Immunity and Autoimmunity Flashcards
Define
Clonal expansion
the process by which daughter cells arise from a parent cell. When B-cells undergo this process, many copies of that B cell are produced that share affinity with and specificity of the same antigen
How does genetic predisposition contribute to RA?
Genetic predisposition results in presentation of CPA on HLA and recognition by CD4 T cells; inflammatory environment promotes T cell activation
Describe the steps of B-cell proliferation and the early stages of T-cell dependent immunity
- T- and B-cells interation; selection step 1
- Outer follicle and differentation for germinal centre, plasma cells and memory; selection step 2
- Germinal centre; mutation; selection; differentiation; selection step 3
- Maintenance of memory; selection step 4
Describe somatic hypermutation including the segregation between the dark and light zones
Describe the life of a B-cell including its survival in the bone marrow
What are the two types of light chains?
Kappa (κ)
Lambda (λ)
Definition
The portion of the amino (NH2) terminal of an antibody’s heavy and light chains having a variable amino acid sequence
Variable region
What four things can happen to lymphocytes that are too self-reactive?
Deletion (cell death)
Anergy (cell silencing)
Receptor editing
Exhaustion
• Naïve B cells express Ig__ and Ig__ on their surface, both with the same VH/VL combination.
• Naïve B cells express IgM and IgD on their surface, both with the same VH/VL combination.
Fibroblast-like (Type B) synoviocytes in RA respond to inflammation by producing what?
- Cytokines (e.g. IL-6, IL-8, MIF, M-CSF, GM-CSF, TNF)
- Chemokines to attract inflammatory cells
- Matrix degrading enzymes such as matrix-metalloproteinases (MMPs) which lead to cartilage degradation
- Factors that promote local bone destruction
- Factors that inhibit bone formation activity
Are Rheumatoid arthritis and Lupus systemic or local autoimmune diseases?
Both systemic
What are the treatment options for RA?
- NSAIDs (Non-Steroidal Anti-Inflammatory Drugs
- DMARDs (Disease Modifying Anti-Rheumatic Drugs)
- Methotrexate – a folate analogue that interferes with cellular metabolism, causes cells to release adenosine, and this inhibits lymphocyte proliferation and cytokine expression
- Hydroxylchloroquine – antimalarial
- Low dose prednisone (glucocorticoids/steroids)
- Biologics: Monoclonal antibodies
- Anti-TNF
- Anti-IL-6
- Small molecule inhibitors
- Jak STAT inhibitors
Definition
an interleukin that acts as both a pro-inflammatory cytokine and an anti-inflammatory myokine
IL-6
True or False
The heavy chain undergoes VDJ recombination
True
What is the most common isotype of Ig?
IgG
What is the function of a healthy synovium?
Facilitates movement between non-deformable structures within joint (e.g. bone/cartilage surfaces)
What are the most predominant lymphocyte in RA synovium?
T cells are the predominant lymphocyte in RA synovium:
- CD4+ (helper) T cells are most prevalent
Definition
a biological mechanism that changes a B cell’s production of immunoglobulin from one type to another, such as from the isotype IgM to the isotype IgG.
Class switch recombination (CSR)
What are the 2 distinct cell populations in the healthy intima?
80%: Fibroblast-like synoviocytes (Type B synoviocytes)
20%: Macrophage-like synoviocytes (Type A synoviocytes)
True or False:
CSR occurs at the light chain locus only and requires the enzyme AID
False
CSR occurs at the Heavy chain locus only and requires the enzyme AID
Define
TNFα
a cell signaling protein (cytokine) involved in systemic inflammation and is one of the cytokines that make up the acute phase reaction. It is produced chiefly by activated macrophages, although it can be produced by many other cell types such as CD4+ lymphocytes, NK cells, neutrophils, mast cells, eosinophils, and neurons
Definition
a long-term autoimmune disease in which the body’s immune system becomes hyperactive and attacks normal, healthy tissue. Symptoms include inflammation, swelling, and damage to the joints, skin, kidneys, blood, heart, and lungs
Lupus
How many chains does an Ig molecule have?
4 (2 heavy, 2 light)
What is the order of serotype genes in the constant region of a Ig?
IgM, IgD, IgG, IgE, IgA
Define
Autoantibodies
antibodies (immune proteins) that mistakenly target and react with a person’s own tissues or organs
How do environmental triggers lead to RA?
Environmental trigger causes post-translational modification (citrullination) of selfpeptides → these are now potential autoantigens (citrullinated peptide antigens; CPA)
Definition
cells of the immune system found in primary and secondary lymph follicles of the B cell areas of the lymphoid tissue. They are not derived from the bone-marrow hematopoietic stem cell, but are of mesenchymal origin
Follicular dendritic cells
True or False
The light chain undergoes VDJ recombination
False
The light chain undergoes VJ recombination
Definition
a toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies
Antigen
How Do Cytokines Target Class Switch Recombination in B cells?
