The Immune System and T Lymphocytes

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Questions and Answers

What is the primary function of CD8+ T cells?

Present antigens to T cells

Aid in the synthesis of antibodies

Kill other cells as cytotoxic cells (correct)

Secretion of various immunoglobulins

What two signals are required for complete T cell activation?

Antigen recognition and cytokine release

Engagement of TCR with MHC-antigen complex and interaction of CD28 with CD80/CD86 (correct)

Binding of IgM and CD19

Engagement of TCR and interaction with CD40

What percentage of circulating lymphocytes do B-lymphocytes constitute?

25-30%

5-10%

10-20% (correct)

40-50%

Which immunoglobulin is found primarily on the surface of B cells?

IgM Signup and view all the answers

Which role do macrophages NOT perform in immune response?

Directly kill pathogens Signup and view all the answers

Where are Langerhan's cells primarily found?

Epidermis Signup and view all the answers

Which molecule is expressed on B cells and serves as a complement receptor?

CD21 Signup and view all the answers

What is the main characteristic of follicular dendritic cells?

Trap antibodies on their surfaces Signup and view all the answers

What does innate immunity primarily involve?

Epithelial barriers and phagocytic cells Signup and view all the answers

Which type of immunity specifically targets intracellular microbes?

Cell-mediated immunity Signup and view all the answers

What is the main role of T-helper-1 (TH1) cells?

Synthesis and secretion of IL-2 and IFN-γ Signup and view all the answers

Which statement best describes the CD4:CD8 ratio in T-lymphocytes?

It is approximately 2:1 Signup and view all the answers

What kind of molecules do CD4 molecules bind to?

Class II MHC molecules Signup and view all the answers

What makes up the T cell receptor (TCR)?

α and β polypeptide chains Signup and view all the answers

What are the two subsets of T-helper cells?

TH1 and TH2 Signup and view all the answers

Which type of lymphocytes are primarily involved in humoral immunity?

B-lymphocytes Signup and view all the answers

What characterizes the immediate phase of a Type I hypersensitivity reaction?

Vasodilatation and exudation due to vasoactive amines Signup and view all the answers

Which of the following is an example of a Type II hypersensitivity reaction?

Transfusion reaction Signup and view all the answers

What mechanism plays a role in Type II hypersensitivity involving antibody-dependent cellular cytotoxicity (ADCC)?

Opsonization and complement-mediated phagocytosis Signup and view all the answers

Which of the following conditions is associated with Type III hypersensitivity?

Poststreptococcal glomerulonephritis Signup and view all the answers

What are the primary T cells involved in Type IV hypersensitivity reactions?

CD4+ T cells primarily Signup and view all the answers

Which reaction characterizes the late phase of a Type I hypersensitivity reaction?

Influx of leukocytes lasting for days Signup and view all the answers

Which mechanism is NOT associated with Type II hypersensitivity?

Delayed type hypersensitivity Signup and view all the answers

What percentage of peripheral blood lymphocytes do natural killer (NK) cells comprise?

10-15% Signup and view all the answers

Which of the following receptors are used to identify NK cells?

CD16 and CD56 Signup and view all the answers

What type of antigens do CD8+ cytotoxic T cells recognize?

Endogenous antigens presented on class I MHC Signup and view all the answers

What principal function do class I MHC molecules serve?

Bind peptide fragments for presentation to antigen-specific T cells Signup and view all the answers

Where are the genes encoding MHC molecules located?

Chromosome 6 Signup and view all the answers

Which cells express class I MHC molecules?

All nucleated normal cells and platelets Signup and view all the answers

What type of antigens do class II MHC molecules present?

Exogenous antigens from extracellular microbes Signup and view all the answers

Which cytokine is secreted by natural killer (NK) cells?

IFN-γ Signup and view all the answers

What is the primary role of innate immunity?

To provide rapid defense against infections Signup and view all the answers

Which T lymphocyte subset is primarily responsible for producing IL-4, IL-5, and IL-13?

T-helper-2 (TH2) Signup and view all the answers

What is the main component that distinguishes cell-mediated immunity from humoral immunity?

The role of T lymphocytes Signup and view all the answers

Which component of T-lymphocytes assists with signal transduction?

CD3 complex Signup and view all the answers

What type of cells are primarily involved in the recognition and destruction of intracellular microbes?

T lymphocytes Signup and view all the answers

What does the somatic rearrangement of TCR genes result in?

