T cells Flashcards
What is an antigen presenting cell?
Cells that link the innate immune response with T cell and B cell responses
What do APC’s do?
Take up proteins from pathogens and process them into antigen. Then present antigens on MHC to T cells that then become activated
Where are APC’s?
All over the body ready to meet a pathogen
What are the best APC’s?
Dendritic cells
What are T cells?
Lymphocytes that are specific for a particular antigen
What can T cells do?
Get activated bu APC’s and then increase in number and make cytokines and cytotoxic molecules. They can also destroy pathogens and help other immune cells destroy pathogens
What are the two types of T cells?
CD4 and CD8
What is the first step of the immune response?
Pathogen infects at a tissue site
What happens after a pathogen infects at a tissue site?
Dendritic cells live in the tissue sites and see the pathogen first
What happens after dendritic cells see the pathogen?
Dendritic cells process the pathogen into antigenic peptides and load them onto MHC
What happens after dendritic cells process the pathogen into antigenic peptides and load them onto MHC?
Dendritic cells with antigenic peptide move to the local lymph node
What happens after dendritic cells with antigenic peptide move to the local lymph node?
T cells live in the lymph node and meet up with the dendritic cells
What happens after T cells live in the lymph node and meet up with the dendritic cells?
T cells get activated in the lymph node and make cytokines or become cytotoxic
What happens after T cells get activated in the lymph node and make cytokines or become cytotoxic?
B cells in the lymph node get activated and make antibodies
What are examples of endogenous antigens?
Viral proteins produced during viral replication and proteins produced by intracellular bacteria such as listeria
What are examples of exogenous bacteria?
Fungi, bacteria and parasites
Where do T cells arise?
In the bone marrow
Where do T cells fully develop?
In the thymus
What do T cells express?
A T cell receptor
What does each T cell have?
A unique TCR specific for one peptide antigen and a co-receptor (CD4 or CD8)
What do T cells recognise?
MHC/peptide complexes
What happens in the bone marrow?
Production of T cell precursors and create T cells
What happens in the thymus?
TCR gene rearrangement, make T cells able to recognise antigen and get rid of T cells that recognise self antigens
What do immature T cells do?
Rearrange the variable parts of their TCR genes in the thymus
The rearrangement process is…?
Essentially random
What does Thymic gene rearrangement ensure?
That each individual T cell has a unique TCR
What does Thymic gene rearrangement create?
Diversity in T cell repertoire= can recognise all types of pathogens
What is the result of thymic gene rearrangement?
Mature (naive) T cells expressing unique antigen receptors (TCR)
What happens during recognition?
T cells express a TCR that recognises peptide and MHc
What happens after T cells express a TCR that recognises a peptide and MHC?
CD4 and CD8 co-receptors on T cells bind to MHC
What do CD4 T cells recognise?
Peptide antigen in context of MHC-l
What do CD8 T cells recognise?
Peptide antigen in context of MHC-ll
What do CD4 T cells make?
Cytokines to support other immune cells
What do CD8 T cells make?
Cytotoxic molecules to kill infected cells
What are naive T cells?
T cells which have not been activated by MHC/peptide
What are activated T cells known as?
Effector T cells
What do effector T cells do?
Kill infected cells, make cytokines, support antibody production by B cells and remember the antigen for next time
What does the CD4 T helper cell do?
Recognises MHC-ll/peptide, Helps CD8 T cell become cytotoxic and helps B cell make antibody
What does CD8 T cell do?
Recognises MHC-l/peptide and develops into cytotoxic T lymphocyte (CTL)
As well as effector cells what does T cell activation result in?
Formation of memory T cells
What do memory CD4 or CD8 T cells do?
Reside in the body for long periods of time and can become effector cells again much quicker than naive T cells do for the first time
What is the receptor for HIV?
CD4 molecule on CD4 T cells
What does infection lead to?
Loss of CD4 on T cells
What do CD4 T cells help?
Both B cell and cytotoxic T cell responses
What does HIV impact on?
Immunity to microbes (fungi, bacterial and virus) and to cancer
