Immunology: T-Cell Classification and Activation

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Questions and Answers

What is one of the primary requirements for T-cell activation by antigen-presenting cells (APCs)?

High levels of cytokines present in the environment

Direct recognition of free antigens by T cells

Costimulatory signal involving CD28 and CD80 (correct)

Inhibition of CD3 zeta chain phosphorylation

Which of the following outcomes can occur when T cells are properly activated?

Anergic state observable immediately

Diminished production of cytokines

Proliferation of T cells (correct)

Secretion of IgG without any T cell help

What characterizes T-independent antigens in B cell activation?

They require T cell help for effective activation

They primarily provoke IgM responses and little immunologic memory (correct)

They only induce IgG responses and long-term memory

They are always stronger than T-dependent antigens

What role does super antigen play in immune response?

It cross-links MHC with T cell receptors or B cell receptors Signup and view all the answers

What happens to a T cell if it does not receive a complete set of activation signals?

It becomes anergic or enters a resting state Signup and view all the answers

Which marker is exclusively found on B cells?

CD19/CD20 Signup and view all the answers

What is the role of the thymus in T cell maturation?

To select T cells that respond to pathogens but not self-antigens Signup and view all the answers

What percentage of T cell precursors typically survive the selection process in the thymus?

2-3% Signup and view all the answers

What type of T lymphocyte is characterized by CD4+ markers?

Th-helper T cells Signup and view all the answers

Which CD marker is associated with cytotoxic T cells?

CD8 Signup and view all the answers

What results from the activation of naïve T cells in secondary lymphoid organs?

Proliferation and differentiation into effector and memory cells Signup and view all the answers

What type of T cells are primarily responsible for the regulation of antibody production?

Th2 cells Signup and view all the answers

What molecule on antigen-presenting cells (APCs) do T cells recognize foreign antigens through?

MHC Signup and view all the answers

What method is considered the gold standard for diagnosing immune system function related to lymphocyte activity?

Erythrocyte rosette formation Signup and view all the answers

Which of the following describes a defect associated with T-cell activation?

Defective surface expression of CD3 Signup and view all the answers

In the context of lymphocyte activation, which antigen is commonly used to stimulate T cells?

Phytolacca americana (PHA) Signup and view all the answers

What common condition is associated with a pretranslational defect in interleukin-2 (IL-2) production?

Recurrent viral infections Signup and view all the answers

Which cytokine is notably involved in T-cell signal transduction that may be defective in immunodeficiencies?

Interleukin-2 (IL-2) Signup and view all the answers

Which mechanism is NOT involved in the killing of target cells by cytotoxic T cells (Tc)?

Phagocytosis of infected cells Signup and view all the answers

What role does granzyme play in the apoptosis process initiated by Tc cells?

Activates BID leading to cytochrome release Signup and view all the answers

Which cytokine is involved in binding to TNF receptors to induce apoptosis?

TNF Signup and view all the answers

Which T cell type is characterized by its inability to directly kill infected cells?

CD4+ T-helper cells Signup and view all the answers

The primary function of CD8+ cytotoxic T cells (Tc) includes which of the following?

Direct killing of infected or cancerous cells Signup and view all the answers

What does CAD stand for in the context of apoptosis?

Caspase Activated Deoxyribonuclease Signup and view all the answers

What is a key function of T-helper type 1 (Th1) cells?

Direct activation of macrophages and Tc cells Signup and view all the answers

Which protein is primarily found in the vesicles of NK cells?

Granulysin Signup and view all the answers

What is the primary function of plasma cells in the immune response?

Synthesize and secrete immunoglobulins Signup and view all the answers

Which type of B cell is characterized by having a CD5 marker?

B1 cells Signup and view all the answers

What type of activation involves B cells binding to an antigen and receiving a secondary activation signal through TLR?

Type A T-cell independent activation Signup and view all the answers

Where does B-cell maturation primarily occur?

Bone marrow and GALT Signup and view all the answers

What is a characteristic of T-cell independent activation of B cells?

Leads to a week response Signup and view all the answers

Which of the following is NOT a condition that can lead to an increase in plasma cells?

Acute bacterial infections Signup and view all the answers

What are naive lymphocytes?

