32.2 Induction of Immune Responses Flashcards
What is antigenicity?
The ability to be specifically recognised by the antibodies generated as a result of the immune response to the given substance.
What is immunogenicity?
The ability of a substance to induce cellular and humoral immune responses.
List the features that determine immunogenicity (5)
-Foreignness (self molecules not attacked)
-Large molecular weight = more immunogenic
-Chemically complex (contain more different types of immuno acids = immunogenic)
-Epitopes (parts that bind to antibodies)
-Route and timing of exposure
What are B-cell antigens?
Intact proteins and other native biomolecules.
What are T-cell antigens?
Peptides
What are haptens?
A small molecule which, when combined with a larger carrier such as a protein, can elicit the production of antibodies which bind specifically to it.
What is the function of the hapton-carrier complex?
The hapten carrier protein complex interacts with a B cell receptor on a naïve B cell and is internalised and presented on MHC class II molecules
Helper T cells recognise protein and stimulate B cells to produce an antibody to the hapten.
What is an antigen?
An immunogen that reacts with specific receptors on B and T cells.
What are strong and weak antigens?
Strong = Thymus (T)-dependent antigens.
Weak = Thymus (T)-independent antigens.
Why are T-dependent antigens stronger?
They require the recognition of peptide fragments on MHC class I/II by T-cells. Therefore, they have greater specificity and memory function.
Why are T-independent antigens weaker?
The absence of T cell involvement means there is a weak, short-lived response.
Which type of molecule will give the best immune response and grant best memory function?
Peptides/ Proteins
Why are bacterial polysaccharides generally not used as vaccinations?
Polysaccharides cannot be recognised by T cells because they are not peptides which can be presented on MHC molecules so there is no T cell stimulation leading to a weaker short lived response with less memory function
How T-independent antigens important in vaccines?
They can be adjuvants.
What are adjuvants?
These enhance the immune response to an immunogen without binding to an antibody.
What is the professional antigen presenting cell (APCs) and what do they activate?
Dendritic cells activate naïve CD4 and CD8 T-cells.
How are dendritic cells able to detect pathogens?
They have PRRs that allow them to detect PAMPs and subsequently phagocytose the pathogen and process the antigens.
How do dendritic cells cross present peptides?
-Endocytose antigens
-Process the proteins into peptides
-Bind the peptide to the MHC complex
-Express on cell membrane
What are other types of APC?
B-cells and Macrophages.
Describe the structure of MHC class I molecules
Contain a distal deep groove which peptide fragments are placed to expose certain residues to the outer surface
What is the function of MHC class I molecules?
They are expressed on all nucleated cell types and are primarily used int eh identification of cells infected with IC pathogens.
Describe the structure of MHC class II molecules.
2 integral domains each possessing an EC grove that link together to form a grove without true end barriers, much more open than MHCI.
What is the function of MHC class II molecules?
Mostly restricted expression to APCs. They can take antigens up from EC pathogens and present them to immune system for stimulation of humoral response.
Can any peptide bind to any MHC molecule?
No, it depends on their structure. They must have the correct anchoring residues at the right positions.
What is the significance of polymorphisms in MHC molecules?
They are primarily localised to the peptide binding grove and determine the characteristic binding motif, determining the peptides the MHC molecule can present.
What is the structural basis of peptide binding?
Peptide binding grove differes between MHC class:
- MHC I = closed (peptide must fit precisely in groove)
- MHC II = Open (ends of longer peptides are able to extend out of groove)
Anchor residues = certain parts of peptide that interacts more strongly w/ binding groove –> critical in determining binding affinity.
Hydrogen/ Van der Waals –> stabilise peptide/ MHC.
Describe how peptides are displayed on MHC class II molecules
Endocytosis of extracellular antigens/proteins
Secretion of protons, enzymes and lysosomes in phagolysosome kills pathogen and breaks down target protein into smaller peptides for presentation
MHC2 molecules transported to the endosome to associate with the peptides which are then embedded into plasmalemma.
*Presented to CD4 T-cells
Describe the process by which peptides become displayed by MHC class I molecules?
ENDOGENOUS PATHWAY (displays both host proteins and viral intracellular proteins)
-Proteins are targeted for breakdown by ubiquitin
-Tags them for degradation by the proteasome which releases small peptide fragments
-Peptides bind to MHC class I molecules and are displayed on the membrane
*Presented to CD8 CTLs.
