Cell-Mediated Immunity Overview

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Questions and Answers

What is the role of IL-2 in relation to T lymphocytes?

It acts as a death signal for T lymphocytes.

It inhibits the proliferation of T lymphocytes.

It stimulates the survival and proliferation of T lymphocytes. (correct)

It solely promotes the differentiation of naive T cells.

Which IL-2 receptor complex is expressed by resting T lymphocytes?

IL-2Rβγ complex (correct)

IL-2Rαβγ complex

IL-2Rγc complex

IL-2Rα complex

Which factor leads to the expression of the IL-2Rα chain in T cells?

Activation by antigen and costimulators (correct)

Aging of T cells

Deprivation of nutrients

Inhibition by cytokines

What characteristic is associated with the high-affinity IL-2Rαβγ complex?

It is formed only after T cell activation. Signup and view all the answers

How does IL-2 influence regulatory T cells?

It maintains their function. Signup and view all the answers

What happens to most effector T cells after encountering an antigen and costimulation?

They undergo apoptosis. Signup and view all the answers

Which cytokine is important in the structure of its trimeric receptor?

IL-2 Signup and view all the answers

What is a significant consequence of IL-2 receptor expression in activated T cells?

Increased sensitivity to IL-2. Signup and view all the answers

What is the primary role of dendritic cells in T lymphocyte activation?

They present antigens to T lymphocytes. Signup and view all the answers

What distinguishes T-cell epitopes from B-cell epitopes?

T-cell epitopes require antigen-presenting cells for recognition. Signup and view all the answers

Which process occurs first in the T cell response sequence?

Migration of T lymphocytes to lymph nodes. Signup and view all the answers

What is the main source of interleukin 2 production?

Activated T cells. Signup and view all the answers

Which of the following roles does interleukin 2 play in T lymphocyte activation?

Stimulates proliferation and differentiation of activated T lymphocytes. Signup and view all the answers

What is the function of CTLA-4 in T lymphocyte activation?

Inhibits T cell activation. Signup and view all the answers

What distinguishes helper T lymphocytes from killer T lymphocytes?

Helper T lymphocytes do not kill target cells. Signup and view all the answers

Which mechanism is used by killer T lymphocytes to eliminate target cells?

Granule release and induction of apoptosis. Signup and view all the answers

What can contribute to granuloma formation in certain diseases?

Imperfect functioning of cellular immunity. Signup and view all the answers

Which statement accurately describes T-cell activation?

It requires recognition of antigens by T lymphocytes and co-stimulatory signals. Signup and view all the answers

Study Notes

Cell-Mediated Immunity: Activation and Effector Mechanisms

Dendritic cells are primarily responsible for antigen presentation to T lymphocytes.
Dendritic cells take up antigens in the skin and transport them to draining lymph nodes.
Antigen presentation occurs in T-cell areas of lymph nodes.
T cell activation is dependent upon antigen recognition and costimulation.
T cells proliferate and differentiate upon activation, leading to effector cells.
Effector T cells migrate to sites of infection or inflammation.
Migration of T lymphocytes to lymph nodes involves several steps including L-selectin binding, rolling interaction, chemokine activation and firm adhesion.
T lymphocytes circulate through lymph nodes, searching for specific antigens.
T cell activation results from antigen recognition and costimulation.

B-cell Epitopes

B-cell epitopes can be peptide, polysaccharide or nucleic acid structures.
B-cell epitopes are recognized directly without antigen presentation.
B-cell epitopes can be linear or conformational.

T-cell Epitopes

T-cell epitopes are peptide structures.
T-cell epitopes are recognized with the help of antigen-presenting cells.
T-cell epitopes are only of linear type.

Sequence of Events in T Cell Responses

Activation of macrophages and other cells, leading to inflammation.
T cell activation by antigen in lymphoid tissues.
CD4+ T cell differentiation into various subtypes.
CD8+ T cell differentiation into cytotoxic T lymphocytes (CTLs).
CTLs and memory cells develop after antigen exposure and activation.
Production of memory cells to provide a faster response to subsequent encounters with the same antigen.
Cytotoxic T cells eliminate infected or cancerous cells.
The sequence involves antigen recognition, lymphocyte activation, proliferation, and differentiation into effector and memory cells.

Role of Interleukin 2

Activated T cells produce interleukin-2 (IL-2).
IL-2 stimulates the survival, proliferation and differentiation of other activated lymphocytes such as T-cells, B-cells and NK cells.
IL-2 promotes the survival and function of regulatory T cells.

