Immune Response To Infection Flashcards
What are some pathogen niches?
Extracellular - eg candida and worms
Intracellular vacuolar - salmonella and chlamidya
Surface adherent - enteropathigenic and enterohaemorrhagic E. coli
Intracellular cytosolic - viruses, listeria
How does an immune response start?
Tissue damage
Molecular detection of microbes
Inter cellular communication (eg interleukins)
Pruning the adaptive immune response
How does an immune response come to an end?
Clearing infection
Stopping inflammatory cytokine production
Repairing tissue damage
Remembering the infection (immune memory)
What are some of the differences between the innate and adaptive immune systems?
Timing
Cell types
Receptors and Ligands
Cytokines and chemokines
Molecular effector machieneries
How are naive resting immune cells activated?
Microbial molecules are detected by naive host cells either by binding ligands, or the activities of the pathogen
The gene expression on the host cell changes allowing the hot cells to release antimicrobial molecules and communication signals (eg. Interleukins and chemokines) these may have an autocrine effect
This leads to an activation of host cells
What are the first responders to the site of Injury?
Neutrophils
Followed my macrophages
These become activated and control infection and limit tissue damage
How do neutrophils etc recognise the type of pathogen?
Bacteria - by specific cell wall components. They can also recognise dead or alice bacteria and change the response depending
Fungi - cell surface molecules (beta glucan)
Viral - eg viral RNA or DNA that are released into the cytoplasm. Results in the release of interferons by host cells
What is macrophage activation?
Crosstalk between macrophages and lymphocytes during infection by intracellular pathogens
Eg in the case of salmonella, the macrophage releases certain Interleukins. The T cell detects these and releases IFN-gamma. This activated the macrophage
Activated macrophages show enhanced: phagocytosis and migration, cytokine/chemokine production, expression of cell surface molecules, antomicrobial activity, antigen presentation
What are interferons?
Special cytokines
Released by host cells after infection by viruses of gram negative bacteria
types: 1 and 3 (alpha and beta) and 2 (gamma)
Every single primary infected cell can produce type 1 interferons. Type 3 can only be produced by epithelial cells. Type 2 is only produced by lymphocytes.
They have direct antiviral activities
Type 1 and 3 are antiviral, type 2 are antibacterial
How are virally infected cells killed and removed?
They are killed by cytotoxic T cells and NK cells. These kill directly and are contact dependant
Cell death removes viral replication niches
Happens after a reduction of expression of MHC complexes on the infected cell
How are B cells activated?
Antigen presenting cells (DC and macrophages) are activated but infection and cytokines
T cells are activated by cognate MHC + foreign peptide recognition
B cells become licensed for antibody production against antigen being presented on BCR
How do T and B cells enhance antimicrobial activity?
They cause opsonisation
Phagocyte activation
Direct killing of infected cells
B cell activation
Innate lymphoid cells (gamma delta T cells) present on mucosal surfaces. Innate as don’t rely on MHC
What are the relative time scales of innate and adaptive immunity?
Innate - within 12 hours (DCs, phagocytes, mast cells, complement, NK cells)
Adaptive - 1-5 days. With plasma cells being generated at the end
What is characteristic of the secondary response?
Faster and more antibodies
How do blood T cells change with age?
Thymic output decreases
More circulating T cells
Fewer circulating naive cells
