Adaptive immunity Flashcards
Which cells are involved in the adaptive immune system?
T cells
B cells
Dendritic cells
Give an example of clonal variation
Billions of ready-made identical neutrophils
Give an example of clonal selection
Billions of different B cells that require several days of differentiation
What happens when a B cell detects an antigen?
Rapid proliferation of lymphocytes
Lymphocytes produced are clones and are specific
What is an antigen?
Any molecule that is specifically recognised by T cells or antibodies
What is an epitope?
The site on the antigen that binds directly to the antibody or T cell
What is a T cell antigen?
A peptide derived from an antigenic protein
What is a B cell antigen?
A protein or carbohydrate
What are the two parts to an antibody molecule?
The antigen receptor (variable region) The effector (constant region)
What is the structure of a T-cell receptor?
Variable region
Membrane bound constant region
What creates a diverse range of T and B cell receptors?
Random genetic recombination
What is the estimated number of possible T and B cells?
100 billion
What is the normal activity of B and T cells in the body?
They constantly circulate the body through the lymph nodes, lymphatic vessels and blood vessels
This increases the chance of them detecting an antigen
Describe immunoglobulin structure
Two heavy chains and two lights chains
Bonded by disulphide bridges
What does the heavy chain determine?
The function of the antibody
Immunoglobulins form part of the structure of B cell receptors. What is the other component?
CD79 A+B
What do plasma cells release?
Plasma cells release immunoglobulins as antibodies
Name the three roles of antibodies
Neutralisation
Opsonisation
Complement activation
What is the purpose of neutralisation?
The antibody prevents bacterial adherence
What is the purpose of opsonisation?
The antibody promotes phagocytosis
What is the purpose of compliment activation?
Antibody activates complement
Enhances opsonisation
May lyse the bacteria
Which cell pathway are antibodies involved in?
The antibody triggers C1q which then activates CD3
Describe B cell development
Naive B cell develops in bone marrow
Describe B cell development
B cell matures in bone marrow
B cell detects antigen and is activated
Memory B cells are produced
Plasma cells are produced
What is a plasma cell?
A cell that produces specific antibodies in response to an infection
Outline T cell development
T cell precursor made in bone marrow, migrates to thymus Thymus produces CD4 and CD8 cells These circulate the body Detect antigen Develop into effector or memory T cells
What must an antigen be presented on for it to be recognised by a T cell?
A MHC protein
Why must an antigen be presented on a MHC protein?
The epitope is usually hidden within the peptide
The antigen must be fragmented
The epitope then binds to MHC where it can be recognised
What activates a naive T cell
A dendritic cell
What does a CD4+ T cell recognise?
Epitopes bound to a class II MHC protein
What does a CD8+ T cell recognise?
Epitopes bound to a class I MHC protein
What do the following T cell helpers do? Th1 cell Th2 cell Th17 cell Tfh cell
Th1 cells provide signals to macrophages
Th2 cells provide signals to B cells (production of IgE)
Th17 is responsible for inflammation
Tfh support B cell differentiation
Describe the functions of these antibodies IgM IgA IgG IgD IgE
IgM is produced early in immune response IgA is secreted to mucous membranes IgG has the highest serum concentration IgD is a membrane receptor IgE is mainly localised on mast cells
How does the action of CD4+ and CD8+ cells differ?
CD4+ cells recruit macrophages
CD8+ cells trigger apoptosis
They referred to as cytotoxic T cells
What is the action of a cytotoxic T cell?
The cell binds to virus-infected cell
Programs cell death by DNA fragmentation
Moves to next target
Cell dies by apoptosis
