Adaptive Immunity in action L10 Flashcards
what do B cells make
antibodies
what do T cells make
CD4 helper T cells and CD8 cytotoxic T cells
what do T helper cells do
activate B cells
provide signals eg cytokines which can activate other immune cells, for example phagocytosis by macrophages
what do regulatory T cells do
suppress activity of other lymphocytes , to try and limit the damage caused by immune response
how are B and T cell receptors compared
Antibodies have light chain heavy chain
T cells alpha chain and beta chain
what do all nucleated cells have
MHC class I
what do only antigen presenting cells have
MHC class II
when can T cells recognise peptides
only recognise peptides when presented in a MHC molecule
what must primarily match in an organ transplant
primarily the MHC type that needs matching
what is somatic recombination
rearrangement of gene segments to give huge diversity in variable regions
what is the clonal selection theory
a single progenitor cell gives rise to large number of lymphocytes, each with different specificity
removal of potentially self-reactive immature lymphocytes by clonal deletion
pool of mature naive lymphocytes
proliferation and differentiation of activated specific lymphocytes to form a clone of effector cells
what are the postulates of clonal selection hypothesis
- each lymphocyte bears a single type of receptor with a unique specificity
- interaction between foreign molecule and lymphocyte receptor capable of binding that molecule with high affinity leads to lymphocyte activation
- differentiated effector cells derived from an activated lymphocyte will have receptors of identical specificity to parental cell lymphocyte is derived from
- lymphocytes with receptors specific for always present self molecules are deleted at each early stage in lymphoid cell development and are absent from repertoire of mature lymphocytes
what is the innate immune system response
inflammation
complement activation
phagocytosis
destruction of pathogen
how long after infection till innate immune response starts
minutes
how long does the innate immune response last
days
what is the adaptive immune response
interaction between antigen-presenting dendritic cells and antigen-specific T cells
antigen-specific B cells activated
memory T cells and effector form
T cell and B cell interaction
emigration of effector lymphocytes from peripheral lymphoid organs
elimination of pathogen by effector cells and antibody
what happens when there is is an interaction between antigen-presenting dendritic cells and antigen-specific T cells in adaptive immune response
recognition of antigen adhesion co-stimulation T-cell proliferation differentiation
what happens when there is T cell and B cell interaction in adaptive immune response
formation of germinal centres
formation of effector B cells (plasma cells) and memory B cells
produce antibody
which parts of adaptive immune response take hours after infection
interaction between antigen-presenting dendritic cells and antigen-specific T cells
antigen-specific B cells activated
which parts of the adaptive immune response take days after infection
memory T cells and effector form
T cell and B cell interaction - antibodies produced
which parts of the adaptive immune response take a few days after infection
emigration of effector lymphocytes from peripheral lymphoid organs
elimination of pathogen by effector cells and antibody
which parts of the adaptive immune response last only days
interaction between antigen-presenting dendritic cells and antigen-specific T cells
antigen-specific B cells activated
which parts of the adaptive immune response last weeks
memory T cells and effector form
T cell and B cell interaction
emigration of effector lymphocytes from peripheral lymphoid organs
elimination of pathogen by effector cells and antibody
what is the immunological memory
maintenance of memory B cells and T cells and high serum or mucosal antibody levels
protection against reinforcement
how long does immunological memory response take after infection
days to weeks
how long does immunological memory last
can be life
what is the crucial role of dendritic cells
act as a crucial link between innate and adaptive immune systems
activating the adaptive immune response
what can dentritic cells do
“talk” to lymphocytes
where are immature dendritic cells
peripheral tissues
where do dendritic cells migrate
via lymphatic vessels to regional lymph nodes
where do mature dendritic cells activate molecules, and what
mature dendritic cells activate naive T cells in lymphoid organs e.g. lymph nodes
what is the CD4 positive cell for
is a helper cell
what is the antigen presented to
CD4 positive T
how are CD4 positive proteins identified
protein called CD4 on their surface, a co-receptor which is required to enable interaction between their T cell receptor and MHC class II