What is the main tissue target for inflammation in RA?
Synovium
Define
Follicular dendritic cells
cells of the immune system found in primary and secondary lymph follicles of the B cell areas of the lymphoid tissue. They are not derived from the bone-marrow hematopoietic stem cell, but are of mesenchymal origin
Describe the process of humanising a monoclonal antibody by CDR grafting
Why is immunological tolerance falliable?
- Not all self-antigens are in the bone marrow or thymus, spatially and/or temporally
- B-cells need a degree of self-reactivity to signal successful rearrangement and indeed to signal for continued survival
- Self-reactive B-cells may encounter their antigen in an inflammatory context
How does AID cause somatic hypermutation?
AID introduces point mutations into the V regions of the genes of GC B-cells
These may cause amino acid replacements in the V genes, affecting the abilit of Ig/BCR to bind antigen
They may improve or reduce affinity or cripple the Ig completely, or do nothing
Define
Anergy
the functional silencing of self-reactive cells so they become non-responsive to stimulation. Appears to be the fate of less high affinity anti-self B-cells
How do polymorphisms in SLE genes involved in the immune clearance of apoptotic particles and nucleic acids contribute to SLE?
Polymorphisms in genes involved in the immune clearance of apoptotic particles and nucleic-acid– containing immune complexes (orange) may induce the enhanced activation of pDCs and autoreactive B cells, leading to the production of type I interferon (IFN) and the expansion of autoreactive effector cells, respectively.
Define
Exhaustion
T-cells particularly, are rendered non-functional after extensive proliferation in the face of an undiminishing antigen load
B-cells need intructions from ____________ to proliferate and differentiate
B-cells need intructions from CD4 T-cells to proliferate and differentiate
What cells influence the outcome of class switch recombination?
T-cells and/or the antigen
Definition
the killing of self-reactive cells, appears to be the fate of high affinity anti-self. E.g. activation-induced cell death (AICD)
Deletion
Definition
antibodies (immune proteins) that mistakenly target and react with a person’s own tissues or organs
Autoantibodies
How do polymorphisms of SLE genes involved in innate immunity contribute to SLE?
Polymorphisms in genes involved in innate immunity (green) regulate the induction of, as well as the response to, type I IFN.
Definition
an antibody isotype that makes up about 1% of proteins in the plasma membranes of immature B-lymphocytes where it is usually co-expressed with another cell surface antibody called IgM
IgD
Definition
antibodies that are made by identical immune cells that are all clones of a unique parent cell. They can have monovalent affinity, in that they bind to the same epitope (the part of an antigen that is recognized by the antibody)
Monoclonal antibodies
Definition
a cellular mechanism by which the immune system adapts to the new foreign elements that confront it (e.g. microbes), as seen during class switching
Somatic hypermutation (SHM)
Which Ig exists as a pentamer? Which as a dimer?
IgA is a dimer
IgM is a pentamer
Definition
the part of an antigen molecule to which an antibody attaches itself
Epitope
Why is IFN stimulated in Lupus?
Type I interferon normally activates the antiviral response.
Nucleic acids in circulation or in the cytoplasm, which shouldn’t usually be there, act as danger-associated molecular patterns (DAMPs). These are detected by sensor proteins, like pattern recognition receptors (PRRs) which include Toll-like receptors (TLRs).
These activate signal transduction pathways that culminate in the transcription of the type I IFN genes.
Define
Antigen
a toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies
What enzyme(s) mediate V(D)J recombination?
RAG 1&2
True or False
VDJ segment is unaffected by CSR
True
Definition
a rare type of immune cell that are known to secrete large quantities of type 1 interferon (IFNs) in response to a viral infection. They circulate in the blood and are found in peripheral lymphoid organs.
Plasmacytoid dendritic cell (pDC)
How does IL-6 contribute to RA?
- Pro-inflammatory cytokine
- Involved in fever and acute phase response
- In RA, produced by macrophages, synovial fibroblast-like synovial cells, T cells
- Increases acute phase response in liver (systemic inflammation)
- Induces immunoglobulin production by B cells
- Promotes differentiation of TH17 cells
- Induces cytokine production by synovial fibroblasts and macrophages
- Promotes osteoclast differentiation via induction of RANKL
- Found at high levels in RA synovial fluid and serum
How does JAK-STAT signaling mediate the action of IL-6?
