adaptive immunity Flashcards
what is adaptive immunity consist of?
cell mediated responses and antibody (humoral) responses
adaptive immunity is carried out by which two cells?
B and T cells
which cell drives cell-mediated immunity?
T cell
cell-mediated immunity involves the activation of which cells?
macrophages, NK cells ad antigen-specific cytotoxic T cells
what is the key feature of adaptive immunity?
immunological memory - each pathogen is remembered by signature T cell or B cell receptor
how does adaptive immunity differ from innate in the number of genes required?
adaptive immunity requires several where as innate requires 1
name the 3 receptors involved in adaptive immunity?
- T cell receptor (TCR)
- B cell receptor (immunoglobulin [IgA])
- major histocompatibility complex (MHC protein)
T cells can be classified into two types, what are these?
- CD4+
- CD8+
which type of T cells are CD4+?
helper T cells
which type of T cells are CD8+?
Cytotoxic T cells
what is the CD antigen on T cells?
a cluster of differentiation cell surface markers involved in signalling
what are the 2 types of MHC molecules?
MHC class i and MHC class ii
what are MHC molecules?
cell surface markers involve din signalling
which cells contain MHC class i on their surface?
all nucleated cells
which cells contain MHC class ii on their surface?
antigen presenting cells, dendritic cells, macrophages, and B cells
CD4+ helps signalling through which molecule?
MHC class ii
CD8+ helps signalling through which molecule?
MHC class i
when CD is seen alone, it refers to which type of T cell?
CD8+ (cytotoxic)
what co-receptor is involved in the binding/activation to MHC class i?
CD8+
what co-receptor is involved in the binding/activation to MHC class ii?
CD4+
what co-receptor is involved in the binding/activation of both CD4+ and CD8+ T cells?
CD3
what are the 2 structural classes of T cell receptors?
alpha-beta T cells (most common) and gamma-delta T cells
describe the structure of a T cell receptor?
- can have either an alpha and beta chain or a gamma and delta chain
- has constant and variable region
- transmembrane region
which region of a T cell receptor determines variable binding?
variable region
how many gene segments encode the variable region of the alpha chain of a T cell receptor?
2 gene segments
how many gene segments encode the variable region of the Beta chain of a T cell receptor?
3 gene segments
which gene segments encode the variable region of the alpha chain?
- V (variable)
- J (joining)
which gene segments encode the variable region of the Beta chain?
- V (variable)
- J (joining)
- D (diversity)
where do B cells mature?
bone marrow
where are B cells found?
largely in lymphoid organs, also circulating blood and lymph
B cells recognise antigens through which molecule?
BCR
The B cell receptor is actually what immunological molecule?
the antibody
what happens to B cells once they are activated?
turn into plasma cells and churn out lots of antibodies against specific pathogens
what is another term for antibodies?
immunoglobulins
describe the structure of an immunoglobulin?
- 2 chains: heavy and light
- constant (bottom) and variable (top) region
- Y shape
- flexibility round tail
what are the 5 classes of antibodies?
- IgG
- IgE
- IgD
- IgM
- IgA
what is the main function of an antibody?
prevent microorganism adhesion, activation of complement, neutralise toxin, opsonisation to promote phagocytosis and destruction
heavy chain region of immunoglobulin involve the rearrangement of which gene segments?
- V (variable)
- D (diversity)
- J (joining)
light chain region of immunoglobulin involve the rearrangement of which gene segments?
- V (variable)
- J (joining)
immature BCRs are usually which antibody?
IgM
which cells, B or T, undergo only negative selection?
B cells
what occurs during negative section of B cells?
B cells are show lots of self antigens to see if they respond, ensures no reactivity against self antigens
antibodies consist of light & heavy chains which come together to create which two regions?
FAB (fragment-antigen-binding) antigen binding region and Fc (tail) region which binds to cellular receptors and complement
which two classes of antibody are BCRs?
IgM and IgD
how is diversity of antibody specificity generated?
gene re-arrangement during development
B cell activation can occur dependant or independent of which molecule?
T cell
what determines whether a B cell requires T cell activation?
the type of antigen presented on the B cell
antigens on the B cell requiring T cell help are called?
thymus-dependant antigens (TD)
antigens on the B cell not requiring T cell help are called
thymus-independent antigens (TI)
where does B cell activation mainly occur?
lymphoid organs
some B cell activation occurs the periphery, which type of activation is this?
thymus independent
activation naive B cells produces which type of cell?
plasma cell
if a B cell requires T cell activation, this usually occurs where?
lymph node
B cells producing which antibodies don’t need T cell help during activation?
