Immunology Lec 4 & 5

Question 1

Lecture 4:
What are the three main types of T cells?

Answer 1

Cytotoxic T Cells (CD8+)
Helper T Cells (CD4+)
Regulatory T Cells

Question 2

How do Helper T Cells (CD4+) assist in the immune response?

Answer 2

Helper T Cells assist in activating immune cells by recognizing antigens presented by MHC Class II molecules and producing cytokines.

Question 3

What is the primary function of Cytotoxic T Cells (CD8+)?

Answer 3

Cytotoxic T Cells kill virus-infected and abnormal cells by inducing apoptosis.

Question 4

What is the role of Regulatory T Cells?

Answer 4

Regulatory T Cells inhibit immune responses to prevent autoimmunity by producing cytokines like IL-10 and TGF-beta.

Question 5

Where are T cells activated?

Answer 5

T cells are activated in secondary lymphoid tissues, such as lymph nodes and the spleen.

Question 6

Describe the structure of T-cell receptors (TCR).

Answer 6

T-cell receptors have a similar structure to immunoglobulins but remain membrane-bound, consisting of constant and variable regions. They come in two forms: αβ (common) and γδ (less common).

Question 7

What is antigen presentation?

Answer 7

Antigen presentation is the process by which protein fragments from pathogens or other foreign substances are displayed on the surface of cells by MHC molecules, allowing T cells to recognize and respond to the antigens.

Question 8

Differentiate between MHC Class I and MHC Class II molecules.

Answer 8

MHC Class I: Present on all nucleated cells, present intracellular antigens to CD8+ T cells.
MHC Class II: Present on antigen-presenting cells (APCs) like dendritic cells, macrophages, and B cells, present extracellular antigens to CD4+ T cells.

Question 9

How are antigens processed in the MHC Class I pathway?

Answer 9

Intracellular antigens are processed in the endoplasmic reticulum and presented on the cell surface by MHC Class I molecules.

Question 10

How are antigens processed in the MHC Class II pathway?

Answer 10

Extracellular antigens are processed in acidified endosomes and presented on the cell surface by MHC Class II molecules.

Question 11

What mechanisms do Cytotoxic T Cells use to kill infected cells?

Answer 11

Cytotoxic T Cells induce apoptosis in infected cells using perforin, granzymes, and granulysin.

Question 12

What is the role of Helper T Cells in activating macrophages and assisting B cells?

Answer 12

Th1 cells activate macrophages, while Th2 cells assist B cells in antibody production.

Question 13

Explain the concept of MHC polymorphism and its significance.

Answer 13

MHC polymorphism refers to the high variability in MHC genes, allowing for a broad range of antigen presentation, which is essential for effective immune responses and complicates organ transplantation.

Question 14

What is apoptosis, and why is it important in the immune response?

Answer 14

Apoptosis is programmed cell death used by cytotoxic T cells to eliminate infected cells without releasing pathogens, ensuring controlled cell death to prevent the spread of infections.

Question 15

Define cytokines and their primary functions.

Answer 15

Cytokines are low molecular weight proteins secreted by immune cells to regulate immune responses, acting in autocrine, paracrine, and endocrine manners.

Question 16

What are the properties of cytokines?

Answer 16

Cytokines are pleotropic, synergistic, and can have a cascade effect, meaning they have different effects depending on the target cell, work together to enhance effects, and one cytokine can stimulate the production of others.

Question 17

Name and describe the cytokine families

Answer 17

Haematopoietin Family: IL-2, IL-4
Interferon Family: IFN-alpha, beta, gamma
Chemokine Family: Attracts cells to sites of infection
Tumor Necrosis Family: Involved in inflammation and cell death

Question 18

What is the function of IL-2 and IL-4 cytokines?

Answer 18

IL-2: T cell growth factor.
IL-4: B cell growth factor.

Question 19

What is the role of Interferon-gamma (IFN-γ)?

Answer 19

Interferon-gamma (IFN-γ) activates macrophages and has antiviral properties.

Question 20

What are the effects of TNF-alpha cytokine?

Answer 20

TNF-alpha promotes inflammation and can kill cancer cells.

Question 21

What can result from a cytokine imbalance?

Answer 21

Cytokine imbalance can lead to diseases such as cytokine storm, which involves excessive cytokine release causing multi-organ failure.

Question 22

How do inflammatory cytokines contribute to sepsis?

Answer 22

Inflammatory cytokines like TNF-alpha, IL-1, and IL-6 contribute to the symptoms and severity of sepsis, leading to septic shock with poor blood perfusion, abnormal clotting, and organ dysfunction.

Question 23

Summarize the primary functions of MHC-I and MHC-II molecules.

Answer 23

MHC-I: Presents intracellular antigens to CD8+ T cells.
MHC-II: Presents extracellular antigens to CD4+ T cells.

Question 24

What is a cytokine storm, and what are its consequences?

Answer 24

A cytokine storm is an excessive cytokine release causing multi-organ failure and is often associated with severe infections and immune responses.

Question 25

Name the three pathways that activate the complement system.

Answer 25

Classical Pathway Lectin Pathway Alternative Pathway

Question 26

How is the Classical Pathway triggered?

Answer 26

The Classical Pathway is triggered by C1q binding to immune complexes (antigen-bound IgM or IgG).

Question 27

What does the Classical Pathway produce that is crucial for its function?

Answer 27

It produces C3 convertase (C4b2a) which cleaves C3 into C3a and C3b, leading to the formation of C5 convertase (C4b2aC3b) and ultimately the Membrane Attack Complex (MAC) (C5b C6 C7 C8 C9).

Question 28

What activates the Lectin Pathway?

Answer 28

The Lectin Pathway is activated by mannose-binding lectin (MBL) binding to pathogens.

Question 29

What is the role of the alternative pathway in complement activation?

Answer 29

The Alternative Pathway is continuously active at a low level ("tick-over" mechanism) and is activated by pathogen surfaces.

Question 30

What are the primary roles of the complement system?

Answer 30

Opsonization: C3b binds to pathogens marking them for phagocytosis. Inflammation: C3a and C5a act as anaphylatoxins promoting inflammation. Pathogen Lysis: MAC creates pores in pathogen membranes causing cell lysis.

Question 31

What are the main regulatory proteins of the complement system?

Answer 31

C1 Inhibitor C4-binding Protein (C4BP) Membrane Cofactor Protein (MCP/CD46) Factor H and Factor I Decay-Accelerating Factor (DAF) CD59

Question 32

What disease is associated with C1 Inhibitor Deficiency?

Answer 32

C1 Inhibitor Deficiency leads to hereditary angioedema characterized by episodic swelling due to increased bradykinin.

Question 33

What conditions arise from Factor H or Factor I Deficiency?

Answer 33

Factor H or Factor I Deficiency causes uncontrolled activation of the alternative pathway leading to rapid consumption of complement proteins and increased susceptibility to infections.

Question 34

What is the result of Decay-Accelerating Factor (DAF) Deficiency?

Answer 34

DAF Deficiency results in paroxysmal nocturnal hemoglobinuria, a condition with recurrent red blood cell lysis.

Question 35

What is the consequence of Complement Receptor 1 (CR1) Deficiency?

Answer 35

CR1 Deficiency impairs the clearance of immune complexes associated with conditions like systemic lupus erythematosus.

Question 36

Summarize the importance and function of the complement system.

Answer 36

The complement system is a critical part of the immune response bridging innate and adaptive immunity. It is activated through three pathways that converge to form C3 convertase leading to opsonization, inflammation, and pathogen lysis. Proper regulation is essential to prevent damage to host cells and deficiencies in complement proteins can lead to various diseases.