Podcast
Questions and Answers
What is one of the primary roles of CD4+ T cells in the immune response?
What is one of the primary roles of CD4+ T cells in the immune response?
What is the main function of MHC class I molecules in the immune response?
What is the main function of MHC class I molecules in the immune response?
How does TNF (Tumor Necrosis Factor) contribute to inflammation?
How does TNF (Tumor Necrosis Factor) contribute to inflammation?
What is the role of cytokines such as IL-6 in the immune response?
What is the role of cytokines such as IL-6 in the immune response?
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What triggers the activation of CD8+ T cells?
What triggers the activation of CD8+ T cells?
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Which statement about IFN-α is true?
Which statement about IFN-α is true?
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What is the initial goal of the immediate innate immune response?
What is the initial goal of the immediate innate immune response?
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What distinguishes the adaptive immune response from the innate response?
What distinguishes the adaptive immune response from the innate response?
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Which signals are crucial for T cell activation?
Which signals are crucial for T cell activation?
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What role do CD4+ T cells play in adaptive immunity?
What role do CD4+ T cells play in adaptive immunity?
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What is the function of CD8+ T cells in the immune response?
What is the function of CD8+ T cells in the immune response?
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How do MHC class I and class II molecules differ in their interactions with T cells?
How do MHC class I and class II molecules differ in their interactions with T cells?
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What role do cytokines play in the immune response?
What role do cytokines play in the immune response?
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What initiates the signaling cascade within a T cell upon TCR activation?
What initiates the signaling cascade within a T cell upon TCR activation?
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Which types of T cells recognize antigens presented on MHC class II molecules?
Which types of T cells recognize antigens presented on MHC class II molecules?
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What is the primary function of co-stimulatory signals in T cell activation?
What is the primary function of co-stimulatory signals in T cell activation?
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Which cytokine signaling does NOT contribute to T cell differentiation?
Which cytokine signaling does NOT contribute to T cell differentiation?
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Which of the following transcription factors is activated following TCR engagement?
Which of the following transcription factors is activated following TCR engagement?
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What role does MHC class I molecules serve in relation to CD8+ T cells?
What role does MHC class I molecules serve in relation to CD8+ T cells?
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What is a major outcome of cytokine signaling in T cell activation?
What is a major outcome of cytokine signaling in T cell activation?
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Which of the following describes the importance of the TCR-MHC binding?
Which of the following describes the importance of the TCR-MHC binding?
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Which co-stimulatory molecules are involved in T cell activation?
Which co-stimulatory molecules are involved in T cell activation?
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What is the consequence of TCR binding to a peptide-MHC complex without co-stimulatory signals?
What is the consequence of TCR binding to a peptide-MHC complex without co-stimulatory signals?
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What is the primary role of Signal 1 in T cell activation?
What is the primary role of Signal 1 in T cell activation?
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Which cytokines are typically secreted by CD4+ T helper cells to enhance the immune response?
Which cytokines are typically secreted by CD4+ T helper cells to enhance the immune response?
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How do CD8+ cytotoxic T cells primarily eliminate infected or abnormal cells?
How do CD8+ cytotoxic T cells primarily eliminate infected or abnormal cells?
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What is the contribution of MHC molecules in T cell activation?
What is the contribution of MHC molecules in T cell activation?
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What distinguishes memory T cells from effector T cells?
What distinguishes memory T cells from effector T cells?
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Which statement correctly describes the process of clonal expansion in T cells?
Which statement correctly describes the process of clonal expansion in T cells?
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What is the role of cytokine signaling during T cell activation?
What is the role of cytokine signaling during T cell activation?
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Which CD4+ T cell subset is primarily involved in activating macrophages to enhance phagocytosis?
Which CD4+ T cell subset is primarily involved in activating macrophages to enhance phagocytosis?
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During T cell activation, what is the purpose of co-stimulation?
During T cell activation, what is the purpose of co-stimulation?
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What initiates a cytotoxic response from NK cells?
What initiates a cytotoxic response from NK cells?
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What key feature allows each T cell subtype to target its specific ligand?
