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What type of immunity is primarily mediated by T lymphocytes?
What type of immunity is primarily mediated by T lymphocytes?
Which T cell subset plays a significant role in combating intracellular pathogens?
Which T cell subset plays a significant role in combating intracellular pathogens?
How do CD8+ cytotoxic T lymphocytes eliminate infected host cells?
How do CD8+ cytotoxic T lymphocytes eliminate infected host cells?
What is the primary function of CD4+ Helper T cells?
What is the primary function of CD4+ Helper T cells?
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What characterizes delayed hypersensitivity?
What characterizes delayed hypersensitivity?
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Which cytokine is primarily produced by Th1 cells to aid in the defense against microbes?
Which cytokine is primarily produced by Th1 cells to aid in the defense against microbes?
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Which of the following is NOT a characteristic function of regulatory T cells?
Which of the following is NOT a characteristic function of regulatory T cells?
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What is a primary mechanism by which CD4+ Th2 cells defend against helminths?
What is a primary mechanism by which CD4+ Th2 cells defend against helminths?
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Which factor is primarily responsible for directing the differentiation of activated CD4+ T cells?
Which factor is primarily responsible for directing the differentiation of activated CD4+ T cells?
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What is the primary function of Th2 cells in the immune response?
What is the primary function of Th2 cells in the immune response?
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What effect does the balance between Th1 and Th2 cell activation have?
What effect does the balance between Th1 and Th2 cell activation have?
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Which mechanism allows CD8+ T cells to induce apoptosis in infected cells?
Which mechanism allows CD8+ T cells to induce apoptosis in infected cells?
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Which cytokine is primarily associated with the activation of effector CD4+ T cells?
Which cytokine is primarily associated with the activation of effector CD4+ T cells?
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What role do adhesion molecules play in the function of CTLs (cytotoxic T lymphocytes)?
What role do adhesion molecules play in the function of CTLs (cytotoxic T lymphocytes)?
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What is a characteristic feature of lepromatous leprosy?
What is a characteristic feature of lepromatous leprosy?
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How do granzymes contribute to the function of CTLs?
How do granzymes contribute to the function of CTLs?
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What determines the differentiation of naive CD4+ T lymphocytes?
What determines the differentiation of naive CD4+ T lymphocytes?
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What immune response do Th2 cells primarily mediate?
What immune response do Th2 cells primarily mediate?
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Which transcription factor is primarily activated by cytokines to influence T cell differentiation?
Which transcription factor is primarily activated by cytokines to influence T cell differentiation?
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What is the effect of a balance between Th1 and Th2 cell activation?
What is the effect of a balance between Th1 and Th2 cell activation?
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In the context of leprosy, what leads to the development of tuberculoid form?
In the context of leprosy, what leads to the development of tuberculoid form?
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How do cytotoxic T lymphocytes (CTLs) primarily induce apoptosis in target cells?
How do cytotoxic T lymphocytes (CTLs) primarily induce apoptosis in target cells?
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What role do granzymes play in the immune response?
What role do granzymes play in the immune response?
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What is the function of adhesion molecules in the interaction between CTLs and infected cells?
What is the function of adhesion molecules in the interaction between CTLs and infected cells?
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What is the primary role of CD4+ Th1 lymphocytes in cell-mediated immunity?
What is the primary role of CD4+ Th1 lymphocytes in cell-mediated immunity?
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Delayed hypersensitivity reactions are mediated mostly by which type of immune cell?
Delayed hypersensitivity reactions are mediated mostly by which type of immune cell?
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What function do CD8+ cytotoxic T lymphocytes perform in the immune response?
What function do CD8+ cytotoxic T lymphocytes perform in the immune response?
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Which cytokine is a key component produced by Th1 cells to aid in their immune response?
Which cytokine is a key component produced by Th1 cells to aid in their immune response?
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What distinguishes regulatory T lymphocytes from effector T lymphocytes?
What distinguishes regulatory T lymphocytes from effector T lymphocytes?
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The differentiation of CD4+ T cells into Th2 cells is primarily driven by which of the following?
The differentiation of CD4+ T cells into Th2 cells is primarily driven by which of the following?
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Which subset of CD4+ helper T cells is primarily involved in the defense against helminths?
Which subset of CD4+ helper T cells is primarily involved in the defense against helminths?
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What is an essential characteristic of Th1 CD4+ effector T lymphocytes?
What is an essential characteristic of Th1 CD4+ effector T lymphocytes?
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Study Notes
Cellular Immune Response II
- Cellular Immunity (CMI) is the defense against intracellular microbes, mediated by T lymphocytes.
- Some T lymphocytes activate phagocytes to destroy microbes ingested by phagocytes into intracellular vesicles.
