B Cells and Disease Flashcards
Describe primary immunodeficiencies (PIDS)
PIDS are rare disorders resulting from impaired immune response, with over 350 types caused by genetic defects. They lead to recurrent or severe infections, mainly diagnosed in children under 1 year.
Define antibody deficiencies in PIDs
Antibody deficiencies in PIDS involve the loss of humoral immunity while cellular immunity remains intact. Examples include XLA, CVID, and HIGM
How are PIDS treated with severe immune system deficiencies like SCID?
Severe PIDS like SCID can be treated with HSCT (haematopoietic stem cell transplantation) or gene therapy, aiming to replace the entire immune system.
Do B cells originate from stem cells near the endosteal of the bone marrow?
Yes, B cells originate from stem cells near the endosteal of the bone marrow and are quiescent until stimulated
Describe the process of B cells exiting the bone marrow
Immature B cells can only exit bone marrow if they express functional Ig on their surface. Their antigen specificity exists before encountering the antigen.
Define IVIg and SCIg in PIDS treatment
IVIg (Intravenous Ig) and SCIg (Subcutaneous Ig) are treatments involving monthly infusions of antibodies, with SCIg being self-administered weekly via a small pump.
How do B cells and T cells interact in lymphoid organs?
B and T cells sit in discrete areas in lymphoid organs to prevent interaction unless necessary. They meet at the T cell-B cell border for class switch recombination.
Describe the activation of B cells in lymphoid organs
B cells in lymphoid organs await their specific antigen in the follicle, where they become activated upon encountering the antigen via their B cell receptor (BCR).
Describe the process of B cell activation and interaction with T cells.
B cells present antigens to T cells via MHC 2 molecules, and activated T cells upregulate surface receptors like ICOS and CD40L to provide help to B cells.
Define the role of germinal centers in B cell development.
Germinal centers are sites of B cell proliferation in secondary lymphoid tissue, where B cells undergo clonal expansion, somatic hypermutation, and affinity maturation.
How do memory B cells differ from plasma cells in function?
Memory B cells circulate through the body and are reactivated upon reexposure to the same pathogen, while plasma cells are resident in the bone marrow and produce antibodies for immediate protection
Do B cells play a role in directing other immune cells?
Yes, B cells release cytokines to direct other immune cells and have roles in tumor immunity, wound healing, and dendritic cell regulation.
Describe the structure and function of IgG antibodies.
IgG is the most abundant Ig in plasma, monomeric and major in the secondary immune response with a hald-life of 20-24 days. it has 4 subclasses: IgG1, IgG2, IgG3, IgG4
Define the role of IgE antibodies in the immune system.
IgE antibodies are involved in parasitic helminth infections and allergic responses, being the major Ig in these situations. They are the scarcest Ig and have a structure similar to IgM with additional C regions.
How is antigen receptor diversity generated in B cells?
Antigen receptor diversity in B cells is generated through mechanisms like random selection and rearrangement of minigene segments in heavy and light chain genes, allowing for combinatorial diversity despite limited genetic diversity
Describe the process of VDJ rearrangement in B cells.
VDJ rearrangement involves the somatic recombination of V, D and J gene segments to generate a diverse range of antigen receptors in B cells
Define somatic hypermutation and affinity maturation in B cells.
Somatic hypermutation is the generation of single point mutations in hypervariable regions, while affinity maturation is the selection of B cells with the highest affinity binding receptors during B cell activation and differentiation.
How does the process of VJ recombination differ between heavy and light chains in B cells?
VJ recombination of light chains is independent of VDJ recombination of heavy chains, allowing for separate rearrangement processes in B cell development
Describe the role of TdT in immunoglobulin gene rearrangement.
Terminal deoxynucleotidyltransferase (TdT) adds random nucleotides at junction regions between gene segments during VDJ rearrangement, contributing to the diversity of immunoglobulin genes
How is the pre BCR formed in B cell development?
the Ig heavy chain pairs with surrogate light chains to form the pre BCR, which then associates with Ig alpha and Ig beta signalling chains to signal successful rearrangement and continue B cell development
Describe the process of negative selection in immature B cells before they exit the bone marrow.
Negative selection in immature B cells involves testing for auto-reactivity. B cells with highly cross-linking self-antigen undergo apoptosis, while those with minimal cross-linking become anergic
What is the significance of KRECs and TRECs in newborn screening for SCID?
