Immunology - Adaptive Immune Response Flashcards
Components of Adaptive Immune System
B cells, antibodies
T cells
Recognising Pathogens
Antigen/Antigen receptors
response is unique to each antigen
Antigens
Any substance which can cause an adaptive immune response by stimulating B ells and T cells
PAMPs vs Antigens
PAMPs = Non specific Limited number of PAMPs common to many pathogens Small number of PRRs Antigens = Specific Millions of different antigens Individual T cells and B cells only express one specific antigen receptor, which binds to one specific antigen
T Cell Antigen Receptor
Membrane bound protein heterodimer
Alpha and Beta chains
B Cell Antigen Receptor
Membrane bound antibody (IgM or IgD)
Light chain and heavy chain
Antibody Composition
Heavy and light chains each contain a variable ad constant region
Variable region forms antigen binding site
Heavy chain constant region defines type of antibody
Antibody Segmentation
Heavy and light chain proteins are encoded for by segmented genes
Random rearrangement of these gene segments occurs in individual B cells as they develop
This allows us to have many antibodies without using up a lot of DNA
How do Antigens enter a Lymph Node?
Antigens released by phagocytes
TNFa stimulate immature tissue resident dendritic cells - B7 expression
Dendritic cells phagocytose antigens
Dendritic cells digest antigens and display small peptides on surface in complex with MHC
Pathogen derived particles, antigens and mature dendritic cells travel to local draining lymph nodes
B Cell Activation
Opsonised antigen trapped by stromal cell
B cell binds to antigen, but needs a 2nd signal to activate
Antigen is protein = 2nd signal comes from T cell
Antigen is not a protein = 2nd signal from PRR+PAMP interaction on same antigen
Antigen is nuclei etc. = No 2nd signal needed, but must have multiple B cells binded
T Cell Activation
Only recognise peptide antigens presented by MHC
Needs two signals
Classes of MHC Proteins
Class I =
Expressed on all nucleated cells
Present peptide antigens to cytotoxic T cells
Class II =
Expressed only on professional antigen presenting cells (dendritic cells, macrophages, B cells)
Present peptide antigen to helper T cells
Clonal Expansion
Only antigen specific T cells and B cells will divide
Once there are enough, differentiation will occur
B Cell Differentiation
After clonal expansion, differentiate to plasma cells (effector B cells)
Produce antibodies
Non-protein antigens become low affinity, antigen specific antibodies
Peptide antigens (that used T cell help) become high affinity, antigen specific antibodies with memory cells
All are originally IgM, but high affinity antibodies differentiate further
Five Different Secreted Antibody Types
IgM IgG IgA IgD IgE
IgM
Surface bound monomer = BCR
First type produced during an immune reaction
IgG
Most abundant Ig in plasma
Actively transports across placenta
4 subtypes
IgA
Second most abundant Ig type
Monomeric form in blood
Dimeric form in breast milk, saliva, tears, mucosal secretions
IgD
Extremely low levels in blood
Surface bound = BCR
IgE
Extremely low levels normally
Produced in response to parasitic infection and allergic responses
Dual Biological Functions of Antibodies
Recognition Function
Effector Function
Recognition Function of Antibodies
Binding to antigen mediated by variable region sites
Prevent viruses from infecting host cells
Prevent microbial toxins from disrupting normal cell function
Effector Function of Antibodies
Clearance mechanisms mediated interaction of the content region with effector molecules Activate classical complement pathway Act as opsonins Help stimulate NK cells Can trigger allergic responses
Helper T Cells
Effector Th Cells
Come from CD4+ cells
Help to activate other immune cells
Cytotoxic T Cells
Effector Tc Cells
Come from CD8+ cells
Kill infected cells
Kill cancer cells
Effector Th Cells Helping Macrophages
Effector Th cells migrate from lymph node to infected/inflamed site
Th cells are reactivated by macrophages in an antigen specific manner
Th cells enhance macrophage killing activity and pro-inflammatory response due to expression of co-stimulatory molecules
Effector Th Cells Helping B Cells
Effector Th cells help B cels respond to protein antigens by providing the 2nd signal
Stimulate the Germinal Centre Response = B cell proliferation Antibody heavy chain switching Generation of high affinity antibodies Differentiation into plasma cells and memory B cells
Cytotoxic T Cells Killing Infected Host Cells
Effector Tc cells exit lymph node and migrate to site of infection
They recognise and kill infected tissue cells in an antigen specific manner
Their bigger, and full of granules which are directed to target cells
Which cells are responsible for Immunological Memory?
Memory Th cells
Memory Tc cells
Memory B cells
Long-lived plasma cells
Secondary (Memory) Response
Mainly IgG
Smaller lag phase
More antibodies produced
Probably fight the infection before you know you have it
