Innate Immune System Overview
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Questions and Answers

What role does Mannose Binding Lectin (MBL) play in the innate immune system?

MBL targets and activates the complement system at the surface of microbes.

How does the classical complement pathway typically get activated?

The classical pathway is activated by the binding of antibodies to antigens on pathogens.

Describe one primary function of acute phase proteins in innate immunity.

Acute phase proteins like CRP facilitate the recognition and clearance of pathogens.

What is a key feature of innate immunity regarding its response time and memory?

<p>Innate immunity is always present and provides a rapid response without generating memory.</p> Signup and view all the answers

What initiates the alternative pathway of complement activation?

<p>The alternative pathway is activated by the spontaneous hydrolysis of C3 in the absence of antibodies.</p> Signup and view all the answers

What is the overall purpose of the complement system in innate immunity?

<p>The complement system aids in opsonization, attracting immune cells, and promoting pathogen lysis.</p> Signup and view all the answers

Explain the significance of neutrophils in the immune response.

<p>Neutrophils are crucial for quickly responding to infections and clearing pathogens through phagocytosis.</p> Signup and view all the answers

What does the term 'PAMPs' refer to in the context of innate immunity?

<p>PAMPs are pathogen-associated molecular patterns recognized by pattern recognition receptors (PRRs).</p> Signup and view all the answers

What is the primary function of Pattern Recognition Receptors (PRRs) in the innate immune system?

<p>PRRs detect Pathogen-Associated Molecular Patterns (PAMPs) that are unique to microbes, allowing for the identification of various pathogens.</p> Signup and view all the answers

How do Toll-like receptors (TLRs) differ in their mechanisms of recognizing pathogens?

<p>Different TLRs are designated to recognize specific components of pathogens, like TLR4 for lipopolysaccharides in Gram-negative bacteria and TLR3 for viral RNA.</p> Signup and view all the answers

What role do C-type lectin receptors (CLRs) play in the immune response?

<p>CLRs primarily recognize carbohydrate components of fungi, bacteria, and parasites, which aids in pathogen detection and immune activation.</p> Signup and view all the answers

Can you explain what Acute Phase Response (APR) involves in the context of innate immunity?

<p>The Acute Phase Response involves the rapid production of proteins and cytokines by the liver in response to infection or inflammation, enhancing immune fighting capacity.</p> Signup and view all the answers

What distinguishes the Alternative Pathway from the Classical Pathway in the complement system?

<p>The Alternative Pathway is activated spontaneously on pathogen surfaces, while the Classical Pathway requires the presence of antibodies bound to pathogens for activation.</p> Signup and view all the answers

Identify one specific example of a pathogen recognized by a TLR and its corresponding PAMP.

<p>TLR5 recognizes flagellin, a PAMP present in the flagella of motile bacteria.</p> Signup and view all the answers

Describe the role of RIG-1 like receptors (RLRs) in responding to infections.

<p>RLRs detect viral RNA in the cytosol and initiate antiviral responses, including the production of interferons.</p> Signup and view all the answers

How do NOD-like receptors (NLRs) function in the immune system?

<p>NLRs reside in the cytosol and detect intracellular pathogens and stress signals, triggering immune responses such as inflammation.</p> Signup and view all the answers

What is one of the major outcomes of recognizing PAMPs through PRRs in immune cells?

<p>The recognition of PAMPs leads to the activation of signaling pathways that promote the production of pro-inflammatory cytokines.</p> Signup and view all the answers

In what way do PRRs contribute to the adaptive immune response?

<p>PRRs enhance the adaptive immune response by informing and activating other immune cells, bridging innate and adaptive immunity.</p> Signup and view all the answers

What initiator molecules are involved in the Lectin Pathway of complement activation?

<p>Mannose Binding Lectin (MBL) serves as the initiator molecule in the Lectin Pathway.</p> Signup and view all the answers

Describe the role of C-reactive protein (CRP) in the Classical Pathway.

<p>CRP acts as an initiator molecule by binding to specific antigens on microbes, triggering the Classical Pathway of the complement system.</p> Signup and view all the answers

How does the Alternative Pathway differ from the Lectin and Classical Pathways?

<p>The Alternative Pathway can be activated spontaneously in the presence of pathogens without the need for antibodies.</p> Signup and view all the answers

What is the significance of the acute phase response proteins produced by the liver?

<p>Acute phase response proteins, such as MBL and CRP, help amplify the immune response and target pathogens for destruction.</p> Signup and view all the answers

What role do C3 convertases play in the complement system?

<p>C3 convertases activate the complement cascade by cleaving C3 into C3a and C3b, amplifying the immune response.</p> Signup and view all the answers

Explain the process of opsonization in the context of the complement system.

<p>Opsonization involves complement proteins, such as C3b, binding to the surface of pathogens, aiding in their recognition and ingestion by phagocytes.</p> Signup and view all the answers

What triggers the production of inflammatory cytokines leading to the acute phase response?

<p>Infection and tissue injury trigger the secretion of inflammatory cytokines such as IL-1 and IL-6.</p> Signup and view all the answers

Describe how C5 convertases function within the complement system.

<p>C5 convertases activate C5, leading to the formation of C5a and C5b, which are crucial for inflammation and membrane attack complex formation.</p> Signup and view all the answers

What are the key effector functions of the complement system once activated?

<p>The key effector functions include opsonization, lysis of pathogens, and inflammation.</p> Signup and view all the answers

How do neutrophils and macrophages recognize complement-coated pathogens?

<p>Neutrophils and macrophages express complement receptors (CR's) that specifically bind to complement proteins on pathogen surfaces.</p> Signup and view all the answers

What components are involved in the formation of the membrane attack complex (MAC)?

