Induction of mucossal tolerance in AI disease Flashcards
What is mucosal tolerance?
peripheral immunological tolerance may be induced by the mucosal administration of autoantigens
Why can induction of mucosal tolerance be a double edged sword?
can prevent and improve disease but also worsen AI disease
Why is nasal adminsitration more effective then oral administration of autoantigen?
disgestive enzymes can destroy the antigen
What suggests that mucosal tolerance depends on the dose of antigen administered?
high doses may lead to clonal deletion of anergy whereas lower doses favrou the devleopment of suppressor mechanisms
When has mucosal tolerance been used to suppress AI disease?
after nasal administration of soluble peptides that contained defined T cell epitopes, suppression has been documented in EAE; arthritis; EAMG; GN
What is the suppression of AI disease in mucosal tolerance though to be due to?
a distinct subset of Treg cells that secrete anti-inflammatory cytokines
What defines the balance between Th1 and Th2 cells?
a regulatory subset called Th3 cells - this has been shown to be important in the induction of mucosal tolerance
How do Th3 cells suppress the immune response?
release of TGF-b
What other cell type apart from Th3 have been shown to be involved in mucosal tolerance?
Tregs
What cytokine do Tregs use to downregulate T cell function?
IL-10
What is Goodpasture’s syndrome?
rapidly progressive GN with or withou lung haemorrhage defined by circulating and deposited anti-GBM autoantibodies of proven pathogenicity
What is the autoantigen in Goodpastures?
NC1 domain of the a3 chain of type IV collagen
What HLA associations does anti-GBM have?
strong positive association with HLA DR15 with a negative assocaition with DR7
What are the treatments for Goodpastures?
pred; cyclophosphamide and plasma exchange
How has mucosal tolerance been used in Goodpasture’s?
oral and nasal administration of glomulerular basement membrane/ recombinant rat z3 (IV) NC1 has prevented the development of EAG
What are the steps in creating an antigen-specific therapy for the treatment of anti-GBM disease?
identify an immunodominant T and B cell epitope from a3 (IV) NC1; investigate whether this peptide is nephritogenic; examine the effect of nasal administration in the induction of mucosal tolerance and if effective as treatment in established disease
How was the immunodominant peptide for EAG determined?
2 epitopes that goodpasture antivodies recognise; from one of them, different peptides were constructed and rats were immunsed with the 5 different overlapping peptides and looks to see if rat developed disease and use the rat blood to see the antibody and T cell responses to the different peptides
How were the antibody responses to the peptides determined?
ELISA plates coated with a3 (IV) NC1 and the different peptides; rat immunised with either a3 or P2 reacted most strongly to a3 (IV) Nc1 plate; P2 plate, rats blood immunised with both a3 and P2 reponded to P2–P2 is the B cell epitope
How were the T cell repsonses to the different peptides detemrined?
immunised animals with the different peptides and a3 had their spleen T cells cultured with the 5 peptides and a3 (IV)NC1 and looked at T cell prolfieration. Rate immunised with a3 had highest proliferation in response to a3 and P2; whilst rate immunised with peptide 2 reponded to a3 and P2
What happens if a rat is immunised with P2?
it induces EAG
How was the ability of P2 to prevent EAG determined?
immunodominant P2 was given nasally to rats at different doses prior to immunisation with a3 and monitored for disease
What was the antibody repsonse of rats given P2 prior to immunisation?
the middle dose of 300 reduced circulating antibodies a little; whilst the lower and higher doses had no effect, deposited antibodies were greatly reduced by P2
What was the effect of P2 administration before immunisation on disease severity?
reduced on immunofluoresence; proteinuria to the level of negative control; massively redued noumbers of abnormal glomeruli on histolgy; reduced macrophage and scarring in the tissue
What was the effect of P2 administration on mucosal tolerance?
mice immunised with P2 had much lower T cell prolfieration in repsonse to a3 (IV) NC1 suggesting some tolerance had been induced
How was P2 as a treatment tried?
peptide 2 was given at different doses 16-18 days after rat immunisation with a3 and disease monitored
What was hte effect of using P2 to treat on antibodies?
no effect on circulating or deposted antibodies (already estabilshed by day 16- T cell disease by then)
What was the effect of P2 as a treatment on the disease severity?
there was a dose reponse effect with proteinuria- increased dose had massively reduced proteinuria; reduced abnormal glomeruli; cell infiltration by both T cells and macrophages;
What was the effect of P2 in inducing immunological tolerance inestabished disease?