- Ligand binds to receptor
- JAK autophosphorylates the receptor
- STAT binds to phosphorylated receptor
- JAK phosphorylates STAT
- Phosphorylated STAT is released & dimerises with another phosphorylated STAT
- STAT dimer translocates to cell nucleus where it binds to DNA, initiating gene transcription
Define
Phage display
a laboratory technique for the study of protein–protein, protein–peptide, and protein–DNA interactions that uses bacteriophages (viruses that infect bacteria) to connect proteins with the genetic information that encodes them
Define
Monoclonal antibodies
antibodies that are made by identical immune cells that are all clones of a unique parent cell. They can have monovalent affinity, in that they bind to the same epitope (the part of an antigen that is recognized by the antibody)
How do inflammatory cytokines contribute to SLE?
Inflammatory cytokines strongly stimulate further maturation of self-reactive B cells and contribute to organ damage
What enzyme(s) mediate somatic hypermutation?
Activation Induced Cytidine Deaminase (AID)
Define
Central tolerance
also known as negative selection, is the process of eliminating any developing T or B lymphocytes that are reactive to self. Through elimination of autoreactive lymphocytes, tolerance ensures that the immune system does not attack self peptides.
What is the function of synovial cells?
- Produce collagens and fibronectin
- Provide nutrients
- Produce lubricants
Define
Constant region
The portion of the amino acid sequence of an antibody’s heavy or light chains that determines the class of the antibody and does not vary within a given class
Definition
a natural mode of immune response exhibited by the adaptive immune system of mammals. It ensures that a single antigen is recognized and attacked through its overlapping parts, called epitopes, by multiple clones of B cell
Polyclonal response
Why is the constant region of an Ig important?
It determines the effector functions of the Ig.
Each isotype has a different role to plat
Define
IL-6
an interleukin that acts as both a pro-inflammatory cytokine and an anti-inflammatory myokine
Define
RAG enzymes
plays important roles in the rearrangement and recombination of the genes encoding immunoglobulin and T cell receptor molecules
Definition
the genetic variations or differences in the constant regions of the heavy and light chains
Isotype
What are three methods that can be used to bypass mouse Ig genes to make human mAbs?
- Make a mouse that uses human Ig genes
- Humanisation via isolation from Ag-specific B-cells: Abs from HIV-infected individuals
- Antibody discovery and affinity maturation using phage displays
What type of bond connects the two heavy chains of a Ig molecule?
Disulphide bond
Describe the cross-talk between synoviocytes during inflammation
Definition
a type of antibody produced by the immune system. If you have an allergy, your immune system overreacts to an allergen by producing this antibody type
IgE
Definition
A hybrid cell used as the basis for the production of antibodies in large amounts for diagnostic or therapeutic use. They are produced by injecting a specific antigen into a mouse, collecting an antibody-producing cell from the mouse’s spleen, and fusing it with a tumor cell called a myeloma cell
Hybridomas
Definition
white blood cells that are also one of the body’s main types of immune cells. They are made in the bone marrow and found in the blood and lymph tissue
Lymphocyte
What are the function of Type A and Type B synoviocytes?
Type A: Clearance of debris in joint, recognition of immune complexes, present antigens, initiate inflammatory responses (cytokine release)
Type B: Joint lubrication, produce collagen and fibronectin (cell adherance molecules)
How can monoclonals be humanised?
What happens to the Macrophages (Type A synoviocytes) in RA inflammation?
- “Activated phenotype”:
- Increased phagocytosis
- Increased antigen presentation to CD4+ T cells
- Major source of:
- Cytokines (e.g. TNF, IL-1β, IL-6, IL-18, MIF)
- Chemokines to attract inflammatory cells
Define
IgE
a type of antibody produced by the immune system. If you have an allergy, your immune system overreacts to an allergen by producing this antibody type
Define
IgM
one of several isotypes of antibody (also known as immunoglobulin) that are produced by vertebrates. It is the largest antibody, and it is the first antibody to appear in the response to initial exposure to an antigen
What is the overall process of making monoclonal antibodies?
Where are B-cells located during changes to their affinity and Ig class?
Germinal centres
Draw a graph showing the difference between primary and secondary exposure to an antigen in terms of serum Ig levels, affinity and predominant Ig serotype
Define
IgD
an antibody isotype that makes up about 1% of proteins in the plasma membranes of immature B-lymphocytes where it is usually co-expressed with another cell surface antibody called IgM
Definition
a diverse set of microbial molecules that share a number of different general “patterns,” or structures, that alert immune cells to destroy intruding pathogens
PAMPs
What are the advantages of using a phage display to make human mAbs?
Can recover specificities to anything…not limited by self/non-self, or species conserved antigens
Why do B-cells initially make IgM but then change?
Pentameric IgM allows low affinity antibody to bind antigen. As affinity increases via clonal selection and SHM, IgM can be replaced with IgG, IgA or IgE with their specialised effector functions
Definition
secondary rounds of V-J gene segment rearrangement to generate a revised BCR that is no longer self-reactive
Receptor editing
Define
Variable region
The portion of the amino (NH2) terminal of an antibody’s heavy and light chains having a variable amino acid sequence
Definition
one of several isotypes of antibody (also known as immunoglobulin) that are produced by vertebrates. It is the largest antibody, and it is the first antibody to appear in the response to initial exposure to an antigen
IgM
What happens to immune complexes in autoimmune diseases?
