topic 5 Flashcards
How are intracellular organisms able to survive?
They resist destruction within vesicles
They get out of the vesicles into cytoplasm
They only replicate within the cytoplasm, not within vesicles
Where do positive and negative selection occur in the thymus
positive selection in the cortical epithelial cells
Negative selection on the phagocytic cells in the paracorticomedullary junction
What 3 kinds of intracellular microbes exist
microbes that don’t enter through phagocytosis
microbes that can survive in phagolysosome
microbes that can escape from phagolysosomes
What are the steps of naive t cell response to an antigen
binds apc
IL-2 is released by T-cell and taken up by IL-2R (autocrine). IL-2 is a t cell growth factor
Clonal expansion
Differentiation into effector T cells or memory t cells
What kinds of molecules are involved in T cell activation
Recognition cells, signal transduction cells, and adhesion cells
What molecules are in a T cell receptor complex and what molecules are co-receptors and what are their functions?
CD4/8 are co-receptors and are involved in recognition (of the MHC) but also in signal transduction
TCR bind to the MHC/peptide complex. It is part of the T cell receptor complex
CD3 and zeta don’t bind to anything on the APC but are part of the T cell receptor complex and thus when TCR binds, they send out a signal
What are super antigens?
They are components of microbes that cause a tcr to bind with a non-specific or non-match MHC/peptide complex. Therefore, many T cells are activated which leads to excess cytokine release which contributes to disease.
This allows the microbe to grow while the t cells are distracted with other things
Staphylcoccus aureus and streptococcus pyogenes are examples
What is co-stimulation
If an APC doesn’t express a co-stimulator (B7-1/2), then no t-cell response occurs even if the TCR binds correctly.
However, when an APC does express costimulator B7-1, it is recognized by CD28 on the t cell and leads to IL-2 being express and thus proliferation and differentiation.
What is the role of adhesion molecules? What steps take place?
T cells need to be in close proximity with APC for a certain amount of time. Adhesion molecules allow this.
Initially, the integrins (LFA-1) on the T-cell are in a low affinity state.
Signals delivered by chemokines and antigen recognition activate integrins to put them in a high affinity state.
Integrins (LFA-1) binds ICAM-1 on the APC, then integrins cluster creating adhesion which leads to a t cell response.
What is an immune synapse and a SMAC?
Receptors and ligands cluster around AG recognition site leading to stable adhesion and optimal signal transduction.
This area of adhesion is referred to as the immunological synapse.
The cluster of molecules is referred to as a supramolecular activation complex (SMAC)
On the inside is the cSMAC containing TCR, CD4/8, CD28, CD3.
On the outside is the p-SMAC containing the LFA-1 and ICAM-1.
What are the basic steps in signal transduction
receptor
ITAM-Immunoreceptor tyrosine-based activation motif
biochemical intermediates
active enzymes
Transcription factors
Expression of IL-2, IL-2R, other cytokines and growth factors.
What are some general properties of T cell cytokines
Produced in response to antigen, only when needed
Acts usually by autocrine means but maybe paracrine with nearby cells
pleiotropism-Each has multiple biological affects
Redudancy-many do the same thing
What are the special activation requirements for CD8 T cells and how does it happen?
They require co-stimulation
They require helper T cells.
A dendritic cell binds to a CD8 cell and a CD4 cell.
The dendritic cell expresses a costimulator
The CD4 cell releases cytokines which allow the CD8 cell to be activated.
Steps of clonal expansion due to IL-2
Before a T cell encounters an antigen, its IL-2R is in a low affinity, dimeric state.
T cell is activated by antigen and costimulator
IL-2 is secreted
Another subunit of the IL-2R is expressed due to activation and the trimeric IL-2R is in a high affinity state.
Cell proliferation ensues.
What are general characteristics of TH1 and what are the steps in its response?
Th-1 cell uses IFN-gamma, it activats macrophages and produces IgG, it fights intracellular microbes, and is involved with autoimmune diseases and tissue damage associated with chronic infections
Bacteria binds to APC, APC binds to naive T cell, Naive T cell releases IFN-gamma which:
Activates macrophages, causes complement binding and opsonizing IgG antibodies, and activates CD8 T cell
