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Questions and Answers
What does immunology study?
What does immunology study?
The immune system and its responses to diseases.
Which of the following is a type of immunity?
Which of the following is a type of immunity?
What are the two main types of immune responses?
What are the two main types of immune responses?
Innate and adaptive immune responses.
Phagocytosis is a process by which immune cells engulf and destroy pathogens.
Phagocytosis is a process by which immune cells engulf and destroy pathogens.
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Which cell type is most abundant in peripheral blood?
Which cell type is most abundant in peripheral blood?
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What is the role of antibodies in the immune system?
What is the role of antibodies in the immune system?
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The immune system consists of the tissue, organs, cells, molecules, and ______ responsible for protection from disease.
The immune system consists of the tissue, organs, cells, molecules, and ______ responsible for protection from disease.
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What type of immune cell is a macrophage?
What type of immune cell is a macrophage?
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Natural Killer (NK) cells are part of the adaptive immune system.
Natural Killer (NK) cells are part of the adaptive immune system.
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The process where microbes are coated with proteins to facilitate phagocytosis is called ______.
The process where microbes are coated with proteins to facilitate phagocytosis is called ______.
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What are the two main categories of immunity?
What are the two main categories of immunity?
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Which type of cell is known for its role in phagocytosis?
Which type of cell is known for its role in phagocytosis?
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Adaptive immunity provides an immediate response upon infection.
Adaptive immunity provides an immediate response upon infection.
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Match the immune cells with their descriptions:
Match the immune cells with their descriptions:
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The phenomenon of coating microbes with proteins to facilitate phagocytosis is known as ______.
The phenomenon of coating microbes with proteins to facilitate phagocytosis is known as ______.
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What is the primary function of phagocytes?
What is the primary function of phagocytes?
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Natural Killer cells play a role in adaptive immunity.
Natural Killer cells play a role in adaptive immunity.
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Which of the following is a type of granulocyte?
Which of the following is a type of granulocyte?
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Name one physical barrier in the immune system.
Name one physical barrier in the immune system.
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Study Notes
Immunology Introduction
- Immunology is a clinically important discipline that explores the body's defense mechanisms against diseases.
- The immune system comprises tissues, organs, cells, molecules, and genes crucial for protection against diseases.
- Microbes are omnipresent in nature, diverse, and rapidly evolve to infect hosts and evade their immune systems.
Challenges and Defences
- Some microbes hijack cellular machinery for replication and spread.
- Intracellular pathogens include viruses like influenza and coronavirus, intracellular bacteria like Listeria, and intracellular parasites like malaria and toxoplasma.
- The immune system provides physical and chemical defenses against infectious agents.
Physical and Chemical Defences
- Physical barriers include skin, mucous membranes, and cilia.
- Chemical barriers include antimicrobial peptides, lysozyme, stomach acid, and digestive enzymes.
Skin Barrier Function
- Keratinocytes in the skin's stratum spinosum produce β-defensins and cathelicidins, cationic peptides stored in lamellar bodies and secreted into the intercellular space as antimicrobial agents.
Antimicrobial Peptides
- Antimicrobial peptides like defensins are secreted by epithelial cells and phagocytes, disrupting bacterial and fungal cell membranes and some viral envelopes.
Innate and Adaptive Immune Responses
- Innate immunity provides an immediate response using pre-existing mechanisms.
- Adaptive immunity is stimulated by exposure to specific pathogens and reacts to antigens, recognizing specific pathogen structures.
Cells of the Immune System
- Various white blood cells (leukocytes) with specialized functions and roles in the immune system include neutrophils, macrophages, T cells, and B cells.
Macrophages: The Patrol
- Macrophages patrol tissues, and subsets in specific tissues are given unique names (e.g., Kupffer cells in the liver).
Phagocytosis
- Phagocytosis is the engulfing of particulate matter to form a vesicle (phagosome) containing ingested material, important for eliminating pathogens, foreign materials, cell debris, apoptotic cells, and damaged tissue.
Phagocytosis Steps
- Phagocytosis involves adherence of the microbe, engulfment, phagosome formation, phagosome–lysosome fusion, and destruction of the microbe using reactive oxygen species (ROS) and inducible nitric oxide (iNOS) production.
Opsonisation
- Some microbes, especially those with capsules, are difficult to phagocytose.
- Opsonisation coats microbes with proteins like antibodies or complement facilitating phagocytosis.
- Acute phase proteins, such as C-reactive protein (CRP), bind to bacterial phosphocholine and act as opsonins.
Phagocytes: Defenders
- Phagocytes include macrophages, neutrophils, eosinophils, basophils, and immature dendritic cells.
- Their primary functions include engulfing and destroying pathogens, and activating adaptive immunity for immature dendritic cells.
Neutrophils: The Abundant
- Neutrophils are the most abundant white blood cells in peripheral blood, characterized by a multilobed nucleus.
- They are not typically found in tissues but can be recruited and have a short lifespan after activation.
Monocytes: The Non-Granulocyte
- Monocytes comprise about 10% of white blood cells in peripheral blood and are not classified as granulocytes.
Eosinophils: The Anti-Parasitic
- Eosinophils are present in low numbers in the blood.
- Their granules contain enzymes that attack parasite cell walls but can also damage host tissue.
Basophils: The Inflammatory Mediator
- Basophils are found in small numbers in the blood.
- Their granules contain potent inflammatory mediators, aiding in the defense against parasites.
Mast Cells: Tissue Defenders
- Mast cells, not found in blood but in tissues, are similar to basophils with potent inflammatory mediators, aiding in the defense against parasites and involved in allergic responses.