- Other T lymphocytes kill any host cell harboring infectious microbes in the cytoplasm.
- Two types of cell-mediated immune reactions eliminate different types of microbes.
- CD4+ helper T cells, secrete cytokines that recruit and activate other leukocytes to phagocytose and destroy microbes.
- CD8+ cytotoxic T lymphocytes kill any infected cell containing microbial proteins in the cytosol or nucleus.
- Th1 cells:
- Stimulate the production of antibodies that promote ingestion of microbes by phagocytes.
- Kill microbes by producing IFN-γ, a key component of cell-mediated immunity.
- Role of Th1 cells in defense against intracellular pathogens:
- Activation of effector cells.
- Activation of macrophages.
- Responses of activated macrophages (killing phagocytosed bacteria, secretion of cytokines like TNF, IL-1, IL-12, chemokines, increased expression of MHC and costimulators (B7 molecules)).
- Delayed hypersensitivity (Type IV hypersensitivity):
- An immune reaction taking 24-72 hours to develop after exposure to an antigen.
- Mediated by T cells rather than antibodies.
- Mechanisms determining CD4+ T cell differentiation:
- Pathogen type (intracellular or extracellular).
- Cytokines from antigen-presenting cells (APCs).
- Activation of transcription factors such as GATA-3, T-bet, and RORγt.
- Cytokine production by the effector cell.
- Characteristics of subsets of CD4 helper T cells:
- Th1: associated with intracellular pathogens, uses IFN-γ, and causes autoimmunity and chronic inflammation.
- Th2: associated with parasites (helminths), uses IL-4, IL-5, IL-13, and causes allergy.
- Th17: associated with extracellular pathogens (bacteria and fungi), uses IL-17, IL-22, and causes autoimmunity and inflammation.
- Th: associated with extracellular pathogens, uses IL-21 (and IFN-γ or IL-4) and causes autoimmunity (autoantibodies).
- General properties of T cell cytokines:
- Produced transiently in response to antigen.
- Usually acts on the same cell that produces the cytokine (autocrine) or nearby cells (paracrine).
- Pleiotropism: each cytokine has multiple biological actions.
- Redundancy: multiple cytokines may share similar biological activities.
- Biologic actions of selected T cell cytokines (updated):
- IL-2: T-cell proliferation and survival, including regulatory T-cell survival.
- IFN-γ: activation of macrophages.
- IL-4: B-cell switching to IgE, activation of eosinophils.
- IL-5: activation of eosinophils.
- IL-17: stimulation of acute inflammation, neutrophil recruitment.
- IL-22: maintenance of epithelial barrier function.
- TGF-β: inhibition of T-cell activation and differentiation of regulatory T cells.
- IL-1: involved in acute inflammation. IL-12: critical Th1 development. IL-13: involved in fibrosis & inflammation. TNF: involved in acute inflammation & tissue damage.
- Role of Th2 cells in defense against helminths:
- Th2 cells stimulate phagocyte and eosinophil-mediated immunity, especially effective against helminths.
- Important in chronic parasitic infections and allergic diseases.
- Classical & Alternative macrophage activation:
- Classically activated macrophages (M1) are triggered by microbial products and interferon-γ. These macrophages exhibit microbicidal activity with ROS and NO.
- Alternatively activated macrophages (M2) are induced by cytokines like IL-4 and IL-13. These participate in tissue repair.
- Balance between Th1 & Th2 cell activation determines outcome of intracellular infection:
- Th1 cells activate phagocytes to kill ingested microbes, while Th2 cells can inhibit classical macrophage activation, which is important in the balance of immune response.
- Cooperation between CD4+ and CD8+ T cells:
- CD4+ T cells recognize antigens from vesicular microbes, activating macrophages to kill microbes in the vesicles.
- CD8+ T cells recognize antigens from cytoplasmic microbes, killing the infected cells.
- Regulatory T Lymphocytes:
- Crucial for suppressing immune responses.
- CTLA-4 binds to costimulatory molecules on APCs, shutting off T cell responses.
- Critical for maintaining tolerance to self-antigens.
CD8+ Effector T Cells
- Recognize class I MHC molecules expressed on infected cells.
- Form adhesion with infected cells, stabilizing the binding.
- Activated CTL release granules containing perforin and granzymes.
- Perforin creates pores in the target cell membrane, allowing granzymes to enter.
- Granzymes induce apoptosis in the target cell. Granzymes induce apoptosis.
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Description
Explore the intricate mechanisms of cellular immunity mediated by T lymphocytes in this quiz. Learn about the roles of different T cell types, including CD4+ helper T cells and CD8+ cytotoxic T lymphocytes, in the defense against intracellular microbes. Test your understanding of how these immune responses eliminate infections.