T cells from mice immunised with highest dose of P2 showed the same level of T cell proliferation to a3 as the negative control
Overall what was the effect of nasally administering P2?
prior to immunisation prevented the development of EAG, whilst after onset of disease, ameliorated the development
What are the possibilities in the future given the success of P2 in EAG?
antigen-specific therapy should be of value in designing new therapeutic stratgies fro patients with anti-GBM and other autoimmune disorders
When have trials been done in inducing mucosal tolerance in other diseases?
oral myelin in MS; type II colagen in RA; insulin in T1DM- but htese have not demonstrated clinical efficacy
What are the potenital reasons why clinical therapies for mucosal tolerance in AI disease not been effecive?
have used oral administration- less effective; specific peptides rather than complex antigens may improve efficacy
What are the 2 major mechanisms of mucosal tolerance induction?
anergy/deletion of antigen-specific T ells and/or selective expansion of cells producing immunosuppressive cytokines
What animal models has oral or nasal administration been effective again?
EAE; collagen induced arthritis; IDDM; EAMG (myasthenia)
How can the effectiveness of mucosal tolerance be improved?
conjunction of toleragens with cytokines may enhance suppression
What are the benefits of oral/nasal antigen administration over parenteral immunisation?
higher efficacy to achieve both mucosal and systemic immunity; minimisation of adverse effects; easy delivery and low costs
Why may stimulation of MALT in neonates contrubite to autoimmunity?
immunological priming- oral administration of myelin basic protein to neonatal animals enhanced disease expression- immaturity of the immunoregulatory netowrk association with oral toleracne and sensitisation may contribute to pathogenesis of AI disease, this effect decreases at around 4 weeks of life
Give an example of how the specific peptide chosen from a protein determines the response ?
MBP peptide 21-40 suppressed EAE induced by 71-90 peptide but not delayed hypersensitivity to that peptide, although it did suppress DTH to the whole MBP, there was no suppression seen after administration of 71-90–distinct suppressor determinants exist on MBP ; one amino acid difference meant there was no protection- structure is very important
How does the affinity of the peptide to MHC affect the immune response induced?
high affinity binding to MHC are more likely to induce tolerance whereas low affinity peptides will allow autoreactive cells to persist in health individuals
What does the clustering of autoimmune disases in patients suggest about their aetiology?
general inherited perdisposition to autoimmunity that might arise from breakdown of a common mechanism of immunological self-toleracne
What is the mechanism by which low doses of orally administered antigen induce regulatory T cells?
taken up by mucosa-associated APCs which preferentially induce Tregs
What is the process by which high doses of orally adminstered antigen induce anergy ?
appear to pass through the gut and enter the systemic circulation and induce clonal deletion/anergy
What is the use of bystander suppression in mucosal tolerance?
process by which regulatory cells induced by oral antigen secrete antigen-nonspecific cytokines fter being triggered which suppress all immune response –don’t need to know the specific antigen for an organ specific inflammatory disease
When has bystander suppression been shown in inducing mucosal toleracne?
PLP (proteolipid protein) peptide-induced EAE has been inhibited by feeding MBP; MBP-specific T cells can suppress PLP-induced disease
What indicates that self-tolerance is often incomplete?
frequency of AI disease and the ability to readily recruit autoreactive T cells from peripheral lymphoid organs
Give an exmaple of where dosing can cause problems in mucosal tolerance?
oral administration of large amounts of OVA increased disease in a murine model of IDDM after adoptive transfer
Why is prevention using mucosal tolerance easier than treatment?
in ongoing AI dsiease, most T cells are activated and easy to expand if exposed to the same protein
What rat strain are used to induce anti-GBM?
WKY strain
How have the pathogenic role for anti-GBM antibodies been demonstrated?
passive transfer studies- using antibodies from the serum of nephritic mice
How have the pathogenic role of T cells in EAG been deomnstrated?
they are present in the glomeruli of animals with EAG, proliferate in response to a3(IV) NC1 and transfer disease to naive recipients ; immunotherapy against T cells prevetns or ameliorates disease e.g anti-CD4 and anti-CD8 prevent disease
Why has there been a need to identify a specific peptide in anti-GBM?
oral administration of GBM antigen and nasal administration of recombinant are effective in preventing disease but not treatment- which is more relevant to patient management
Why was an immunodominant peptide thought to be more effective in treating disease than crude preparations of antigen?
in other models, nasal administration of synthetic immunodominant peitides has been shown to be more effective in treatment
Why may immunodominant peptides be more effective than crude antigen preparations at treating dsiease?
peptides containing defined T cell epitopes induce a more specific regulatory immune response than complex antigens
Why was higher doses of peptides used in treating EAG than was shown effective in preveting disease?
previous studies showed that higher doses of peptides were necessary to treat established disase than prevent
What suggestsed that nasal administration of pCol had a preferential inhibitory effect on cell-mediated immunity?
there was a significant reduction in number of infiltrating T cell and macrophages despite presence of deposited natibody
