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Questions and Answers
What is the primary function of the complement system?
What is one of the benefits of moderate fever?
Which type of immunity involves antibodies and is part of the adaptive immune system?
What role do antimicrobial peptides (AMPs) like dermcidin and defensins serve?
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What produces pyrogens that reset the body’s thermostat during an infection?
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What type of macrophages are permanently residing in specific organs?
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Which of the following processes do Natural Killer cells NOT engage in?
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Which sequence correctly describes the steps of phagocyte mobilization?
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What is a primary benefit of the inflammatory response?
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Which cells are primarily responsible for the release of antiviral proteins in response to Interferons?
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What triggers the inflammatory response in tissues?
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What role do chemotactic agents play in inflammation?
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What is the primary result of artificially acquired immunity?
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Which immune response is characterized by T lymphocytes attacking target cells directly?
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Which of the following statements about Interferons is true?
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How do antibodies primarily disable antigens?
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Which type of MHC proteins is presented by all nucleated cells except red blood cells?
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What role do regulatory T cells (Treg) play in the immune system?
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What is the main purpose of positive selection in T cell maturation?
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How are self-reactive B cells typically dealt with in the red bone marrow?
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Which cell type is NOT considered an antigen-presenting cell (APC)?
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What initiates the activation of B cells during a humoral immune response?
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What characterizes the secondary immune response?
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What is primarily produced by activated B cells during a humoral immune response?
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Which of the following correctly describes active humoral immunity?
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What is the lag period for the primary immune response upon first exposure to an antigen?
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What type of MHC protein do CD4 T cells bind to during their activation?
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Which of the following functions is NOT associated with Helper T (TH) cells?
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What mechanism do Cytotoxic T (TC) cells use to induce cell death in target cells?
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What is the primary role of Regulatory T (Treg) cells in the immune system?
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What type of cells do Cytotoxic T (TC) cells primarily target?
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Study Notes
Phagocytes
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Macrophages are large, phagocytic cells that develop from monocytes.
- Free macrophages wander through tissue spaces, e.g., alveolar macrophages in the lungs.
- Fixed macrophages reside permanently in specific organs, e.g., Kupffer cells in the liver and microglia in the brain.
- Neutrophils become phagocytic when encountering infectious material in tissues
Natural Killer Cells
- Natural Killer (NK) cells are large granular lymphocytes that are NOT phagocytic.
- They target cells lacking "self" cell-surface receptors (MHC).
- NK cells directly contact target cells and induce:
- Apoptosis (programmed cell death) in cancer and virus-infected cells.
- Secretion of potent chemicals that enhance the inflammatory response.
Inflammation
- Inflammation is the tissue response to injury, clearing the area of pathogens, dead cells, and debris.
- It's triggered by:
- Physical trauma
- Intense heat
- Irritating chemicals
- Infection by bacteria, viruses, and fungi.
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Beneficial effects of inflammation:
- Prevents the spread of damaging agents
- Disposes of cell debris and pathogens
- Alerts the adaptive immune system
- Sets the stage for tissue repair
Inflammatory Response: Phagocyte Mobilization
- Leukocytosis: increased production and release of neutrophils from bone marrow in response to leukocytosis-inducing factors from injured cells.
- Margination: neutrophils adhere to the walls of capillaries in the inflamed area, facilitated by cell adhesion molecules (CAMs).
- Diapedesis/Emigration: neutrophils squeeze between capillary cells to enter the inflamed tissue.
- Chemotaxis: inflammatory chemicals (chemotactic agents) attract neutrophils to the site of injury.
Antimicrobial Proteins: Interferons
- Interferons (IFNs) are proteins released by virus-infected cells, activating neighboring cells to produce antiviral proteins, blocking viral reproduction.
- IFNs are non-specific and act against viruses.
Antimicrobial Proteins: Complement System
- Complement is a group of 20 plasma proteins (C1-C9, factors B, D, and P, plus regulatory proteins).
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Functions of the complement system:
- Amplifies the inflammatory response
- Promotes phagocytosis
- Kills bacteria and certain cells through cell lysis (membrane attack complex)
- Enhances both innate and adaptive defenses.
Fever
- Fever is a systemic response to invading microorganisms.
- Pyrogens (released from leukocytes and macrophages) reset the body's thermostat upward, causing a rise in body temperature.
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Benefits of moderate fever:
- Sequesters iron and zinc (needed by microorganisms) in the liver and spleen.
- Increases metabolic rate, speeding up tissue repair.
The Adaptive Immune System
- The adaptive immune system is a specific defense system with two arms:
- Humoral immunity (antibody-mediated): Antibodies target extracellular antigens.
