Innate Immunity

Question 1

What are the three main functions of the immune system?

Answer 1

Recognize invaders, eliminate pathogens, and repair/limit tissue damage.

Question 2

What activates the immune system?

Answer 2

• Infections (bacteria, viruses, fungi, parasites)
• Toxins (e.g., bacterial toxins)
• Tissue damage
• Foreign objects & toxicants

Question 3

What are the main physical barriers of the immune system?

Answer 3

• Skin
• Oral cavity (salivary glands, lysozyme)
• Stomach (low pH)
• Mucosal surfaces
• Normal flora
• Complement System

Question 4

What are the three main functions of the complement cascade?

Answer 4

• Inflammation – Recruits immune cells that secrete pro-inflammatory molecules.
• Opsonization – Coats pathogens to help phagocytosis.
• Membrane Attack Complex (MAC) – Forms pores in pathogens, causing lysis.

Question 5

What are the major cell types of the innate immune system?

Answer 5

• Macrophages
• Dendritic cells
• Granulocytes (Neutrophils, Mast cells, Basophils, Eosinophils)
• Natural Killer (NK) cells

Question 6

What are the two major phenotypic classifications of macrophages, and how do they differ?

Answer 6

• M1 (‘active’) – Pro-inflammatory, fights pathogens.
• M2 (‘inactive’) – Anti-inflammatory, promotes tissue repair.

Question 7

What are the four major receptor types involved in macrophage phagocytosis?

Answer 7

• C-type lectin receptors (e.g., Dectin-1, Mannose receptors)
• Scavenger receptors (recognize bacterial surface components)
• Complement and Fc receptors (help recognize opsonized pathogens)
• Pattern-recognition receptors (PRRs) (e.g., Toll-like receptors, TLRs)

Question 8

What is the primary function of dendritic cells in the immune system?

Answer 8

Best antigen-presenting cells (APCs) and critical for T cell activation.

Question 9

What are the key features of neutrophils that make them effective first responders?

Answer 9

• Most abundant leukocytes in circulation
• Rapid responders – Quickly mobilize
• Phagocytic – Engulf and destroy pathogens
• Contain granules with enzymes and antimicrobial agents
• Short-lived but act fast
• Can form Neutrophil Extracellular Traps (NETs)

Question 10

What do mast cells release from their granules, and what is their role in inflammation?

Answer 10

• Histamine – Vasodilation & vascular permeability
• Proteases – Contribute to inflammation
• IL-5 – Helps recruit immune cells

Question 11

What are the key differences between basophils and eosinophils?

Answer 11

• Eosinophils – Involved in parasitic infections & allergies, secrete IL-5.
• Basophils – Secrete histamine, IL-4, IL-13, and leukotrienes, contribute to allergic responses.

Question 12

What two main cytotoxic molecules do NK cells release to kill infected cells?

Answer 12

• Perforin – Creates pores in the target cell membrane.
• Granzyme – Enters through the pores and induces apoptosis (cell death).

Question 13

What two conditions activate NK cells?

Answer 13

• Too little inhibition (low MHC-I expression on target cells).
• Too much activation (high MICA/B levels).

Question 14

What are the five steps of inflammation?

Answer 14

• Recognition of pathogen
• Recruitment of innate immune cells
• Activation of immune cells
• Regulation and termination
• Tissue repair

Question 15

What are the four key chemical mediators of inflammation, and what do they do?

Answer 15

• Histamine → Vasodilation, vascular permeability (mast cells, basophils!)
• Prostaglandin E2 → Vasodilation, pain
• Leukotrienes → Vascular permeability, vasodilation, chemotaxis, adhesion
• Cytokines → Adhesion and immune cell signaling

Question 16

What are the five steps of immune cell movement during inflammation?

Answer 16

• Capture – Immune cells slow down near the infection site.
• Rolling – Cells roll along the endothelium.
• Crawling – Cells extend projections to find an exit point.
• Adhesion – Cells firmly attach to the endothelium.
• Passage (Transmigration) – Cells move through the vessel wall into the tissue.