What is the structure of an antibody?
Identical, paired heavy (50 kDa) + light (25 kDa) polypeptide chains
*Linked by disulphide bonds
*Identical → 2 identical antigen binding sites
What is the function of the light chains on an Ab?
Fab region –> recognises antigen
What is the function of the heavy chains on an Ab?
Define class and function.
*Distinctive functional properties determined by carboxy-terminus of heavy chain.
*Fc → where immune effector function engaged
What does the Fc region of an immunoglobulin do?
- Complement activation
- Binding to receptors on different cell types:
- Macrophages and neutrophils -> Triggers phagocytosis and activation
- Mast cells -> Triggers degranulation
- Epithelial cells -> This causes the immunoglobulin to be secreted into tears, saliva etc.
What is the structure of IgM?
Cross-link together, Mediated by the J-chain, to form a pentamer that can bind tightly to the pathogen
What is the major functions of IgM?
Activates classical complement pathway (binds to C1q → cascade stimulated → production of MAC, C3b + C4b, and C5a
Where are IgM Abs found?
Intravascular
Why do IgM Abs have low affinity for antigens?
initial immunoglobulins produced→ low affinity for the antigen
What is the structure of IgE?
Monomer
What are the major functions of IgE?
Involved in hypersensitivity + allergic responses
Where are IgE Abs found?
Bind to FcεRI on mast cells, basophils, Langerhans cells and eosinophils
What is the structure of IgA?
Exist in multiple molecular forms
E.g. monomers, dimers, and tetramers.
mediated by the J chain.
What is the function of IgA
neutralise + block pathogen activity through direct interaction w/ pathogen’s antigen.
E.g. agglutination
Where are IgA Abs found?
Cross epithelia to reach mucosal surface (extremely vulnerable sites due to exposure to outside environment)
What is the structure of IgG?
Monomer
4 subclasses w/ different functional activities
What is the function of IgG?
Main antibody in 20 response. Many different functions, e.g.
neutralisation, opsonisation, activation of complement + transport across the placenta.
Where are IgG Abs found?
Intra/ Extravascular
What is the structure of IgD?
Monomer
What is the function of IgD?
Recognition of antigens by B cells
Where are IgD Abs found?
B-cell surface
What is V/D/J recombination?
random selection of V/ D/ J genes (of which there are multiple) encoding variable regions of antibodies
How is V/D/J recombination initiated?
Initiated by ds breaks in RAG-1/ RAG-2 proteins at specific recombination signal sequences
RAG complex catalyses nicking + hairpin formation.
What provides affinity maturation of Abs?
Somatic Hypermutation.
What happens during SHM?
*Point mutations in variable regions of heavy + light chains happen due to activation of a nucleotide substitution mechanism.
*AID (activation-induced cytosine deaminase) → targets ssDNA of Ab V-regions + deaminates cytosine → uracil.
- Error-prone DNA repair pathways (mismatch repair/ base excision repair) then create ds breaks → introduce mutation.
- Accumulation of point mutations → alter Ab specificity
*↑er-affinity → selected for in light zone of GC where B cells compete
How are Ag receptors expressed by lymphocytes?
Each lymphocyte expresses many copies of one Ag receptor (Ig or TCR).
How is the wide diversity of Ag receptor expression achieved?
Although each lymphocyte expresses only one isoform of an Ag receptor. However, due to the large number of lymphocytes there is a wide variety of receptors expressed across the cell population.
How many specificities of Ag receptor are produced?
10^9
What happens when lymphocytes bund strongly to antigens?
They divide and produce clones of effector/ memory cells.
How are antigens transported to the secondary lymphatic organs?
By dendritic cells or free in the lymph.
How do Dendritic cells transport antigens to the SLOs?
*Uptake + present antigenic peptides/ proteins –> present on MHC2 molecules of DCs
*Transported to SLO through afferent lymphatics/ specialised vessels (e.g. high endothelial venules)
*enter periarterial sheath/ cortical areas where interact with antigen-specific T-cells.
What happens when the activated lymphocytes exit the SLO?
They become effector/ memory cells. They move to the infection via chemoattractant gradient.
How do T cells bind to the MHC molecule carrying a peptide?
Using the T-cell receptor (TCR).