IC can accumulate on the walls of fine blood vessels, triggering activation of granulocytes and causing tissue damage
Define
Tertiary lymphoid sites
ectopic lymphoid organs that develop in non-lymphoid tissues at sites of chronic inflammation including tumours
Definition
also known as negative selection, is the process of eliminating any developing T or B lymphocytes that are reactive to self. Through elimination of autoreactive lymphocytes, tolerance ensures that the immune system does not attack self peptides.
Central tolerance
What cells produce TNF in RA?
In RA, produced by activated macrophages (predominantly), activated fibroblast-like synoviocytes and other cells types (e.g. T cells)
How does adaptive immune system activation contribute to Lupus?
Definition
the unique mechanism of genetic recombination that occurs only in developing lymphocytes during the early stages of T and B cell maturation. It involves somatic recombination, and results in the highly diverse repertoire of antibodies/immunoglobulins and T cell receptors (TCRs) found in B cells and T cells, respectively
V(D)J recombination
What type of specialised cells secretes Igs?
Plasma cells
Definition
plays important roles in the rearrangement and recombination of the genes encoding immunoglobulin and T cell receptor molecules
RAG enzymes
Define
Lupus
a long-term autoimmune disease in which the body’s immune system becomes hyperactive and attacks normal, healthy tissue. Symptoms include inflammation, swelling, and damage to the joints, skin, kidneys, blood, heart, and lungs
Define
Transfectoma
A myeloma cell into which immunoglobulin genes have been transfected
Define
Pathogen recognition receptor (PRR)
proteins capable of recognizing molecules frequently found in pathogens (the so-called Pathogen-Associated Molecular Patterns—PAMPs), or molecules released by damaged cells (the Damage-Associated Molecular Patterns—DAMPs)
Genetic predisposition results in evasion of _________selection, and subsequent activation, of selfreactive B and T cells in SLE
Genetic predisposition results in evasion of negative selection, and subsequent activation, of selfreactive B and T cells in SLE
How many loci encode for the immunoglobulin genes?
3
What does TNF release do in RA?
Definition
T-cells particularly, are rendered non-functional after extensive proliferation in the face of an undiminishing antigen load
Exhaustion
Define
CD4 T-cells
a type of T cell that play an important role in the immune system, particularly in the adaptive immune system. They help the activity of other immune cells by releasing T cell cytokines. These cells help suppress or regulate immune responses
Define
Class switch recombination (CSR)
a biological mechanism that changes a B cell’s production of immunoglobulin from one type to another, such as from the isotype IgM to the isotype IgG.
How do TH17 and T regulatory cells contribute to RA inflammation?
TH17 cells:
- Subset of CD4+ T cells that express IL-17
- Recruitment and differentiation induced by IL-6, IL-23 and IL-1
- Express RANKL, the essential differentiation factor for osteoclasts (the bone resorbing cell); promotes bone erosion
- IL-17 induces expression of other pro-inflammatory cytokines and also RANKL in other cell types; promotes inflammatory response
T regulatory (Treg) cells:
- Subset of T cells identified by CD25+ , FoxP3+
- Normally act to suppress immune/inflammatory response
- In RA: cells are present within synovial tissues but are not functional (e.g. reduced expression of cytokines IL-10, IL-4) – have lost their regulatory (anti-inflammatory) capability
True or False:
TNF is a common target for monoclonal antibodies to treat RA
True
How do B-cells contribute to RA inflammation?
- Presence and distribution of B cells is variable among RA patients:
- Likely depends on stage of disease
- Responsible for antibody production in response to T cell activation by antigen presenting cells.
- Local production of autoantibodies (e.g. rheumatoid factor, anti-citrullinated peptide antibodies (ACPA), anti-collagen type II)
- Present antigen to CD4+ T cell and secrete cytokines
- Source of RANKL - required for osteoclast differentiation, contributing to bone resorption.
True or False:
Class switch recombination changes the constant region without changing antigen binding
True
Definition
the functional silencing of self-reactive cells so they become non-responsive to stimulation. Appears to be the fate of less high affinity anti-self B-cells
Anergy
What factors contribute to the altered post-transcriptional regulation (citrullination) that triggers Rheumatoid arthritis?
Environmental factors (periodontitis, smoking, microbiome)
Epigenetic modification
Susceptibility genes
What are the two parts of the synovium and what are their features?
Intima:
- 1-3 cell layers deep
- Cells = synoviocytes
Subintima
- Contains blood vessels, lymphatic vessels and nerves, but few cells
What cell type are prevalent mediators of inflammation within the RA joint?