Natural Killer (NK) Cells: The Innate Killers
- NK cells are part of the innate immune system, killing host cells like virally infected or transformed (malignant) cells and producing chemical mediators called cytokines.
NK Cell Activation
- NK cells can be activated by engaging activating receptors like CD16 and NKG2D.
- CD16 on NK cells binds to antibodies, triggering cell death via antibody-dependent cell cytotoxicity (ADCC).
- NKG2D on NK cells binds to NKG2D ligands upregulated during cellular and metabolic stress (infection or cancer), leading to cell death.
"Missing Self" Activation
- NK cells can be activated by the absence of MHC Class I on unhealthy cells.
- All nucleated cells express MHC Class I that engages inhibitory receptors (Killer Immunoglobulin-like receptors, KIR) on NK cells.
- Downregulation of MHC Class I during viral infection or cancer triggers NK cell activation, known as "missing self".
Introduction to Immunology
- Immunology plays a crucial role in understanding and treating various diseases.
- Immunology examines the body's defense mechanisms against pathogens and other foreign invaders.
Immune System Roles
- The immune system defends against infectious diseases.
- It plays a vital role in maintaining health and preventing disease development.
Immunology in Medicine
- Immunology is a foundation for developing vaccines, antibody therapies, and other medical treatments.
- It helps understand transplant rejection, immune suppression, and allergic reactions.
Immune System Challenges
- Microbes are incredibly diverse and rapidly evolve to evade immune systems.
- Pathogens like viruses, bacteria, and parasites exploit host cells and mechanisms for their survival and replication.
Physical and Chemical Defenses
- The body's first line of defense includes physical barriers, like skin and mucous membranes, that act as a physical barrier against invading pathogens.
- Chemical barriers involve secretions of antimicrobial substances, such as lysozyme, stomach acid, and digestive enzymes to inhibit or kill microbes.
Skin Barrier
- Keratinocytes in the skin's outer layer produce antimicrobial peptides like β-defensins and cathelicidins.
- These peptides are stored in lamellar bodies and released into the intercellular space.
- They act as a crucial defense against invading microbes.
- The skin functions as a physical barrier, preventing entry of pathogens.
Innate and Adaptive Immunity
- Innate Immunity provides an immediate, non-specific defense against pathogens.
- It recognizes common pathogen structures using pattern recognition receptors.
- Adaptive immunity provides a specific, long-lasting response to a particular pathogen and forms a memory for faster responses upon re-exposure..
- The innate immune system kicks in first and triggers an adaptive immune response when needed.
Immune Cells
- The immune system comprises various white blood cells (leukocytes) with specialized functions.
- Leukocytes include neutrophils, macrophages, T cells, B cells, and others.
Macrophages
- Macrophages are patrolling cells in the tissues.
- They engulf and destroy pathogens through phagocytosis.
- Different tissue macrophage subsets have specific names, like Kupffer cells in the liver.
Phagocytosis
- Phagocytosis is the process of engulfing and internalizing particulate matter, forming a phagosome for digestion.
- Phagocytosis eliminates pathogens, foreign material, cell debris, apoptotic cells, and damaged tissue.
Phagocytosis Steps
- Attachment: The phagocyte attaches to the target.
- Ingestion: The phagocyte engulfs the target, forming a phagosome.
- Fusion: The phagosome fuses with lysosomes.
- Digestion: Lysosomal enzymes degrade the target within the phagosome
Opsonisation
- Opsonization involves coating microbes with opsonin proteins (like antibodies or complement).
- Opsonins facilitate phagocytosis by making invaders easier to engulf.
- Acute phase proteins from the liver (e.g., C-reactive protein, CRP) bind to bacteria and act as opsonins.
Cells of the Innate Immune System
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Phagocytes:
- Macrophages
- Granulocytes: neutrophils, eosinophils, and basophils.
- Immature dendritic cells
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Non-phagocytic cells:
- Natural Killer (NK) cells
- Mast cells
Neutrophils
- Neutrophils are the most abundant white blood cells in the blood.
- They have multi-lobed nuclei.
- They are typically short-lived after activation.
Monocytes
- Monocytes are not classified as granulocytes.
- They are ~10% of white blood cells in the blood.
Eosinophils
- Eosinophils are found in low numbers in the blood.
- Their granules contain enzymes that attack parasites and can cause damage to host tissue.
Basophils
- Basophils are found in low numbers in the blood.
- They contain granules with potent inflammatory mediators that help fight against parasites.
Mast cells
- Mast cells are found in tissues, not in the blood.
- They share similarities with basophils and contain potent inflammatory mediators.
NK cells
- NK cells are lymphocytes that belong to the innate immune system.
- They are responsible for killing host cells infected with viruses or transformed (cancerous) cells.
- They release chemical mediators (cytokines).
NK Cell Activation
- Antibody-dependent cell cytotoxicity (ADCC): CD16 on NK cells binds to antibodies, activating the NK cell to kill the antibody-coated cell.
- Missing self: NK cells are activated when unhealthy cells lack MHC Class I, a molecule normally present on all nucleated cells. NK cells recognize this "missing self" and kill the cells.
Reading List
- Resources like Clinical Key provide relevant information to enhance understanding of immunology topics.
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Description
Explore the essentials of immunology, focusing on the immune system's components and the challenges posed by various microbes. This quiz covers the body's physical and chemical defenses and highlights the significance of barriers like skin and mucous membranes in disease prevention.