Where does activation of naïve lymphocytes occur?
Secondary lymphoid organs
What are the different signals required to activate a T cell?
- Signal 1
- Binding of the TCR to the MHC-peptide complex on dendritic cells
- Signal 2 (co-stimulatory molecules)
- Binding of CD28 receptor to B7 proteins (CD80 and CD86) on APCs
- Cytokines (sometimes called signal 3)
How do CD4+ T-cells aid in the CTL response?
Provide 2nd signal needed for differentiation + formation of long-lasting memory CTLs.
Why is an additional signal from CD4+ T cells required in the activation of CTLs?
prevent inadvertent activation of self-reactive CTLs.
How do DCs and CD4+ T-cells interact during the activation of CTLs?
*DCs stimulate CD4+ T-cells to temporarily form a bridge with CTLs.
*CD4+ T-cells license DCs, providing a transient change evoking a potent activating signal helping them to activate CTLs directly.
What cell surface receptor defines T and B cells?
- T cells -> CD3
- B cells -> CD20
Which MHC class do the different T-cells recognise?
CD4+ T-cells –> MHC II
CD8+ T-cells –> MHC I
What are the 3 signals required for T cell activation?
- TCR + CoR binding MHD antigen
- Co-stimulatory molecules
- CKs
What does the TCR and co-receptor binding to the MHC antigen acheive?
*TCR –bind→ antigen on MHC molecule → initial activation triggered
*CD4/8 also bind to MHC → stabilise immunological synapse
What do the co-stimulatory molecules do during T-cell activation?
Promote survival + expansion of T cell.
*Initial encounter in presence of Co-SF triggers entry of T-cell into G1 phase of cycle.
What are some co-stimulatory molecules for CD4+ T-cell activation?
CD4: CD28 → CD80/ CD86 on APC (initiates proliferation)
What are some co-stimulatory molecules for CD8+ T-cell activation?
CD8: CD70/ CD137
What is the role of CKs during T-cell activation?
Polarising cytokines determine type of T cell
What T cell type does IL-12 promote?
Th1
What T cell type does IL-4 promote?
Th2
What T cell type does IL-6/23 promote?
IL 17 type
What doe TCRs recognise?
only Peptide MHC
What is the role of immunological synapse during T-cell activation?
acts as a platform for signal transduction enabling T-cell to integrate signals from APC and respond appropriately.
What are the different subsets of CD4+ T-cell?
Th1, Th2, Tfh, Th17, Treg.
What is the effector function of Th1 cells?
Macrophage activation, B-cell isotype switching and activation of CTLS and NK cells
What CKs does Th-1 produce?
IFN-gamma and TNF-alpha and IL-2
What is the effector functions of Th-2 cells?
Activation of eosinophils and mast cells. Stimulation of switch to IgE in B cells.
What CKs does Th-2 produce
IL-4, 5, 13 and 9
What is the effector function of Th-17 cells?
Stimulates phagocytes and lead to neutrophil recruitement.
What CKs does Th-17 produce
IL-17
What is the effector function of Tfh cells?
Stimulate Ig production from B cells for humoral immunity
What CKs do Tfh cells produce?
IL-21
What is the effector function of Treg cells?
Immune regulation
What CKs do Treg cells produce?
IL-10
What is the general role of CKs secreted by Th cells?
promote growth and differentiation of other lymphocytes.
In which disease is the Th2 response ineffective?
Leprosy
What id FoxP3?
A TF determining regulatory T-cells. It is sufficient and essential for the induction of immunosuppressive function.
What does FoxP3 induce?
- It commits the cell to the regulatory lineage
- It leads to the expression of anti-inflammatory CKs including IL-10, IL-35 and TGFβ
What are induced Treg cells?
Formed outside of the thymus from CD4+ T cells under specific conditions, namely during inflammation and when the cell is sub-optimally activated.
What are natural Treg cells?
Formed during selection in the thymus, with a threshold for positive selection that is higher than for helper/cytotoxic T cells, meaning that they have a relatively high affinity for self-antigens.
How do Treg cells complete their function?
CKs secreted directly inhibit effector T-cell activation + induce tolerogenic state in DCs (so they are unable to fully activate other T-cells so instead they become Treg cells).
What is the difference in function between induced and natural Treg cells?