KRECs (Kappa deleting recombination excision circles) and TRECs (T cell receptor excision circles) are circular DNA segments formed during successful VDJ rearrangement, serving as surrogate markers for new B cell and T cell production and used in early detection of SCID
Define SCID (Severe Combined Immunodeficiency) and its impact on the immune system.
SCID is a severe form of primary immunodeficiency where patients lack functional T cells, leading to recurrent viral, fungal, and bacterial infections due to compromised immunity.
How is SCID diagnosed and what are the genetic causes associated with it?
SCID can be diagnosed through genetic testing of 20 known genes, family history, or newborn screening. Genetic causes include mutations in genes like ADA, RAG1/2, and Artemis.
Do mature B cells express both surface IgM and IgD, and what signifies their identification?
Yes, mature B cells express both surface IgM and IgD with the same antigen specificity, and the downregulation of VDJ machinery signifies their identification.
Describe the treatment options for SCID and the importance of early diagnosis.
SCID is managed with prophylactic antivirals, antifungals, and immunoglobulin supplementation. Early diagnosis is crucial for timely HSCT, the most effective curative treatment.
Explain the role of Bruton’s tyrosine kinase (BTK) in B cell development and antibody production.
BTK is essential for signaling rearrangement success in developing B cells. Mutations in BTK can lead to X-linked agammaglobulinaemia (XLA) where B cells cannot progress to produce antibodies.
Describe the clinical presentation of XLA patients.
XLA patients present complete absence of serum Ig and B cells, leading to susceptibility to recurrent and severe bacterial infections.
What is the genetic basis of XLA?
XLA is caused by mutations in the BTK gene located on the X chromosome, predominantly affecting males.
How is XLA diagnosed?
XLA is diagnosed through clinical presentation, family history, measuring serum Ig levels, enumerating CD19+ B cells, and BTK gene sequencing.
Define Class Switch Recombination (CSR) in B cells.
CSR is the process where B cells switch antibody isotypes without changing antigen specificity, directed by signals from T cells and/or antigens.
Describe the process of Somatic Hypermutation in B cells.
Somatic Hypermutation occurs in the periphery and involves introducing random point mutations in the variable region genes of B cells to improve antibody affinity.
What are the treatment options for XLA?
Treatment for XLA includes Subcutaneous Immunoglobulin (SCIg) and Intravenous Immunoglobulin (IVIg) therapy.
Explain the significance of memory B cells in secondary immune responses.
Memory B cells proliferate rapidly and produce higher-affinity antibodies like IgG upon re-exposure to antigens, leading to faster and stronger immune responses.
How does the absence of BTK expression affect XLA patients?
Without functional BTK, immature B cells cannot exit the bone marrow, leading to a lack of serum Ig and B cells, making patients susceptible to bacterial infections.
Describe the process of affinity maturation in B cells.
Affinity maturation involves B cells undergoing somatic hypermutation to produce amino acid changes that can increase, decrease, or have no effect on affinity to antigens. B cells with higher affinity immunoglobulins compete better for antigens and T cell help, leading to clonal proliferation and exit from the germinal center.
Define somatic hypermutation (SHM) and its role in the immune response.
Somatic hypermutation is a process where B cells introduce mutations in the DNA of their antibody genes, particularly in hypervariable regions, to generate antibodies with increased affinity for antigens. SHM is essential for generating high-affinity antibodies during an immune response.
What are the common symptoms of Hyper IgM syndrome?
Common symptoms of Hyper IgM syndrome include recurrent bacterial infections of the respiratory tract, susceptibility to opportunistic infections, autoimmunity against blood cells, hypertrophy of tonsils, chronic diarrhea, and increased risk of lymphatic cancers.
How does a defect in CD40L on T cells impact the immune response in Hyper IgM syndrome?
A defect in CD40L on T cells, as seen in X-linked Hyper IgM syndrome, disrupts the interaction with CD40 on B cells, leading to impaired B cell proliferation, defective germinal center formation, and a lack of class switch recombination and somatic hypermutation.
Describe the role of AID enzyme in the immune response and its significance in Hyper IgM syndrome.
AID enzyme is essential for class switch recombination and somatic hypermutation in B cells, allowing for the production of different antibody isotypes and higher affinity antibodies. Mutations in AID can lead to Hyper IgM syndrome with impaired immune responses.
How is Hyper IgM syndrome diagnosed and treated?
Hyper IgM syndrome is diagnosed through lymphocyte counts, clinical presentation, family history, and serum testing for immunoglobulins. Treatment involves intravenous or subcutaneous immunoglobulin therapy to manage the immune deficiencies.