Lymphocytes that have yet to encounter their specific antigen Signup and view all the answers

Which type of immune cell accounts for the majority of B lymphocytes in adults?

B2 cells Signup and view all the answers

Study Notes

Cell Classification

B cells are distinguished by the B-cell receptor (BCR), which is a surface immunoglobulin.
T cells are distinguished by the T-cell receptor (TCR).
Helper T cells (Th) are characterized by the presence of CD4.
Cytotoxic T cells (Tc) are characterized by the presence of CD8.
Both Tc and Th cells express CD3, which is part of the TCR complex.

Lymphocyte Maturation

T cells originate in the bone marrow and mature in the thymus.
T cells undergo random recombination of TCR genes during maturation in the thymus.
Mature T cells with receptors that recognize self-antigens undergo apoptosis.

T-cell Maturation in the Thymus

Immature T cells undergo positive and negative selection in the thymus.
Only a small percentage (2-3%) of T-cell precursors survive these selection processes.
Mature T cells are either CD4+ or CD8+.

T-cell Activation

Mature, naive T cells circulate in the peripheral blood until they encounter foreign antigens presented on MHC molecules of antigen-presenting cells (APCs).
This encounter leads to T-cell activation, proliferation, and differentiation into effector and memory cells.

T-Lymphocyte Subsets

Helper T (Th, CD4+) lymphocytes produce various cytokines.
Th1 cells promote cell-mediated immunity, activating Tc, NK cells, and macrophages.
Th2 cells regulate antibody production by B cells.

General Functions of CD8+ Cytotoxic T cells

CD8+ Tc cells are cytotoxic and destroy infected cells.
Tc cells are important in the immune response to viruses, intracellular bacteria, and tumors.

Mechanisms of Target Cell Killing by NK or Tc Cells

NK and Tc cells release cytotoxic vesicles containing perforins, granzymes, and TNF.
Perforins create pores in target cell membranes, allowing granzymes to enter.
Granzymes activate caspases, which trigger apoptosis.
TNF binds to TNFR and activates apoptosis.
Granulysin is an antimicrobial compound found in NK vesicles.
FasL on Tc cells binds to Fas on target cells, also activating apoptosis.

General Functions of CD4+ T-helper Cells

Th cells promote the activation and direction of other immune cells.
Th1 cells activate cell-mediated immunity.
Th2 cells promote antibody-mediated immunity.

Antigen Recognition by T Cells

T cells recognize antigens only when presented by self-MHC molecules.

T-cell Activation by APCs

T-cell activation requires three signals:
- Binding of CD4 or CD8 to MHC class II or MHC-I, respectively.
- Phosphorylation of CD3 zeta chain and specific kinases.
- Costimulatory signal, such as the interaction between CD28 on T cells and CD80 on APCs.
T-cell activation leads to proliferation, cytokine secretion, and differentiation into effector and memory cells.
T-cell anergy occurs when a cell doesn't receive a full set of signals.

B Lymphocyte Activation and Maturation

B cells mature in the bone marrow and gut-associated lymphoid tissue (GALT).
B-cell activation leads to enlargement, development of synthetic machinery, division, maturation, and antibody secretion.
B cells can activate independently from T cells, for example, through stimulation by LPS.

Types of B- Cell Activation

T-cell dependent activation: requires interaction with Th cells.
T-cell independent activation: can occur through stimulation by mitogens or some antigens.

Plasma Cell Biology

Plasma cells are the end stage of B-cell differentiation, specializing in antibody production.
Plasma cells can be found in high numbers in infections, autoimmune diseases, and malignant disorders like multiple myeloma.

Other Types of Lymphocytes

NK cells: Granulated lymphocytes responsible for killing infected cells.
Memory cells: Long-lived T or B cells that have encountered antigen.
Virgin or naive lymphocytes: Have not encountered their specific antigen.

Immune-Mediated Disease

Characterized by chronic inflammation and recurrent antibody production.
Can be caused by dysregulation of the immune system, leading to autoimmune reactions.

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Description

This quiz covers the classification and maturation of T-cells, including the roles of CD4 and CD8, as well as their activation processes. Learn about the path T-cells take from the bone marrow to the thymus and the selection processes they undergo. Test your knowledge on immune system functionality and T-cell responses!