T cell Immunity Flashcards
Glossary of terms
Anergy
state of nonresponsiveness to antigen; can’t respond under optimal conditions of stimulation
APC
specialized cells that present antigen and display their peptide fragments on the cell surface together with other costimulatory proteins required for activating naive T cells
what are the major APCs that activate naive T cells?
dendrites, macrophages, and B cells
B7 molecules
major T cell co-stimulatory molecules, B7.1 and B7.2. Closely related and both bind CD28
how many B7 molecules are there? what expresses them?
2; APC
What is another name for the B7 molecules?
B7.1=CD80, B7.2=CD86
CD28
receptor on T cells for the B7 costimulatory molecules
why is Cd28 important?
plays a huge role in activation and proliferation of T cells after they first encounter an antigen
Why is CTLA-4 important?
high affininity receptor for B7 molecules on T cells; plays a critical role in shutting of the T cell response
Granzymes
serine proteases that are involved in inducing apoptosis in the target cells
Homeostatis
state of physiological normality; in case of immune system
What does homeostatsis mean in the immune system
its state when the person is unaffected (ie numbers of lymphocytes)
IL-2 is
it functions to
cytokine produced by activated naive T cells; promote further differentiation and proliferation
why is IL-2 important?
key cytokine in development and contraction of the an adaptive immune response
IL-7 is
it functions to:
hematopoietic growth factor secreted by stromal cells in the bone marrow and thymus and other cells
promote T cell development, survival, and homeostasis
Perforin
protein that can polymerize to form membrane pores that are an important part of the killing mechanism in cell-mediated cytotoxicity
Other than stromal cells in the bone marrow and thymus, what other cells secrete IL-7
keratinocytes, dendritic cells, hepatocytes, neurons, and epithelial cells
what is a naive T cell?
Naive T cells have not yet encountered their antigen
What are the signals needed to maintain T cell homeostatis?
TCR: pMHC interaction
IL-7
What are the steps for T cells encountering their antigen?
- T cells enter a lymph node across a high endothelial venule in the cortex
- T cells monitor antigen presented by macrophages and dendritic cells
- Cells that do not encounter specific antigen leave by efferent lymph
- T cells that encounter their specific antigen proliferate and differentiate into effector cells
What are the functions of the accessory molecules?
control routes of T migrations, strengthen adhesion with APCs, signal transduction
how is control of cell migration routes maintained?
selectins, integrins, and chemokine receptors control migration in and out of lymph nodes
control release of effector and memory T cells to site of infection
How is the adhesion with APC’s strengthed?
integrins;
How is affinity of integrins increased?
affinity of integrins is increased by cytokines produced during inflammation and Ag recognition
What molecules facilitate transduction and how?
CD4 and CD8 coreceptors recognize MHC molecules
CD28-CD40L are receptors for costimulators expressed on APCs
What is the role of the interaction between ICAM-1 and LFA-1
prolongs cell to cell contact between the APC and T cell, as they must be bound for 6-12 hours to activate the naive T cell
Describe the process of the T cells and APCs
1.T cell binds APC through LFA1:ICAM1, acts as tether
2.subsequent binding of T cell receptor signals LFA1
3. LFA1 undergoes a conformational change that increases the affinity for ICAM1
allows for a stronger interaction between APC and T cell
What are the 2 signals required for activating naive T cells?
signal 1: antigen recognition
signal 2: microbes or substances released during innate immune response to microbes
Why do you need signal 1 (antigen recognition)?
ensures that the response is antigen specific
Why do you need signal 2? what does it mean?
ensures that the immune system is responding to microbes and not to harmless antigenic substances
activated APCs express molecules which in turn bind their respective ligands on T cells to deliver a costimulatory signal.