- iTreg modulate responses to harmless foreign antigens
- nTreg inhibit responses to self antigens
What is the difference between primary and secondary follicles?
naïve B cells in primary follicles are activated during the immune response and then form germinal centres. The follicles are then known as secondary follicles.
What is the germinal centre reaction?
Activated B cells (via CD40-CD40L interaction w/ Th-cells) enter primary follicle and form germinal centre where affinity maturation takes place (and class switching)
What happens in the germinal centres?
*SHM + affinity maturation.
*Immunoglobulin class switching
*Development of memory B-cells
What is required for a robust Ab response?
CD4+ T-cell help.
What will happen to B-cells that do not receive co-stimulatory signals in the germinal centre?
They will die by neglect if they do not receive survival signals from the T-cells. This is a form of selection for B-cells producing IgM Abs with the highest antigen affinity.
What is class switching?
antibody isotype produced can be changed via gene rearrangement in germinal centre. From IgM/ IgD to others (e.g. IgG/ IgA/ IgE).
Different FC domains → bind to different FC receptors on different domains → different functions
Where does affinity maturation take place?
Via SHM in the germinal centre.
Where are antibody secreting cells (plasma cells) located?
In the SLOs, mucosae (IgA) and bone marrow.
What is immunological memory?
Following an initial response, some adapted (SHM/ affinity maturation) lymphocytes and leukocytes differentiate into B/T-memory cells. These can survive in a non-proliferative state for many years.
What happens when a memory cell encounters its antigen?
Rapid reactivation + production of effector cells in vast quantities.
How long does tetanus immunization last?
10 years - demonstrating longevity of memory T/B cells.
Describe the mechanisms of B cell memory.
- Follicular dendritic cells have important functions in the selection of memory B lymphocytes during germinal center reactions (GCR).
- They present native antigens to potential memory cells, of which only B cells with high affinity B cell receptors (BCR) can bind.
- Retention of antigen-antibody complexes is required for B cell memory.
What are central memory T-cells?
*Generated late in the immune response
*Express CD62L and CCR7 causing them to home to the secondary lymphoid organs
How do central memory T-cells respond to MHC activation?
Secrete IL-2 only.
*Helps stimulate B-cell response alongside Tfh signalling, improving response to secondary exposure to pathogens.
What are effector memory T-cells?
*Generated early in the immune response
*Lack CD62L and CCR7 but express homing
receptors for peripheral tissues enabling them to
patrol lungs, liver, gut etc
*primarily located in mucosae (majority in lungs/ gut/ liver).
How do effector memory T-cells respond to a secondary exposure?
Produce IFN-γ (recruiting macrophages to the area to deal with the threat), IL-4 and IL-5 (stimulating Th2 generation)
What is the difference between Naïve and memory B cells?
Memory cells have already undergone class switching and are,
therefore, capable of producing an isotype appropriate for the
pathogen
Memory cells show constitutive down-regulation of cell cycle
inhibitors enabling them to rapidly undergo clonal expansion
Somatic mutation ensures that the affinity of antibodies is many
orders of magnitude higher than that of naïve B cells
How does the smallpox vaccine demonstrate evidence for Ag-dependnce of memory?
How is Ag specificity generated?
Ag specificity is randomly generated in newly-formed lymphocytes.
What happens to lymphocytes with receptors for self-antigens?
They are inactivated in the thymus (central tolerance) or in the periphery (peripheral tolerance).
What are the two types of tolerance?
- Central tolerance
- Peripheral tolerance
What is central tolerance?
Autoreactive lymphocytes are selectively prevented from entering periphery.
Where does central tolerance of T-cells take place?
Thymus, specifically in the medulla.
Describe central tolerance of T-cells
*AIRE allows tissue-specific self-antigens to be expressed in medullary epithelial cells of thymus.
*High affinity –>
- elimination (via apoptosis/ anergy
* 1st step + majority.
- Cultivation
* capacity to later inhibit selected immune responses in periphery.
Which interactions between the TCR and self MHC antigen seem to favour engagement or elimination?
*Short, ↑ affinity + transient engagement between TCR + MHC-antigen “Hit + run model” → seems to favour engagement
*Sustained, ↑ affinity + TCR engagement → seems to favour elimination
Where does central tolerance of B cells take place?
