t cells

Question 1

where do t cells develop

Answer 1

T cells develop in thymus (B cells in bone marrow) from common lymphoid precursor

Question 2

how does diversity of T cells effect antigen recognition

Answer 2

diversity of TCRs means multiple antigens can be recognised however very few T cells that can recognise any given antigen

Question 3

what happens following antigen recognition by TCRs

Answer 3

clonal expansion of T cell follows after TCR antigen recognition

memory T cells are long lived cells following exposure to antigen and allow secondary response

CD3 complex transduces the signal received by the TCR to the cell, T cells need antigens presented to them, B cells do not (MHC presentation)

T cell activation requires costimulation, via CD28 receptors which binds to costimulatory ligands on antigen presenting cell (e.g B7)

Question 4

what are different types of TCR

Answer 4

90% of T cells have TCRalphabeta (CD4+ and CD8+ cells), 5-10% T cells have TCRgammadelta (enriched in the skin and gut)

Question 5

where do T cells bind to antigen presenting cell

Answer 5

CD4/CD8 receptors bind to non specific region of antigen presenting cell (specificity comes from TCR)

CD4 interacts with MHC class 2 and CD8 interacts with MHC class 1

Question 6

what are types of CD4 cells

Answer 6

CD4 cells can either be helper T cells (Th cells) or regulatory T cells (suppress immune responses)

Question 7

what are types of CD8 cells, how do these act

Answer 7

CD8 t cells are cytotoxic T lymphocytes (CTL), they have cytotoxic granules containing perforin and granzymes

perforin facilitates entry of the granzymes by forming pores, which cause apoptosis

CTL can also kill by binding to “death receptors” on target cells such as virally infected cells

Question 8

how do helper T cells act

Answer 8

CD4 helper T cells; when naive T cells become activated they can differentiate, into Th1, Th2 and Th17 etc (lots of types), they are defined by production of certain cytokines.

Th1 cell is defined by production of interferon gamma which acts on macrophages and is effective on intracellular pathogens

Th2 has IL-4, IL-5 and IL-13 which activates eosinophils, which is effective on parasites (helminths)

Th17 has IL-17 and IL-22 which activates neutrophils which is effective on extracellular pathogens

Question 9

where are T cells found

Answer 9

T cells circulate in both blood and lymph systems, they tend to get activated in lymph nodes since this is where antigen presenting cells and t cells are most concentrated together