Describe the diagnosis process for CVID (Common Variable Immunodeficiency).
CVID diagnosis is made by excluding other Primary Immunodeficiency Disorders (PID), characterized by hypogammaglobulinemia and recurrent bacterial infections.
Define CDRs (Complementarity Determining Regions) in immunology.
CDRs are stretches of amino acids within the tips of the variable region of antibodies, crucial for antigen recognition and binding.
How are polyclonal antibodies different from monoclonal antibodies?
Polyclonal antibodies are derived from different B cell clones and recognize multiple epitopes, offering broader protection, while monoclonal antibodies are from a single clone and target a specific epitope
Do live attenuated vaccines provide a stronger immune response compared to inactivated vaccines?
Yes, live attenuated vaccines generate a robust immune response due to the live virus, making them highly effective.
Describe the process of creating polyclonal antibodies like Anti-thymocyte globulin (ATG).
Animals are immunized with human cells, serum is collected, purified to obtain specific antibodies, and then injected into patients to target specific cells.
How do CDR3 regions in antibodies contribute to antigen-binding specificity?
CDR3 regions are highly variable and are created during VDJ rearrangement, leading to diverse amino acid sequences that enhance the antibody’s ability to bind to different antigens.
Describe the role of plasmid DNA in development for viruses like.
Plasmid DNA encodes specific parts of the virus or protein subunit, allowing the body to produce the viral protein and trigger an immune response.
How do recombinant viruses contribute to vaccine development?
Recombinant viruses are engineered to mimic viral infections without causing harm, ensuring they carry target proteins to stimulate an immune response
Define the unique challenges associated with creating an HIV vaccine.
Challenges include lack of natural immunity, HIV variability, absence of a reliable animal model, and the virus’s preference for infecting CD4 T cells.
Explain the interaction between HIV envelope and CD4 T cells in the infection process
The gp120 protein on HIV binds to CD4 on T cells, leading to a conformational change that allows the virus to interact with chemokine coreceptors and with the host cell membrane.
What are long-term nonors of HIV, and how do they differ in immune response?
Long-term non-progressors are individuals who do not experience rapid CD4 T cell decline. They produce broadly neutralizing antibodies that block various HIV strains.
How can monoclonal antibodies be used to target specific sites on the HIV virus?
By isolating monoclonal antibodies from HIV patients and testing them against protein probes, antibodies specific to the CD4 binding site can be selected for, aiding in vaccine development
Describe the process of sequential immunization in generating broad neutralizing antibodies against HIV.
Sequential immunization involves guiding the HIV virus to its final structure by introducing modified glycoprotein structures in each dose to activate B cells, undergo clonal expansion, and develop higher affinity antibodies with each round.
How can the modular nature of Ig be utilized in therapies like CAR-T cell therapy and cancer treatment?
The modular nature of Ig allows for linking Fv to target specific cells and Fc for effector functions. In cancer treatment, radionuclides can be attached to Ig for targeted radiotherapy, and bispecific antibodies can bring T cells close to cancer cells for enhanced killing.
Define the concept of broadly neutralizing monoclonal antibodies and their use in HIV therapy.
Broadly neutralizing monoclonal antibodies can suppress viraemia in HIV patients, allowing breaks from retroviral therapy. They can also prevent HIV transmission from mother to infant and induce long-lasting immunity in monkeys.
Describe the process of creating chimeric antibodies and their significance in avoiding immune responses.
Chimeric antibodies involve replacing mouse IgH and IgL constant regions with human sequences to avoid human anti-mouse antibodies (HAMA). They are significant in reducing immune responses against foreign antibodies.
Explain the method of generating fully human monoclonal antibodies from humans using phage display.
Fully human monoclonal antibodies can be generated by recovering B cells with desired antibody specificity from humans, converting bacteriophages into B cells displaying VH and VL segments, screening the library on target antigens, and selecting high-affinity antibodies with human constant regions.
How does early monoclonal antibody therapy contribute to inducing immunity against HIV in monkeys?
Early monoclonal antibody therapy suppresses viral expansion, allowing CD4 T cells to survive and generate an immune response of CD8 cytotoxic T cells. This induces long-lasting immunity against the simian version of HIV in monkeys.
