Dendritic cells:
- Direct initiation of adaptive immune response
- Process and present antigen to T cells
1.
2.
3.
4.
5.
MHC:
-
Pathogen captured by DC
Pathogen engulfed and broken down into peptides
Peptide loaded onto MHC molecule and transported to surface
DC travels from site of infection to lymph node
Within lymph node aim to find T cell specific for pathogen
Present peptides
T cells interact with
All cells express class 1 except RBC – all have peptide in groove (self or pathogen)
Only specific cells have 1 and 2
Dendritic cells, B cells and macrophages
T-Cells
Express receptors on their surface called antigen receptors
- Defines binding specifity
CD4 and CD8 are surface molecules associated with TCR that help TCR bind to MHC
- Provide binding stability and signalling in T cell
- CD4 bings MHC class 2
- CD8 class 1
B-cells:
Recognise antigen/pathogen via surface receptor
- Receptor will become antibody secreted by B cells
- Once activated, secrete this receptor
- Called antibody or immunoglobin
Antibodies bind to structures as they appear in nature
- Different classes/isotypes
- igG, igE, IgA and IgM
- localise to different parts of body
How variation occurs:
Molecular shuffling that can occur at DNA level
- happens in developing T and B cells
- variable region
Variable region encoded by gene segments within genome
- broken into gene segments
- each segment encodes a different part of receptor
- variable region encoded by V, D and J segments in genome
- contant region by C segments in genome
- random recombination of VDJ segements generate unique gene that encodes a unique
receptor
- heavy chain has 1 of each VDJ segment
-
light chain 1 of each VJ segment
V = variable
D = diversity
J = joining
For heavy chains
- 44 V
- 27 D
- 6J
= 7128 possiblities
Light chains:
- 31 V
- 5J
= 155 different
Gene segments for TCR and BCR on different chromosomes
- Not shared
Process happens only in T and B cells as they develop from bone marrow cells
- Random and independent to each cell
- Cannot be inherited
Steps in Immune Response:
1. Pathogen exposure and presentation
- APC engulfs, degrades and displays on MHC class 2
2. Migration
- Moves from site of infection to lymph node
3. T cell activation
- Helper T binds to complex via antigen receptor and an accessory protein (CD4)
- CD8 on cytotoxic binds to class 1 MHC
4.
-
B cell activation:
Cytokines from t cell
T and B cell interact via TCR on T cell and MHC on B cell
B cell presenting antigen to T cell via MHC class 2
5. T and B cell effector functions
- Antibodies secreted
- Cytotoxic T cells
Viral Infection:
At site of infection viral antigens presented onto MHC
- Dendritic cells take up virus or virus infected dead cells and present on MHC
- Geneate helper T and cytotoxic T
-
Antigen specific B cells interact with antigen specific T cells and are activated to
produce virus specific antibodies
At site of infection viruses being generated and infected cells present viral antigens on
surface of MHC
New viruses released from infected cells bound by antibody and prevented from infecting
new cell
Cytotoxic enter circulation and kill cell via apoptosis
- Eliminates capacity to make new viruses
Recognition, Acticatoon, Effector (elimination of antigens), decline, memory
Ability to generate memory cells enables us to remember past infections
- Immune response faster and stronger 2nd
- Vaccination effective