What key feature allows each T cell subtype to target its specific ligand?
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How do perforin and granzymes function together in NK cell cytotoxicity?
How do perforin and granzymes function together in NK cell cytotoxicity?
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Which mechanism do NK cells use to kill cells that may resist perforin?
Which mechanism do NK cells use to kill cells that may resist perforin?
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What role does Interleukin-12 (IL-12) play in NK cell function?
What role does Interleukin-12 (IL-12) play in NK cell function?
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What is the primary function of cytokines in the context of NK cell activity?
What is the primary function of cytokines in the context of NK cell activity?
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What is the outcome of the Fas-FasL interaction in the target cell?
What is the outcome of the Fas-FasL interaction in the target cell?
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Which action is triggered by the lack of MHC class I on a target cell?
Which action is triggered by the lack of MHC class I on a target cell?
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What characteristic distinguishes activating signals from inhibitory signals in NK cell recognition?
What characteristic distinguishes activating signals from inhibitory signals in NK cell recognition?
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How do IFN-α and IFN-β specifically affect NK cell cytotoxicity?
How do IFN-α and IFN-β specifically affect NK cell cytotoxicity?
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What triggers the coordinated immune response to pathogens?
What triggers the coordinated immune response to pathogens?
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Study Notes
Immune System Overview
- The immune system has two main branches: innate and adaptive.
- Innate immunity acts quickly, providing immediate response (minutes to hours).
- Adaptive immunity takes longer to activate (days to weeks), but responds faster upon re-exposure due to memory cells.
Innate Immune System
- Non-specific; recognizes broad categories of pathogens (e.g., bacteria, viruses) using generic pathogen-associated molecular patterns (PAMPs).
- Lacking memory; each encounter with a pathogen triggers the same response.
- Key components: Physical barriers (skin, mucous membranes), cells (macrophages, neutrophils, dendritic cells, natural killer (NK) cells), and soluble factors (cytokines, complement proteins).
Adaptive Immune System
- Highly specific; recognizes unique antigens on pathogens using specific receptors on B and T cells.
- Possesses immunological memory; upon re-exposure to the same pathogen, memory B and T cells facilitate a faster, stronger response.
- Key components: Cells (B cells, T cells - helper and cytotoxic), and antibodies (immunoglobulins) targeting pathogens specifically.
Diversity of Response
- Innate immunity has limited diversity, using a fixed set of receptors to recognize PAMPs.
- Adaptive immunity has highly diverse receptors for specific antigens due to genetic recombination in B and T cells.
Role in Immune Response
- Innate immunity serves as the first line of defense, managing infections and activating adaptive immunity.
- Adaptive immunity provides long-lasting, targeted response and resolves infections that innate immunity cannot.
Summary Table
| Feature | Innate Immune System | Adaptive Immune System |
|---|---|---|
| Response Speed | Immediate | Delayed (days to weeks) |
| Specificity | Broad, non-specific | Highly specific |
| Memory | No | Yes (immunological memory) |
| Components | Physical barriers, phagocytes, NK cells, cytokines | B cells, T cells, antibodies |
| Diversity | Limited | High (receptor diversity) |
| Function | Initial, rapid response | Long-term, targeted pathogen clearance |
Antigen, Epitope, and Hapten
- Antigen: Any substance that can be recognized by the immune system and elicits an immune response. Can be monovalent, multivalent, or polyvalent.
- Epitope: Specific region on an antigen that is recognized by immune receptors.
- Hapten: A small molecule that is not immunogenic on its own but becomes immunogenic when bound to a larger carrier protein.
Pattern Recognition Receptors (PRRs)
- Specialized receptors on immune cells recognizing pathogen-associated molecular patterns (PAMPs) on pathogens.
- Types include Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and C-type lectin receptors (CLRs).
- Critical for innate immune system, providing a first line of defense.
- Expressed on various innate immune cells (macrophages, dendritic cells, neutrophils, NK cells) and even some non-immune cells (epithelial cells).
