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Questions and Answers
What is the difference between T-dependent and T-independent antibody production?
T-dependent antibody production requires help from T cells, whereas T-independent antibody production does not.
What is the process of T cell help for B cell antibody production?
The process involves interactions between activated T helper cells and B cells, leading to B cell proliferation and differentiation into plasma cells.
What is isotype switching?
Isotype switching is the process by which a B cell changes the isotype of antibody it produces without altering its specificity for the antigen.
What is affinity maturation?
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What is the function of Activation-Induced Deaminase (AID)?
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What are plasma cells?
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Which type of B cells secretes IgM antibodies without requiring prior antigenic stimulation?
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Follicular B cells are the most common type of antibody-producing lymphocytes in circulation.
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What is necessary for the full activation of B cells producing different antibody isotypes?
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What are the effector mechanisms of cytotoxic T cells?
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Which cells recognize antigens on class I MHC?
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CTLs are the major killers of virus-infected cells and cancer cells.
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The activation of naïve CTL requires Class I and Class II antigen presentation on the same ______.
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What is the role of perforin in CTL function?
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What method do CTLs use to induce apoptosis in target cells?
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What characterizes regulatory T cells (TREGs)?
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Which cytokines do TREG cells produce?
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Memory T cells require significant co-stimulation to function.
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What growth factor stimulates the proliferation of antigen-activated T cells?
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Match the following T cell characteristics with their definitions:
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Study Notes
### B Cell Subsets
- B-1 cells are self-renewing and found in the peritoneum and mucosa
- Marginal zone B cells are found in the spleen and lymph nodes
- Follicular B cells are the most common type of antibody-producing cell
Stages of Antigen-Specific B Cell Development
- Antibody response to protein antigens takes 3-7 days after antigen exposure
- Naïve B cells with IgM and IgD receptors encounter antigen within secondary lymphoid organs
- Lymph node B and T cells are located in distinct zones - B cell zones and T cell zones.
- The lymphoid follicle is the B cell zone.
- Germinal centers (GCs) are found within follicles and contain actively proliferating B cells and a periphery containing non-proliferating B cells.
- Primary follicles lack GCs and are composed of rapidly dividing plasmablasts actively producing antibody.
Antigen Presentation to B Cells
- Naïve B cells circulate via the blood and lymph until they encounter antigen
- Follicular dendritic cells (FDCs) capture opsonized antigens and present them to follicular B cells
- Macrophages transport antigens from the lymph to follicular B cells
- Differentiation from naïve to effector cells requires co-stimulatory signals from PRRs, TFH cells, or both
- For full B cell activation to occur, these additional factors are needed:
- Help from T helper cells
- CD40-CD40L interactions
Antibody Production by B Lymphocytes to T-dependent Antigens
- For a protein antigen to stimulate an antibody response, B lymphocytes and TH cells must come together in lymphoid organs and interact.
- This interaction stimulates B cell proliferation and differentiation into antibody-producing cells.
Function and Properties of Cytotoxic T Cells
- Cytotoxic T cells (CTLs) recognize antigens presented by class I MHC, and are mainly responsible for killing virus-infected cells and cancer cells.
- CTLs are a major source of pro-inflammatory cytokine, mostly IFNγ.
Activation of Cytotoxic CD8+ T Cells
CTLs are activated from naïve cells to effector cells by acquiring target cell antigens through cross-presentation by antigen presenting cells (APCs).
- Cross-presentation requires both class I and class II antigen presentation on the same APC to activate TH1 and CTLs at the same time.
CTL Killing by Exocytosis of Cytotoxic Granules
- CTLs contain lytic granules containing cytotoxic proteins granzyme and perforin.
- When a CTL interacts with a target cell, a synapse is formed between them.
- Perforin creates pores in the target cell membrane allowing granzyme to enter.
- Granzyme activates caspases to induce apoptosis in the target cell.
- The CTL detaches itself from the target cell and can kill multiple targets.
Intrinsic and Extrinsic Pathways of Apoptosis
- Apoptosis, or programmed cell death, can be initiated by intrinsic or extrinsic pathways.
- The intrinsic pathway involves the release of cytochrome C from the mitochondria, leading to the activation of caspases that initiate the caspase cascade.
- Granzyme and perforin released by CTLs trigger the intrinsic pathway.
- CTLs can also induce apoptosis through the extrinsic pathway by expressing Fas-L, TNFα, and LTβ, which bind to their receptors (Fas, TNFR-I, and TNFR-II) on target cells.
Memory Cells
- Memory cells don’t require antigen exposure to survive, and are long-lived compared to naïve or effector cells.
- Memory cells respond more rapidly to antigen stimulation than naïve cells, and are more numerous than naïve cells specific to the same antigen.
- Memory cells migrate to peripheral tissues, like the skin, and respond to antigen exposure at these sites.
- Memory cells require less co-stimulation than naïve cells to function.
- Maintenance of memory cells is dependent on cytokines (IL-7) and not on repeated antigen exposure.
Regulatory T Cells (TREGs)
- TREGs express the transcription factor FoxP3, which directs expression of high levels of CD25 (IL-2R), and anti-inflammatory cytokines IL-10 and TGF-β.
- TGF-β and IL-10 suppress activation of T, B, and NK cells and hinder APCs from stimulating T cells.
- Their main function is to maintain peripheral tolerance.
- TREGs express high levels of the negative co-stimulator CTLA-4, which competes with CD86(B7) on APC for binding to CD28 on T cells.
- TREGs are mainly generated by self-antigen recognition in the thymus, and by self- and foreign antigen recognition in peripheral lymphoid organs.
- They express high levels of the receptor for the T cell growth factor IL-2.
Interleukin 2 (IL-2) T cell Growth Factor
- IL-2 stimulates the proliferation and differentiation of antigen-activated T cells (clonal expansion).
- It promotes survival of T cells by upregulating expression of Bcl-2, an anti-apoptotic protein.
- IL-2 acts in an autocrine and paracrine manner.
- It stimulates the production of effector cytokines like IFNγ and IL-4 by T cells.
- IL-2 is important for the survival and function of TREG cells.
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Description
Test your knowledge on B cell subsets and their development stages. This quiz covers topics such as various types of B cells, their locations, and the processes involved in antigen-specific responses. Enhance your understanding of immune response mechanisms with this focused assessment.
