Lecture 6D - The Role of T and B cells Flashcards
What can lymphocytes restore?
humoral and cell mediated immunity
What are the three main types of lymphocytes?
B cells
T cells
natural killer (NK) cells
Where do B cells mature?
in bone marrow
What happens when B cells are stimulated?
proliferate and develop into antibody producing plasma cells
Where do T cells mature?
in the thymus
What are the subtypes of T cells?
cytotoxic and helper
How do T cells work?
they do not secrete antibodies
they act by direct contact with antigens and by the secretion of regulatory factors
What can natural killer cells do?
have a separate lineage from T cells, but can kill cancer cells and cells infected with virus
What do B cells do?
they cannot kill directly but stimulate phagocytosis
What do plasma B cells produce?
antibodies
What do memory B cells do?
lead secondary immune response
When do B cells exist in the bone marrow from?
before birth
How are B cells activated?
by free antigen binding to the antibody, like receptor molecules which are entrenched in the cell membrane of B cells
Activation of B cells?
when free antigens bind to the immunoglobulins (IgM or IgD) receptors on the surface of B cells
What matches the antibody the B cells produce?
the Ig class and specificity of the receptors
What do most B cells in the blood stream express?
IgM or IgD
Where are B cells expressing other antibody classes?
they are localised to particular regions e.g. large amounts of IgA bearing B cells in intestinal mucosa
What does clonal selection theory postulate?
as each lymphocyte develops it becomes specifically programmaed to react with one particular antigen, even before being exposed to it
What do millions of different cell clones allow?
millions of different antigens to be recognised
During development in the bone marrow, what is each lymphocyte programmed to do?
react with one specific antigen
What does each cell have?
immunoglobulin surface receptors specific for the antigen which it is directed against
What is the binding of a particular antigen able to do?
selectively stimulate cell division of a specific clone
When do cells that recognise specific antigens exist?
before the body encounters the antigen
What is the diversity of millions of families of cell clones due to?
genetics
What are eliminated during development?
self reactive clones
this removes the danger of autoimmunity against the body’s own tissue
During infection, the binding of antigen to T or B cell causes?
stimulates division and proliferation of specific cell clones
What is a polyclonal response?
if a large antigen stimulates a response in a large number of B cells and causes the production of a variety of antibodies, each directed against a particular facet of the molecule
What is oligoclonal response?
when a few clone families are stimulated
What is a monoclonal response?
when a single T or B cell clone is involved in producing antibodies or a response
When is a monoclonal response seen?
only happens commonly in the cell culture situation
What do T cells need to have the antigen presented to them on?
Major histocompatibility complex protein
For many T and B cells, what will the lymphocytes do?
divide and become active cells
What do the active cells provide?
an immediate immune response
What do active B cells do?
secrete antibodies specifically directed against the antigen which first stimulated them
What do active T cells do?
carry out cell mediated responses against the antigen
What do some of the stimulates virgin cells become?
they multiply and develop as memory cells
What do memory cells do?
do not provide an immediate immune response
they become receptive to the antigen at a later date
What can memory cells lead to?
the secondary immune response
meaning they can kickstart the immune system response very quickly if the antigen reinfects, allowing us to overcome the infection very quickly
What are memory cells the reason for?
vaccines
they are vital to the lasting effectiveness of vaccines
What does the antigen fragment used in the vaccine do?
produces increase amount of antibody and T cells, it creates a long lasting population of memory cells which can lead to a rapid and greatly enhanced response to a specific infectious organism if encountered at a later date
What does the response of memory cells do?
quickly eliminates the previously encountered pathogen before it can become established and cause disease
What are manager T cells?
memory T cells
helper (CD4+) cells
suppressor/regulatory T cells
What are helper T cells?
coordinate and amplify the immune response - they release interleukins
Where are immature T cells found?
in the bone marrow, but they migrate and reach maturity in the thymus
What are effector T cells?
T death cells
cytotoxic (CD8+)
NK cells (different cell lineage)
What are suppressor T cells?
T cells which have suppressor activity, these might be continuously active and work behind development of tolerance and can dampen down activity of self reactive clones
What do cytotoxic T cells do?
kill upon contact with the target cell
What happens once contact between cytotoxic cell and target cell?
cell- cell adhesion proteins strengthen the contact and toxic agents are released locally which kill the target cell
Give an example of a toxic agent released by cytotoxic T cells?
the peptide perforin, which forms a porous channel like the complement system
How else can killer cells achieve results?
by perforin independent means
What an cytotoxic T cells act against?
virally infective cells and cancer cells
What are T death cells?
T delated type hypersensitivity cells
a specific subset of T cells that can induce cell death in an infected cell
What are T death cells important mediators of?
long lasting immune responses
What can T death cells bind to?
an infected cell and induce it to undergo hapitosis
What do T death cells help to kill?
macrophages infected by TB
What are memory T cells?
corresponding to memory B cells and give a kickstart to responding to a repeat infection
What do helper T cells release?
interleukins
What do interleukins do?
these are hormones that mean helper T cells can exert an influence at a distance of other T cell clones and start to get them active to rapidly exert an immune response
What does T cell activation require?
peptide antigens to be present to the Ig like receptors on their cell surface by special proteins on another cell called MHC
What do class 1 MHC proteins activate?
cytotoxic T cells
What do antigenic peptides presented on class 2 glycoproteins activate?
Helper T cells
What do activated Th cells seek out?
B cells (in lymph nodes) with same antigen specificity and they dock together
What does Th cell stimulate B cell to do?
proliferate, differentiate and secrete IgE antibodies against the target
Why can Th cells dock to B cells?
the MHC proteins are very variable in structure and so there will be a particular MHC cell surface protein which can pick up the same fragment that a B cell reacts to
How can B and T cells interact to enhance the immune response?
empowered by both antibody producing B and cytotoxic T cells
When is an immunological synapse created?
when the helper T cell with a fragment encounters the B cell which has cell surface receptors and antibodies directed against that same protein fragment