Bone marrow
Describe central tolerance of B-cells
Fc mu receptor expressing stromal cells in the bone marrow present self-proteins and autoreactive B cells are purged.
Why is peripheral tolerance required?
Some potentially self-destructive lymphocytes may still escape PLOs/ evolve during adaptive immunity dev.
*Not all self-antigens expressed in central lymphoid organs (where -ive selection occurs)
*Threshold requirement for affinity to self-antigens not always met
- Some weakly self-reactive clones survive
*Ectopic re-expression of developmental antigens in later life may
activate self-reactive T cells that were never subject to negative
selection
*Molecular mimicry among T cell epitopes may stimulate self-reactive T cell
What is peripheral tolerance?
multiple safeguards to limit/ redirect activity of anti-self cells outside PLOs
*mainly in SLOs/ relevant tissue sites.
what is peripheral tolerance made up of?
T cell anergy helps restrict the impact of autoreactive T cells that evade
negative selection
Some tissues and organs display immune privilege in order to limit
collateral damage
A repertoire of Treg cells polices the immune system to reinstate selftolerance
What are the different mechanisms of innate immune privilege?
■ Physical barriers to sequester tissue-specific antigens from the
immune system
■ Lack of lymphatic drainage isolating the tissue from the adaptive
immune system
■ Expression of inhibitory receptors such as FasL that induce
apoptosis
■ Induction of a local anti-inflammatory environment due to
secretion of TGF-β
■ Depletion of essential amino acids to deprive T cells of the
nutrients they require
What does acquired immune privilege depend on?
Recruitment of Treg cells.
What is self-tolerance of B cells?
lack of T-cell help due to their inherent capacity to change
specificity during somatic hypermutation.
What is self-tolerance of T-cells?
imposed by regulatory T-cells expressing Foxp3. natural
Tregs develop in the thymus during selection on moderate affinity
self antigens. Induced Tregs develop in the periphery from naïve
CD4 T-cells due to the lack of co-stimulation and the presence of
inhibitory cytokines such as TGFβ.
What are tolerogens?
Ags that induce tolerance
What are the different fates of a T-cell engaged by a tolerogen?
*Apoptosis (deletion)
*Anergy (unresponsiveness)
*Regulation (engagement leading to suppression).
What happens when a T-cell becomes anergic?
Anergic T cells are prevented from responding to self antigen and
may cause bystander inhibition by competing for access to
cytokines and co-stimulation
What is innate immune privilege?
Tissues and organs display innate immune privilege which is
dependent on mechanisms such as physical barriers, lack of
lymphatic drainage and catabolism of essential amino acids
Similar mechanisms may be exploited by solid tumours to repel
immune responses directed against them
What evidence is there for deletion as a mechanism of tolerance?
■ Inadequate provision of self-antigens in the thymus may makes
negative selection incomplete
■ Ectopic re-expression of developmental antigens in later life may
activate self-reactive T cells that were never subject to negative
selection
■ Molecular mimicry among T cell epitopes may stimulate selfreactive T cells
How is the foetus able to express non-maternal antigens without producing an immune response?
o Physical barriers to the maternal immune system (e.g. placenta)
o Pacification of NK cells
o Nutrient starvation of infiltrating effector T cells
o Induction of Treg cells
Are immune responses able to be initiated by self-Ag, what does this implicate?
Yes. It implicates that self-reactive lymphocytes exist in the periphery.
What factors contribute to autoimmune recognition in the periphery?
*For T cell recognition of antigen, low affinity of individual epitopes may be compensated by high avidity
*Molecular mimicry may provide a high concentration of cross-reactive peptides that is renewable and presented in the context of acute inflammation
*Physical trauma may compromise immunologically privileged sites causing the release of myelin antigens into the circulation
Which autoimmune disorders are cell-mediated and which are Ab-mediated?
Cell-mediated = insulin-dependent diabetes/ rheumatoid arthritis.
Ab-mediated = Myasthenia gravis/ Grave’s disease/ Rheumatic fever.
Briefly describe the pathogenic mechanism of Insulin-dependent diabetes (DM1).
Autoimmune destruction of the pancreatic beta cells preventing the secretion of inulin.
