42 Questions
Which one of the following is a mechanism used by pathogens to evade phagocytosis?
Producing capsules that are too large to be engulfed by phagocytes
Which of the following is a consequence of fever?
Induction of antimicrobial substances
What is the role of cytokines in the process of inflammation?
Cytokines promote chemotaxis of phagocytes to the site of tissue injury
Which of the following is a characteristic of the complement system?
The complement proteins act in a cascade manner
Which of the following is a mechanism used by pathogens to evade the immune system?
Producing leukocidins to kill phagocytes
Which of the following is a symptom of inflammation?
Redness (erythema) at the site of injury
What is the role of the hypothalamus in the fever response?
The hypothalamus releases cytokines that increase the set point for body temperature
Which of the following is a function of the complement system?
Enhancing the immune system's ability to destroy pathogens
Which of the following is a step in the process of phagocytosis?
All of the above
What is the key difference between innate immunity and adaptive immunity?
All of the above are key differences between innate and adaptive immunity.
Which of the following is NOT a component of the innate immune system's first line of defense?
Adaptive immune responses mediated by T and B cells.
What is the primary function of the innate immune system's second line of defense?
To provide a rapid, non-specific response to pathogens.
Which of the following is a key characteristic of the adaptive immune system?
It can recognize and mount a specific response to a particular pathogen.
What is the primary difference between resistance and susceptibility in the context of host defenses?
Resistance refers to the host's ability to fight off pathogens, while susceptibility refers to the host's inability to do so.
Which of the following is a key feature of the adaptive immune system's third line of defense?
It involves the formation of immunological memory for future infections.
Which of the following statements best describes the relationship between host defenses and immunity?
Immunity is a subset of host defenses, as it refers to the ability to prevent disease.
Which of the following is a key characteristic of the innate immune system's first line of defense?
It includes physical and chemical barriers that prevent pathogen entry.
How do the innate and adaptive immune systems differ in their response time to pathogens?
The innate immune system provides a more rapid response than the adaptive immune system.
What is the mechanism of action by which normal microbiota defeat invading pathogenic bacteria?
Produce substances harmful to invading pathogens
Which type of leukocytes is involved in allergic responses through releasing histamine?
Basophils
What is the term for the ingestion of microbes or other substances by a phagocyte?
Phagocytosis
Where are monocytes found before maturing into macrophages?
Tissues
Which leukocytes are characterized by having granules in their cytoplasm that are visible with a light microscope?
Basophils
What is the primary role of eosinophils?
Toxicity against parasites and worms
What is the primary function of the ciliary escalator in the respiratory tract?
To move mucus and trapped pathogens out of the body
Which of the following is NOT a function of the skin as a physical barrier?
Secretion of antimicrobial substances like lysozymes
What is the primary role of blood transferrins in host defense?
To bind and sequester iron, depriving pathogens of this essential nutrient
What is the primary mechanism by which the normal microbiota provides protection against pathogens?
Outcompeting pathogens for available nutrients and attachment sites
Which of the following is NOT a function of the lacrimal apparatus (tear production system) in host defense?
Maintaining a slightly acidic pH in the eyes to inhibit microbial growth
Which of the following is a chemical barrier in host defense?
The slightly acidic pH of the skin
What is the primary function of gastric juices in host defense?
To create an acidic environment that kills pathogens ingested with food
Which of the following statements about beneficial microbes is NOT true?
They stimulate the host's immune system to mount a stronger response
Which of the following is NOT a physical barrier in host defense?
Lysozymes found in body secretions
What is the primary role of opsonization in the complement system?
To promote the attraction and attachment of phagocytes to pathogens
What is the primary outcome of inflammation mediated by the complement system?
Increased blood vessel permeability and chemotactic attraction of phagocytes
Which process describes the cytolytic action of the complement system?
Complement proteins create a membrane attack complex (MAC) that forms a channel in the pathogen's cell wall/membrane, causing lysis
How do some pathogens evade the complement system through capsule production?
Capsules prevent complement proteins from binding to the pathogen's surface
What is the mechanism by which interferons (IFNs) provide anti-viral defense in uninfected neighboring cells?
