T Cells and Cell Mediated Immunity Flashcards
Characteristics of T cells
cannot be distinguished from B cells
only recognize antigen when presented by an APC iwth MHC proteins (have to be spoonfed)
Sequence of events involved in T cell ontogeny
- Prothymocytes from bone marrow migrate to thymus
- Thymocytes differentiate into mature T cells
- Mature T cells from thymus travel to peripheral lymphoid tissues
- Memory T cells reside in the bloodstream until directed to enter non-lymphoid tissues
Th cells
conductor
subsets of CD4+
TH1 cells
cell mediated immunity
IgG can be produced
TH2 cells
humoral immunity
especially IgE
TH17 cells
ehance inflammation
Tfh cells
promotes germinal center formation in lymphoid organs
cytotoxic T lymphocytes (CTLs) (CD8 cells)
lyse virus infected cells
regulatory T cells (treg)
downregulate immunity
alpha-beta T cell antigen receptor function
encompasses the proteins on the surface of T cells that allow them to recognize and respond to antigen
not response for MHC restriction
involved in binding antigen and MHC
cytoplasmic tail not long enough to act as signal transducer, requires CD3
alpha-beta T cell antigen receptor structure
heterodimer of disulfide-linked alpha and beta chains
has constant and variable regions
different antigen specificity generated by altering variable regions
has single antigen binding site
CD3
composed of invariant polypeptides
phosphorylation sites on cytoplasmic tails for signal transduction (helps with t-rex arm problem)
Function of costimulatory moleulces
aid the T cell to become activated by triggering signal transduction
what does CD28 bind to
B7
What does CD40 ligand (CD40L) bind to?
CD40
CD4 characteristics
transmembrane glycoprotein consisting of a single polypeptide
present in small quanitites on the surface of macrophages
expressed on Th cells
are targets of HIV
CD4 functions
cell adhesion
signal transduction
restricts T cell responses to recognizing only class II MHC proteins
CD8 characteristics
composed of homodimer or heterodimer
most CD8-expressing lymphocytes are cytotoxic T lymphocytes
CD8 functions
cell adhesion
signal transduction
restricts T cell responses to recognizing only class I MHC proteins
TH1 cell activation
develop from uncommitted naive T cells
Cytokine signal: IL-12
produced under conditions of inflammation
TH2 cell activation
develop from uncommitted naive T cells
cytokine signal: IL-4
IL-4 produced by mast cells or antigen activated T cells
What type of immunity does TH1 help with and how
cell-mediated. produced IFN-gamma and activates macrophages and CTLs
What type of immunity does TH2 help with and how
humoral immunity
produces IgE for anti-parasite defense through production of IL-4, IL-5, IL-13
TH17 cell activativation
develop from uncommitted naive T cells when exposed to TGF-beta.
What does TH17 help with and how
promotes inflammation by producing IL-17 and IL-22
How do cytotoxic T lymphocyties become activated
part of cell-mediated immunited stimulated by TH1 cells
Function of CTL
destroy intracellular microbes, some tumor cells and transplanted tissues and organs
Steps of CTL killing process
1) bind to target cell
2) CTL activation
3) deliver lethal hit
4) disengage
5) target cell dies
Principle killing mechanism of CTL
perforin facilitates delivery of granzyme B to target cell cytoplasm
Granzyme B activates caspase pathway and you get apoptosis
Secondary killing mechanism of CTL
binding of CTL expressed Fas ligands targets Fas protein, this activates caspases and you get apoptosis
