B and T Cell Activation and Regulation Flashcards
What 2 things must happen for T cells to be activated by an APC?
Signal 1 = recognition of Ag bound to MHC I or MHC II via T cell’s TCR
Signal 2 = costimulatory ligand
What is signal 2?
Co-stimulatory molecules and cytokines
The TCR recognizes antigen bound to MHC but it cannot transmit that signal to the interior of the cell to produce a response. What other molecules are part of the TCR complex that lead to this respone?
CD4 –> binds to MHC II Beta 2 region and stabilizes interaction –> activates kinase that phosphorylates CD3 and zeta chain intracellular effector regions –> signal transduction and activation of Ras and MAPK pathways
For a T cell, what is signal 1?
The TCR complex (TCR + CD 4/8 + CD3 etc.)
What is signal 2 that is needed for interaction between dendritic cells and T cells in lymph nodes?
Dendritic cell expresses B7, which is the ligand for receptor (CD28) on T cells
Describe the process of dendritic cell maturation to express signal 2.
What are the downstream effects of activation of a t cell by signal 1 and signal 2?
Cell survival
Cell proliferation
Differentiation into effector and memory cells
Describe how activation by signal 1 and signal 2 leads to proliferation.
Signal 1 + signal 2 leads to T cell secreting IL-2, which leads to clonal expansion of that activated T cell
Activated T cells upregulate CD40 ligand. CD40 ligand binds to CD40 receptor on several cell types. Describe what happens when CD40 Ligand on the activated T cell binds to CD40 receptor on:
- A dendritic cell that is activating the T cell?
- B cells?
- Macrophages?
Intracellular microbes activate dendritic cells to secrete ______ which activates T cells to become Th# cells.
IL-12
Th1
Intracellular microbes trigger NK cells to secrete _____ which activates Th cells to differentiate into Th# cells.
INF-gamma
1
Secretion of IL-# in response to helminths causes Th cells to differentiate into Th# cells.
IL-4
Th2
Th cells are triggered to differentiate into Th17 cells in response to _______ pathogens.
Extracellular
Th 1 Differentiation
- Induced by what 2 cytokines?
- What cytokine is secreted by Th1 cells?
- What is the function of Th1 cells?
- IL-12 and INF-gamma
- INF-gamma
- Promotes killing of phagocytosed microbes and inhibits development of Th2 or Th17 differentiation
Th2 Differentiation
- What 2 cytokines induce differentiation?
- What cells induce differentiation?
- Cells that induce differentiation do so in response to what?
- What cytokines do Th2 cells secrete?
- What is the function of Th2 cells?
- IL-4 and IL-25
- Mast cells and eosinophils
- Helminths and allergens
- IL-4 and IL-5
What are 2 ways in which CD4+ cells can activate CD8+ cells?
Once activated, what do CD8+ cells do?
Same mechanisms as NK cells
What happens to a B cell after it has been activated by microbe/Ag binding to its cellular receptors (IgM or IgD)?
What is the ultimate outcome of T-dependent B cell activation?
Initial B cell undergoes minimal isotype switching and produces low affinity Ab. It then migrates to the germinal center of follicle in lymph nodes where it undergoes isotype switching and somatic hypermutation (via AID) to affinity mature.
How is B cell activation regulated?
Once sufficient Ab has been made, it will bind to a receptor (Fc receptor) on the surface of the B cell and block the effector signal from binding of microbe / Ag.
