Questions and Answers
What is the purpose of the first line of defense in innate immunity?
What is the primary function of Sebum in innate immunity?
forms a protective layer over skin and inhibits the growth of certain pathogenic bacteria and fungi
Fever inhibits the growth of all microbes.
False
Interferons are antiviral proteins that interfere with viral ________.
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Match the following blood cell types with their functions:
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What is the first line of defense in the immune system?
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What is the oily substance produced by sebaceous glands that forms a protective layer over the skin?
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Interferons are antifungal proteins.
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______ is the enzyme found in nasal secretions, saliva, and tears that breaks down gram-positive cell walls.
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Match the following cellular elements of blood with their functions:
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Study Notes
Innate Immunity
- Resistance and Susceptibility: Ability to ward off disease (resistance) and vulnerability or lack of resistance (susceptibility)
- Three Lines of Defense:
- First Line of Defense: Non-specific natural barriers that restrict entry of pathogens (e.g., skin and mucous membranes)
- Second Line of Defense: Innate non-specific immune defenses that provide rapid local response to pathogens (e.g., fever, phagocytes, inflammation, and interferon)
- Third Line of Defense: Antigen-specific immune responses that specifically target and attack invaders that get past the first two lines of defense (e.g., antibodies and lymphocytes)
Mechanical Defenses
- Skin:
- Two layers: epidermis (thin outer layer of epithelial tissue) and dermis (thick inner layer of connective tissue)
- Contains Langerhans cells, dead cells, and keratin (waterproof)
- Intact skin is an effective barrier against most pathogens, but exceptions include hookworms and dermatophytes
- Mucous Membranes:
- Line gastrointestinal, genitourinary, and respiratory tracts
- Two layers: outer epithelial and inner connective layer
- Epithelial layer secretes mucus that maintains moist surfaces
- Although they inhibit microbial entry, they offer less protection than skin
- Some microorganisms can penetrate mucous membranes, such as papillomavirus and Treponema pallidum
- Other Mechanical Defenses:
- Lacrimal apparatus: continual washing and blinking prevents microbes from settling on the eye surface
- Saliva: washes microbes from teeth and mouth mucous membranes
- Mucus: traps many microbes
- Nose hair: coated with mucus, filters dust, pollen, and microbes
- Ciliary escalator: cilia on mucous membranes of lower respiratory tract move upwards towards throat at 1-3 cm/hour
- Coughing and sneezing: expel foreign objects
- Epiglottis: covers larynx during swallowing
- Urination: cleanses urethra
- Vaginal secretions: remove microbes from genital tract
Chemical Defenses
- Sebum: oily substance produced by sebaceous glands that forms a protective layer over skin
- Contains unsaturated fatty acids that inhibit growth of certain pathogenic bacteria and fungi
- pH: low, skin pH usually between 3 and 5, caused by lactic acid and fatty acids
- Perspiration: produced by sweat glands, contains lysozyme and acids
- Lysozyme: enzyme that breaks down gram-positive cell walls, found in nasal secretions, saliva, and tears
- Gastric Juice: mixture of hydrochloric acid, enzymes, and mucus, pH between 1.2 to 3, kills many microbes and destroys most toxins
- Transferrins: iron-binding proteins in blood that inhibit bacterial growth by reducing available iron
Cellular Elements of Blood
- Erythrocytes (RBC): transport O2 and CO2
-
Leukocytes (WBC): various functions, including phagocytosis and antibody production
- Granulocytes: phagocytosis (neutrophils, basophils, and eosinophils)
- Monocytes/Macrophages: phagocytosis
- Lymphocytes: antibody production (B cells) and cell-mediated immunity (T cells)
- Platelets: blood clotting
Second Line of Defense
- Phagocytosis: process by which phagocytes (macrophages, neutrophils, and eosinophils) engulf and digest foreign particles and microorganisms
- Phagocytes: attracted to site of infection by chemotaxis
-
Stages of Phagocytosis:
- Chemotaxis: phagocytes are chemically attracted to site of infection
- Adherence: phagocyte plasma membrane attaches to surface of pathogen or foreign material
- Ingestion: plasma membrane of phagocytes extends projections (pseudopods) that engulf the microbe
- Digestion: inside the cell, phagosome fuses with lysosome to form a phagolysosome, where lysosomal enzymes kill most bacteria
Inflammation
- Triggered by: tissue damage due to infection, heat, wound, etc.
