OIA1010 COMPLEMENT SYSTEM

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30 Terms

1
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What is the complement system?

A part of the immune system comprising 30 soluble and membrane-bound proteins that act in innate and adaptive immunity.

2
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Where are complement proteins synthesized?

In the liver.

3
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How is the complement system activated?

By three pathways: classical, lectin, and alternative.

4
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What triggers the classical pathway?

Antigen-antibody complexes involving IgG or IgM.

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How is the lectin pathway activated?

By mannose-binding lectin (MBL) binding to terminal mannose residues on microbial surfaces.

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What activates the alternative pathway?

Direct contact with microbial surfaces and C3b deposition.

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What is the key enzyme in complement activation?

C3 convertase, which cleaves C3 into C3a and C3b.

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What is the function of C5 convertase?

It cleaves C5 into C5a and C5b, initiating the formation of the membrane attack complex (MAC).

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What is opsonization?

The process of marking pathogens for phagocytosis by binding opsonins like C3b.

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What are anaphylatoxins, and give examples.

Small peptides (C3a, C4a, and C5a) that induce inflammation and attract immune cells.

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What is the membrane attack complex (MAC)?

A structure formed by C5b, C6, C7, C8, and multiple C9 proteins that causes cell lysis.

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What are the initial components of the classical pathway?

C1 (C1q, C1r, C1s), C2, C3, and C4.

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Which immunoglobulin classes activate C1 in the classical pathway?

IgM and IgG (IgG3 > IgG1 > IgG2; IgG4 does not bind).

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What is the role of C4b2a in the classical pathway?

It functions as a C3 convertase.

15
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Which components are unique to the alternative pathway?

Factors B, D, and properdin (factor P).

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How does properdin stabilize the alternative pathway?

By binding to C3bBb, prolonging its activity.

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What is the amplification loop in the alternative pathway?

The continuous activation of C3 by C3bBb to generate more C3b.

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What activates the lectin pathway?

MBL binding to mannose residues on bacteria and fungi.

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What is MASP, and what is its role?

MBL-associated serine protease (MASP) cleaves C4 and C2 to form C3 convertase.

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How does complement enhance B cell responses?

By interacting with complement receptors on B cells to amplify antibody production.

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What is the role of complement in removing immune complexes?

It clears complexes from circulation to prevent tissue deposition and inflammation.

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How does complement aid in removing necrotic cells?

By tagging damaged cells for clearance by phagocytes.

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Why is complement regulation important?

To prevent uncontrolled activation and damage to host tissues.

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Name a regulatory protein of the complement system.

Decay-accelerating factor (DAF), which disrupts C3 convertase formation.

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What happens in complement deficiency?

Increased susceptibility to infections and autoimmune diseases like systemic lupus erythematosus (SLE).

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What diseases are associated with complement deficiencies?

Pyogenic infections, glomerulonephritis, and recurrent bacterial infections.

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What role does complement play in sepsis?

Overactivation can lead to excessive inflammation and tissue damage.

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What are the three main outcomes of complement activation?

Opsonization, inflammation, and pathogen lysis.

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What is the convergence point of all complement pathways?

The cleavage of C3 to form C3a and C3b.

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What is the final step of complement activation?

Formation of the membrane attack complex (MAC) leading to cell lysis.