Adaptive Immunity Flashcards
When does adaptive immunity come in to place
Infection overcomes innate defence mechanisms
so pathogen continues to replicate and antigen accumulates
What cells activate the adaptive immune response?
Dendritic cells
What does adaptive immunity involve?
Humoral response- antibodies
T and B lymphocytes
Slower
Specific to antigen
What do T and B lymphocytes provide?
Immunological memory
What are antigens?
Proteins/peptides on pathogen surface that are recognised by lymphocytes to initiate an immune response
Name of primary lymphoid organs?
Thymus, Red bone marrow
What occurs in primary lymphoid organs?
Sites of lymphocyte development and maturation from bone marrow derived stem cells
Where are B and T lymphocytes made?
Bone marrow
Where do B cells mature and develop?
Bone marrow
Where do T cells mature and develop?
Thymus gland
Examples of secondary lymphoid organs?
Lymph nodes
Spleen
MALT
What occurs in secondary lymphoid organs?
Lymphocytes are activated
Immune response is coordinated
What happens during development and maturation of B cells in bone marrow?
Express receptor- BCR (antibody) that binds to antigen
Plasma cells produce antibodies
What happens during development and maturation of T cells in the thymus gland?
Express a T cell receptor(TCR)- binds to antigen on APC
What are the 3 types of T effector cell?
Cytotoxic T cell
Helper T cell
Regulatory T cell
What does the regulatory T cell do?
Suppresses the immune system
preventing autoimmune responses
What does T helper cell do?
Activates other T cells and B plasma cells to produce antibodies
What happens when BCR binds to antigen?
Phagocytosis of pathogen
Phagolysosome destroys pathogen
Antigens are loaded onto MHC II in phagolysosome
Antigens are presented onto surface
B cell APC MHC II
B cell becomes activated by T helper cell- costimulation (CD40), Cytokines (IL-4,IL-10,IFN-Gamma) Induce class switching
What happens when TCR binds to antigen?
Proliferation causing:
Cytotoxicity (killing cells)
Helping other immune cells
Regulation (turning off immunity)
Advantage of secondary immune response?
Triggers a quicker secondary response when same pathogen re-infects
Correct, specific antibodies produced in a shorter time before symptoms arrive
Why are BCRs and TCRs different?
Each bind to a specific antigen
Therefore each cell responds to a certain pathogen
How are different BCRs and TCRs made?
Chopped into segments
Stuck back together
Structure of TCR
Heterodimeric 2 chains- alpha and beta held together by disulphide bonds C= Constant region J= Junctional - join things together V= Variable region D= Diversity- only found in Beta chain
Name of process of creating new TCRs?
VDJ recombination (somatic recombination) Gene rearrangement
Alpha chain of TCR
54 V segments
61 J segments
1 C segment
Beta chain of TCR
67 V segments
2 D segments
14 J segments
2 C segments
Structure of BCR
Heterodimeric receptors 2 chains Light and heavy chains held by disulphide bonds Variable region (top bit) Constant region (bottom bit)
How are new BCRs made?
Nucleotides can be added/removed to make them more specific to antigen
Somatic recombination- done in bone marrow
What are the differences between BCRs and TCRs?
BCRs- bind directly to antigen even if they are still attached to pathogen
TCRs- binds to antigens present on surface of APCs
So TCRs must bind to APC e.g macrophages/dendritic cells
What are the 3 signals T cells need to be activated?
- TCR binding to antigen presented by MHC on APC
- Costimulation (B7 molecules)
- Cytokines (IL-4/10/12/23)
2 main types of T cell
T helper cell
Cytotoxic T cell
co-receptor of cytotoxic T cell?
CD8
What kind of APCs do cytotoxic T CD8 cells bind to?
MHC I
Function of cytotoxic T cell
Kills virally infected cells directly
co -receptor on T helper cell?
CD4
What kind of APCs do T helper CD4 cells bind to?
MHC II (professional)
Function of T helper cell
releases cytokines
activates other T cells and B plasma cells to make antibodies
What are human leukocyte antigens (HLA)
Group of proteins that are encoded by the MHC gene
What HLAs do MHC class I code for?
A,B,C
What HLAs do MHC class II code for?
DP, DR, DQ
What are epitopes?
When large protein antigens are digested into small peptides
Where are epitopes bound to in a HLA encoded by a MHC gene?
Antigen binding groove- on MHC
Where are MHC class I found?
All nucleated cells
How many amino acids can antigen binding groove of MHC I hold?
8-10
Where are MHC II found?
On professional APCS
e.g macrophages and dendritic cells
how many amino acids does antigen binding groove of MHC II hold?
at least 13
What are MHC genes like and why?
Highly polymorphic
To protect from population from infection
Have a broad specificity meaning they can bind to many types of antigens
Apart from HLAs that MHC genes code for what do other proteins do that the MHC gene codes for?
Processes antigen
What does the p arm (short arm) of MHC gene on chromosome 6 code for?
Many HLAs
How does an APC MHC I present antigens onto its surface?
- Body cell is infected by virus
- virus enters cell
- Virus is degraded and broken down by proteosome
- Antigens are retained and loaded onto MHC I in the endoplasmic reticulum
- Antigens are on antigen binding groove of MHC I
- Antigens are presented onto cell membrane
- Activates CD8 cytotoxic T cells
How do cytotoxic cells kill cells expressing MHC I foreign antigen?
Release perforin- punctures holes in cell membrane
Surface of cytotoxic T cell has fas ligand= induces apoptosis of infected cell when FADD binds to it
How does cytotoxic T cell kill cells? (4 steps)
- Conjugate formation
- Membrane attack
- T cell detaches from target cell
- Target cell killed by apoptosis