Chapter 11: Innate Immunity Study Guide

Comprehensive practice flashcards covering Chapter 11 Innate Immunity, detailing first-line defenses, secondary cellular and molecular defenses, the lymphatic system, inflammation, and fever.

How is self-tolerance defined in immunology?

The immune system's ability to recognize the body's own cells and molecules as self and avoid attacking them.

What characterizes a person who is immune to a specific pathogen?

An immune person has defenses that prevent infection or disease from that pathogen, often because of prior infection or vaccination.

What characterizes a person who is susceptible to a pathogen?

A susceptible person lacks sufficient protective immunity and is more likely to become infected or ill after exposure.

What are three similarities shared by innate and adaptive immunity?

Both help protect the body from pathogens; both use cells and soluble molecules to detect or respond to threats; and both communicate and work together to eliminate infection and limit damage.

What are three key differences when comparing innate and adaptive immunity?

Innate immunity is present from birth and responds rapidly, whereas adaptive immunity develops after exposure and is usually slower on first exposure; innate defenses recognize broad patterns shared by groups of microbes, while adaptive defenses recognize specific antigens; and adaptive immunity forms long-lasting memory, while innate immunity generally has little or no antigen-specific memory.

How does the normal microbiota contribute to the training and development of the host immune system?

Normal microbiota help train and regulate immune defenses and support the development of immune tissues.

How do our normal microbiota and host immune defenses interact to protect tissues and maintain balance?

Normal microbiota compete with pathogens for space and nutrients, while host immune defenses help keep the microbiota in balance and contained in its usual locations.

What is the hygiene hypothesis?

The hypothesis that reduced exposure to diverse microbes early in life may interfere with normal immune-system development and increase the risk of allergies or some autoimmune conditions.

Does the hygiene hypothesis advocate that hygiene practices should be abandoned?

No, it is a proposed explanation for immune-system development and allergy risk, not a claim that hygiene should be abandoned.

What is the main goal of first-line innate defenses?

To prevent pathogens from entering the body or becoming established on its surfaces.

Into which barrier category (physical, mechanical, or chemical) is the skin classified?

Physical barrier.

Into which barrier category are the rinsing action of tears and the flushing action of urine classified?

Mechanical barrier.

Into which barrier category is stomach acid classified?

Chemical barrier.

Into which barrier category is the trapping and sweeping action of mucus and cilia classified?

Mechanical barrier.

Into which barrier category is lysozyme in tears, mucus, saliva, and breast milk classified?

Chemical barrier.

Into which barrier category are antimicrobial peptides such as defensins classified?

Chemical barrier.

How is earwax classified among first-line barrier defenses?

It is mainly mechanical because it traps particles, but it also contains chemical substances that help inhibit microbes.

What is the function of the mucociliary escalator?

Mucus traps inhaled microbes and particles in the respiratory tract, and cilia move the mucus toward the throat, where it can be swallowed or expelled, helping clear the airways.

What is the chemical function of lysozyme?

Lysozyme breaks bonds in peptidoglycan, a structural component of bacterial cell walls, which can weaken susceptible bacteria and cause them to lyse.

What is the general function of antimicrobial peptides (AMPs)?

AMPs inhibit or kill microbes, often by disrupting their membranes, and help protect skin and mucosal surfaces.

What are defensins and what functions do they perform?

Defensins are small antimicrobial peptides made by epithelial cells and some immune cells that can damage microbial membranes and help signal or recruit immune cells.

What is the main first-line defense physical barrier in animals?

The skin.

What cellular and structural features of the epidermis make the skin one of our most important physical barriers?

The epidermis is a tightly packed, multilayered sheet of cells whose outer cells are keratinized and continually shed, making penetration difficult, removing attached microbes, and presenting few openings compared with mucosal surfaces.

What is the lymphatic system and what role does it play in the body?

A network of vessels, tissues, and organs that collects excess fluid from tissues, returns it to the bloodstream, transports immune cells and antigens, and provides sites where immune responses can be organized.

What is plasma?

The liquid portion of blood in which blood cells, proteins, nutrients, hormones, and other dissolved substances are suspended.

How is edema defined?

Swelling caused by excess fluid accumulating in tissues.

What is lymph, where is it found, and what is its function?

Lymph is interstitial fluid that has entered lymphatic vessels; it flows through the lymphatic network carrying fluid, immune cells, and collected tissue material before eventually returning to the blood.

Are the thymus and bone marrow classified as primary or secondary lymphoid tissues?

Primary lymphoid tissues.

Are lymph nodes and the spleen classified as primary or secondary lymphoid tissues?

Secondary lymphoid tissues.

How are adenoids and tonsils classified in the lymphoid tissue system?

