Immunology Part 4 Flashcards
How long does the adaptive immune system take to respond?
Days-weeks
What method of recognition does the adaptive immune system use to recognise pathogens?
Antigens: antigen receptors
What are antigens?
any substance which can stimulate the adaptive immune system
What do CD4T+T cells do?
key regulators of the entire immune system
What do CD8+T cells do?
Kill virally infected body cells
How many antigen receptors do T and B cells express?
Multiple copies of one receptor
How do T cells recognise an antigen?
T cell antigen receptor (TCR)
Membrane-bound αβ heterodimer
How do B cells recognise antigens?
B cell antigen receptor (BCR)
Membrane bound antibody (IgM or IgD)
Light chain and heavy vhain
What are antibodies also known as?
Immunoglobulins
Where are antibodies produced?
By B cells in response to antigen
What do B cells do with antibodies?
Express them on their surface
Secreted as soluble proteins in extracellular fluids
What holds the two Ig light and Ig heavy chains together?
Disulphide bonds
What does each Ig heavy and Ig light chain contain?
Variable region and a constant domain
What are the heavy chains found in the following?
IgM
IgG
IgA
IgE
IgD
micro gamma alpha epsilon sigma
What forms the antigen binding site?
Hypervariable regions of Ig light and Ig heavy chains combined
How can the body defend against millions of antigens?
Process of gene rearrangement is entirely random
Gives rise to hugely diverse B cell and T cell populations
Potential for generation of auto-reactive cells
Where do adaptive immune responses occur?
Secondary lymphoid tissues
How do antigens enter a lymph node?
- Particles and antigens derived from pathogens are released by phagocytes
- Inflammatory cytokines stimulate immature, tissue-resident dendritic cells –> expression of co-stimulatory molecules
- dendritic cells recognise and phagocytose pathogen-derived particles and antigens
- Dendritic cells dies the internalised pathogen-derived antigens and display small peptides on surface in complex with MHC proteins
- Pathogen derived particles, antigens and mature dendritic cells travel to local draining lymph nodes
What do MHC proteins do?
display peptide antigens to T cells
What are the two classes of MHC proteins?
Class I MHC
Class II MHC
Describe MHC I
Expressed on all nucleated cells
Present peptide antigens to CD8+T cells
Describe MHC II
Expressed only on professional antigen presenting cells
- dendritic cells
- macrophages, B cells
Present peptide antigen to CD4+T cells
What two signals does T cell activation require?
MHC binding to TCR
B7 binding to CD28
What is the role of stromal cells?
Trap opsonised antigens in B cell zones
What two signals does B cell activation require?
Protein antigen;
Signal 1:BCR + antigen
Signal 2: TFH cell help
Any antigen;
Signal 1: BCR + antigen
Signal 2: PRR + PAMP
Antigens with repetitive antigenic epitopes;
Signal 1 + 2 : multiple BCRs engaged
What can B cells do that T cells cannot?
Can recognise antigens independent of MHC molecules
Describe the fate of antigen activated B cells and T cells
Resting cells
-specific antigen + co-stimulation
Activated cells
-Entry into cell cycle, mitosis
Clonal expansion
-differentiation
Effector cells and T cells
