Clocks, microbes, and immunity Flashcards
Describe the adaptive vs innate immune response
What cell types are involved in both processes?
Innate: Performed defenses, immediate and general
Adaptive: Antibodies, slower, specific
Both responses involve T cells and natural killer T cells
Describe cytokine-induced sickness behaviour
Behavoural alterations that might be related to circadian disturbances
How does the circadian clock respond to inflammation?
In Rheumatoid arthritis:
Swelling/inflammation occurs mostly in morning hours
Asthma/dyspnea:
Occurs more in morning
Sepsis:
More deaths between 2-6 AM
Describe the rhythmicity of immune cells
Lymphocyte concentration in blood is rhythmic and peaks in early day
Spleen has many different cell types, each with rhythmic REVERBa and PER2
Describe the function and rhythmicity of Natural Killer cells
NK cells kill unwanted cells (eg infected/cancer) by secreting cytolytic enzymes (perforin)
Rat spleen NK cells have rhythmic perforin expression (phase different from mRNA)
The effectiveness of NK cells depends on time of day (peaks at CT ~18), and jet-lagged rats have no rhythmicity of response
How does macrophage BMAL1 regulate immune response? How was this tested?
Regulates variation of cytokine response to LPS and monocyte counts
BMAL1 KO mice have no time difference in LPS response nor monocyte counts
Inject LPS intranasally in wt and BMAL1KO mice, measure neutrophils concs in lungs
wt had increased response during early day, wt had no variation
Why would vaccines be more effective if the time they were administered was taken into account?
Injected rats with antigen during day or night and measured specific T cells after a few days
Vaccination during day had 2-3 fold increase than at night
- Not a great study, but shows the same mechanism could occur in humans as well*
- Clock within T cells is necessary for this (no Bmal1 in CD8+ T cells removes this effect)*
How are autoimmune disorders affected by circadian rhythms?
eg. rheumatoid arthritis: stronger response at day than at night (same exp in constant light, lost difference)
eg multiple sclerosis: immunisation to give MS, response stronger in day than at night (more demyelination in day, makes sense*)
*synaptic homeostasis
Knocking out Bmal1 (in either T cells or macrophages) eliminates this difference
How are viral infections affected by the circadian rhythm?
More of a virus infection when infected in the morning (in mice)
full body bmal1 KO eliminates difference
How are parasitic infections affected by the circadian clock?
Laishmania major infection
Inject in paw and measure parasite load over time
Infection at early night had higher parasite load
Infection at early night had increased neutrophil recruitment response
L. major needs neutrophils to survive as it infects them
In vitro test of parasite infection after serum shock
- Circadian rhythm of parasite attachment to macrophages
- The macrophage clock makes it easier for parasites to attache (somehow)
How does the microbiome’s rhythmicity become affected by the host’s circadian rhythm?
Many bacteria in the gut is roughly circadian
Per1/2 knockout hosts have arrhythmic microbiome
wt mice with switched feeding times have antiphase microbiome
8 hour time difference every three days
“jet lag” removes rhythmicity of Ruminococcaceae
Jet lagged mice gained more weight and had poorer glucose tolerance*
To prove microbiome was at play, antibiotics were used to eliminate microbiome –> same effect as control
What did the case study of two human subjects travelling to israel prove?
Changes in circadian rhythms is enough to change microbiota, and that is enough to affect metabolism
Microbiome sampled before, during and after jet lag
Injected samples into germ free mice
before and after weights/GTT were similar
During jet lag, mice gained more weight and had poorer GTT
What is a race tube and how can it be used? What did its use prove?
Tube with cotton on one side, neurospora grown along the length of the tube (it can only grow in one direction)
Neurospora occaisionally grow Conidia (can be viewed from above)
The growing of conidia is roughly circadian and responds to light
Describe the genetic basis for the neurospora clock
WC-1:WC-2 stimulate frq to produce FRQ
FRQ becomes phosphorylated, (conidia grow)
FRQ-P inhibits WC-1:WC-2
Describe the current putative TTFL loop in cyanobacteria
What was noticed about protein levels in this clock?
Describe the other clock found in cyanobacteria
Which of these clocks necessary? Why?
TTFL:
- KaiA binds PR-P and promotes transcription of kaiBC
- KaiB and KaiC associate (with SasA), and the KaiB:KaiC:SasA complex promotes the dephosphorylation of PR-P
- Dephosphorylated PR inhibits translation of KaiB and KaiC
- (KaiC:SasA inhibits the dephosphorylation pathway)
Phosphorylation cycle:
- KaiC binds KaiA, which bi-phosphorylates KaiC
- KaiB then binds, dephosphorylates, and unbinds KaiA
- KaiB then unbinds and dephosphorylates KaiC
KaiABC proteins are all that are needed to establish a 24 hr cycle via the phosphorylation pathway, however the TTFL is necessary to make it robust (i.e. temperature compensated)