B cells producing IgA or IgD
B cells producing which antibodies need T cell help during activation?
B cells producing IgM or IgG
interaction between B and T cells requires the binding of which co-receptor to which ligand?
CD40 to CD40L
before undergoing class switching, B cells normally express which antibody?
IgM
which antibody id more effective, IgM or IgG?
IgG
the second immunological response is said to have higher?
affinity and avidity
what is affinity?
strength of binding of single antibody to antigen
What is avidity?
ability of antibodies to form complexes
IgM response is weak so antibodies change class to IgG/A/E, this occurs by?
gene rearrangement (antibody binding site remains the same)
certain antigens can active B cells directly without the need for a T cell, give an example of one of these antigens?
bacterial LPS
does thymus independent B cell activation produce memory cells?
no
what is the primary immune response?
- primary exposure to antigen leads to development of immunological memory which takes time
- IgM acts early on before class switching
what is the secondary immune response?
- due to generation of memory T and B cells, we already have a pool of cells waiting to respond immediately
- cells are also primed to produce a more effective IgG (rather than IgM)
what is immunological tolerance?
state of immune unresponsiveness to a particular antigen or set of antigens
which tolerance, B cell or T cell is more important and why?
T cell tolerance is more important- b cells cannot make antibodies without the help of T cells
what are the 2 types of immune tolerance?
- central
- peripheral
what is central tolerance?
occurs while developing immune cells are still present in primary lymphoid organs, prior to exportation to periphery
what is peripheral tolersance?
occurs outwit thymus and bone marrow
central T cell tolerance is referred to as what?
thymus education
is T cell central tolerance 100% effective?
no - 10% of self reacting T cells remain after
describe the process of central T cell tolerance?
- T cells must bind with the correct strength to MHC molecules, those that do survive positive selection
- T cells must not bind to self antigens, those that do are elevated by negative selection
- rest of T cells emigrate to peripheral tissue and lymphoid organs
describe the process of peripheral T cell tolerance?
- not all self reactive T cells are eliminated centrally
- T cell activation is a 3 signal process
- signal 1 but no signal 2 = anergy (absence of normal immune response)
- Signal 1&2 but not 3 = apoptosis
where does central tolerance of B cells occur?
bone marrow
does central B cell tolerance contain positive selection, negative selection or both positive and negative selection?
just negative
does central T cell tolerance contain positive selection, negative selection or both positive and negative selection?
both negative and positive
where does peripheral B cell tolerance occur?
secondary lymphoid oragns
describe the mechanism od peripheral B cell tolerance?
- self reactive b cells still require help from self reactive T cells
- most self reactive T cells have been eliminated
- self reactive B cells do not recieve T cell help ad become anergic
breach of tolerance may cause what?
autoimmune disease
cross talk between B and T cells in lymphoid organs ensures the generation of what?
cellular and humour adaptive immunity and memory
what is the function tolerance?
ensure immune system does not attack self antigens
describe the process of thymus education
- pre-thymic cells enter thymus, they express both CD8 and CD4 at low levels
- as they mature they move into the cortex where positive section takes place
- those cells incapable of binding MHC are phagocytosed
- dendritic cells and macrophages express auto antigens during negative selection
- remaining cells migrate to medulla and enter periphery
which immune cells do lymph nodes contain?
b cells, t cells and dendritic
which cells are responsible for activating CD4+ T cells?
dendritic
the binding of an antigen to a TCR is not enough to prime a naive T cell, what else is required?
- CD28 must bind CD80/86
- cytokines also needed
during T cell priming, what determines whether the T cell will be CD4 or CD8
cytokines released by the antigen presenting dendritic cell
T helper cells/CD4+ cells can be divided into 5 subsets, what are these?
- Th17 cells
- Th1 cells
- Th2 cells
- Tfh cells
- T reg cells
what is the function of Th1 cells?
promote cellular immunity particularly in macrophages
what is the function of Th17 cells?
express IL-17, support innate immunity
what is the function of Th2 cells?
support antibody immunity (humoral)
what is the function of Tfh cells?
support B cell response
what is the function of T reg cells?
immune suppression, negatively regulate T cell activity
what does CD8 activation require?
antigen presented on MHC 1 to TCR
what is the function of cytotoxic T cells?
- induce apoptosis by releasing contents of granules (granzyme and perforin)
- perforin facilitates granzyme into cell
- granzyme induces apoptosis
how do dendritic cells prime T helper cells?
by presenting antigen of MHC ii