Different Messages of Antigen-Presenting Cells to T Lymphocytes

MHC class II molecules present antigens in lymphoid tissues.
Costimulatory molecules (B7.1 and B7.2) are crucial for T cell activation.
Cytokines (IL-6, IL-12, TGF-β, IL-4) further direct differentiation to different T helper subtypes.
The activated T cell receives multiple signals from the antigen and the antigen-presenting cell.

The Role of CTLA-4

CTLA-4 binds B7 more strongly than CD28 and transmits inhibitory signals.
CTLA-4 regulation of T cell activity is essential to prevent excessive immune responses.

Therapeutic Use of CTLA-4 Inhibition

CTLA-4-Ig inhibits T cell activation by binding B7.
Blocking B7 signalling with CTLA-4-Ig mitigates or inhibits immune activation against transplantation or tumor cells.

Different Subtypes of T Lymphocytes

CD8+ cytotoxic T lymphocytes (CTLs) kill virus-infected cells.
CD4+ T helper (Th) cells coordinate the immune response by providing signals to other immune cells.
Different Th subtypes (TH1, TH2, TH17, TFH, Treg) have distinct functions in immunity.
Subtypes include TH1, TH2, TH17, regulatory T cells, and follicular helper T cells.
Different T cell subtypes have unique roles in host defense against pathogens, inflammation and regulation.

Effector Mechanisms of Cellular Immunity

Phagocytosis is a process in which a cell engulfs a particle, such as a pathogen, and then digests it.
T cell activity induces inflammation to recruit more immune cells to the infection site.
Cellular immunity is essential to eradicate infections.

Granules of Cytotoxic T Cells

Perforin forms pores in the target cell membrane.
Granzymes enter the target cell and activate caspase enzymes.
Granulysin has antimicrobial activity.

Apoptosis Induction by Killer T Lymphocytes

Perforin/granzyme pathway forms pores in the target cell.
Granzymes enter the target cell and activate caspases.
Fas/FasL pathway activates caspase-8, which initiates apoptosis.

Mechanism of Killing of Target Cells

CTLs recognize and bind to virus-infected cells.
CTLs release granules containing perforin and granzymes into the target cell.
Target cell DNA fragments, triggering apoptosis (cell death).

Contact Between Killer T Cell and Target Cell

CTLs and target cells form a close contact.
This contact is crucial to induce activation of apoptosis in the infected cell.

Activation of Macrophages

Macrophages can be activated by Th1 cells via the release of cytokines such as IFN-γ.
Classical activation leads to enhanced killing of microbes.
Activated macrophages increase the killing of microorganisms.
Enhanced microbial killing through increased reactive oxygen species production and enzyme secretion.

Granuloma Formation

Granulomas are structures formed in response to persistent infections when cellular immunity functions are compromised.

Executive Functions of TH2 Helper T Lymphocytes

TH2 cells provide help to B cells, particularly for antibody production that targets helminthic pathogens.
TH2 cells induce an immune response to helminth parasites, which elicit a type 2 immune response.
TH2 cells regulate tissue repair after inflammation and helminthic infection.

Activation of Macrophages (Classical and Alternative)

Classically activated macrophages (M1) kill microbes via phagocytosis and inflammation and are induced by direct interaction with activated T cells.
Alternatively activated macrophages (M2) promote tissue repair and dampen inflammation and are activated by Th2 cytokines.

Exective Functions of TH17

TH17 cells induce inflammation and recruit neutrophils, important in fighting extracellular bacteria.
TH17 cells promote neutrophil recruitment to sites of infection via the production of IL-17, enabling effective combat against extracellular pathogens.

Stimulation of Killer T Lymphocytes

Specific antigens stimulate proliferation and differentiation of T cells to CTLs.
CTLs migrate to sites of infection and kill infected cells, enabling effective host defense.

Summary of T Lymphocyte Activation

T-cell activation requires antigen recognition and costimulation.
T-cell activation results in the production of effector T cells and memory T cells.
CTLs recognize and kill infected cells or tumor cells by apoptosis.
Cytotoxic T lymphocytes induce apoptosis in target cells.

Activation of T Lymphocytes (Costimulatory Molecules and Interleukin 2)

Costimulatory molecules (e.g., CD28 and B7) are essential for T cell activation.
IL-2 is crucial for T cell survival, proliferation, and differentiation, including the development of memory cells.

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Description

This quiz covers the mechanisms of cell-mediated immunity, focusing on T lymphocyte activation and effector functions, as well as the role of dendritic cells in antigen presentation. Additionally, it explores the structures recognized by B-cell epitopes, highlighting their importance in the immune response. Test your knowledge on these fundamental concepts of immunology.