IFNs bind to the cell membrane of uninfected neighboring cells, causing them to produce anti-viral proteins (AVPs) that can destroy incoming viruses
Which of the following is NOT a mechanism by which pathogens can evade the complement system?
Releasing interferons to heighten anti-viral defenses in neighboring cells
What is the primary function of interferons (IFNs) in the context of innate immunity?
To cause neighboring cells to heighten their anti-viral defenses
Which component of the innate immune system is responsible for the production of interferons (IFNs)?
Host cells
Which of the following statements about the innate immune system is correct?
Phagocytes are attracted and attached to pathogens through the process of opsonization
Study Notes
Innate Immunity: Non-Specific Defenses of the Host
- Immunity: the ability to fight off pathogens and prevent disease
- Host defenses: the ability of the host to remove pathogens to prevent disease
- Innate immunity (non-specific host defenses): present at birth, no specific recognition of microbes, no immunological memory response, rapid immune response
- Adaptive immunity (specific host defenses): develops later, specific recognition and response to specific microbe, has immunological memory, slower immune response
1st Line of Host Defense: Physical Barriers
- Intact skin:
- Closely packed epithelial cells
- Continuous layering
- Keratin protein in top layer
- Dryness
- Shedding of top layer
- Mucous membranes and ciliary escalator:
- Epithelial layer that lines gastrointestinal, respiratory, and genitourinary tracts
- Secrete viscous fluid called mucus
- Cilia move together and sweep mucus up and out of the body
- Lacrimal apparatus and saliva, urine, and vaginal secretions:
- Protect the eyes
- Continuous washing action
- Flushing mechanism to wash away pathogens
1st Line of Host Defense: Chemical Barriers
- Chemical factors of the skin:
- pH of skin (slightly acidic)
- Salinity
- Sebum
- Lysozymes:
- Enzymes found in body secretions (sweat, tears, saliva)
- Break chemical bonds in peptidoglycan, destroying bacterial cell wall
- Gastric juices and blood transferrins:
- Gastric juices produced by stomach, containing enzymes and acid
- Blood transferrins: proteins that bind to iron, necessary for bacterial growth
1st Line of Host Defense: Biological Barriers
- Normal microbiota:
- Commensal microbes
- Beneficial microbes
- Competitive exclusion
Phagocytosis
- Phagocytosis: ingestion of microbes or other substances by a phagocyte
- Phagocyte: non-specific host cell capable of phagocytosis (e.g., neutrophils, macrophages, dendritic cells)
- Mechanism/phases of phagocytosis:
- Chemotaxis: release of chemical signals by pathogen attracts phagocytes
- Adherence: attachment of phagocyte to surface of pathogen
- Ingestion: endocytosis of pathogen, forming a phagosome that merges with a lysosome to form a phagolysosome
- Digestion: pathogen is digested inside a phagolysosome
Microbial Evasion of Phagocytosis
- Capsule production: making the pathogen too big to be engulfed
- Leukocidins: pore-forming toxin capable of killing phagocytes
- Mycolic acid: waxy lipid inhibiting lysosome enzymes of phagocyte
Inflammation
- Signs and symptoms:
- Pain due to release of certain chemicals by leukocytes
- Redness (erythema) due to increased blood flow
- Immobility due to local loss of function in severe inflammation
- Swelling (edema) due to accumulation of fluids
- Heat due to increased blood flow
- Process of inflammation:
- Tissue or cells get damaged
- Damaged cells release chemicals such as cytokines
- Cytokines promote chemotaxis of phagocytes
- Phagocytosis of invading pathogens begins
- Tissue gets repaired
Fever
- Toxins released by bacteria induce cytokine release from phagocytes
- Cytokines bind to hypothalamus receptors, increasing the set point for body temperature
- Person feels cold (chills) and increases their body temperature
- Once the new set point is reached, person experiences abnormally high body temperature (fever)
- As pathogens are eliminated, toxins and cytokines get eliminated, and body temperature falls, causing the decline of fever (crisis)
Consequences of Fever
- Increases metabolic rate
- Enhances immune response
- Induces antimicrobial substances
Test your knowledge on innate immunity, host defenses, and the concept of immunity in protecting the human host from pathogens. Learn about the difference between resistance and susceptibility, and how host defenses can prevent disease.
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