Mucosal immune system - block D lecture 2 Flashcards
what is oral tolerance ?
Oral tolerance (OT) is the term used to refer to the state of unresponsiveness that exists for non-pathogenic antigens present within the gut lumen. This state is NOT a passive lack of response; it is a specifically down-regulated system essential for homeostasis.
how do you demonstrate an immune response ?
Demonstrate an immune response, immunise in scruff of neck with soluble antigen in the present of an adjuvant. Then challenge this in the footpad to measure the type of delayed hypersensitivity, will swell in size. If cells taken there would be high levels of antibody and IFN gamma.
If you were to challenge with another antigen, there would be no delayed type hypersensitivity, shows antigen specific.
Feed antigen, repeat after 2 days then challenge in foot pad, then there will be no DTH or antibody and IFN gamma. When challenged with another antigen, there would be no change in response. You would need to challenge with the same antigen that was fed
features of oral tolerance induced by ?
Virtually all proteins as well as heavy metals and contact sensitising agents can induce OT, OT can be induced to both humoral and cell mediated immunity. Cell mediated immune responses easier to tolerise than humoral responses as it requires less antigen and lasts longer.
are Th1 or Th2 responses easier to tolerise ?
Th1 responses are easier to tolerise than Th2 responses , IgE responses are extremely sensitive to OT, good for using as a therapy.
OT on lymphocyte migration ?
OT induces defective lymphocyte migration, as activates the antigen responding T cells in the gut, where once active they do not travel systemically, they stay in the gut.
how quickly can OT be induced ?
Tolerance can be induced as quickly as 1-2 days after feeding and lasts ±18 months in the mouse. Antigen persistence is required for maintenance of OT, needs to be present all the time.
effector functions (IgE and DTH) most associated with and OT ?
Effector functions (IgE and DTH) most associated with pathology are easiest to tolerise.
OT and carrier specificity ?
Carrier specificity uses a hapten and carrier, the carrier can be a large protein such as albumin, and hapten can be the poison ivy or nickel which is pentameric.
If you immunised the mouse with this there would be antibodies against the carrier (albumin) , antibodies against hapten (nickel or poison ivy). Also, there would be antibodies against the conjugate of carrier and hapten.
Tolerance of antibody production can be broken if the defective Th cells are bypassed with an unrelated carrier or LPS
factor affecting OT , nature of antigen ?
Active immunity Tolerance
Particulate Soluble
Viable Non-living
Locally invasive Rapidly absorbed ( by epithelail cells)
Peyer’s Patch uptake Mucosal uptake
dose and frequency ?
Dose and frequency
low dose versus high dose tolerance
genetic background ?
Genetic background have correct MHC phenotype to respond to
coeliac disease is linked closely to HLA-DQw2 locus
age ?
Age - young animals are more likely to be primed than tolerised
intestinal flora ?
Intestinal flora - germ free mice are resistant to OT
nutrition ?
Nutrition -poor nutrition decreases OT
immunological status ?
Immunological status - can you tolerise immune animals?
mechanisms of OT , clonal deletion ?
Clonal deletion
T cells responding to oral antigens are deleted in same way as selection in thymus.
clonal anergy ?
Clonal anergy
T cells exposed to antigen in absence of costimulatory molecules do not respond , T cells know antigen is there by MHC presentation but no danger signal or co stimulatory molecule so no activation.
regulatory T cells ?
Regulatory T cells
T cells exposed to antigen in presence of TGF-b and/or IL-10 are polarised to become Treg
TGF-b found in high levels in epithelial cells in gut
why does oral tolerance occur ?
Oral tolerance to proteins protects against inappropriate responses to food antigens and commensal bacteria
what happens to food we digest ?
Once ingested protein passes through the stomach where it is exposed to gastric acids and enzymes , it then enters the small intestine (SI) and is exposed to pancreatic enzymes. Once in the SI , there are long finger like extension that allow efficient absorption of protein. Protein can be absorbed two ways : either across epithelial cells or by the Peyer’s patch
how does epithelial uptake of protein antigens occur ?
epithelial cells- lamina propria
lymphatic system and circulation
epithelial cell route ?
the first way is the most important, protein is taken up by epithelial cells, once in the lamina propria it is absorbed by the High endothelial venules , these blood vessels take the protein from the small intestine and merge into the portal vein into the liver where it is processed and enters the circulation through the spleen before coming back to the liver.
lymphtic system ?
The other route is entering the lymphatic system where it drains from the gut into the mesenteric lymph node where it leaves via other lymphatic vessels into the thoracic duct into the thymus and goes back into the circulation or by other lymphatics back to the gut
what does intestinal processing generate ?
Intestinal processing generates tolerogenic protein, it changes the antigen ingested. Immunological intact protein is absorbed from gut
depth explaination of clonal deletion ?
Clonal deletion - remove reactive T cells
Seen when there is a high antigen dose
Mechanism of tolerance of self reactive T cells
Uncommon after peripheral tolerance
Very high doses can induce apoptosis of responding T cells but lower doses do not do this
Tolerance is normal in Fas deficient mice , this is what causes apoptosis
Tolerance cannot be induced in TNF-R1 KO mice , shows TNF-R1 is required for apoptosis.
in depth explanation of clonal anergy ?
Clonal anergy
Low dose of antigen over a longer period of time
Highly soluble, monomeric, lacks inflammatory signals
Basis of peripheral tolerance to many self Ag
Can be reversed by addition of IL-2 to activate them and limiting dilution analysis.
