Innate and Adaptive Immunity Quiz

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Questions and Answers

What is the primary function of the complement system?

  • To directly kill all bacteria
  • To identify and destroy viruses
  • To activate mast cells and induce inflammation (correct)
  • To inhibit the formation of immune complexes

Which of these is NOT a function of the complement system?

  • Directly killing viruses (correct)
  • Promotion of inflammation
  • Solubilization of immune complexes
  • Lysis of target cells

What is the mechanism by which the complement system leads to cell lysis?

  • Directly binding to and neutralizing the cell's DNA
  • Induction of apoptosis by releasing cytotoxic enzymes
  • Formation of the Membrane Attack Complex (MAC) (correct)
  • Direct enzymatic degradation of the cell membrane

What is the role of the complement system in immune complex solubilization?

<p>Binding to the Fc region of antibodies in the complex (D)</p> Signup and view all the answers

Which of the following is NOT a complement fragment known to induce inflammation?

<p>C6a (A)</p> Signup and view all the answers

Why is complement-mediated lysis not effective against all bacteria?

<p>Some bacteria have thick cell walls that protect them from MAC insertion (A)</p> Signup and view all the answers

Which of these bacterial genera is known to be susceptible to complement-mediated lysis?

<p>Neisseria (C)</p> Signup and view all the answers

What is the term used to describe the complement fragments C3a and C5a due to their ability to trigger mast cell degranulation?

<p>Anaphylatoxins (D)</p> Signup and view all the answers

What is the likely reason why complement-mediated lysis is considered a "classical pathway"?

<p>This pathway only requires antibody binding to initiate (A)</p> Signup and view all the answers

Why is it crucial for immune complexes to be properly cleared?

<p>They can cause inflammation and endothelial damage (C)</p> Signup and view all the answers

What is primarily responsible for the significant drop in C3 levels in serum?

<p>Increased consumption of C3 due to lack of regulation by Factor I (C)</p> Signup and view all the answers

What role does CR1 play in the complement system?

<p>It helps break down C3 convertases (A)</p> Signup and view all the answers

Which of the following is a result of deficiencies in the classical pathway components?

<p>Accumulation of immune complexes (A)</p> Signup and view all the answers

What triggers the production of auto-antibodies in patients with lupus?

<p>Presence of auto-reactive B and T cells targeting circulating DNA (A)</p> Signup and view all the answers

What is the main consequence of insufficient regulation by complement receptors in the complement system?

<p>Excessive complement activation (D)</p> Signup and view all the answers

Which of the following statements is TRUE regarding the classical pathway of the complement system?

<p>It relies on antibodies, which are a component of the adaptive immune system. (B)</p> Signup and view all the answers

What is the primary role of C5 convertase in the complement pathway?

<p>To cleave C5 into C5a and C5b (B)</p> Signup and view all the answers

Which of the following proteins is a serine protease involved in the classical pathway of the complement system?

<p>C1r (B)</p> Signup and view all the answers

What process occurs due to the action of C9 in the complement pathway?

<p>Osmotic lysis of the target cell (A)</p> Signup and view all the answers

What is the function of C4b, a cleavage product of C4, in the classical pathway of the complement system?

<p>It binds to the pathogen surface, marking it for destruction. (C)</p> Signup and view all the answers

Which of the following is NOT a characteristic of the classical pathway of the complement system?

<p>It is activated directly by the presence of pathogens. (C)</p> Signup and view all the answers

What leads to the formation of C5 convertase from C3 convertases?

<p>Binding of additional C3b to C3 convertases (C)</p> Signup and view all the answers

Which proteins are recruited in sequence after C5 is cleaved by C5 convertase?

<p>C6, C7, C8 (D)</p> Signup and view all the answers

Which complement protein is a key component, crucial for activation and function, in all three complement pathways?

<p>C3 (A)</p> Signup and view all the answers

Why does the classical pathway of the complement system require multiple IgG molecules to bind to a pathogen to initiate the pathway?

<p>Multiple IgG molecules provide stronger binding to the pathogen surface. (D)</p> Signup and view all the answers

How do complement proteins differ from the actions of perforins used by immune cells?

<p>Complement proteins form membrane attack complexes while perforins do not (D)</p> Signup and view all the answers

What is the primary function of the complement system, as mentioned in the text?