Fibroblast-like (Type B) synoviocytes)
True or False:
All autoimmune disease antibodies are pathogenic
False
In some autoimmune diseases it is not the antibody that drives the condition
CSR is deletion recombination mediated by S-S recognition and requires double stranded breaks in the DNA that are generated by AID and repaired by ________________
CSR is deletion recombination mediated by S-S recognition and requires double stranded breaks in the DNA that are generated by AID and repaired by nonhomologous end joining (NHEJ)
What happens to immunecomplexes in normal people?
IC are usually cleared by phagocytosis, facilitated by the complement system
Define
Switch (S) region
conserved nucleotide motifs upstream from gene segments that encode the constant regions of antibody heavy chains; the site of double-stranded breaks
The genetic predisposition of SLE involves many alleles involved in what?
Reduction of tolerance
Where do immune complexes accumulate in Lupus?
Glomeruli in kidneys and many other sites
What does transciptome data show about people with Lupus?
They have a interferon signature of genes that are downregulated compared to healthy controls
In what ways can mAbs be changed to improve therapeutic effect?
• Improve potency • Improve functionality • Longer half-life • Tissue distribution • Solubility • Reduce Cost
Describe the pathogenesis of RA
What happens to the synovium in RA?
- Cell proliferation (hyperplasia) causing the intima to expand → up to 12 cells
- Infiltration of inflammatory cells into the subintima: macrophages, T cells, B cells, neutrophils (less common)
- Formation of new blood vessels (neovascularisation)
- Ectopic lymphoid neogenesis
- Deposition of fibrin in active disease – citrullinated fibrinogen may contribute to localized ACPA
True or False:
Organ damage in lupus patients is a major predictor of mortality
True
How do you make antibody production long-lived?
Fuse the population of antigen-reactive B cells with an immortal cell line (longevity, in vitro growth, high level antibody secretion)
Definition
a cell signaling protein (cytokine) involved in systemic inflammation and is one of the cytokines that make up the acute phase reaction. It is produced chiefly by activated macrophages, although it can be produced by many other cell types such as CD4+ lymphocytes, NK cells, neutrophils, mast cells, eosinophils, and neurons
TNFα
Why can Naive B-cells express IgM and IgD on their surface?
Alternate splicing from the one mRNA transcript that starts from the promoter that is upstream of the VH segment.
Define
Epitope
the part of an antigen molecule to which an antibody attaches itself
How do B-cells solicit help from T-cells?
- Activated B cells process and present antigen to T cells via MHCII and express ICOSL
- Activated T cells “see” antigen and co-stimulation (ICOSL), provide “help”
- Help = CD40L (proliferation and AID inducing) and interleukins (differentiation, CSR)
- CD40 activates B cells by activating the NFkB signaling pathway
- In the absence of CD4 help, B-cells do nothing in a T cell dependent response
Describe the Relationship Between Antigen and Immunoglobulin Isotype Switching T-cell derived Signals Target AID to particular S-regions thus directing CSR
CDRs _______ are encoded in the germline, where as CDR _____ is created during rearrangement
CDRs 1 & 2 are encoded in the germline, where as CDR 3 is created during rearrangement
Definition
A myeloma cell into which immunoglobulin genes have been transfected
Transfectoma
True or False:
Somatic hypermutation changes the constant region without changing antigen binding
False
Somatic hypermutation affects antigen binding without changing constant region
Definition
a type of antibody. Representing approximately 75% of serum antibodies in humans, it is the most common type of antibody found in blood circulation
IgG
What type of cells are found within a germinal centre?
B-cells
CD4 helper T-cells
Follicular dendritic cells
Definition
an abnormal layer of fibrovascular tissue or granulation tissue. Common sites include over the cornea, over a joint surface (as seen in rheumatoid arthritis), or on a prosthetic heart valve
Pannus
Define
Activation induced cytidine deaminase (AID)
causes mutations that produce antibody diversity, but that same mutation process leads to B cell lymphoma
How do you use a phage display to make human mAbs?
Step 1: Make a library of phage expressing all possible VH + VL genes, using human B cells as template (NB: ScFv)
Step 2: Screen library on target antigen. Select phage binders. Introduce random mutations in V genes. Select stronger binders. Repeat…until high affinity Add constant regions Examples: adalimumab (Humira) and belimumab .
Definition
conserved nucleotide motifs upstream from gene segments that encode the constant regions of antibody heavy chains; the site of double-stranded breaks
Switch (S) region
Where does somatic hypermutation occur?
Germinal centres
An antigen can hae many tagets for a B-cell response, what is each of these targets referred to as?
