Innate Immunity and Commensal Microbes

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Questions and Answers

What role does innate immunity play in the immune response?

It is effective only after an infection has occurred.

It memorizes specific pathogens for future attacks.

It provides a quick, non-specific blockade of infection. (correct)

It primarily relies on antibodies to neutralize threats.

Which of the following is NOT a method of prevention employed by the immune system?

Mucosal defenses in various tracts.

Secretion of antibodies by plasma cells. (correct)

Keratinized skin providing a physical barrier.

Cilia helping to move bacteria out of the body.

How do commensal microbes contribute to the immune system?

By replacing damaged immune cells after an infection.

By increasing the number of pathogens present in the body.

By enhancing immune responses and preventing pathogen colonization. (correct)

By exclusively producing vitamins necessary for metabolism.

What is the primary function of lysozymes secreted by sebaceous glands?

To break down bacteria and reduce infection risk. Signup and view all the answers

What can be a consequence of over-washing hands?

Higher risk of infection due to removal of natural barriers. Signup and view all the answers

Which component of the immune system is primarily involved in mechanically clearing bacterial pathogens?

Cilia and flagella. Signup and view all the answers

What is an example of the role played by lactoferrin in the immune system?

Providing antibacterial and antiviral properties. Signup and view all the answers

What characteristic is true about the innate immune response?

It acts immediately upon encountering an infectious agent. Signup and view all the answers

What is a primary function of macrophages in innate immunity?

Engulf and digest bacteria and viruses Signup and view all the answers

Which substance is produced by macrophages to help kill bacteria?

Reactive nitrogen species (RNS) Signup and view all the answers

What initiates the activation of Natural Killer (NK) cells?

IL-12 secreted by macrophages Signup and view all the answers

How do infected cells influence NK cell activation?

Downregulate MHC class I and upregulate activating ligands Signup and view all the answers

What is the role of the Complement System in innate immunity?

Opsonize pathogens and induce inflammation Signup and view all the answers

Which pathway in the Complement System involves antibody-antigen complexes?

Classical pathway Signup and view all the answers

What is the function of C3b in the Complement System?

Promotes phagocytosis of pathogens Signup and view all the answers

What effect does the Membrane Attack Complex (MAC) have on target cells?

Creates pores in the membrane to induce lysis Signup and view all the answers

What is the primary role of reactive oxygen species (ROS) produced by macrophages?

Kill bacteria and pathogens Signup and view all the answers

What do Killing Inhibiting Receptors (KIRs) on NK cells do?

Inhibit NK cell activation by binding to MHC class I Signup and view all the answers

What is the primary role of dietary fiber in relation to gut health?

It enhances the function of gut bacteria. Signup and view all the answers

Which component of the immune system is responsible for targeting microbes once inside the body?

Natural killer cells and macrophages Signup and view all the answers

What characterizes adaptive immunity?

A long-term and specific immune response Signup and view all the answers

Which phase of infection is characterized by no visible signs of disease despite bacterial colonization?

Asymptomatic phase Signup and view all the answers

What function do antibodies serve in the immune response?

Neutralize toxins and enhance pathogen removal Signup and view all the answers

Which of the following is NOT a function of neutrophils in the immune response?

Production of antibodies Signup and view all the answers

What triggers the release of cytokines in response to pathogen recognition?

Binding of pattern recognition receptors to pathogen-associated molecular patterns Signup and view all the answers

Which white blood cells are derived from monocytes?

Macrophages Signup and view all the answers

What role do dendritic cells play in the immune system?

They activate T cells and initiate adaptive immune response. Signup and view all the answers

Which of the following is considered a pro-inflammatory function of macrophages?

Fighting infections Signup and view all the answers

What is the role of serum transferrin in the immune response?

It binds to iron, restricting its availability to bacteria. Signup and view all the answers

What is the half-life of neutrophils in vivo?

About 10-12 hours Signup and view all the answers

What distinguishes Toll-like receptors (TLRs) from other pattern recognition receptors?

They play a significant role in the interferon response. Signup and view all the answers

What is one function of neutrophil extracellular traps (NETs)?

To capture and expose bacteria to toxic substances Signup and view all the answers

What defines the term 'immune' in the context of the immune system?

