Basic Medical Sciences Lecture 2 & 3

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Questions and Answers

What is one characteristic that differentiates innate immunity from adaptive immunity?

It is pre-formed. (correct)

It has immunological memory.

It targets specific pathogens only.

It can improve over time.

Which type of immune cell is primarily responsible for the phagocytic barrier to infection?

Cytotoxic T cells

B lymphocytes

Basophils

Macrophages (correct)

Which complement pathway is not correctly matched with its characteristic?

Lectin pathway - activated by mannose-binding lectin.

Alternative pathway - requires prior exposure to antigens. (correct)

Classical pathway - triggered by antigen-antibody complexes.

All complement pathways lead to opsonization.

What role do pattern recognition receptors (PRRs) play in innate immunity?

They identify pathogen associated molecular patterns (PAMPs). Signup and view all the answers

What is the primary function of neutrophils in the immune response?

They perform phagocytosis and release antimicrobial substances. Signup and view all the answers

What differentiates innate immunity's response to pathogens?

It is non-specific and rapid. Signup and view all the answers

What is the function of antimicrobial peptides such as defensins?

They disrupt microbial cell membranes. Signup and view all the answers

Which of the following cell types have the ability to recognize and ingest pathogens via phagocytosis?

Neutrophils Signup and view all the answers

What role does sebum play in skin health?

It maintains a low pH to prevent bacterial colonization. Signup and view all the answers

How does lactobacillus contribute to vaginal health?

By secreting lactic acid to lower pH. Signup and view all the answers

What is the primary role of hydrochloric acid secreted in the stomach?

To create an acidic environment that prevents microbial colonization. Signup and view all the answers

Which of the following cells is crucial for acute infections?

Neutrophils. Signup and view all the answers

What is a mechanism used by phagocytic cells to recognize pathogens?

Utilizing Pattern Recognition Receptors. Signup and view all the answers

What happens when lactobacillus is eliminated in the vagina due to antibiotics?

Risk for fungal infections increases due to higher pH. Signup and view all the answers

Which type of cell can perform both phagocytosis and pinocytosis?

Dendritic cells. Signup and view all the answers

What is the function of defensins secreted by respiratory cells?

To provide antimicrobial effects against pathogens. Signup and view all the answers

What method can be used to determine the phagocytic efficiency of neutrophils and macrophages?

Challenging monocytes with inert particles Signup and view all the answers

What is indicated by the blue color in nitro blue tetrazolium (NBT) staining?

High NADPH oxidase activity Signup and view all the answers

Which of the following statements is true regarding chronic granulomatous disease?

It results in impaired ROI and increased infection risk Signup and view all the answers

What component of Gram-negative bacteria can activate the complement system?

Lipopolysaccharide (LPS) Signup and view all the answers

Which pathway activates complement through antigen-antibody complex formation?

Classical pathway Signup and view all the answers

What is the final structure formed in the complement cascade responsible for lysing bacterial cells?

Membrane attack complex (MAC) Signup and view all the answers

What is the enzyme in macrophages responsible for converting L-arginine to nitric oxide?

Inducible nitric oxide synthase (NOS2) Signup and view all the answers

Which factors are involved in the activation of the complement system in the alternate pathway?

Factor B, D, and Properdin Signup and view all the answers

Which of the following best describes the role of mannose in complement activation?

It initiates the mannose-binding lectin pathway Signup and view all the answers

What is the primary role of complement in innate immunity?

Opsonization and phagocytosis Signup and view all the answers

Which antimicrobial peptide in macrophages sequesters iron to deprive pathogens of a vital nutrient?

Lactoferrin Signup and view all the answers

Which factor inhibits the alternative pathway of complement activation?

Factor H Signup and view all the answers

How does CD55 protect human cells from complement-mediated lysis?

By inactivating C3 and C5 convertase activity Signup and view all the answers

What condition is associated with C1 inhibitor deficiency?

Hereditary angioedema Signup and view all the answers

What is the fate of nitric oxide in macrophages after it is produced?

It is converted to nitrate and nitrite, both of which lack antimicrobial properties. Signup and view all the answers

Which of the following is NOT a method used by macrophages to control intracellular pathogens?

Generation of hypochlorous acid Signup and view all the answers

Which mechanism is NOT involved in the oxygen-independent control of intracellular pathogens by macrophages?