- Cellular immunity (cell-mediated): T lymphocytes directly attack target cells.
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Functions of the adaptive immune system:
- Protects against infectious agents and abnormal body cells.
- Amplifies the inflammatory response.
T-Cell Maturation and Selection
- Positive selection: T cells capable of binding to self-MHC proteins are selected for survival.
- Negative selection: T cells binding to self-antigens displayed by MHC proteins undergo apoptosis, ensuring self-tolerance.
B-Cells
- B-cells mature in the red bone marrow.
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Self-reactive B cells:
- Are eliminated by apoptosis (clonal deletion).
- Undergo receptor editing (receptor rearrangement).
- Are inactivated (anergy) if they escape the bone marrow.
Antigen-Presenting Cells (APCs)
- APCs engulf antigens and present fragments to T cells, activating naive T cells.
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Three major types of APCs:
- Dendritic cells (in connective tissues and epidermis).
- Macrophages (in connective tissues and lymphoid organs).
- B cells (present antigens to T helper cells).
Humoral Immune Response
- Antigen challenge: The first encounter between an antigen and a naive immunocompetent lymphocyte, usually in the spleen or lymph node.
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B cell activation: When antigens bind to B cell surface receptors, the activated B cell clones itself.
- Plasma cells: Produce antibodies.
- Memory B cells: Remain for future encounters with the antigen.
Immunological Memory
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Primary immune response: Occurs upon first exposure to an antigen.
- Lag period: 3-6 days.
- Peak antibody levels: 10 days.
- Antibody levels decline.
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Secondary immune response: Occurs upon re-exposure to the same antigen.
- Response: Faster, more prolonged, and more effective.
- Peak antibody levels: 2-3 days.
Humoral Immunity: Active vs. Passive
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Active humoral immunity: B cells encounter antigens and produce specific antibodies.
- Naturally acquired: Response to an infection.
- Artificially acquired: Response to a vaccine.
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Passive immunity: Protection from antibodies acquired from another source.
- Naturally acquired: Antibodies transferred from mother to fetus (placenta) or infant (breast milk).
- Artificially acquired: Injection of serum (e.g., gamma globulin).
Antibody Types
- Antibodies (immunoglobulins, Igs) are proteins secreted by B cells in response to antigen.
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Antibody functions:
- Neutralization: Block the binding of antigens to cells.
- Agglutination: Clump antigens together, making them easier to phagocytize.
- Precipitation: Form complexes with soluble antigens that can be phagocytized.
- Complement activation: triggers cell lysis; amplifies the inflammatory response, promotes opsonization (marking pathogens for phagocytosis).
Cellular Immune Response
- Cellular immunity consists of T lymphocytes that directly attack target cells or regulate the immune response.
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Two major types of T cells:
- CD4 cells: Become helper T cells (TH) when activated.
- CD8 cells: Become cytotoxic T cells (TC) when activated, destroying cells with foreign antigens.
- Other T cell types: Regulatory T cells (Treg) and memory T cells.
MHC Proteins and T-Cell Activation
- Major histocompatibility complex (MHC) proteins present antigens on the cell surface, alerting the immune system.
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Two types of MHC proteins:
- Class I MHC: Found on all nucleated cells (except red blood cells).
- Class II MHC: Found on APCs (dendritic cells, macrophages, and B cells).
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T-cell activation:
- CD4 cells: Bind to MHC class II on APCs, becoming TH cells.
- CD8 cells: Activated by antigen fragments linked to MHC class I on APCs, becoming TC cells.
Roles of Helper T (TH) and Cytotoxic T (TC) Cells
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TH cells:
- Play a central role in the adaptive immune response.
- Help activate T and B cells.
- Induce T and B cell proliferation.
- Activate macrophages and recruit other immune cells.
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TC cells:
- Directly attack and kill other cells.
- Circulate in blood, lymph, and lymphoid organs.
- Target: Virus-infected cells, cells with intracellular bacteria or parasites, cancer cells, foreign cells (transfusions or transplants).
TC Cell and NK Cell Lethal Mechanism
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TC cells and NK cells release: perforins and granzymes by exocytosis.
- Perforins: Create pores in target cells.
- Granzymes: Enter through pores and stimulate apoptosis.
Regulatory T (Treg) Cells
- Suppress the immune response through direct contact or by secreting inhibitory cytokines (IL-10 and TGF-β).
- Important in preventing autoimmune reactions.
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Description
This quiz covers the roles and characteristics of phagocytes, such as macrophages and neutrophils, along with the function of Natural Killer (NK) cells in the immune response. Learn how these cells protect the body from infection and their involvement in inflammation. Test your knowledge on immune system components and their mechanisms.