Secondary lymphoid tissues (specifically mucosa-associated lymphoid tissue, or MALT).

What is GALT and how is it classified?

Gut-associated lymphoid tissue; it is classified as secondary mucosal lymphoid tissue.

What are four examples of mucosa-associated lymphoid tissue (MALT)?

Tonsils, adenoids, Peyer's patches, and the appendix.

Where are T-cell precursors produced, and where do they mature?

T-cell precursors are produced in the bone marrow and travel to the thymus, where they mature.

Where are B-cell precursors produced, and where do they mature?

B-cell precursors are produced and mature in the bone marrow.

What is the function of lymph nodes?

Lymph nodes filter lymph and bring antigens into contact with lymphocytes and other immune cells, helping detect pathogens and initiate adaptive immune responses.

What biological events cause lymph nodes to swell and become tender during an infection?

Immune cells become activated and multiply in response to infection, and the resulting increase in immune-cell numbers and fluid in the node makes it enlarge and tender.

What are the primary functions of the spleen?

The spleen filters the blood, removes old or damaged blood cells, helps detect blood-borne pathogens, and mounts immune responses against them.

Where are Peyer's patches located in the body?

In the lining of the small intestine, especially the ileum.

Which four leukocyte types are classified as granulocytes?

Neutrophils, eosinophils, basophils, and mast cells.

Which three leukocyte types are classified as agranulocytes?

Monocytes, lymphocytes, and dendritic cells.

What information does a differential white blood cell count determine?

It reports the proportions or numbers of different white blood cell types, revealing changes that help indicate patterns associated with infection, inflammation, allergy, or other conditions.

How is leukocytosis defined?

An abnormally high white blood cell count, often occurring in response to infection or inflammation.

Which leukocyte is the most abundant type in the blood?

The neutrophil.

What are two important antimicrobial molecules released from neutrophil granules?

Lysozyme and defensins.

Besides lysozyme and defensins, what other antimicrobial substances are found in neutrophil granules?

Enzymes and proteins that bind iron.

Which granulocyte is usually the first recruited in large numbers to injured or infected tissues from the bloodstream?

The neutrophil.

How is neutropenia defined?

An abnormally low neutrophil count.

Why does neutropenia increase the risk of serious bacterial and fungal infections?

Because neutrophils are important early phagocytes and antimicrobial cells.

What color do eosinophil granules stain when exposed to eosin dyes?

Red to orange.

Under what medical conditions are eosinophil counts typically elevated in the blood?

During parasitic worm infections and allergic conditions such as asthma.

What color do basophil granules stain?

Dark blue to purple.

What notable chemical mediator is stored in basophil granules, and what does it promote?

Histamine, which promotes inflammation and allergic responses.

Which two agranulocytes serve as key phagocytes?

Monocytes and dendritic cells (as well as tissue macrophages derived from monocytes).

What do monocytes become once they migrate out of the blood and enter tissues?

They commonly differentiate into macrophages; some can also become dendritic cells depending on the tissue and signals received.

Which agranulocytes are abundant at barrier tissues that contact the environment, such as the skin and body openings?

Dendritic cells.

What is the primary immunological role of dendritic cells at epithelial surfaces?

To capture antigens and help activate adaptive immunity.

Which lymphocytes function primarily in innate immunity?

Natural killer (NK) cells.

Which lymphocytes function primarily in adaptive immunity?

B cells and T cells.

How are cytokines defined?

Small signaling proteins released by cells that influence the behavior, activity, movement, growth, or survival of other cells, especially immune cells.

What is a cytokine storm?

An excessive, poorly controlled release of inflammatory cytokines.

What severe physiological results can occur during a cytokine storm?

Widespread inflammation, tissue damage, shock, and potentially organ failure.

What are chemokines?

Cytokines that attract immune cells and guide their movement toward sites of infection or tissue damage.

How is chemotaxis defined?

Directed cell movement along a chemical gradient, such as immune cells moving toward a higher concentration of signals released at an infection site.

What roles do interleukins play in immune responses?

They are signaling molecules that help immune cells communicate and regulate immune-cell activation, growth, differentiation, and coordination of responses.

How is apoptosis defined?

A regulated form of programmed cell death that allows the body to remove unwanted, damaged, or infected cells while limiting inflammation.

What cell type is a major primary source of tumor necrosis factor alpha ($\text{TNF-}\alpha$)?

Activated macrophages.

What are the physiological functions of tumor necrosis factor alpha ($\text{TNF-}\alpha$)?

It promotes inflammation, activates blood-vessel lining cells, helps recruit immune cells, and can contribute to fever and systemic responses.

What is the function of microbial siderophores?

They bind iron very tightly and help microbes capture and import iron, which is scarce in the host because host proteins bind it.

