Innate Immunity & Inflammation – Lecture Review

These flashcards review key concepts from the lecture on innate immunity, physical and chemical barriers, cellular components, and the inflammatory response.

What is innate immunity?

The in-born, non-specific component of the immune system that provides immediate defense without prior exposure to a pathogen.

How does innate immunity differ from adaptive (acquired) immunity?

Innate immunity is present at birth and non-specific; adaptive immunity develops after exposure and is highly specific to particular pathogens.

Define pathogen.

Any agent capable of causing harm or infection, including living organisms (bacteria, parasites) and non-living agents (viruses, prions, pollen).

Why is the lumen of the digestive tract considered "outside" the body?

Because contents in the lumen have not crossed epithelial barriers into the bloodstream or tissues.

Name three major physical (first-line) barriers of innate immunity.

Skin (keratinized epidermis), mucous membranes (e.g., respiratory and GI tracts), and cilia (e.g., mucociliary escalator).

What role does mucus play in innate defense?

It traps debris and pathogens; cilia then sweep the mucus out of the body (mucociliary escalator).

How do tears and saliva function as innate barriers?

They wash away pathogens and contain antimicrobial chemicals such as lysozyme.

Give two examples of mechanical barriers that physically flush pathogens from entry points.

Guard hairs in nose/ears and urine flow through the urinary tract.

What genetic trait confers resistance to malaria?

Carrying the sickle-cell trait (heterozygous for the sickle-cell allele).

Why do individuals with the sickle-cell trait resist malaria?

Altered hemoglobin in red blood cells impairs the malaria parasite’s life cycle.

How does low pH act as a chemical barrier?

Acidic environments (stomach acid, vaginal canal) are inhospitable and lethal to many pathogens.

What does lysozyme do?

Breaks down the peptidoglycan cell wall of bacteria, leading to bacterial lysis.

What are defensins?

Small antimicrobial peptides that disrupt bacterial plasma membranes.

Why are most innate defenses considered non-specific?

They act broadly against many pathogens rather than targeting a single species or strain.

What is the microbiome’s protective role?

Commensal microbes compete with pathogens and secrete toxins that inhibit pathogen growth.

Which two leukocyte types belong to adaptive immunity?

T-cells and B-cells.

Which white blood cell is most abundant and what is its primary function?

Neutrophils (~70% of circulating WBCs); they perform phagocytosis and release antimicrobial chemicals.

Define phagocytosis.

The process by which cells engulf and digest microorganisms, debris, or dead cells.

What are monocytes and macrophages?

Monocytes circulate in blood; when they enter tissues they differentiate into macrophages, which are phagocytic and antigen-presenting.

How do basophils differ from mast cells?

Basophils circulate in blood; mast cells reside in tissues, but both release histamine and chemokines.

Which leukocytes are especially important in combating parasitic worms (helminths)?

Basophils, mast cells, and eosinophils.

What does histamine do during inflammation?

Causes vasodilation and increases capillary permeability, promoting leukocyte entry to the tissue.

What are pathogen-associated molecular patterns (PAMPs)?

Distinct molecular motifs on pathogens recognized by innate immune receptors to identify foreign agents.

List the three main goals of inflammation.

1) Eradicate the pathogen, 2) Prevent spread (wall-off effect), 3) Initiate tissue repair.

Which liver-derived protein is an early marker of inflammation?

C-reactive protein (CRP).

During inflammation, why is the venule constricted?

Vasoconstriction raises pressure, backing up blood into the capillary bed to localize inflammatory mediators.

What effect does arteriole vasodilation have in inflammation?

Decreases resistance, bringing more blood and leukocytes to the affected tissue.

What is exudate?

Protein-rich plasma fluid that leaks into tissues during inflammation, causing swelling (edema).

Which two major plasma proteins exit capillaries due to increased permeability?

Antibodies (immunoglobulins) and fibrinogen.

Explain the wall-off effect.

Fibrinogen converts to fibrin, forming a barrier around the infection to prevent its spread.

Define chemotaxis in the context of immunity.

Directed movement of leukocytes toward higher concentrations of chemokines at the infection site.

What is the relationship between pathogen toxin strength and the wall-off effect?

Stronger or faster-acting toxins often trigger a more robust fibrin wall-off response.

Why can elevated CRP levels be clinically significant?

They suggest ongoing systemic inflammation and may indicate cardiovascular disease risk.

Which innate cells act as antigen-presenting cells to link innate and adaptive immunity?

Macrophages (and dendritic cells, though not detailed in this lecture).