Being partially or totally resistant to an infectious disease Signup and view all the answers

What is the primary function of keratinized skin in the immune system?

To create a physical barrier against pathogens Signup and view all the answers

Which method is employed by the innate immune system to remove infectious agents?

Activating macrophages and natural killer cells Signup and view all the answers

How do commensal bacteria support the immune system?

By competing with pathogens for nutrients and space Signup and view all the answers

What is the role of mucosal defenses in the respiratory tract?

To mechanically clean and control bacterial proliferation Signup and view all the answers

How do lysozymes contribute to immune defense?

By breaking down unwanted bacteria Signup and view all the answers

What is a function of lactoferrin in the immune system?

To provide antimicrobial and anti-inflammatory properties Signup and view all the answers

What happens during over-washing of hands in relation to immune defense?

It removes protective lysozymes and sebum, increasing infection risk Signup and view all the answers

What is the primary purpose of reactive nitrogen species (RNS) produced by macrophages?

To damage cellular structures of microorganisms Signup and view all the answers

How do Natural Killer (NK) cells discriminate between healthy and infected cells?

By monitoring the expression of MHC class I and activating ligands Signup and view all the answers

What is the consequence of downregulating MHC class I on infected cells for NK cell activity?

Activation of NK cells to target the infected cells Signup and view all the answers

Which pathway of the Complement System is initiated by the direct binding of complement proteins to pathogen surfaces?

Alternative pathway Signup and view all the answers

What is the role of perforin in the function of NK cells?

To create pores in target cell membranes Signup and view all the answers

C3a, a product of C3 activation in the Complement System, primarily functions to:

Chemoattract immune cells to the site of infection Signup and view all the answers

What occurs when the Membrane Attack Complex (MAC) forms in target cells?

It creates pores that lead to cell lysis Signup and view all the answers

Which cytokines are significantly released by macrophages to attract neutrophils and monocytes?

IL-1 beta, TNF alpha, IL-8 Signup and view all the answers

The function of reactive oxygen species (ROS) in macrophages is primarily to:

Kill engulfed pathogens Signup and view all the answers

What key role does the classical pathway of the Complement System play?

Promoting phagocytosis through opsonization Signup and view all the answers

What is the primary role of adaptive immunity?

Long-term specific immune response Signup and view all the answers

What triggers the activation of T and B cells in the adaptive immune response?

Antigen exposure Signup and view all the answers

Which immune cells are primarily involved in the phagocytosis of pathogens?

Neutrophils and macrophages Signup and view all the answers

Which of the following statements about neutrophils is true?

They produce reactive oxygen species that damage cells. Signup and view all the answers

What is the role of dendritic cells in the immune response?

To link innate and adaptive immunity Signup and view all the answers

What defines the asymptomatic phase of infection?

Bacteria colonize without causing symptoms. Signup and view all the answers

Which phase of the immune response is characterized by increased white blood cell production?

Symptomatic phase Signup and view all the answers

Which cellular component is essential for recognizing pathogens and triggering a rapid immune response?

Pattern recognition receptors (PRRs) Signup and view all the answers

How do neutrophils contribute to inflammation?

By producing cytokines and phagocytosing pathogens Signup and view all the answers

What role does serum transferrin play in the immune response?

Reduces iron availability to bacteria Signup and view all the answers

What is one of the main functions of macrophages after a successful immune response?

Promote tissue repair Signup and view all the answers

Which response is characteristic of the systemic immune response?

Protein production that tags pathogens Signup and view all the answers

What is a key function of antibodies in adaptive immunity?

Increase phagocytosis and neutralize toxins Signup and view all the answers

What is the significance of Toll-like receptors (TLRs) in the immune response?

They trigger inflammatory cytokine production. Signup and view all the answers

Study Notes

Innate Immunity

Definition: A rapid, non-specific defense mechanism against pathogens. Recognizes pathogens through receptors and sensors, activating cells like macrophages and NK cells, and triggering inflammation to eliminate the threat.
Prevention Methods:
- Physical barriers: Intact skin (keratinized), sebaceous gland secretions (lysozymes, lipids, ions) create a barrier against microorganisms. Mucosal defenses in the GI, respiratory, and reproductive tracts utilize mechanical cleaning (cilia, flagella), bactericidal factors (lysozymes), and iron limitation.
- Mechanical defenses: Mucus secretion, peristalsis, cilia in the GI, respiratory, urinary, and reproductive tracts remove pathogens.
Destruction Methods:
- Uses natural killer (NK) cells, neutrophils, macrophages, and the complement system to destroy internal pathogens.