What are four general mechanisms microbes use to circumvent host iron-binding proteins?

(1) Releasing siderophores that remove iron from host proteins; (2) using surface receptors to capture iron directly from transferrin or lactoferrin; (3) acquiring heme or hemoglobin iron using heme-binding proteins/receptors; and (4) damaging red blood cells or tissues with hemolysins or other factors to release hemoglobin and heme.

How do microbial surface receptors capture iron directly from the host?

They bind directly to host transferrin or lactoferrin to extract and capture iron.

How do hemolysins facilitate microbial iron acquisition?

They damage red blood cells or host tissues to release hemoglobin and heme, which the microbe can then bind and utilize.

Why is C3 considered the central component of the complement system?

C3 is the central component where all three activation pathways converge, and its cleavage generates fragments that drive inflammation, opsonization, and later complement cascade steps.

What are the distinct functions of the complement cleavage fragments C3a and C3b?

C3a promotes inflammation, while C3b coats microbes for opsonization and helps form enzyme complexes that drive later complement steps.

How is the classical complement pathway activated?

Mainly when antibodies bound to a target recruit complement.

How is the lectin complement pathway activated?

It begins when mannose-binding lectin or related recognition proteins bind microbial carbohydrates.

How is the alternative complement pathway initiated and amplified?

It begins through low-level spontaneous C3 activation that is amplified on microbial surfaces lacking protective host regulators.

What are the three main outcomes of complement activation?

(1) Inflammation and immune-cell recruitment; (2) opsonization; and (3) direct lysis of susceptible microbes by the membrane attack complex.

Which small complement fragments promote inflammation and immune-cell recruitment?

C3a and C5a.

How is opsonization defined?

The coating of a pathogen with molecules such as C3b or antibodies that make it easier for phagocytes to recognize and engulf.

How is the membrane attack complex (MAC) defined?

A pore-forming assembly of complement proteins that inserts into a target membrane and can cause cell lysis.

What are regulators of complement activation (RCAs)?

Host proteins that control complement activity, limit its amplification, and protect the body's own cells from complement-mediated damage.

How do some pathogenic microbes use regulators of complement activation (RCAs) to evade the immune system?

Some microbes make or capture RCA-like proteins to protect themselves from complement attack and shut down complement amplification.

What are the three main goals of inflammation?

To eliminate or neutralize the cause of injury or infection; contain it and limit its spread; and begin removal of damaged tissue and repair.

What are the four main cardinal signs of inflammation?

Redness, heat, swelling, and pain.

What additional sign often accompanies the four cardinal signs of inflammation?

Reduced function.

What are the three general phases of inflammation?

1. Vascular changes; 2. Leukocyte recruitment and clearance; 3. Resolution and repair.

What biological events occur during the vascular changes phase of inflammation?

Local vessels dilate and become more permeable, increasing blood flow and allowing fluid and proteins to enter tissue.

What biological events occur during the leukocyte recruitment and clearance phase of inflammation?

Immune cells leave the blood, move to the site, and remove microbes and debris.

What biological events occur during the resolution and repair phase of inflammation?

Inflammation subsides, damaged material is cleared, and tissue healing begins.

How is vasodilation defined?

Widening of blood vessels due to relaxation of smooth muscle in their walls; it increases blood flow to the affected area.

Besides eicosanoids and kinins, what other vasoactive molecule induces vascular changes during inflammation?

Histamine.

What is the main tissue-resident cell type that produces and releases histamine?

Mast cells.

Besides mast cells, what circulating leukocyte can release histamine?

Basophils.

How do antihistamines function to relieve inflammatory symptoms?

They reduce histamine's effects, commonly by blocking histamine receptors, which can lessen itching, swelling, and increased mucus production.

How do nonsteroidal anti-inflammatory drugs (NSAIDs) reduce pain and inflammation?

NSAIDs inhibit cyclooxygenase (COX) enzymes and reduce the production of prostaglandins and related eicosanoids that promote pain and inflammation.

How do steroidal anti-inflammatory drugs (SAIDs, such as glucocorticoids) reduce inflammation?

They act broadly by reducing inflammatory gene expression and diminishing the production of multiple inflammatory mediators.

What two sequential cellular processes allow leukocytes to exit blood vessels and enter infected or damaged tissues?

Margination and diapedesis.

How is margination defined in the context of leukocyte extravasation?

The movement of leukocytes toward and along the inner surface of the blood-vessel wall, where they slow and adhere.

How is diapedesis (transmigration) defined?

The passage of leukocytes between endothelial cells through the vessel wall into tissue.

What preparatory mechanical behaviors do leukocytes display along the vessel wall before margination and diapedesis occur?

Adhesion and rolling.