<p>It helps to defend the body against pathogens. (D)</p> Signup and view all the answers

What is the final outcome of the complement activation cascade involving C9?

<p>Cell membrane disruption (B)</p> Signup and view all the answers

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

<p>C3a, C5b, C6, C7, C8, C9 (B)</p> Signup and view all the answers

Which statement illustrates the effect of C3 convertases in complement activation?

<p>They cleave C3 into C3b and C3a (A)</p> Signup and view all the answers

What is the distinction between apoptosis and osmotic lysis in the context of complement activation?

<p>Apoptosis involves programmed cell death, while osmotic lysis leads to bursting (A)</p> Signup and view all the answers

Which description best fits the function of complement proteins in immune response?

<p>They enhance phagocytosis and directly lyse pathogens (B)</p> Signup and view all the answers

What is the role of the lectin pathway in the immune response?

<p>It activates the complement cascade, leading to the lysis of pathogens. (A)</p> Signup and view all the answers

What distinguishes the lectin pathway from the classical pathway?

<p>The lectin pathway is triggered by the presence of mannose residues on pathogen surfaces. (D)</p> Signup and view all the answers

Which of the following molecules is involved in the initiation of the lectin pathway?

<p>MBL (B)</p> Signup and view all the answers

Which pair of proteins in the lectin pathway are functionally similar to C1r and C1s in the classical pathway?

<p>MASP-1 and MASP-2 (D)</p> Signup and view all the answers

What is the primary outcome of the formation of the C3 convertase in both the lectin and classical pathways?

<p>Activation of the complement cascade. (A)</p> Signup and view all the answers

How does the complement pathway differentiate between soluble antibodies and antibodies bound to a pathogen?

<p>Bound antibodies are more likely to be in close proximity to each other compared to soluble antibodies. (A)</p> Signup and view all the answers

What happens when C3 is cleaved in the complement cascade?

<p>It forms C3b, which can attach to the pathogen surface or bind to C3 convertase. (B)</p> Signup and view all the answers

What is the function of the C1 complex in the classical pathway?

<p>It recognizes and attaches to the Fc regions exposed on antibodies bound to pathogens. (D)</p> Signup and view all the answers

Which of the following is NOT involved in the activation of the lectin pathway?

<p>C1q (B)</p> Signup and view all the answers

Flashcards

Complement Regulation

Prevents continuous activation and inflammation of complement proteins.

Classical Pathway

The first discovered pathway of the complement system, dependent on antibodies.

C1 Complex

A multimeric protein made of C1q, C1r, and C1s initiating the classical pathway.

C1q Function

Binds to Fc portions of IgG or IgM antibodies on pathogens to start activation.

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C3 Convertase

An enzyme formed by C4b and C2a that cleaves C3, crucial in all pathways.

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C4 Role

Recruited by C1 complex, cleaved into C4b which binds to pathogens, and C4a which promotes inflammation.

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IgG and IgM

Antibodies that must bind to pathogens to initiate the classical pathway.

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C3 cleavage

The process where C3 is cleaved to produce C3b, which can attach to pathogens.

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Classical pathway initiation

The process starts when antibodies bind to pathogens and allow C1 complex to attach.

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Role of C1 complex

The C1 complex recognizes and attaches to exposed Fc regions on antibodies bound to pathogens.

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Lectin pathway trigger

Initiated by plasma lectins like mannose-binding lectin, which recognize carbohydrates on pathogens.

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Mannose-binding lectin (MBL)

A collectin that binds to mannose residues on pathogens, starting the lectin pathway.

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MASP-1 and MASP-2

Proteases that activate upon MBL binding to a pathogen, similar to C1r and C1s in the classical pathway.

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C4 and C2 cleavage

C4 is cleaved into C4a and C4b, and C2 into C2a and C2b in both classical and lectin pathways.

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C3 amplification process

The cleaving of C3 by C3 convertase increases the effectiveness of the complement system.

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Factor I Role

Regulates C3 levels by preventing excessive consumption of C3.

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C3 Deficiency Effects

Leads to increased susceptibility to infections due to low C3 levels.

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Complement Receptors

Mediators that regulate complement activity, such as CR1 breaking down C3 convertases.

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Autoimmune Diseases from Deficiency

Deficiencies in classical pathway components lead to autoimmune diseases like lupus.

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Pathogenesis of Lupus

Caused by auto-reactive B and T cells producing auto-antibodies against DNA.