Epitope
Define
IgG
a type of antibody. Representing approximately 75% of serum antibodies in humans, it is the most common type of antibody found in blood circulation
Definition
a type of T cell that play an important role in the immune system, particularly in the adaptive immune system. They help the activity of other immune cells by releasing T cell cytokines. These cells help suppress or regulate immune responses
CD4 T-cells
Define
V(D)J recombination
the unique mechanism of genetic recombination that occurs only in developing lymphocytes during the early stages of T and B cell maturation. It involves somatic recombination, and results in the highly diverse repertoire of antibodies/immunoglobulins and T cell receptors (TCRs) found in B cells and T cells, respectively
What do the autoantibodies in Lupus target?
Molecules in the nuclei of cells (dsDNA, fibronucleoproteins, other nuclear proteins complexed with nucleic acids)
What is the issue with using monoclonal antibodies to treat Lupus?
None have shown broad, strong protection
All are expensive
Define
Polyclonal response
a natural mode of immune response exhibited by the adaptive immune system of mammals. It ensures that a single antigen is recognized and attacked through its overlapping parts, called epitopes, by multiple clones of B cell
Define
T regulatory cells
a specialized subpopulation of T cells that act to suppress immune response, thereby maintaining homeostasis and self-tolerance
Definition
thin membrane that extends from skeletal tissue at interface of cartilage and bone and lines the capsule of synovial joints
Synovium
Definition
sites within secondary lymphoid organs – lymph nodes and the spleen where mature B cells proliferate, differentiate, and mutate their antibody genes (through somatic hypermutation aimed at achieving higher affinity) during a normal immune response to an infection
Germinal centres
What 3 methods make the V region of every naive B-cell different?
- A developmental mechanism that generates huge protein diversity from limited genetic diversity (V(D)J recombination mediated by RAG1&2)
- After exposure to the antigen, additional diversification by so-called somatic hypermutation (SHM) mediated by the enzumes Activation Induced Cytidine Deaminase (AID)
- Ig can be further diversified by changing the constant region (Class switch recombination also mediated by AID)
Definition
the process by which daughter cells arise from a parent cell. When B-cells undergo this process, many copies of that B cell are produced that share affinity with and specificity of the same antigen
Clonal expansion
How do environmental triggers lead to Lupus?
Environmental trigger causes tissue damage and localised release of potential autoantigens (e.g. DNA spilling out of nucleus where it’s usually hidden from the immune system)
What happens to some strongly self-reactive CD4 T-cells?
They become regulatory T-cells
Define
Receptor editing
secondary rounds of V-J gene segment rearrangement to generate a revised BCR that is no longer self-reactive
Definition
proteins capable of recognizing molecules frequently found in pathogens (the so-called Pathogen-Associated Molecular Patterns—PAMPs), or molecules released by damaged cells (the Damage-Associated Molecular Patterns—DAMPs)
Pathogen recognition receptor (PRR)
What activates synovial macrophage-like cells in RA? What cytokines do they produce?
Immune complexes activate the cells
Which then produce TNF and IL-6 (and many others)
Why must all T-cell receptors show a degree of self-reactivity?
To avoid death by neglect
How do you isolate individual clones to have a pure antibody species?
Separate each different fusion so that each B cell clone now grows separately from all others (monoclonal culture and antibody production)
What are the four main methods of preventing autoantibody formation?
Deletion of self-reactive clones
B-cell receptor editing
Activation-induced cell death
T-cell dependence
How many times does somatic recombination occur in the heavy and light chains of a Ig molecule?
Light: 1, Heavy: 2
Define
Germinal centres
sites within secondary lymphoid organs – lymph nodes and the spleen where mature B cells proliferate, differentiate, and mutate their antibody genes (through somatic hypermutation aimed at achieving higher affinity) during a normal immune response to an infection
Define
Complementary determining regions (CDR)
part of the variable chains in immunoglobulins (antibodies) and T cell receptors, generated by B-cells and T-cells respectively, where these molecules bind to their specific antigen
What are the treatment options for Lupus?
- Generalised immunosuppression
- Steroids (glucocorticoids): unacceptably severe side effects
- Monoclonal antibodies: poor record of success to date but anifrolumab showed impressive results in trials, when responses were analysed correctly
Why is an immunoglobulin molecule described as a dimer of dimers?
It has two identical heavy chains and two identical light chains
Define
Plasmacytoid dendritic cell (pDC)
a rare type of immune cell that are known to secrete large quantities of type 1 interferon (IFNs) in response to a viral infection. They circulate in the blood and are found in peripheral lymphoid organs.
Define
FcR
a antibody receptor involved in antigen recognition which is located at the membrane of certain immune cells including B lymphocytes, natural killer cells, macrophages, neutrophils, and mast cells. Such receptors recognize Fc fragment of antibodies
True or False:
Lupus occurs mostly in men
False
It occurs more in women 9:1
Define
TH17 cells
by virtue of their production of IL-17 and IL-17F, are generally thought to be pro-inflammatory and play an important role in host defense against infection, by recruiting neutrophils and macrophages to infected tissues
Definition
ectopic lymphoid organs that develop in non-lymphoid tissues at sites of chronic inflammation including tumours
Tertiary lymphoid sites
How do you make fully human mAbs from humans?
