COORDINATING THE IMMUNE RESPONSE TO INFECTION Flashcards
what are the 4 ways in which we characterise T cells from being different to one another?
phenotype, MHC restriction, function and cytokines they produce
what does it mean to say “we can characterise different T cells based on phenotype”?
by identifying different molecules expressed on the surface or inside the cell.
what is MHC restriction?
T cells will only respond to the antigen when it is bound to a particular MHC molecule
which cells are MHC class 1 and class 2 restricted?
class 1- CD8+ class 2- CD4+
describe what happens in the MHC class 1 antigen presentation pathway?
small peptides are delivered into the endoplasmic reticulum. MHC class 1 molecule binds permanently to a small peptide and this is pinched off into a vesicle and migrates to the cell surface where it fuses and presents the antigen to CD8+ T cells.
describe what happens in the MHC class 2 antigen presentation pathway?
exogenous antigens are taken up into cells by endocytosis/engulfed. in the endoscope, antigens interact with MHC class 2 molecules, they bind and the vesicle travels to the cell surface and presents the antigen to CD4+ T helper cells.
what is the function of Cd4+Tfh? and what are they?
T follicular helper cells
help form the germinal centers and B cell antibody affinity maturation
what is the function of CD4+Th1 cells?
activation of phagocytes for enhanced killing of intracellular pathogens
what is the function of CD8+ cells?
activation of phagocytes for enhanced killing of intracellular pathogens
What if the function of CD4+ Th2?
activation of responses targeting extracellular pathogens
what is the function of CD4+ Th17?
activation of neutrophils/autoimmunity/anit-fungal responses
What is the function of CD8+CTL?
direct killing of infected target cells or cancer cells
they are cytotoxic T lymphocytes
What is the function of CD4+ Treg?
inhibits the functions of other T cells
T regulatory cells
What cytokines do CD4+ produce?
IL2
what cytokines do Th1 and CD8+ release?
interferon gamma
What cytokines do Th2 release?
IL-4
what cytokines do Th17 release?
IL-17
what cytokines do T follicular helper cells release?
IL-21
What are the 3 signals T cells need to become activated?
T cell receptor engagement
costimulation
cytokines
what is T cell receptor engagement?
T cell receptors engage with an antigen being presented by an APC
what is costimulation in T cell activation?
ligands present on the antigen present cells bind to ligand receptors on T cell surfaces. This enhances the first signal.
what’s the cytokine phase of T cell activation?
phagocytes release cytokines and these tell the T cell what type of cell it should become.
What happens after T cell activation?
proliferation and differentiation of T cells occurs to produce effector T cells and memory T cells
What are the functions of IL-2?
to stimulate the proliferation of T cells and allows T lymphocytes to survive under homeostatic conditions
Describe clonal expansion of T cells?
naive T cells interact with antigens and this initiate proliferation. Activated T cells produce effector T cells and memory cells. memory cells can either remain as memory cells in lymphoid tissue or become effector cells and migrate to tissues. Effector T cells can die or become memory T cells
What do effector T cells secrete and have on their surfaces?
cytokines
Describe the difference between a primary and secondary immune response?
after first exposure populations of cells expand slowly and contract again but maintain a higher frequency than before. On second exposure, cells expands faster and to a higher degree and when it declines again the baseline is higher than before
why do we have boosters after vaccines?
as it increases our base level of memory
What happens if a T cell comes into contact with an antigen they recognise in.a lymph node?
they start to expand clonally and meet with B cells and help them to produce high affinity antibodies
what do follicular helper cells do?
they move into the germinal centres in the B cell follicles with a B cell where the B cells can undergo affinity maturation and migrate out as plasma and memory cells.
what’s the difference between a type 1 and a type 2 immune response?
1- caused by microbes and tissue damage
2- caused by helminths mainly, but also allergies and fibrotic tissue
What do T helper 1 and T helper 2 cells produce?
Th1- interferon gamma, IL-1, TNF
Th2- IL-4, IL-13, IL-10, Granulocyte-macrophage Colony stimulating factor
What are regulatory T cells?
Tregs
they control the immune responses to self and foreign antigens and help prevent autoimmune diseases
What are senescent T cells?
cells that enter a terminal differentiation state due to excessive cell replication
What are anergic T cells?
an unresponsive state induce by failing to react to an antigen due to only 1/3 signals occuring
What is T cell exhaustion?
a progressive loss of effector function due o prolonged antigen stimulation
why are T cells not effective against cancers?
due to T cell exhaustion
what are checkpoint inhibitors?
Checkpoint Inhibitors Block Antibodies that Hide Cancer Cells from the Immune System
what can dendritic cells do?
detect pathogens and activate an innate response, eliminate pathogens through phagocytosis, activate T cells which can activate B cells, produce antigen-MHCII complexes so can provide costimulation to active T cells
give time scales for the innate and adaptive immune response to kick in
innate- 0-4 hours after infection
adaptive- over 96 hours after infection
why are antibodies in the secondary response more successful in disposing of antigens?
as they have a higher affinity for antigens and there are more of them already
