L44 T Cells Flashcards
(21 cards)
what are the main types of specific T cells and their functions?
T helper (Th) cells (CD4 +ve)
- Help one another
- Activate B cells
- Activate phagocytes
T killer cells
- Cytotoxic T lymphocytes (Tc) (CD8 +ve)
- Effective at attacking viruses
T regulatory cells (Tregs)
- not fully understood
- regulate or suppress other cells in the immune system
- protect against autoimmune disease
how are T cells activated?
need antigens “presented”, otherwise can’t recognise or respond to them eg by antigen presenting cells
which cells can present antigens?
monocytes and macrophages
b cells
dendritic cells
what do t cells do once presented with the antigen?
Boost the immune response –e.g. release IFNg activating macrophages (CD4 +ve)
- Kill directly (CD8 +ve)
what is a TCR and how does it recognise an antigen?
t cell receptor TCR is associated with CD3 molecule (CD3/TCR complex)
the TCR only recognises the antigen when it is presented together with an MHC molecule. In order to signal that the TCR has been activated, the TCR interacts with another membrane bound protein complex called CD3.
how are lymphocytes subdivided?
according to cluster of differentiation:
- CD4 (helper cells)
- CD8 (cytotoxic cells)
how are antigens presented to T cells?
Antigen is processed
Antigen is presented in conjunction with major histocompatibility complex (MHC)
MHC is present on all cells and they are individual-specific:
- MHC I for CD8 Tc
- MHC II for CD4 Th
but a SECOND SIGNAL is required
how does the presentations of MHC I or II differ in immune response?
viral antigens are presented with MHC class I molecules to the T cell by an infected cell. The result is that the Tc cell will kill the infected cell.
APC cells present the foreign peptide to together with MHC class II to Th cells. These cells do not kill the APC, but release cytokines to trigger an immune response.
what is the second signal required for T cell activation?
comes from the recognition of a CD28 molecule on the T cell by a CD80 molecule on the APC cell. The reason for this is to prevent T cells being activated by the body’s own (host) antigens, which would lead to an autoimmune response.
how does a T cell become anergic?
anergic = does not respond to antigen
this happens when there is no second signal
how does activation of T helper cells differ from activation of cytotoxic T cells?
Activation of T helper (Th) cells result in cytokine production
- Chemoattraction (attracting other cells to site)
- Autoactivation (more Th cells become activated)
- Augmentation of inflammation
- Stimulation of Ab production by B cells
Activation of T cytotoxic (Tc) cells result in cellular death
what are cytokines?
Cytokines produced by lymphocytes (mainly T cells)
Draw more cells to site of injury
Activate T cells
Activate B cells and cause Ab production
Activate macrophages
how do Th1 and Th2 cytokines differ?
Th1 activate cell mediated immunity
- IL-2, IL-15, IFN-g
Th2 are responsible for antibody production
- IL-4, IL-10, IL-13
Balance between Th1 and Th2 can decide disease presentation or clinical course
how would activated Th1 and Th2 differ in disease and treatment?
disease:
Th1 response = tuberculoid leprosy. it os contained, fewer bacteria, may fully recover
Th2 response = lepromatous leprosy. more antibody driven response to pathogen. worse, will not recover fully
treatment:
Immune treatment of multiple sclerosis (Th1 disease) can result in the development of Graves’ disease (Th2 condition)!!!
how does HIV spread?
HIV virus has an antigen on the surface called gp120
CD4 forms the receptor for this antigen (virus is attached to CD4 cells like an anchor). this allos the virus to invade the Th cell
Virus injects its RNA and reverse transcriptase into the cell (transforms RNA to DNA) and forces the cell to make viral genes and forget about its own function, with the net result of HIV replication
how is central tolerance built up in the bone marrow and in the thymus?
Bone marrow (B cells):
- Clonal deletion when cells encountering self are recognised
- Receptor tolerance (daily encounter with the antigen)
Thymus (T cells):
- Positive selection: only cells recognising MHC survive
- Negative selection: cells recognising self antigen die (clonal deletion)
what is peripheral tolerance?
Regulatory T cells that eliminate immune cells directed against self antigens
Absence of second signal when lymphocytes are activated (immune cell anergy)
Anatomical barriers and immune privileged areas:
- Inside the eyes (injury to one eye can cause immune destruction to the other eye – complete tragedy = sympathetic ophthalmia)
how are autoimmune diseases caused and what are they?
AD occur when self tolerance against a body antigen is broken.
These include organ specific autoimmune conditions:
- Thyroid disease
- Type 1 diabetes
- Pernicious anaemia
- Some skin conditions
Non-organ specific autoimmune conditions:
- Systemic lupus erythematosus (SLE)
what is the interaction by t and b cells?
antibodies triggered when B cells encounters antigen
b cell takes antigen and digests it
it displays antigen fragments to its distinctive MHC molecule
combination of antigen fragment and MHC molecule attracts help of mature T cell
lymphokines secr. by t cell allow b cell to multiply + mature into plasma cell
antibodies rels. into bloodstream, and lock onto antigens. complex is eliminated by complement system or liver/spleen
(B cell that has recognised its specific antigen will only proliferate and mature after it has interacted with a Th cell)
(image on OneNote)
what is the link between innate and specific immunity for B cells?
innate:
cellular - neutrophils
soluble - complement
then goes to acquired:
b cells
then humoral immunity
extracellular organisms
what is the link between innate and specific immunity for T cells?
innate:
cellular - NK cells
soluble - cytokines
then goes to acquired:
t cells
cell-mediated immunity
intracellular organisms