T and B Cell Receptors
- B cell receptors (BCRs): Membrane-bound immunoglobulins (Ig) found on B cells. Recognize whole antigens directly.
- T cell receptors (TCRs): Membrane-bound proteins on T cells. Require antigen processing and presentation by MHC molecules. Recognize only processed peptides.
Types of Antigens
- Proteins: Often stimulate strong immune responses.
- Carbohydrates: Recognized by BCRs.
- Lipids and Nucleic Acids: Can be recognized by BCRs, especially when part of complex structures.
B-Cell Activation
- Triggered by antigen binding to B cell receptors (BCRs).
- Requires co-stimulation from helper T cells (T-dependent antigens) or cross-linking of multiple BCRs (T-independent antigens) to activate a signaling cascade.
- Differentiates into plasma cells, producing large amounts of antibodies, or memory B cells for future responses.
- Class switching (isotype switching): Changing antibody class to better target specific pathogens or tissues (e.g., from IgM to IgG).
- Affinity maturation: Increasing antibody affinity for the antigen through somatic hypermutation and selection.
T-Cell Activation
- Requires antigen presentation by antigen-presenting cells (APCs) on MHC molecules.
- Requires co-stimulatory signals from the APC (e.g., CD28 interacting with B7 molecules).
- Differentiates into various subsets of helper T cells (Th1, Th2, etc.) and cytotoxic T cells (CTLs), with different functions.
- Cytokines play a critical role in guiding T cell differentiation and function.
Types of Hypersensitivity Reactions
- Type I (Immediate): IgE-mediated; rapid response involving mast cells and basophils (e.g., allergies).
- Type II (Cytotoxic): IgG or IgM antibodies directly attack target cells (e.g., blood transfusions, autoimmune hemolytic anemia).
- Type III (Immune Complex): Immune complexes deposit in tissues, activating complement and causing inflammation (e.g., systemic lupus erythematosus).
- Type IV (Delayed): T cell-mediated; delayed response involving macrophages and T cells (e.g., contact dermatitis, tuberculin skin test).
Immune Checkpoint Inhibitors
- Inhibitory receptors on T cells (e.g., PD-1, CTLA-4) can be targeted for cancer immunotherapy.
- Blocking these receptors can unleash T cell responses to tumor cells to fight cancer.
Graft Types
- Autografts: (Low immunogenicity) self-tissue transplant within same individual.
- Isografts: (Low immunogenicity) identical twin transplant or genetically identical animals.
- Allografts: (High immunogenicity) transplant between two genetically different individuals of the same species.
- Xenografts: (Very high immunogenicity) transplant between individuals of different species.
Transplant Rejection
- Hyperacute: pre-existing antibodies quickly attack graft.
- Acute: T cells and antibodies recognize graft as foreign.
- Chronic: persistent low-level immune response damages the graft over time.
- Graft vs Host: donor immune cells attack recipient's tissues.
Immunosuppressive Agents
- Calcineurin inhibitors: Inhibit calcineurin, reducing IL-2 production (e.g., cyclosporine, tacrolimus).
- mTOR Inhibitors: Block mTOR signaling pathways involved in T cell proliferation (e.g., sirolimus).
- Antimetabolites: Inhibit nucleotide synthesis necessary for DNA and RNA replication. (e.g., mycophenolate mofetil).
Immune Responses to Intracellular Viruses
- Involves innate immune responses (interferons primarily) and adaptive responses (cytotoxic T cells primarily).
- Viruses replicate inside cells, the strategy to target these differs from extracellular bacteria.
Immunological Assays
- Immunodiffusion: Precipitation reactions in agarose gels visualize antibodies/antigens interactions.
- Hemagglutination: Clumping of red blood cells (RBCs) to detect presence of antibodies/antigens.
- ELISA: Enzyme-linked antibodies detect antigens/antibodies with color changes.
- Immunoblot (Western blot): Proteins are separated by electrophoresis and transferred to a membrane. Detected by specific antibodies to identify proteins.
- Immunofluorescence: Fluorescently labeled antibodies/antigens are visualized using a microscope.
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