adaptive immunity 2 Flashcards
what do B cells communicate with?
T cells
what do B cells produce?
antigens
what does clonal expansion of B cells lead to?
generation of 2 subsets
what are the 2 main types of B cells?
plasma b cells
memory B cells
give an example of antibody factories?
plasma cells
what are memory B cells important for?
mount a quicker antibody response to any subsequent infections
where do B cells mature?
bone marrow
where do B cells circulate and where are they found in large numbers?
blood and lymph
- lymphoid organs
how do B cells recognise antigens?
B cell receptor which is the actual antibody (IgM or IgD)
why is the B cell receptor diverse?
to respond to numerous antigens
what happens when B cells are activated?
change to plasma cells “antibody factories”
what are the 3 main receptors in adaptive immunity?
T cell receptor
B cell receptor (immunoglobulins Ig)
major histocompatibility complex (MHC proteins)
what does multiple genes encoding in receptors allow?
development of the repertoire of receptors with wide specificity
describe IgG antibodies?
80% of all antibodies
responsible for resistance against viruses, bacteria and bacterial toxins
what do IgE antibodies do?
attaches as an individual molecule to exposed surfaces of basophils and mast cells
what does IgD do?
individual molecule on surface of B cell where it can bind antigens in extracellular fluid
what does binding of IgD play a role in (b cells)?
sensitisation of the B cell involved
what does binding of IgM do?
anti-A and anti-B antibodies responsible for the angulation of incompatible blood types are IgM antibodies
what is the first class of antibody secreted after an antigen is encountered?
IgM
where is IgA found?
primarily in glandular secretions such as mucus, tears, saliva and semen
what does IgA do?
attack pathogens before they gain access to internal tissues
what are the 5 different types of immunoglobulins produced by B cells?
IgG IgE IgD IgM IgA
describe the B cell receptor structure?
slightly different to T cells
both have variable and constant regions
B cell antibodies have light and heavy chains
what is the difference between B cell receptors and T cell receptors?
B cells = light and heavy chains
T cells = alpha and beta chains
where is the antigen biding site found in b and T cell receptors?
variable region
what are the developmental stages in B cell development defines by?
rearrangements of the immunoglobulins heavy and light chain genes
what happens to B cells in the periphery?
migrate to secondary lymphoid organs
what does heavy chains of B cell receptor involve?
involves rearrangement of variable, diversity and joining genes
what does light chains of B cells receptor involve?
rearrange variable and joining gene
what kind of selection do B cells go through in bone marrow?
negative
what happens if the immature B cell in bone marrow does not react with self antigen?
moves into the blood expressed as IgD and IgM
what happens if the immature B cell in bone marrow does react with self antigen?
retained in bone marrow
what is the immature B cell receptor?
IgM
what is the mature B cell receptor?
mainly IgD but also IgM
what removes self reacting B cells?
macrophages
what are the 3 main functions for antibodies in the human body?
neutralisation
opsonisation
initiation of complement
what is the primary goal of an antibody?
prevent microbial activity and aid removal of threat from host
what are the 3 functions of antibodies?
neutralisation
opsonisation
complement initiation
what do antibodies do in opsonisation?
coat pathogens by antibodies or complement proteins
what drives mast cell degradation?
IgE attachment to allergen
what is antibody dependent cellular cytotoxicity?
- antibodies bind antigens on the surface of target cells
- NK cell CD16 Fc receptors recognise cell bound antibodies
- cross linking of cd16 triggers degranulation into a lytic synapse
- tumour cells die by apoptosis
what is the complement initiation classic pathway?
antibody attached to microbe
what is the B cell receptor?
IgD
what is negative selection of B cell receptors?
during development in bone marrow B cells with self reactive BCR are eliminated
what happens after B cell goes through negative selection and makes its way out of circulation?
B cell activation
in B cell activation, antigens that require T cell help are called?
thymus-dependent antigen
in B cell activation, antigens that don’t require T cell help are called?
thymus-independent antigen
where does B cell activation occur?
lymph nodes
what does the activation of naive B cells result in?
rise of plasma cells
what does T cell and BCR interaction. require?
co-receptor binding
CD40 TO CD40L
give an example of an antigen that can activate B cells directly?
bacterial LPS
what is the first antibody produced in B cell activation?
how many antigen binding sites does it have?
IgM
10
why does IgM class switch to IgG in B cell activation?
IgM response is weak
what is affinity of an antigen?
strength of binding of single antibody to antigen
what is avidity of an antigen?
ability of antibodies to form complexes
what is the affinity and avidity of IgM?
low affinity high avidity
what are germinal centres?
hubs for t and B cells cross talk and:
- proliferation and differentiation
- somatic hypermutation eg. class switching
in lymphoid organs what does cross talk of b and T cells lead to?
generation of both arms of the adaptive immune response
- humoral immunity
- cellular immunity
what does the presence of memory t and B cells mean upon second exposure to a disease?
immune system can respond much faster
what is the basic principle of vaccination?
in the primary immune response IgM acts early but as B cells undergo class switching an IgG response follows
what is immunological tolerance?
immune system becomes dysfunctional and in state of unresponsiveness to a particular antigen - can happen in b and T cells
what are the 2 main types of tolerance and where do they occur?
central = primary lymphoid organs (thymus and bone marrow)
peripheral = occurs out with thymus and bone marrow
what are the 2 types of selection for T cells?
positive - no recognition (apoptosis)
negative - recognition of self antigens (apoptosis)
where does central tolerance occur for T cells?
thymus
what type of selection occurs in B cells?
negatove - B cells that bind strongly to self antigen are eliminated
where does central tolerance occur for B cells?
bone marrow
what prevents the activation of self reactive T cells?
peripheral tolerance
are all self reactive T cells eliminated in peripheral tolerance?
no
what happens in peripheral tolerance of T cells when there is signal 1 but not signal 2?
anergy
what happens in peripheral tolerance when there is signal 1 and 2 but not signal 3?
deletion by apoptosis
what is the cytokine survival signal?
signals 1 and 2 but not 3
what do t regulatory cells do in peripheral tolerance?
directly block activity by binding antigen (both self and foreign antigens)
where does peripheral tolerance occur for B cells?
in secondary lymphoid organs
what help do self reactive B cells require in peripheral tolerance?
help from self reactive T cells
why do most self reactive B cells not receive help from self reactive T cells?
as most self reactive T cells are eliminated
what happens when a self reactive B cell does not receive help from self reactive T cells?
become anergic
what does a breach of tolerance to ‘self antigens’ or commensal organisms drive?
many autoimmune diseases
what are the 5 classes of antibody?
IgA
IgD
IgE
IgG
IgM
where does class switching of IgM to IgG occur?
in mature B cells
what does tolerance ensure?
immune system does not attack self antigens
what do central and peripheral tolerance checkpoints prevent?
autoimmunity (particularly effective for self reactive t cells)
what does a breach of tolerance lead to?
reactivity against self antigens