-
Four Major Symptoms:
- Redness
- Pain
- Heat
- Swelling
-
Functions:
- Destroy and remove pathogens
- Limit effects by confining the pathogen and its products
- Repair and replace tissue damaged by pathogen and its products
-
Stages of Inflammation:
- Vasodilation: increase in diameter of blood vessels
- Phagocyte migration and margination
- Phagocytes destroy microbes, as well as dead and damaged host cells
- Tissue repair: dead and damaged cells are replaced
Antimicrobial Substances
-
Complement System: large group of serum proteins that participate in the lysis of foreign cells, inflammation, and phagocytosis
- Classical Pathway: initiated by an immune reaction of antibodies
- Alternative Pathway: initiated by direct interaction of complement proteins with microbial polysaccharides
-
Consequences of Complement Activation:
- Cytolysis: due to the formation of a membrane attack complex (MAC) that produces lesions in microbial membranes
- Inflammation: complement components trigger the release of histamine, which increases vascular permeability
- Opsonization: complement components bind to microbial surface and promote phagocytosis
-
Interferons: antiviral proteins that interfere with viral multiplication
- Alpha and Beta Interferon: produced by virus-infected cells and diffuse to neighboring cells, causing uninfected cells to produce antiviral proteins (AVPs)
- Gamma Interferon: produced by lymphocytes, causes neutrophils to kill bacteria
Fever Response
- Fever: body temperature above 37°C or 98.7°F
-
Positive Effects:
- Enhances interferon effects
- Tissue repair
- Phagocytosis
- Inhibits some microbes
-
Negative Effects:
- Causes discomfort, body aches, malaise, and fatigue
- If fever is too high, critical proteins are denatured and nerve impulses are inhibited, resulting in hallucinations, coma, and death
-
Steps of Fever Response:
- Phagocytes release chemical signals called pyrogens (interleukin-1, etc.) which enter bloodstream
- Hypothalamic thermostat is reset
- Hypothalamus communicates with other areas of the brain which initiate shivering, increased metabolic rate, and constriction of blood vessels of the skin
- Body core temperature increases until reaches the setting prescribed by the hypothalamus
- As infection subsides and pyrogens decrease, thermostat is reset to normal by hypothalamus
Innate Immunity
- Resistance: The ability to ward off disease, which can be further divided into nonspecific resistance and specific resistance.
Nonspecific Resistance
-
First Line of Defense: Non-specific natural barriers that restrict the entry of pathogens, including:
- Skin (epidermis and dermis)
- Mucous membranes (gastrointestinal, genitourinary, and respiratory tracts)
- Lacrimal apparatus (continuous washing and blinking prevents microbes from settling on the eye surface)
- Saliva (washes microbes from teeth and mouth mucous membranes)
- Mucus (thick secretion that traps many microbes)
- Nose hair (coated with mucus, filters dust, pollen, and microbes)
- Ciliary escalator (cilia on mucous membranes of the lower respiratory tract move upwards towards the throat at 1-3 cm/hour)
- Coughing and sneezing (expel foreign objects)
- Epiglottis (covers the larynx during swallowing)
- Urination (cleanses the urethra)
- Vaginal secretions (remove microbes from the genital tract)
Chemical Defenses
- Sebum: An oily substance produced by sebaceous glands that forms a protective layer over the skin, containing unsaturated fatty acids that inhibit the growth of certain pathogenic bacteria and fungi.
- pH: The skin's low pH, usually between 3 and 5, caused by lactic acid and fatty acids, which inhibits the growth of certain pathogens.
- Perspiration: Produced by sweat glands, containing lysozyme and acids that inhibit the growth of certain pathogens.
- Lysozyme: An enzyme that breaks down gram-positive cell walls, found in nasal secretions, saliva, and tears.
- Gastric Juice: A mixture of hydrochloric acid, enzymes, and mucus, with a pH between 1.2 to 3, which kills many microbes and destroys most toxins.
- Transferrins: Iron-binding proteins in blood that inhibit bacterial growth by reducing available iron.
Cellular Elements of Blood
- Erythrocytes (RBC): Responsible for transporting oxygen and carbon dioxide, with a count of 4.8-5.4 million cells/mm3.
- Leukocytes (WBC): Responsible for various functions, including phagocytosis, with a count of 5000-9000 cells/mm3.
- Neutrophils: Phagocytic cells that predominate early in infection, making up 70% of WBC.
- Basophils: Produce histamine, making up 1% of WBC.
- Eosinophils: Produce toxins against parasites and perform some phagocytosis, making up 4% of WBC.
- Monocytes/Macrophages: Phagocytic cells that make up 5% of WBC.
- Lymphocytes: Responsible for antibody production and cell-mediated immunity, making up 20% of WBC.
- Platelets: Responsible for blood clotting, with a count of 300,000 cells/mm3.
Second Line of Defense
- Phagocytosis: The process of engulfing and digesting foreign particles and microorganisms, carried out by white blood cells.
- Phagocytosis Stages: Include chemotaxis, adherence, ingestion, and digestion.
Inflammation
- Inflammation: Triggered by tissue damage due to infection, heat, or wound, resulting in four major symptoms: redness, pain, heat, and swelling.
- Inflammation Functions: Include destroying and removing pathogens, limiting the effects of infection, and repairing and replacing damaged tissue.
- Inflammation Stages: Include vasodilation, phagocyte migration and margination, and tissue repair.
Antimicrobial Substances
- Complement System: A large group of serum proteins that participate in the lysis of foreign cells, inflammation, and phagocytosis.
- Complement Activation: Can occur through the classical pathway (initiated by an immune reaction of antibodies) or the alternative pathway (initiated by direct interaction of complement proteins with microbial polysaccharides).
- Consequences of Complement Activation: Include cytolysis, inflammation, opsonization, and inactivation of complement.
Interferons
- Interferons: Antiviral proteins that interfere with viral multiplication, produced by virus-infected cells and diffusing to neighboring cells.
- Interferon alpha and beta: Produced by virus-infected cells and causing uninfected cells to produce antiviral proteins.
- Interferon gamma: Produced by lymphocytes and causing neutrophils to kill bacteria.
Fever Response
- Fever: A body temperature above 37°C or 98.7°F, which can have both positive and negative effects on the body.
- Fever Response Steps: Include phagocytes releasing pyrogens, the hypothalamic thermostat being reset, and the body core temperature increasing until it reaches the setting prescribed by the hypothalamus.
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Description
Learn about the three lines of defense in innate immunity, including non-specific natural barriers, rapid local responses, and more. Understand resistance and susceptibility to disease.