what dies the dendritic cell do to help activate T cells
produce soluble signals
how does an activated T cell recognise B cell
activated helper T cell can recognise B cells that have a B cell receptor (surface-antibody) which has bound the same pathogen molecules and are presenting the same peptide
how does the T cell activate the B cell
by both direct cell-to-cell interactions and soluble signals (cytokines)
what does the activated B cell do
will then proliferate and price plasma cells which make large quantities of the specific antibody
how do antibodies improve during infection
antibody affinity improves over an immune response
what are plasma cells
terminally differentiated activated B cells
main antibody secreting cells of body
what can dendritic cells, macrophages and B cells be called
antigen presenting cells
APC
how are dendritic cells specialised
specialised in initiating adaptive immune response§
how are dendritic cells activated, effect
PAMPS binding to PRR’s stimulate dendritic cells to engulf pathogen and degrade it intracellularly (phagocytosis) Can also take up virus particles and bacteria through receptor-independent macropinocytosis
what mainly causes B cell activation
main cause: interaction with CD4 T helper cells
also, can be due to binding of free antigens
what does B cell activation cause
optimal antibody response
how are B cells activated by binding of free antigens
antigen-specific B cell binds antigen
specific antigen is efficiently internalised by receptor mediated endocytosis
high density of specific antigen fragments are presented at B-cell surface
what are the effects of pathogen specific antibodies
Neutralize toxins
Block virus binding to cells
Opsonise pathogens
Activate complement
All aid in removal of pathogens
what is Fc
Fragment crystallisable (Fc), it’s a portion of the antibody in the constant domain
what happens in toxin neutralisation by antibodies
toxin binds to cell surface receptor
endocytosis of toxin:receptor complex
dissociation of toxin to release active chain which poisons cell
neutralising antibody blocks binding of toxin to cell-surface receptor
what happens in pathogen oponisation (tagging) by antibodies
antibody binds to bacterium
antibody-coated bacterium binds to Fc receptors on cell surface
macrophage membrane surrounds bacterium
macrophage membranes fuse, creating a membrane-enclosed vesicle, phagosome
lysosomes fuse with phagosome, creating phagolysosome
what is antibody dependent cell-mediated cytotoxicity used in
Can be used as a therapy – anti-CD20 monoclonal antibody eliminates some types of B cell tumors (rituximab)
what happens in antibody dependent cell-mediated cytotoxicity
The monoclonal IgG antibody binds to cell surface protein CD20, and the Fc receptors on the NK cells can recognise this and lead to cell apoptosis
how are viruses neutralised
virus binds to receptors on cell surface
receptor-mediated endocytosis of virus
acidification of endosome after endocytosis triggers virus and cell fuse and entry of viral DNA
antibody blocks binding to virus receptor and can block fusion event
how are viruses replicated
To replicate viruses have to get genes into host cell
how is bacteria neutralised
colonisation of cell surface by bacteria that bind to surface via bacterial adhesin
some bacteria become internalised and propagate in internal vesicles
antibodies against adhesins block colonisation
what are the T cell effector functions (CD8+ cytotoxic T cell)
cytotoxic T cell recognises complex of viral peptide with MHC class I kills infected cell
what are the T cell effector functions (CD4+ T helper cell)
Th1 cell recognises complex of bacterial peptide with MHC class II, activates macrophage T follicular helper cell recognises complex of antigenic peptide with MHC class II and activates B cell = antibodies
how does CD8+ kill target cells
CD8 cells kill target cells by releasing the content of intracellular granules at the site of cell contact
CD8 T cells can kill cells bearing a specific antigen, whilst sparing neighbouring cells
what granules does CD8+ T cells contain
perforin
granzymes
granulysin
what does perforin do
aids in delivering contents of granules into cytoplasm of target cells
what does granzymes do
serine proteases, which activate apoptosis once in cytoplasm of target cell
what does granulysin do
has antimicrobial action, can induce apoptosis
where are naive T cells
circulate though the blood and lymphoid organs
when are T cells activated
after encountering antigen presenting cells showing a peptide/MHC complex
what do activated T cells do
proliferate in the secondary lymphoid organs (lymph nodes, spleen etc) and two key sorts are produced: most become effector T cells which are actively involved in the immune response, a lesser proportion become long-lived memory T cells
