Immunology Lec 4 & 5 Flashcards
Lecture 4:
What are the three main types of T cells?
Cytotoxic T Cells (CD8+)
Helper T Cells (CD4+)
Regulatory T Cells
How do Helper T Cells (CD4+) assist in the immune response?
Helper T Cells assist in activating immune cells by recognizing antigens presented by MHC Class II molecules and producing cytokines.
What is the primary function of Cytotoxic T Cells (CD8+)?
Cytotoxic T Cells kill virus-infected and abnormal cells by inducing apoptosis.
What is the role of Regulatory T Cells?
Regulatory T Cells inhibit immune responses to prevent autoimmunity by producing cytokines like IL-10 and TGF-beta.
Where are T cells activated?
T cells are activated in secondary lymphoid tissues, such as lymph nodes and the spleen.
Describe the structure of T-cell receptors (TCR).
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).
What is antigen presentation?
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.
Differentiate between MHC Class I and MHC Class II molecules.
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.
How are antigens processed in the MHC Class I pathway?
Intracellular antigens are processed in the endoplasmic reticulum and presented on the cell surface by MHC Class I molecules.
How are antigens processed in the MHC Class II pathway?
Extracellular antigens are processed in acidified endosomes and presented on the cell surface by MHC Class II molecules.
What mechanisms do Cytotoxic T Cells use to kill infected cells?
Cytotoxic T Cells induce apoptosis in infected cells using perforin, granzymes, and granulysin.
What is the role of Helper T Cells in activating macrophages and assisting B cells?
Th1 cells activate macrophages, while Th2 cells assist B cells in antibody production.
Explain the concept of MHC polymorphism and its significance.
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.
What is apoptosis, and why is it important in the immune response?
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.
Define cytokines and their primary functions.
Cytokines are low molecular weight proteins secreted by immune cells to regulate immune responses, acting in autocrine, paracrine, and endocrine manners.
What are the properties of cytokines?
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.
Name and describe the cytokine families
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
What is the function of IL-2 and IL-4 cytokines?
IL-2: T cell growth factor.
IL-4: B cell growth factor.
What is the role of Interferon-gamma (IFN-γ)?
Interferon-gamma (IFN-γ) activates macrophages and has antiviral properties.
What are the effects of TNF-alpha cytokine?
TNF-alpha promotes inflammation and can kill cancer cells.
What can result from a cytokine imbalance?
Cytokine imbalance can lead to diseases such as cytokine storm, which involves excessive cytokine release causing multi-organ failure.
How do inflammatory cytokines contribute to sepsis?
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.
Summarize the primary functions of MHC-I and MHC-II molecules.
MHC-I: Presents intracellular antigens to CD8+ T cells.
MHC-II: Presents extracellular antigens to CD4+ T cells.
What is a cytokine storm, and what are its consequences?
A cytokine storm is an excessive cytokine release causing multi-organ failure and is often associated with severe infections and immune responses.
Name the three pathways that activate the complement system.
Classical Pathway
Lectin Pathway
Alternative Pathway
How is the Classical Pathway triggered?
The Classical Pathway is triggered by C1q binding to immune complexes (antigen-bound IgM or IgG).
What does the Classical Pathway produce that is crucial for its function?
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).
What activates the Lectin Pathway?
The Lectin Pathway is activated by mannose-binding lectin (MBL) binding to pathogens.
What is the role of the alternative pathway in complement activation?
The Alternative Pathway is continuously active at a low level (“tick-over” mechanism) and is activated by pathogen surfaces.
What are the primary roles of the complement system?
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.
What are the main regulatory proteins of the complement system?
C1 Inhibitor
C4-binding Protein (C4BP)
Membrane Cofactor Protein (MCP/CD46)
Factor H and Factor I
Decay-Accelerating Factor (DAF)
CD59
What disease is associated with C1 Inhibitor Deficiency?
C1 Inhibitor Deficiency leads to hereditary angioedema characterized by episodic swelling due to increased bradykinin.
What conditions arise from Factor H or Factor I Deficiency?
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.
What is the result of Decay-Accelerating Factor (DAF) Deficiency?
DAF Deficiency results in paroxysmal nocturnal hemoglobinuria, a condition with recurrent red blood cell lysis.
What is the consequence of Complement Receptor 1 (CR1) Deficiency?
CR1 Deficiency impairs the clearance of immune complexes associated with conditions like systemic lupus erythematosus.
Summarize the importance and function of the complement system.
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.
