module 3 Flashcards
what is the adaptive immune response ?
second line of defence when the innate immune response is not enough , known as being antigen specific
what are the 5 phases of the adaptive immune response ?
antigen recognition, lymphocyte activation, elimination of pathogens , contraction, memory
antigen recognition
- NEED to identify and activate cells from adaptive immunity that recognize antigens . PAMPs are seen by APCs like dendritic cells and macrophages - APC will present antigen to naive T cell via MHC complex proteins
Lymphocyte activation
- this step is used to produce a large quantity of immune cells specific to the pathogen
requires a series of cellular interactions leading to T cell and B cell differentiation and clonal expansion
elimination of pathogen
- step is used to completely destroy pathogen where humoral and cell mediated immunity are used
contraction
Majority of lymphocytes will undergo apoptosis after removal of pathogen. vast majority of immune cells will die becasue they can cause more harm than good in the body
Memory
establishment of immunological memory, the few adaptive immune cells that remain will become memory cells -ability to produce fast immune response if reinfected
why is antigen presentation needed ?
adaptive immune system has specific immune cells capable of recognizing a specific antigen , presentation is needed to identify which cells should be activated
What is the MHC ?
serves as a self label, which helps recognize and identify self from non self molecules to make sure the immune system wont attack the host
role of MHC molecules
display antigenic peptides on the surface of cells, which can be recognized by the TCR and co receptors ( CD4 and CD8) to initiate adaptive immune response
what are the different classes of MHC molecules and why are they needed ?
MHC class 1 and MHC class 2
which help distinguish between the different recognition patterns
what is the role of Antigen presenting cells ?( APC )
They are needed because T cells cannot recognize pathogens themselves . An APC will internalize a pathogen by either phagocytosis or receptor mediated endocytosis where peptides ( antigens will be presented on the MHC on the cell surface which will be recognized by T cells
professional APCs
Macrophages, B cells , dendritic cells –> These cells are the most efficient in presenting antigens to MHC class 2 and will send cositmodulatory signals to activate T cells
non profESSIONAL APCs
fibroblasts and glial cells - can be induced to express MHC 2 but normally they dont ( in sustained inflammatory responses ).
antigens are processed to form what effective peptide?
MHC singalling complex , there are 2 pathways to form this
Pathways to form MHC signalling complex
endogenous and exogenous pathways
endogenous pathway
formation of MHC complex 1 that is recognized by CD+8 cytotoxic T cells
exogenous pathway
formation of MHC complex 2 recognized by CD4+ helper T cells
role of endogenous pathway
cell will be able to process self and foreign particles and present them at surface to be recognized by T cell receptors on cytotoxic T cells
what are the 5 steps in the exogenous antigen processing ?
antigen engulfment, proteolytic processing, formation of MHC antigen complex, cell surface expression, recognition by helper T cell
What is antigen engulfment ?
macrophages, B cells and dendritic cells engulf foreign antigen by endocytosis forming an endosome
what is proteolytic processing ?
foreign antigens inside endosome are broken down into fragments by proteolytic processing (Protease cleaves bonds in one or more proteins ).
formation of MHC antigen complex
vesicle with foreign fragments will fuse with vesicles containing MHC molecules( from ER). creating MHC antigen complexes
Cell surface expression
MHC antigen complex is transported to the plasma membrane where it will be displayed on the surface of the cell
recognition by helper T cell
TCR will bind to MHC antigen complex on the cell surface of APC to initiate adaptive immune response
B cell receptors
B cell receptors needed for antigen recognition which will have a membrane bound antibody and signal transduction molecules- they will recognize and bind to pathogens directly
T cell receptors
made up of membrane bound antigen specific molecule and signal transduction molecules (CD3 and ITAMS )
CD4 co receptors are expressed on
Helper T cells and will recognize peptide MHC class 2 complex
CD8 co receptors are expressed on
Cytotoxic T cells which will recognize peptide MHC class 1
what are cytokine networks
coordinate immune responses and modulate balance between the humoral and cell mediated immunity
4 classes of cytokines
chemokines, interleukins, interferons , tumour necrosis factor and growth factor
what is lymphocyte activation ?
