Week 7 Flashcards
physical barriers
Skin Mucus Acid in gut Enzymes in secretions Commensal bacteria
soluble responses
circulating proteins that can recognise pathogen, deal with pathogen or assist in this
cellular responses
range of immune cells that can recognise and deal with pathogen
Cells associated predominantly with innate immunity
myeloid lineage
cell migration events
docking (rolling), adhesion, migration (extravasation)
How do our immune cells recognise a pathogen?
Pathogen recognition receptors (PRRs)
What features of pathogens do we recognise?
Pathogen associated molecular patterns (PAMPS)
PAMPS
Structures associated with pathogens and not found in our tissues
Important for survival of a pathogen as a species
toll like receptors (TLRs)
A family of PRRs
Innate receptors found in vertebrates and invertebrates
In vertebrates TLRs are found on cell surface and intracellularly
phagocytes
neutrophil; macrophage; dendritic cell
steps in phagocytosis
Recognition of pathogen (PRR: PAMP)
Engulfment in phagosome
Fusion of phagosome with lysosome (contains destructive cocktail of substances like enzymes and reactive oxygen species)
Generation of phagolysosome exposes pathogen to lysosome content (destruction of pathogen)
Granulocytes
Deals with pathogens that are too large to engulf
Intracellular granules which contain cocktail of destructive substances
Act by releasing their granules onto the surface of pathogen (degranulation)
Many cells work together to achieve this
key mechanisms of innate immunity
phagocytes- phagocytosis
granulocytes- degranulation
complement- promotes phagocytosis, cell destruction
antigen processing and presentation
dendritic cells capturing pathogen and processing it so that T cells can be activated
MHC Class I
expressed on all nucleated cells of body
MHC Class II
expressed by DC, macrophages, B cells
MHC Class I explain
Presents pathogen proteins that are found in the cytoplasm
For a DC initiating the immune response, it presents to CD8 T cells (which only recognise MHC Class 1+ peptide)
For other cells of the body,, if they are infected with virus, they use this MHC to display viral peptide to be recognised by the cytotoxic CD8 T cell for killing
MHC Class II
Processes and presents pathogen proteins that originate from outside the cell
For a dendritic cell initiating a response (bacteria or dead infected cells) it presents to CD4 T cells (only recognises MHC Class II + peptide)
Activated CD4 T cells are also called helper T cells
They help CD8 T cells become better cytotoxic T cells
They help B cells secrete the right type of antibody
autoimmunity
based on the process of recombination, we will also generate receptors on T and B cells that could react to our own tissues and cause self reactive immunity
This requires a mechanism of immune tolerance to prevent this
T cells develop
thymus
B cells develop
bone marrow
During development t cells undergo tests
If they fail to make a TCR receptor they die
If they make a functional TCR that can recognise the MHC they survive (Positive selection)
During this development process the antigen receptors on T cell can sample our own molecules in the thymus
Negative selection t cells
If interaction of the receptors and self molecules is very strong, the cell is triggered to die
This removes many of the self reactive T cells that are generated because of the random nature that recombination generates unique receptors
IgD
found on surface of B cells
IgG
single unit secreted in high amount into the circulation and important against bacterial and viruses
can cross placenta to baby
IgE
single unit and found mainly attached to the surface of Mast cells
epithelial layers
IgM
large and made up of 5 singles units joined at the tail
blood circulation
IgA
dimer and actively transported across epithelial surfaces found in respiratory, gastrointestinal system etc.; transported in breast milk
neutralisation
antibodies bind to bacteria and prevent their invasion or entry
opsonisation
coating of pathogen by antibody
2 parts of the viral life cycle
Intracellular: following infection and assembly
Extracellular: upon release to infect new cells
Humoral response
b cells and antibodies
stem cells specialised
into a type of two progenitor cells (myeloid or lymphoid)
myeloid are innate cells
lymphoid become adaptive cells
lymph nodes
Lymph nodes allow cells and fluid from the tissues to drain through the lymph nodes and mount an immune response; the lymph fluid then drains back into the blood circulation
When a pathogen is encountered, it is carried to the lymph node by a dendritic cell
Within the lymph node there are many T and B cells that continually circulate
if infection in blood
taken by dendritic cell to spleen
CD8 cytotoxic T cell
only interact with MHC Class I
CD4 helper T cells
only interact with MHC Class II
t cell antigen receptor
surface of t cells
each t cell expresses only 1 type of TCR
cannot be secreted
amino acid sequence in TCR vary most
in variable region
b cell antigen receptor
when expressed on b cell surface, called b cell receptor (BCR)
can be secreted to form antibodies
B cell antigen receptors regions
variable
diverse
junctional
each B cells chooses one of V D and J genomic segments to make antigen binding site
Adaptive immune response
pathogen/antigen captured and DC moves to the lymph node where they can present pathogen
Within the lymph node, DC and T cell interact
T cell with TCR that recognises the MHC + Peptide will be activated
For CD4 T cells this is via MHC Class II, for CD8 T cells this is via MHC Class I
Clonal expansion of antigen specific t cells
This will generate a group of CD4 T helper cells and a group of CD8 cytotoxic T cells
T helper cells will then interact with antigen specific B cells to promote their proliferation
B cell can also process and present antigen on surface MHC class II
If the TCR on the T cell sees the same MHC+peptide on the B cell as presented by the DC it will activate the B cell to proliferate and secrete antibodies
Within the lymph node, the interaction of dendritic cell, T and B cells leads to generation of: CD4 T helper cells; CD8 cytotoxic T cells; antibody producing B cells (plasma cells )
monomer AB
igG
IgD
IgE
pentameter AB
IgM
dimer AB
IgA
Adaptive immune responses are generated in
lymphoid organs
