Cell Mediated Immunity Flashcards
(34 cards)
What do CD4+ cells do?
Secrete cytokines to help other immune cells gain functional ability.
What do CD8+ cells do?
CTL. Kill infected cells, tumor cells, and sometimes even healthy cells in an autoimmune response.
How are naive T cells activated?
Activated by pAPC (macrophages, DC, active B cells). DCs activate naive T cells most efficiently due to their high levels of costimulators.
What are the functions of cell adhesion molecules in immunity? What is an example of a cell adhesion molecule?
They glue t-cells and APC’s together so that TCRs can sample everything sufficiently. CD58 (on APC) and CD2 (on T cell).
What molecules give T cells signal 2?
B7 (on APC) and CD28 (on T cell). Also, CD40 (on APC), and CD40L (on T cell).
CTLA4
Can also bind to B7 on APCs with a higher affinity than CD28. Provides a suppressive signal to ensure proper T cell regulation. Gets upregulated when B7 binds to CD28.
Where does T Cell activation occur?
Lymphoid organs, then they migrate to the site of infection.
What happens if a T cell receives signal 1, but not signal 2?
Anergy, a state of partial paralysis, occurs.
CD40 and CD40L
Costimulatory molecules that activate APC’s to continue activating T Cells (through cytokine release, upregulation of B7, etc.)
What is signal 3?
Cytokines secreted following the delivery of signals 1 and 2 that determine the effector response.
Why are DC’s such powerful APCs?
Because they have a lot of costimulatory molecules.
TCR structure
Alpha and Beta chains, which, when bound, induce activation of the CD3 complex, a series of proteins that propagates the activation signals. CD3 complex also serves as a marker of mature T cells.
Marker of mature T cells?
CD3 complex
How do CD4 and CD8 participate in T Cell activation?
They stabilize the binding of the MHC to the TCR, and can stimulate ITAM phosphorylation which upregulates effector genes.
What happens when a CD4 cell is activated by signals 1 and 2?
It creates Th Cell that upregulates IL2R and releases IL-2, which causes clonal expansion of both CD4 and CD8 cells.
Th1 Cells
Secrete IL-2 and IFN-Gamma after signals 1 and 2 (MHC and CD40), promoting macrophage activation, T cell proliferation, antibody production.
IL-2
Induces T-cell proliferation. Released from Th1 cells.
IFN Gamma
Released from Th1 cells. Activates pAPCs by increasing expression of MHC and B7. This will activate both CTLs and Ths. Stimulates intra-APC destruction of pathogens. Also, helps B cells make antibodies, specifically IgG, which promote complement binding and opsonization.
Th2 Cells
Secrete IL4 and IL5. Involved in allergy and helminth attack.
IL-4
Induces production of IgE antibodies that mediate allergic responses.
IL-5
Activates eosinophils involved in allergy.
Th17 Cells
Secrete IL-17.
IL-17
Induce inflammatory response by activating neutrophils, promote secretion of defensins, and increase epithelial barriers.
Treg Cells
Suppress T cell responses by secreting TGF B and IL-10.