How does the pannus destroy cartilage and cone?
Cells within the pannus release factors that destroy articular cartilage and bone
Define
IgA
an antibody that plays a crucial role in the immune function of mucous membranes
What five activities occur within germinal centres?
- Proliferation: T cells drive clonal expansion of antigen-specific B cells
- Isotype switching: Changing the constant region of the antibody heavy chain without changing the V regions and thus the specificity. Changes effector function of the Ab
- Somatic hypermutation: Random introduction of point mutations into the V gene segments of the H and L chains to diversify binding to antigen.
- Affinity maturation: Select those mutated B cells with improved affinity for antigen. Let the remainder die. Improves average affinity.
- Memory formation: Induce high affinity GC B cells to differentiate into either memory B cells of plasma cells that leave the GC and live for long periods
Where is AID expressed?
AID is expressed only in activated B cells and thus in all Germinal Centre B cells
What happens to germinal centres after the immune response ends?
They disappear
How does the activation of the innate immune system contribyte to Lupus?
How does AID induce class switch recombination?
- The enzyme Activation Induced Cytidine Deaminase (AID) introduces nicks into S region DNA (contains ‘hot spots’ for AID activity, which converts C to U in DNA )
- AID is expressed only in activated B cells and thus in all Germinal Centre B cells
- Enough nicks are made to create double stranded (ds) breaks in two S regions
- Ends are joined, DNA is repaired, deleting the intervening chromosomal region.
- CSR is deletion recombination mediated by S-S recognition and requires double stranded breaks in the DNA that are generated by AID and repaired by nonhomologous end joining (NHEJ)
Define
Hybridomas
A hybrid cell used as the basis for the production of antibodies in large amounts for diagnostic or therapeutic use. They are produced by injecting a specific antigen into a mouse, collecting an antibody-producing cell from the mouse’s spleen, and fusing it with a tumor cell called a myeloma cell
Exons encoding Ig constant regions can’t be expressed until what?
Exons encoding Ig constant regions can’t be expressed until a V segment is placed upstream of them – true for all isotypes, H and L (stable, high level transcription).
How does the antibody response to an antigen switch from predominantly IgM to IgG during initial exposure?
Class switch recombination
What enzyme(s) mediate class switch recombination?
Activation Induced Cytidine Deaminase (AID)
When does B-cell tolerance occur?
After B-cell receptor (Ig) assembly and expression
Define
Lymphocyte
white blood cells that are also one of the body’s main types of immune cells. They are made in the bone marrow and found in the blood and lymph tissue
How are high affinity Ig/BCRs selected for following somatic hypermutation?
B-cells with higher affinity Ig compete bettwen for antigen and thus T-cell help
Since T-cells drive proliferation, high affinity B-cells contrinue to proliferate
Low affinity B-cells die in the GC
Definition
an autoimmune disease that can cause joint pain and damage throughout your body
Rheumatoid arthritis
Definition
an antibody that plays a crucial role in the immune function of mucous membranes
IgA
Define
Avidity
the overall strength of binding between an antibody and an antigen
Definition
the overall strength of binding between an antibody and an antigen
Avidity
Definition
a specialized subpopulation of T cells that act to suppress immune response, thereby maintaining homeostasis and self-tolerance
T regulatory cells
True or False
Switch (S) regions are all homologous
True
In Rheumatoid arthritis, what is degraded by inflammatory processes?
Synovium
Bone tissue
What serotype is initially involved in a secondary exposure to an antigen?
IgG
Definition
in a state or period of inactivity or dormancy
Quiescent
Define
Isotype
the genetic variations or differences in the constant regions of the heavy and light chains
Define
Pannus
an abnormal layer of fibrovascular tissue or granulation tissue. Common sites include over the cornea, over a joint surface (as seen in rheumatoid arthritis), or on a prosthetic heart valve
Autoantibodies are produced and can contribute to tissue damage in SLE. What happens when self-antigens continue to be produced?
Further release of self-antigens can stimulate innate activation and type I IFN production
Define
Peripheral tolerance
the second branch of immunological tolerance, after central tolerance. It takes place in the immune periphery (after T and B cells egress from primary lymphoid organs). Its main purpose is to ensure that self-reactive T and B cells which escaped central tolerance do not cause autoimmune disease
Why are polyclonal antibodies a very useful therapeutic?
Useful because:
- Polyclonality covers a multitude of types for one protein (cross-reactivity)
- Easy, cheap, reliable
- Recognise multiple epitopes on one antigen
Define
Deletion
the killing of self-reactive cells, appears to be the fate of high affinity anti-self. E.g. activation-induced cell death (AICD)
Definition
causes mutations that produce antibody diversity, but that same mutation process leads to B cell lymphoma
Activation induced cytidine deaminase (AID)
What determines the shape of a binding site of a Ig molecules?