Describe the major steps in antibody gene rearrangement and B-cell development
- Ig gene rearrangement
- V(D)J recombination
- signalling success in Ig gene rearrangement
B-cell exit from bone marrow to periphery - mature B cell
- tolerance mechanisms
Ig Gene rearrangement
occurs in the bone marrow
V(D)J recombination
includes the use of RAG1/RAG2, HMG1, Artemis, DNA-PKcs, Ku79/Ku80, DNA ligase IV/XRRCC4, TdT
outcome = a unique DNA sequence encoding the variable region
V(D)J recombination overview
- initiation: RAG1/RAG2 cut DNA at randomly selected RSS
- formation: coding joint (D-J, then V-D), signal end joints (loop of DNA deleting intervening DNA)
- repair: DNA-PKcs, Artemis, Ku70/KU80 complex, DNA ligase IV
- diversity mechanisms: combinatorial generation, independent rearrangment, imprecision of junctions, somatic hypermutation
signalling success in Ig gene rearrangement
- pre-BCR formaion - Ig heavy chain with surrogate light chains
- BCR formation - real Ig light chain pairs with Ig heavy chain
- success signal: Btk, BLNK activation
B-cell exit from bone marrow to periphery
criteria - expression of functional surface Ig (BCR)
Mature B cell
characteristics - down-regulation of VDJ machinery, production of IgD, expression of both surface IgM and IgD
tolerance mechanisms
screening - immature B-cells screened for auto-reactivity
outcome - apoptosis if highly-cross-linked self antigens, anergy for minimily cross-linked, receptor editing for alternative light chain
Major steps of B-cell differentiation in an immune response
B cell development in bone marrow
maturation and exit from bone marrow
activation and differentiation in peripheral lymphoid organs
Explain the molecular basis of primary immunodeficiencies and their therapeutic options.
- over 500 rare disorders
- result in impaired immune responses, leading to current infections
- often diagnosed in childhood; some can be fatal
Genetic aetiology of SCID
involves defects in early T-cell development
diagnosed through lymphocyte counts, serum Ig levels and genetic testing
newborn screens (TRECs) aid in early detection
therapeutic options for SCID
medications for infection preventions
enzyme replacement therapy (PEG-ADA - for ADA deficiency)
hematopoeitic stem cell transplantation (HSCT) is curative
gene therapy trials for specific SCID types
Generating mAbs
isolation from immunised animals through phage display technology
hybridoma technology to produce monoclonal antibodies
modifying mAbs for therapeutic use
humanisation to reduce immunogenicity
glycosylation for improved half-life
conjugation with toxins for targeted therapy
diseases benefiting from mAbs
- cancer - rituximab targets B-cell lymphomas
- autoimmune diseases - infliximab for rheumatoid arthritis
- infections diseases - Palivizuman for respiratory syncytial vieus
Appreciate that diseases arising from errors in normal B cell behaviour are a ‘cost’ that is balanced by the ‘benefit’ of an adaptive immune system to the
organism and the population.
COSTS
- diseases resulting from B cells errors (e.g. PIDs) can lead to recurrent infections
- treatment ay require lifelong interventions
BENEFITS
- adaptive immune system provides specific responses to diverse pathogens
- B cells contribute to immune memory, offering long-term protection
- the over benefit out-weights the costs, providing robust immunity
Describe selected primary immunodeficiencies that arise from problems with Bcell development
XLA
- defect in B-cell development, due to BTK gene
- diagnosed by low Ig levels and absent B cells
CVID
- defect in B-cell development, diagnosed by reduced antibody production and treated using immunoglobulin replacement therapy
antigen recognition and activation
- BCR binds to specific antigens
- T-cells help activate B cells
- clonal expansion and differentiation into plasma cells
Affinity maturation and somatic hypermutation
- processed by B cells in secondary lymphoid organs
- improves antibody affinity and specificity
- results in the generation of high-affinity antibodies
Describe primary immunodeficiencies that arise from problems with the B cell
response to antigen
Hyper IgM syndromes
- defects in B-cell activation/differenciation
caused by gene defects (e.g. CD40L deficiency)
- diagnosis involves elevated IgM and reduced IgG/IgA
Suggest therapies available for selected primary immunodeficiencies
Immunoglobulin replacement therapy (IRT)
Hematopoeitic stem cell transplantation (HSCT)
Hematopoeitic stem cell transplantation (HSCT)
can be curative for severe PIDS like SCID
Immunoglobulin replacement therapy (IRT)
administered via IVIg or SCIg
lifelong treatment for antibody deficiencies
provides passive immunity