Cells proliferate prior to induction of tolerance and give similar numbers of specific T cells, primed at beginning with antigen but after tolerance they no longer proliferate
Inappropriate antigen presentation/ costimulation?
can Ag specific cytokine production occur in the abscence of cell proliferation
yes
how can tolerance be induced ?
olerance can be induced with peptides, enhanced availability of antigen to APC
how is OT prevented ?
OT is prevented if upregulate APC functions are activated for example by LPS
what can epithelial cells selectively present Ag to ?
Epithelial cells may selectively present Ag to CD8 regulatory cells lymphocytes surveying the muscosal surfaces.
what can unusual population of APC in PP and LP induce ?
Unusual population of APC in PP and LP induce tolerance in naïve recipients.
what can local tolerance presentation induce ?
Local presentation of Ag would induce local tolerance.
intestinal DC which lack CD80 and CD86 do ?
Intestinal DC lack CD80 and CD86 and cannot respond as lack co stimulatory molecules.
what augments and increases OT ?
IL-2 - stimulate production of regT cells
IL-4/IL-10
Anti-IL-12 as they supress Th1 response
LPS
IFN-b
Multiple emulsions
what decreases OT as inflammatory cytokines ?
IFN-g
IL-12
Anti-MCP-1
Anti-gd
Cyclophosphamide
Graft versus host disease
Parasite infection
as this provides danger signals so D T cells are activated
when does clonal anergy occur ?
Clonal anergy induced when antigen presented in absences of costimulatory antigens
bystander supression ?
Associated with feeding of low doses of Ag, OT cells suppress proliferation of unrelated Ag-specific cells - factor is soluble, TGF- b1. T cells induced by OT secrete regulatory cytokines following challenge by OT Ag - suppress inflammation locally. In human autoimmune diseases there are multiple autoantigens (e.g., in MS, there is reactivity to MBP, PLP and MOG) you only need to induce OT to one protein to tolerise all.
transplant and bystander suppression ?
In this circumstance, the mouse is tolerised, then the transplant occurs, the transplant is still rejected. However, if there is immunisation around the transplant area, this is successful as the regulatory T cells are supressed which would respond to the MHC mix match. This is bystander supression.
role of CD4+ T cells in OT ?
Depletion of CD4 prevents OT , this shows they play a role in OT. Tolerance can be transferred by CD4 cells
Preferential upregulation of T cell subsets
Th2, increased, Th1 decreased
Th1 and Th2 dependent cytokine and antibody responses can be tolerised by different regimes.
IgE is VERY susceptible to OT but IL-4 KO can be tolerised.
CD4 Th3 cells, like Th2 cells produce IL-4 and IL-10 but also produce TGF-b
role of gd T cells in OT ?
OT can be transferred with gd CD8+ T cells intraepithelial lymphocytes. Only suppresses IgE and not IgG. Diabetes in NOD mice can be prevented by transfer of tolerised CD8 gd T cells.OT can be prevented or abrogated by depleting gd T cells. OT cannot be induced in defeicinet TcR KO mice
gd T cells may suppress conventional Ag specific ab T cells in an idiotype specific manner. Emphasises role of gd T cells in intestinal homeostasis.
is OT induction the result of switching the T helper response ?
OT can be induced normally in anti-IL-4 treated or IL-4 KO mice , shows this is not due to switching.OT is normal in IL-5 and IL-6 KO mice , suggesting these do not play a role.
IL-10 treatment can restore tolerance to microflora , IL-10 KO mice develop IBD in response to gut microflora.
IL-10 and IL-4 are upregulated following OT. OT is normal in IL-10 depleted mice and anti-IL-10 cannot abrogate induced OT. Some experiments that support and refute this , what experiments were they high dose or low dose of antigens, what were the factors.
IFN-g is suppressed by OT but is preceded by priming of Ag-specific IFN- g response. OT of IgE is dependent on IFN- g. OT is normal following IFN- g depletion and in IFN- g R KO mice.
where is TGF beta abundant and what is it’s role ?
TGF-b is abundant in gut
mediator of epithelial cell differentiation
IgA class switching
Immunosuppressive
why is bystander supression dependent on TGF beta ?
Bystander suppression dependent on TGF-b
TGF-b associated with prevention of colitis
TGF-b secreting CD4 and CD8 isolated from PP and MLN following OT
TGF-b produced by Th3 T regulatory cells, macrophages, enterocytes
regulatory T cells ?
Early studies suggested that CD8 regulatory or suppressor T cells mediated OT as the induction of tolerance could be prevented with cyclophosphamide. IL-10 and TGF-b enhanced following oral tolerance. Blocking TGF- b blocks oral tolerance
Treg cells secrete IL-10 and TGF- b.
low dose tolerance ?
Low doses of antigen , the APC ( epithelial or dendritic) will lack the co stimulatory molecules and will produce TGF beta and IL-10 to induce reg T cells , T reg cells themselves will also be producing TGF beta and IL-10.
Tr1 will produce IL-10 and TH-3 produce TGF beta, both of these will supress the responses of antigen specific cell and induce the responses to the antigens that are not the same as the inducing antigen (by stander).
myasthenia gravis ?
Myasthenia gravis is a reaction to the acetylcholine receptor, by feeding this protein there is prevention of the autoimmune disease in the model.
Some are in clinical trials, but none are in clinical use now
peanut allergy and OT ?
Small number of peanut proteins and upped the dose to restore oral tolerance without the anaphylaxis reaction, needs to be done under medical supervision.
when can OT be a problem ?
Developing oral vaccines
Oral vaccines against mucosal pathogens would be desirable as they are direct immune response where it is needed, however if oral tolerance then vaccine is not effective.
Oral vaccines mean you don’t need needles expensive, painful) …HIV and hepatitis
Development of recombinant vaccines that could be incorporated into transgenic plants e.g. bananas.