*Genetic susceptibility + Environmental triggers (e.g. virus)
*Many candidate genes (e.g. MDA5/PTPN2/TYK2) regulate antiviral response in β-cells + immune system)
Briefly describe the pathogenic mechanism of Rheumatoid Arthritis.
amplification takes place following abnormal inflammation in the synovium, where CD4+ T-cells are used to start to produce immunoglobulins to stimulate macrophage action in these areas and include a chronic inflammatory state
Describe two theories for the initiation of myasthenia gravis.
- Molecular mimicry -> The nAChR contains a seven amino acid sequence in the α-subunit that cross-reacts with a shared immunodominant domain of gpD of the herpes simplex virus (HSV)
- Ectopic re-expression of the fetal nAChR -> The fetal nAChR has a γ chain, but this is changed usually before tolerance can develop. If the γ chain is ectopically re-expressed, an immune response can be launched.
Briefly describe the pathogenic mechanism of Grave’s disease.
hyperthyroidism resulting from antibody-dependent activation of TSH receptors in the thyroid, increasing thyroxine/tri-iodothyronine secretions independently of the HPT axis and thus without negative feedback, leading to a goitre, feeling hot and tired, tachycardia, weight loss, and the other classic symptoms of thyroid overactivity.
Briefly describe the pathogenic mechanism of rheumatic fever.
Inappropriate inflammation in the heart, skin, joints or brain following the production of antibodies to connective tissue proteins such as myosin and collagen. This typically follows antibody mutations during the response to an infection with Streptococcus pyogenes
What is IPEX syndrome caused by?
FoxP3 mutation (associated w/ early onset autoimmune disease)
What is APECED caused by?
Failure of the AIRE gene.
What is the epitope?
The part of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells.
What is epitope spreading in autoimmune diseases?
[IMPORTANT]
- The diversification of specificity towards epitopes
- In other words, the autoimmunity first affects one epitope on a self-antigen and then it spreads to more epitopes
- These epitopes can be on other epitopes on the same self-protein (intramolecular spreading) or other proteins (intermolecular spreading)
What is the problem with epitope spreading in autoimmune diseases?
Epitope spreading leads to diversification of the autoimmune repertoire, greatly complicating treatment options
Describe how epitope spreading occur.
- Infection leads to an immune response against the bacterial epitopes
- This leads to T cell activation and macrophage activation
- The macrophages lead to tissue damage that releases self-proteins
- These self-proteins may be taken up by APC and presented to T cells, leading to an autoimmune response against the self-proteins
- This is a positive feedback loop, where each round of self-protein release leads to triggering of an autoimmune response against the protein and therefore epitope spreading, so that there is more damage and more self-protein release
What is allelic polymorphism?
Allelic polymorphism refers to the presence of more than one allele at a specific locus within a population
What does allelic polymorphism of MHC genes lead to?
Preferential presentation of certain antigens which may lead to disease associations (e.g. insulin-dependent diabetes/ rheumatoid arthritis).
*as more likely to present host Ags outside of PLO –> increased likelihood of dev of certain autoimmune.
How are mAbs produced?
*B-lymphocyte + myeloma → hybridoma
*Grows indefinitely + secretes same antibody in vast amounts
What are the uses of mAbs?
*Therapeutic
*Flow cytometry
*ELISA
What are the main targets of mAbs in neoplasias (incl haematological malignancies + solid tumours)?
Main targets = growth factor receptors overexpressed in tumour cells (e.g. EGFR/ HER2) → ↓ growth rate, induce apoptosis, sensitise tumours to chemotherapy.
E.g. trastuzumab blocks HER2 receptor. Used for HER2-positive breast cancer.
Why are mAbs useful for treating cancers?
*They can be used as a delivery system for anti-mitotic drugs such as Taxol
*Specific target –> reduced systemic effect/ less effect on bystander cells.
What mAbs are often used in the treatment of autoimmune disorders?
anti-Abs
What is Rituximab?
*anti-lymphocyte monoclonal antibody causing B lymphocyte lysis.
*rheumatoid arthritis, non-Hodgkin’s lymphoma, + Pemphigus vulgaris.
What is Mepolizumab?
*Anti-IL-5 monoclonal antibody.
*↓ eosinophils’ production + survival.
*add on treatment for severe refractory eosinophilic asthma.
What is Infliximab?
*Chimeric mAb targeting TNF-alpha cytokine.
*autoimmune diseases.
- Active + fistulating Crohn’s disease, rheumatoid arthritis, + plaque psoriasis.