Diversity of T cell receptors Signup and view all the answers

What is the CD4:CD8 ratio in normal T lymphocytes?

2:1 Signup and view all the answers

Which of the following statements is true about TH1 cells?

They facilitate macrophage activation Signup and view all the answers

Which role is NOT performed by macrophages in the immune response?

Secretion of antibodies Signup and view all the answers

What ensures the unique antigen specificity of B cells?

Somatic rearrangement of immunoglobulin genes Signup and view all the answers

Which of the following statements holds true about T cell activation?

TCR engagement requires CD28 interaction Signup and view all the answers

What is the primary role of follicular dendritic cells?

Trapping antibodies through Fc receptors Signup and view all the answers

Where are B-lymphocytes primarily located in the spleen?

White pulp Signup and view all the answers

Which cytokine type is primarily secreted by CD8+ T cells?

TH1 cytokines Signup and view all the answers

Which molecule on B cells interacts with activated T-lymphocytes?

CD40 Signup and view all the answers

What is a distinguishing feature of Langerhan's cells?

Located in the epidermis Signup and view all the answers

What characterizes the late phase of Type I hypersensitivity reactions?

Influx of leukocytes and prolonged symptoms Signup and view all the answers

Which mechanism is NOT involved in the destruction of antigens in Type II hypersensitivity reactions?

Direct viral lysis by natural killer cells Signup and view all the answers

What is a common consequence of Type III hypersensitivity reactions?

Formation of antigen-antibody complexes in tissues Signup and view all the answers

Which of the following is a characteristic of Type IV hypersensitivity?

Primarily mediated by T lymphocytes Signup and view all the answers

Which type of hypersensitivity is most commonly associated with autoimmune hemolytic anemia?

Type II Signup and view all the answers

In which type of hypersensitivity do antigen-antibody complexes primarily elicit tissue damage?

Type III Signup and view all the answers

What is a major feature of delayed-type hypersensitivity reactions in Type IV hypersensitivity?

Mediated by CD4+ T cells Signup and view all the answers

Which of the following conditions falls under the umbrella of Type III hypersensitivity?

Systemic lupus erythematosus Signup and view all the answers

What is the primary characteristic that distinguishes natural killer (NK) cells from T lymphocytes?

NK cells have azurophilic granules Signup and view all the answers

Which receptors on natural killer (NK) cells are responsible for mediating the recognition of target cells?

Activators and inhibitors Signup and view all the answers

Which of the following statements about class I MHC molecules is true?

They are expressed on all nucleated cells. Signup and view all the answers

What is the role of class II MHC molecules in the immune response?

They present exogenous antigens to CD4+ helper T cells. Signup and view all the answers

Which cytokine is primarily secreted by natural killer (NK) cells?

Interferon-gamma (IFN-γ) Signup and view all the answers

What would happen if a cell does not express class I MHC molecules?

It may be targeted and killed by NK cells. Signup and view all the answers

What segments of chromosome 6 encode the genes for MHC class I molecules?

HLA-A, HLA-B, and HLA-C Signup and view all the answers

What type of antigens do CD8+ T cells primarily recognize?

Endogenous viral antigens presented by class I MHC Signup and view all the answers

Study Notes

Immune Response

The immune system protects the body from foreign invaders, such as microbes and viruses.
There are two main types of immune responses: innate immunity and adaptive immunity.
Innate immunity, also called natural immunity, is the body's first line of defense against infection.
- It is present even before infection.
- Composed of physical barriers such as epithelial cells, phagocytic cells like neutrophils and macrophages, natural killer (NK) cells, and various proteins in the blood (including complement system).
- The innate immune system targets general patterns associated with pathogens, not specific invaders.
Adaptive immunity, also called acquired or specific immunity, develops over time based on exposure to particular pathogens.
- It relies on the ability of the body to remember and respond to specific antigens.
- Composed of T and B lymphocytes (white blood cells).
- Cellular immunity, mediated by T cells, targets intracellular pathogens.
- Humoral immunity, mediated by B cells, targets extracellular pathogens and toxins.