interactions with many immune cells which will mediate a specific immune response
why is the interaction between B cells and T cells important ?
interactions will induce the exchange of activation signals between the 2 lymphocytes allowing strong humoral immune response
3 signals leading to B cell activation
1) TCR- peptide : MHC complex
2) co stimulation ( B7:CD28, CD 40: CD40L )
3) cytokines
step 1 in B cell activation
antigen binds to BCR, on B cell, if signal is not string enough to activate cell , antigen will be internalized by receptor mediated endocytosis and will be displayed on the membrane of the MHC
STEP 2 in B cell activation
Specific TCR complex and CD4 co receptor on the T cell recognizes
Step 3 in B cell activation
expression of co stimulatory molecules , where signal 1 will induce the expression of CD40L on the cell surface of the helper T cell
step 4 B cell activation
CD40L and CD28 will bind to CD40 and B 7 expressed on the B cell creating a costimodulatory signal in both cells
Step 4 B cell activation
known as signal 3 , activated helper T cell ill secrete cytokines which will bind to cytokine receptors
what do the 3 signals cause ?
stimulate the proliferation and differentiaton of B cells into plasma cells and memory B cells causing the humoral response against a specific antigen
interaction between T cell and APC will form what ?
immune synapse
what is an immune synapse
made of signal molecules and adhesion proteins
3 components of an immune response
signal molecules, adhesion molecules, signal regulation molecules
signal molecules ( cSMAC)
Has the molecules needed for signalling between 2 cells like TCR and Peptide: MHC molecules
adhesion molecules (pSMAC)
has adhesion proteins such as integrins and cytoskeletal protein linkers needed to keep all cells in contact long enough for signal propogation
signal regulation molecules (dSMAC)
proteins containing larger extracellular domains that regulate signal transduction
why is an immune synapse needed ?( 4 things )
- activation of T cell
- hold signal proteins together longer to form stronger connections , allowing proper signal to be produced
- synapse allows for reorganization inside the T cell which will release of cytokines close to target cell
- synapse regulates lymphocyte activation
what would happen if immune cell activation was incomplete ?
down regulation of an immune response preventing T cell proliferation and development of anergic phenotype
why are cytokines needed ? what are they used for ?
they are chemical messengers that are secreted by immune cells needed for cell to cell communication and needed to regulate immune function
types of cytokines
chemokines, interleukin, interferons , tumour necrosis factor, growth factor
chemokines function
induce chemotaxis, call in cells to region of infection are needed for wound healing , cell mediated and humoral immune responses , inflammation
Interleukins
contains 10 sub families , regulate immune and inflammatory responses , primarily effect proliferation and differentiation of immune cells and hematopoietic cells
interferons
induce antiviral state and inhibit replication of viruses , regulate immune responses
Tumor necrosis factor
invovled in systemic inflammation, involved in tumor regression, can cause apoptosis
Growth factors
stimulate growth, proliferation, healing, cell differentiation
what is the outcome of B cell activation ?
proliferation and differentiation into plasma cells and memory B cells
what is immunological memory ?
ability for lymphocytes to respond more efficiently to re- infection by previously encountered antigen, where there will be a faster immune response - central feature of adaptive immunity
natural passive immunity
Short lived immunity (6 months around )
aquired by the fetus from the mother , where there is placental transfer of antibodies in pregnancy and breastfeeding
NO immunological memory
artificial passive immunity
injection of serum of antibodies , temporary immunity
NO immunological memory
Natural active immunity
acquired through infection by a pathogen , innate and adaptive immune responses
- high chance of developing immunological memory
artificial active immunity
vaccination, innate and adaptive and innate immune responses but with no symptoms , High chance of immunological memory development