Commensal Microbes

Role: Outnumber human cells, colonize skin and mucosal surfaces.
Benefit: Induce protective responses against pathogens, support the immune system, enhance immune responses, and secrete substances to break down invasive bacteria.
Enhancement: A diverse microbiota (achieved through a balanced diet with fiber) supports immune system function.

Adaptive Immunity

Definition: A specific and long-term immune response.
Activation: Infection stimulates T and B cell activation in lymphoid organs. Activated cells migrate to the infection site.
Antibody-mediated responses:
- Antigen-presenting cells (APCs) present antigens to helper T cells (CD4+).
- Helper T cells coordinate B cell activation.
- B cells produce antibodies that inactivate toxins, enhance phagocytosis, and provide mucosal defense (IgA).
Cell-mediated responses: Cytotoxic T cells (CTLs) directly kill infected cells
Link to Innate Immunity: Dendritic cells bridge innate and adaptive immunity by presenting antigens to T cells following an innate response.

Phases of Infection

Asymptomatic: Pathogens colonize without symptoms.
Symptomatic: Pathogen evasion triggers symptoms that worsen as immune system weakens, allowing bacterial replication to increase.

Inflammatory Responses

Local (Acute): Limits injury and infection spread.
Local Vasculature Response: Vasoconstriction followed by vasodilation.
- Neutrophil infiltration: Kills bacteria.
Systemic (Acute-Phase):
- Protein production: Marks pathogens for antibody or cell-killing attack.
- Cytokine release: Activates immune cells.
- WBC production: Increased WBC count.
- Fever: Reduces bacterial activity.
- Serum transferrin: Binds iron, limiting bacterial growth.

Cellular Components of Innate Immunity

Origin: Hemopoietic stem cells in bone marrow differentiate into myeloid and lymphoid progenitors.
First Line of Defense: Neutrophils, monocytes (macrophages), and NK cells.

Neutrophils

Role: Phagocytosis and killing of pathogens following skin and mucus barrier traversal.
Motility: Circulate in blood or infiltrate infection sites.
Activation: Chemokines produced by inflammatory cells and pathogens.
Killing Mechanisms: Phagocytosis, toxic granule release (proteases, myeloperoxidase, ROS, lysozymes, cationic proteins), NET formation.
Short Half-Life: 10-12 hours (in vitro), ~1 day (in vivo).

Monocytes and Macrophages

Role: Phagocytosis, cytotoxicity, cytokine production.
Tissue-Specific Types: Microglia (brain), osteoclasts (bone), Kupffer cells (liver), alveolar macrophages (lungs), red pulp macrophages (spleen).
Pro-inflammatory and Pro-resolution: Involved in fighting infection, removing dead cells, and promoting tissue repair / anti-inflammatory response.
Killing Mechanisms: Phagocytosis, killing pathogens employing ROS (NADPH, peroxide, OHCL) and RNS (peroxynitrate).

Natural Killer (NK) Cells

Role: Detect altered self-cells (e.g., virally infected, cancerous).
Killing Mechanics: Release of perforin and granzymes inducing apoptosis (programming cell death).
Activation: IL-12 triggers by macrophages.
"Missing Self": Loss of MHC Class I expression on infected cells triggers NK activation.

Complement System

Definition: Plasma proteins that work together to enhance immune responses and target pathogens (opsonization, inflammation, pathogen lysis).
Activation Pathways: Classical (antibody-antigen complexes), MB-lectin, alternative (direct pathogen binding).
C3 Activation: A key trigger leading to inflammation, opsonization, and target cell lysis.
Membrane Attack Complex (MAC): Forms pores in target cell membranes, causing cell lysis.

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Description

Explore the essentials of innate immunity, which acts as the body's first line of defense against pathogens through rapid, non-specific mechanisms. Delve into the roles of physical and mechanical barriers, as well as the importance of commensal microbes in maintaining health.