Immune Cells

T-lymphocytes (T cells): 60-70% of circulating lymphocytes.
- Found in the paracortical area of lymph nodes and periarteriolar sheath of the spleen.
- Each T cell has a specific T cell receptor (TCR) composed of alpha (α) and beta (β) polypeptide chains connected by a disulfide bond.
- Both α and β complexes are linked to a CD3 complex important for signal transduction during antigen recognition.
- Somatic rearrangement of TCR genes leads to diverse TCRs, allowing recognition of various antigens.
- Two main subsets of T cells: CD4+ and CD8+.
  - CD4+ T cells (helper T cells):
    - Express CD4 protein that binds to class II MHC molecules on antigen-presenting cells.
    - Help activate B cells and other immune cells.
    - Divided into two subsets:
      - TH1: Involved in macrophage activation and delayed hypersensitivity.
      - TH2: Primarily involved in activating B cells to produce antibodies.
  - CD8+ T cells (cytotoxic T cells):
    - Express CD8 that binds to class I MHC molecules.
    - Directly kill cells infected with viruses or other pathogens.
B-lymphocytes (B cells): 10-20% of circulating lymphocytes.
- Found in the superficial cortex of lymph nodes and the white pulp of the spleen.
- When activated by antigens, B cells differentiate into plasma cells that secrete antibodies.
- Antibodies:
  - IgG, IgM, IgA are the most abundant immunoglobulins.
  - IgE is present in trace amounts in the serum.
  - IgD is only found on B cells, serving as an antigen receptor.
- Monomeric IgM is expressed on the surface of B cells, acting as a B cell receptor (BCR).
- Like T cells, B cells undergo somatic rearrangement of immunoglobulin genes to generate diverse antibodies.
- Express various surface molecules, including CD19, CD20, CD21, and CD40.
Macrophages:
- Phagocytize and destroy pathogens.
- Present antigens to T cells through class II MHC molecules.
- Secrete cytokines that influence the activity of other immune cells such as T and B cells.
Dendritic cells:
- Found in lymphoid tissue and skin (Langerhans cells).
- Highly efficient antigen-presenting cells with poor phagocytic activity.
- Play a critical role in initiating primary immune responses.
Natural killer (NK) cells:
- Large granular lymphocytes with no TCR or immunoglobulin.
- Belong to the innate immune system responsible for killing infected cells and tumor cells without prior sensitization.
- Express CD16 and CD56, which help identify them.
- Important in eliminating virally infected cells and cells with abnormal MHC expression.

Major Histocompatibility Complex (MHC)

MHC molecules determine an individual's tissue compatibility.
Found on the surface of cells and present antigens to T cells, mediating immune responses.
MHC genes are located on chromosome 6.
Divided into three classes:
- Class I MHC: Expressed on all nucleated cells.
  - Present peptides derived from intracellular proteins, like viral antigens, to CD8+ T cells.
- Class II MHC: Expressed on antigen-presenting cells, like macrophages and dendritic cells.
  - Present peptides derived from extracellular proteins, like bacterial antigens, to CD4+ T cells.
- Class III MHC: Encode complement components that play a role in innate immunity.

Hypersensitivity Reactions

Excessive immune responses can be harmful, leading to various diseases categorized as hypersensitivity reactions.
Four main types:
- Type I (Immediate) hypersensitivity:
  - Rapid reaction within minutes after exposure to an antigen.
  - Mediated by IgE antibodies binding to mast cells.
  - Characterized by vasodilation, edema, and bronchospasm.
  - Examples: Allergies, anaphylaxis.
- Type II (Cytotoxic) hypersensitivity:
  - Occurs when antibodies bind to antigens on the cell surface or extracellular matrix.
  - Can lead to cell destruction through opsonization, complement-mediated lysis, or antibody-dependent cellular cytotoxicity (ADCC).
  - Examples: Transfusion reactions, autoimmune hemolytic anemia.
- Type III (Immune Complex) hypersensitivity:
  - Immune complexes (antigen-antibody) deposit in tissues, triggering inflammation.
  - Examples: Systemic lupus erythematosus (SLE), serum sickness.
- Type IV (Delayed-Type) hypersensitivity:
  - Response develops 2-3 days after antigen exposure.
  - Mediated by T cell-mediated immune responses, like T cell activation and cytokine release.
  - Examples: Contact dermatitis, tuberculosis, transplant rejection.

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Description

Explore the intricacies of the immune system, focusing on the distinctions between innate and adaptive immunity. Delve into the role of T lymphocytes, their unique receptors, and the mechanisms of TCR diversity. This quiz will enhance your understanding of how our bodies defend against pathogens.