Production of hydrogen peroxide Signup and view all the answers

What role does IL-8 play in the immune response involving macrophages?

Promotes neutrophil migration to extravascular sites Signup and view all the answers

What happens due to an exacerbation of the complement cascade?

Leaky vasculature promoting inflammation Signup and view all the answers

What is a characteristic feature of macrophages concerning their cellular structure?

They can fuse to form giant cells. Signup and view all the answers

Which of the following factors plays a role in regulating both classical and alternate pathways of complement activation?

Factor I Signup and view all the answers

What characteristic is associated with complement deficiency?

Increased susceptibility to specific infections Signup and view all the answers

Which antimicrobial effect is attributed to lysozyme found in macrophages?

Degradation of peptidoglycan in bacterial cells Signup and view all the answers

Which mechanism is NOT involved in oxygen-independent killing by neutrophils?

Reactive oxygen intermediates (ROI) Signup and view all the answers

Study Notes

Introduction to Host Defense

Key objective of lectures: Understand monocytes, macrophages, dendritic cells, and their immune functions.
Monocytes differentiate into macrophages and dendritic cells, both crucial for innate immunity.
Reactive oxygen species (ROS) are generated during the oxidative burst after tissue injury, aiding in pathogen elimination.

Innate Immune System

Characteristics: pre-formed, active, non-specific, lacks immunological memory, does not improve over time.
Innate immunity is often the first line of defense, but can be inadequate, prompting activation of adaptive immunity.
Physical barriers include skin, mucous membranes, and secretions with antimicrobial properties, such as lysozyme.

Components of Innate Immunity

Phagocytic cells: neutrophils (short-lived, target acute infections), macrophages (long-lived, handle acute and chronic infections), and dendritic cells (also long-lived, involved in antigen presentation).
Neutrophils induce pus formation and utilize primary granules containing myeloperoxidase, lysozyme, and defensins.
Macrophages generate superoxide and hydrogen peroxide but lack myeloperoxidase and thus produce no hypochlorous acid.

Role of Phagocytosis

Phagocytic cells utilize pattern recognition receptors (PRRs) like TLR-2 and TLR-4 to identify pathogens.
Intracellular killing mechanisms involve oxygen-dependent (oxidative burst) and oxygen-independent methods (lysosomal enzymes, defensins).
Lysozyme disrupts the peptidoglycan layer in Gram-positive bacteria; lactoferrin sequesters iron, limiting pathogen growth.

Complement System

Complement proteins become activated via three pathways: classical, alternative, and mannose-binding lectin pathway.
Classical pathway starts with antigen-antibody complexes, resulting in the membrane attack complex (MAC) formation leading to bacterial lysis.
Alternative pathway activates directly in the presence of Gram-negative bacteria's LPS.
Complement functions include opsonization (tagging pathogens for phagocytosis) and aiding in inflammation.

Regulatory Mechanisms and Disorders

Complement activation is tightly regulated by factors like C1 inhibitor, Factor H, and Factor I to prevent excessive inflammation.
Deficiencies in components lead to increased susceptibility to infections, particularly Neisseria.
Conditions such as chronic granulomatous disease arise from NADPH oxidase deficiencies, impairing the production of reactive oxygen species and increasing infection risk.

Comparisons in Immunity

Innate immunity is fast but general; adaptive immunity is slower but provides targeted defense and immunological memory.
Antigenicity refers to the ability of a substance to bind to an immune receptor, while immunogenicity is the ability to provoke an immune response.

Laboratory Techniques

Phagocytic efficiency of neutrophils and macrophages can be tested with inert particles or pathogens observed microscopically post-staining.
NADPH oxidase activity is assessed using nitro blue tetrazolium (NBT) staining to visualize free radical production.

Summary

Understanding innate and adaptive immunity is crucial for identifying therapeutic interventions and managing immune-related diseases.
Knowledge of phagocytic processes, complement activation, and regulatory mechanisms enhances appreciation for the body's immune defense strategies.

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Description

This quiz covers the fundamentals of host defense mechanisms, focusing on the roles of different immune cells such as monocytes, macrophages, and dendritic cells. Participants will learn about the reactive oxygen burst pathways and the comparative functions of neutrophils, monocytes, eosinophils, and basophils. Essential for understanding basic immunology and host responses to injury.