<p>The MAC is formed by C5b, C6, C7, C8, and multiple C9 proteins which create a pore in the pathogen's membrane.</p> Signup and view all the answers

Identify the three initial pathways of complement activation.

<p>The three pathways are the Lectin Pathway, Classical Pathway, and Alternative Pathway.</p> Signup and view all the answers

How does the complement system contribute to inflammation during an immune response?

<p>The complement system releases effector molecules like C3a and C5a, which promote vasodilation and attract immune cells to the site of infection.</p> Signup and view all the answers

What is the significance of the rapid amplification of the immune response through the complement system?

<p>The rapid amplification ensures an efficient and effective response against invading pathogens, enhancing protection.</p> Signup and view all the answers

Study Notes

Innate Immune System

  • The innate immune system is a crucial part of the body's defense mechanism, acting as the first line of defense against pathogens.
  • It has three lines of defense. The first line of defense occurs outside the body, and the second line within the body.
  • The body contains approximately 10 to the 14th power cells.
  • It is colonized by approximately 10 to the 15th power bacteria.
  • About 90% of the cells in or on the body are not the body's own cells.
  • Mechanical, chemical, and biologic barriers are crucial components of the first line of defense.
  • The second line within the body is primarily made up of the innate immune system.
  • The adaptive immune system is the third line of defense.
  • It effectively removes most pathogens.

Innate Immune System Components

  • The innate immune system comprises humoral and cellular components.
  • Humoral components are plasma proteins involved in various immune responses.
  • Cellular components are immune cells, like white blood cells.
    • Lymphocytes (T cells, B cells, NK cells)
    • Granulocytes (eosinophils, basophils, neutrophils)
    • Monocytes (macrophages, dendritic cells, mast cells)
  • Tissue cells and sentinel cells are crucial too.
    • Sentinel cells include macrophages, mast cells, and dendritic cells.

Pathogen Recognition

  • Cells of the innate immune system need to differentiate between self and pathogens (non-self).
  • Pathogens vary in size.
  • Bacteria: 0.2-20μm
  • Viruses: 20-800nm
  • Protozoa: 10-200μm
  • Worms: 1cm-3m
  • Flukes: 2µm - cm
  • Fungi: 2µm - cm
  • Potential pathogen molecular patterns (antigens) can range from 10¹² to 10¹⁵.
  • Pathogen-Associated Molecular Patterns (PAMPs): Common microbial components on pathogens, unique structures absent in humans.
    • Examples include LPS, LTA, peptidoglycan, flagellin, and viral RNA/DNA.
    • PAMPS are unique structures present on pathogens but not on human cells.

Pattern Recognition Receptors (PRRs)

  • PRRs are receptors expressed on innate immune cells, evolved over time and encoded in DNA.
  • They recognize and bind to PAMPS
  • PRRs are expressed on plasma membranes of innate immune cells (e.g., macrophages, dendritic cells, neutrophils)
  • They can be found in cellular compartments like cytosol, endosomes, and lysosomes.
  • PRRs can detect both extracellular and intracellular PAMPS.
  • Each PRR type can recognize multiple pathogenic species sharing a common molecular pattern (e.g., LPS or flagellin).

Types of PRRs

  • Toll-like receptors (TLRs) recognize bacteria, viruses, and protists.
  • C-type lectin receptors (CLRs) recognize fungi.
  • Nucleotide-binding oligomerization domain-like receptors (NLRs) detect intracellular bacterial invasion and stress signals.
  • RIG-I-like receptors (RLRs) are soluble PRRs found in the cytosol and recognize viruses.
  • CLRs recognize carbohydrate components of pathogens.

Inflammatory Response

  • PAMPs trigger TLRs and other PRRs.
  • This signaling elicits an inflammatory response.
  • Cytokines (IL-1β, TNF-α, IL-6, IL-12) and chemokines (e.g., CXCL8) are released.
  • The inflammatory response causes various symptoms like swelling, redness, heat, and pain.

Adaptive Immunity Role

  • A set of PRR responses to pathogens(PAMPs) to initiate an innate immune response.
  • This response prevents initial infection, spreads infection, recruits effector cells, and alerts and mobilizes B & T cells.

Complement System

  • Complement system = a part of the innate immune system
  • Consists of over 30 proteins; contributes 3g/L of serum protein
  • Three initial pathways: Lectin, Classical, and Alternative. Initiated by various molecules, including mannose-binding lectin (MBL), antibodies, and C3b
  • C3 convertase formation leads to a massive amplification of the response.
  • C5 convertases are also formed, leading to the production of opsonins and the membrane attack complex (MAC).
  • MAC formation results in cell lysis.

Damage-Associated Molecular Patterns (DAMPs)

  • Released by damaged/dying cells
  • Activate PRRs leading to inflammation
  • Examples include: DNA, RNA, ATP, histone proteins, uric acid, heat shock proteins

Natural Killer (NK) Cells

  • A crucial component of the innate immune system.
  • They distinguish between normal and virus-infected or transformed cells.
  • They express both inhibitory and activating receptors.
  • Recognize MHC class I on normal cells
  • Activating signals prevail if the inhibitory signal is reduced or absent.
  • Kill virus-infected or transformed cells by releasing granule contents
    • including Perforin / Granzymes (Granule exocytosis pathway)
    • and / or Fas Pathway

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Recognition of Pathogens I&I L2 PDF

Description

Explore the innate immune system, the body's first line of defense against pathogens. Learn about its components, including humoral and cellular elements, and the three lines of defense. This quiz will test your understanding of how the innate immune system protects against disease.

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