Adaptive immunity Flashcards
Describe the overview of the adaptive response roughly
- infection
- transport of antigen to lymphoid organs
- recognition by native T and B cells
- clonal expansion and differentiation to effector cells
- removal of infectious agent
Why is the adaptive response advantageous?
- generation time for bacteria can only take 20 mins and our generation time is 20 years
- rapid evolution of pathogens means that new receptors will be required continuously
- to compete, new receptors are continuously generated as lymphocytes develop in the bone marrow and thymus
What is an antigen?
any molecule that is specifically recognised by either T cell receptors (TCR) or antibodies
What is an epitope?
the site on an antigen that directly binds to an antibody or TCR
what is a T cell antigen?
peptide derived from an antigenic protein
What is a B cell antigen?
Proteins, carbohydrates
What is an antibody made up of and where does the antigen bind?
- variable region (antigen binding site)
- constant region
How is the structure of the variable region decided?
- in the germ-line DNA there are small segments of DNA in groups V,J and D
- bone marrow cell will randomly select one V, D and J segment which will form the gene that determines the variable region
- this is how diversity is created, by random gene recombination
What happens to newly produced B and T cells?
they are constantly recirculated through lymph nodes, lymphatic vessels and blood which improves the likelihood of encounter of a rare antigen specific cells with the antigen
What type of antibodies are produced at the start of an immune response and why?
- IgM antibodies because they are pentameric so have 10 binding sites
- low affinity
What types of antibodies due you produce later on in the immune response?
- IgA (secreted to mucous membranes)
- IgD (membrane receptor)
- IgE (Localised on Mast cells)
- IgG (highest concentration in serum)
- smaller molecules (find it easier to move into tissue)
- more specific
- all have different roles
In terms of antibodies, what happens when a B cell differentiates into a plasma cell?
-lots of antibodies are released over a long period of time
What are the functions of antibodies?
- neutralisation (prevent bacterial adherence)
- opsonisation (promotes phagocytosis)
- complement activation (antibody activates complement which enhances opsonisation and lyses some bacteria)
Where do T cells differentiate?
in the thymus gland
How are naive T cells produced?
- T cell precursor leaves bone marrow and does into the thymus gland
- in the thymus gland the cells proliferate and undergo TCR gene rearrangement
- selection occurs (removal of self-reactive cells)
What cell type presents antigens to T cells?
Dendritic Cell
How do dendritic cells transport the antigens ti lymph nodes?
- immature dendritic class reside in peripheral tissues
- dendritic cells migrate via lymphatic vessels to regional lymph nodes
- mature dendritic cells activate naive T cells in the lymphoid organs such as lymph nodes
When is the only time that TCR will recognise antigens?
if they are presented on MHC proteins
How does antigen presentation occur?
- the epitopes recognised by T cell receptors are often buried
- the antigen must first be broken down into peptide fragments
- the epitope peptide binds to a self MHC molecule
- the T cell receptor binds to a complex of MHC molecule and epitope peptide
What will CD4+ T cells recognise?
exogenous peptides bound to MHCII proteins
What is the consequence of CD4+ T cell recognising an antigen?
production of cytokines
What is the role of Th1?
provides help signals for macrophages
What is the role of Th2?
help signals to B cells, in particular for production of IgE
What is the role of Th17?
inflammation
What is the role of Tfh?
support B cell differentiation?
What will CD8+ cells recognise?
antigenic peptides bound to MHC I proteins
What is a CD8+ cell also known as?
a cytotoxic T cell (kills infected cells)
How does a cytotoxic T cell cause apoptosis?
- Cytotoxic T-cell recognises and binds to virally infected cell
- T-cell programs the target for death by inducing DNA fragmentation
- T-cell binds to its next target
- The target cell dies by apoptosis
What are the four tasks that the immune system needs to carry out?
- distinguish self from non-self
- effective removal of pathogens
- self regulation
- memory of pathogens encountered in the past