CDR genes
Define
PAMPs
a diverse set of microbial molecules that share a number of different general “patterns,” or structures, that alert immune cells to destroy intruding pathogens
Ig isotypes are defined by the ________ part of the heavy chains
Ig isotypes are defined by the constant part of the heavy chains
Define
Somatic hypermutation (SHM)
a cellular mechanism by which the immune system adapts to the new foreign elements that confront it (e.g. microbes), as seen during class switching
Define
Rheumatoid arthritis
an autoimmune disease that can cause joint pain and damage throughout your body
Definition
The portion of the amino acid sequence of an antibody’s heavy or light chains that determines the class of the antibody and does not vary within a given class
Constant region
When does T-cell tolerance occur?
Tolerance occurs after T-cell receptor assembly and expression
Polymorphisms of genes in which areas tend to contribute to SLE?
Clearance of apoptotic particles and immune complexes
Innate immunity
Adaptive immunity
Tissue damage
Why can’t you convert back into IgD after class switching to IgA?
The IgD gene has been deleted from that cell
Autoantibodies form immune complexes with what?
Autoantibodies form immune complexes with their autoantigen and complement proteins
Describe the cyclic exacerbation of Lupus
How do you make fully human mAbs in mice?
What are the 5 Ig isotypes?
IgG
IgA
IgM
IgD
IgE
Define
Synovium
thin membrane that extends from skeletal tissue at interface of cartilage and bone and lines the capsule of synovial joints
What cells enable a plasma cell to survive by forming a niche?
Myeloid cells (DC, macrophages)
Basophils
Eosinophils
Magakaryocytes
Stromal cells
Neutrophils
Why can self-reactive cells be useful to protect against some foreign antigens?
Some pathogens mimic host cells in order to avoid the immune system
Why is there an issue with using glucocorticoids to treat Lupus?
Cost $$$
Side-effects (osteoporosis, diabetes, cataracts etc.)
Which of these immune processes are important in Rhumatoid arthritis and Lupus?
Lymphoid organogenesis
Antigen presentation and co-stimulation
Immune complexes
Autoantibodies
Rheumatoid arthritis:
Lymphoid organogenesis
Antigen presentation and co-stimulation
Immune complexes
Lupus:
Antigen presentation and co-stimulation
Immune complexes
Why is the bone marrow a good site for central tolerance?
There shouldn’t be foreign antigens in the bone marrow so any strong BCR signalling inicates self-reactivity
Definition
by virtue of their production of IL-17 and IL-17F, are generally thought to be pro-inflammatory and play an important role in host defense against infection, by recruiting neutrophils and macrophages to infected tissues
TH17 cells
Definition
the second branch of immunological tolerance, after central tolerance. It takes place in the immune periphery (after T and B cells egress from primary lymphoid organs). Its main purpose is to ensure that self-reactive T and B cells which escaped central tolerance do not cause autoimmune disease
Peripheral tolerance
What determines different autoimmune phenotypes?
Self-reactivity in different cell types and pathways drives different autoimmune phenotypes
________ signaling mediates the action of IL-6
JAK-STAT signaling mediates the action of IL-6
What type of stem cell do B-cells originate from?
Harmatopoiteic stem cells (HSC)
Definition
a laboratory technique for the study of protein–protein, protein–peptide, and protein–DNA interactions that uses bacteriophages (viruses that infect bacteria) to connect proteins with the genetic information that encodes them
Phage display
After initial exposure to antigen, there is secretion of Ig__ followed by Ig__ or Ig__
After initial exposure to antigen, there is secretion of IgM followed by IgG or IgA
What happens to self-reactive B-cells?
They go through a round of receptor editing
Pairing of newly rearranged antigen receptor components results in a new antigen specificity that must be tested for what?
- Signal transduction capacity
- Reactivity against self
Definition
a antibody receptor involved in antigen recognition which is located at the membrane of certain immune cells including B lymphocytes, natural killer cells, macrophages, neutrophils, and mast cells. Such receptors recognize Fc fragment of antibodies
FcR
How do JAK/STAT inhibitors treat RA?
Small molecule inhibition of Jak via competitive inhibition at the DNA binding site
Jak inhibitors interrupt many cytokine signalling pathways
True or False
Secondary response to antigen is usually not associated with CSR
True
Definition
part of the variable chains in immunoglobulins (antibodies) and T cell receptors, generated by B-cells and T-cells respectively, where these molecules bind to their specific antigen
Complementary determining regions (CDR)
What enzyme creates a junction between two loci during somatic recombination (V(D)J recombination)?
RAG enzymes
Define
Quiescent
in a state or period of inactivity or dormancy
