for mature B cells?
IgM
IgD
What do B cells undergo before release?
negative selection in bone marrow
What will happen to B cells which do not pass negative selection?
engulfed by macrophages
What are the 3 main functions of antibodies?
Neutralisation
Opsonization
Initiation of complement
What is neutralisation?
attach to toxins or viruses and then inactivate them
What is opsonisation?
coating of pathogens by antibodies or complement proteins
What are the processes that opsonisation can trigger?
Phagocytosis
Antibody dependent cellular cytotoxicity (ADCC)
Mast cell degranulation
What complement pathway are antibodies able to activate?
classic
What is ADCC?
antibody dependent cellular cytotoxicity
target cell or microbe is coated with antibodies and killed by certain types of white blood cells (NK cell).
What antibodies initiate complement?
IgG and IgM
How can B cells be activated and where?
Antigens which require T cell help are called Thymus-dependent antigens
Antigens which don’t are called Thymus-independent antigens
lymph nodes
Where is a 2nd signal required for activation and what is it?
A 2nd signal required in (dependant antigen) is the co-stimulatory molecules on T helper cells and cytokines
What are the receptors that bind between T cells and BCR that activate it?
CD40 to CD40L
Describe B cell activation (dependant)
(1) the engagement of the T cell receptor with the MHC molecule on the surface of B cells that is presenting the pathogen antigen, and
(2) co-stimulatory signals provided by CD40 ligand on the surface of the T cells and CD40L receptor on the surface of the B cells.
IL 4,5,6 help proliferate plasma
Generates a pool of plasma cells which produce antibody
Also generates memory B cells
Plasma cells initially produce IgM before undergoing ‘class switching’ to IgG
Describe B cell activation (independant)
Certain antigens such as bacterial LPS can activate B cells directly
Cells differentiate into plasma cell and produce IgM however antibody response is weaker than T cell dependent B cell activation
Thymus independent B cell activation does not lead to the generation of memory B cells (no long-term immunity)
Why does class switching occur?
IgM response too weak therefore cells switch to IgG
What increases through increased exposure?
antigen affinity in antibody
What is avidity?
ability of antibodies to form complexes
What is valency?
amount of antigen binding sites
What antibodies have high affinity but low avidity?
IgG, IgA and IgE has high affinity but low avidity
What antibody has high avidity but low affinity?
IgM
What are all antibodies?
multivalent
What is the valency of IgM?
decavalent
What is the valency of IgA?
bivalent
What antibody forms dimers after secretions?
IgA
What are subgroups of IgG?
IgG1, IgG2, IgG3, IgG4
What is IgE involved in?
allergy
What does antigen exposure lead to?
immunological memory
What is the basic principle of vaccination?
cells that are primed to produce a more effective IgG (rather than IgM) response immediately as the secondary response is much more specific
What is immune tolerance?
Sometimes the immune system can become unresponsive to a particular antigen or set of antigens
Where does immune tolerance occur?
in B and T cells
What are the 2 types of immune tolerance and where do they occur?
Central – in the primary lymphoid organs (the thymus and bone-marrow)
Peripheral – occurs out with thymus and bone marrow
What are immunogens and what are tolerogens?
Immunogens are antigens that elicit immune responses
Tolerogens are antigens induce a unresponsive state
What are the two types of selection for T cells?
negative
positive
What is selection in thymus and bone marrow an example of?
central tolerance
What prevents activation of non-eliminated self-reactive T cells?
peripheral tolerance
What is anergy
no response to antigens
In peripheral tolerance what does signal 1 but not signal 2 result in?
anergy.
In peripheral tolerance what does signal 1 and signal 2 but no signal 3 result in?
deletion by apoptosis
Where does peripheral tolerance occur?
secondary lymphoid organs
What happens to self-reactive B cells?
self reactive B cells do not receive T cell help and therefore become anergic
What can breach of tolerance cause?
auto immune or allergy
T cell and B cell interactions occur in the _____ of the lymph node.
germinal centre