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C3bBbC3b

C5 convertase in the alternative pathway composed of C3b and Bb.

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C4bC2aC3b

C5 convertase in the classical and lectin pathways formed by C4b, C2a, and C3b.

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Membrane Attack Complex (MAC)

A complex that disrupts target cell membranes, leading to cell lysis.

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C9 Role in MAC

C9 forms a pore in the target cell's membrane for lysis.

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Apoptosis vs Osmotic Lysis

Apoptosis is programmed cell death; lysis causes cells to burst from water influx.

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Natural Killer Cells (NK Cells)

Immune cells that use perforins to create pores in target cells during immune response.

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Complement Activation

A series of reactions that enhance the ability of antibodies to clear pathogens.

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Role of C6, C7, and C8

Proteins recruited after C5 cleavage, but not cleaved themselves.

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MAC (Membrane Attack Complex)

A structure that forms on pathogen membranes to induce lysis.

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Bacterial Resistance to Complement

Some bacteria develop capsules to avoid MAC-mediated lysis.

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Anaphylatoxins

Proteins (C5a, C3a) that induce inflammation and activate immune response.

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C5a

A potent anaphylatoxin that attracts immune cells to inflammation sites.

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C3a

Another anaphylatoxin that promotes inflammation and activates mast cells.

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Immune Complex Solubilization

Process where complement helps clear large antigen-antibody complexes.

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Endothelial Damage

Damage to blood vessel linings caused by immune complexes deposition.

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Neisseria Vulnerability

Pathogens with thin walls that are particularly susceptible to MAC lysis.

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Mast Cell Degranulation

Release of histamines by mast cells in response to complement activation.

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Recall Immunization

A vaccination process that reintroduces an antigen leading to immune complex formation.

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Study Notes

Innate Immunity

  • The immune system has two components: innate and adaptive.
  • Innate immunity acts as the body's first line of defense.
  • It activates quickly, triggers the adaptive response when needed.
  • Innate immunity includes physical barriers (skin, mucosal layers), low pH, saliva enzymes.
  • These barriers create an inhospitable environment for microbes.

Adaptive Immunity

  • The immune response is adaptive, and relies on innate immunity.
  • It helps to enhance innate response.

Complement System

  • The complement system is a factor mechanism of the immune response.
  • It's a group of proteins in the serum supporting antibody functions.
  • Enables effective bacterial killing.
  • Complement proteins are non-specific, present in the serum regardless of immunization.

Discovery of Complement System

  • Jules Bordet and others experimented with bacterial lysis in the late 18th century.
  • They suspected that certain molecules could lyse pathogens.
  • These molecules were later called antibodies.
  • Bordet's experiments showed that immunized serum contained molecules targeting specific pathogens.
  • Heat treatment of immune serum prevented bacterial lysis, suggesting a heat-sensitive component.

Complement Effector Functions

  • Antibodies bind to antigens on pathogens.
  • They neutralize pathogens by blocking interactions with host cells.
  • Opsonization: Antibodies coat a pathogen, marking it for phagocytosis by other immune cells.
  • Complement system also activates in response to pathogens independently of antibodies.

Complement activation pathways

  • Classical pathway: initiated by antibodies binding to pathogens, activating a cascade of complement proteins.
  • Lectin pathway: Initiated by lectins binding to carbohydrates on pathogen surfaces, initiating a cascade.
  • Alternative pathway : initiated by spontaneous activation of C3, and then further activation by the pathogen surface.

Complement Receptors

  • Complement receptors (CRs) facilitate phagocytosis of pathogens and clearance of immune complexes.
  • These receptors bind to complement proteins.
  • There are multiple types of complement receptors, each with specific functions & distribution.

Complement Regulation

  • Complement activation is tightly regulated by regulatory proteins to prevent excessive activation.
  • These regulatory proteins are often present on host cells and absent on microbes.
  • The absence of these regulators can lead to damage of host cells and can result in pathologies.

Complement and Disease

  • Deficiencies in complement components can lead to immune complex diseases and susceptibility to infections.
  • Lupus is associated with deficiencies in complement related pathways.
  • Complement can play a role in autoimmune diseases, infections, and certain cancers.

Complement and Cancer

  • Complement can have pro-tumoral effects (excessive inflammation) or be therapeutic (targeting cancer cells).

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The Complement System PDF

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