Immunology: The Complement System
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Questions and Answers

What is the main goal of complement activation?

The main goal of complement activation is to form a pore through the pathogen, which will eventually induce osmolarity lysis.

What are the three pathways of complement activation?

  • Classical Pathway, Alternative Pathway, Lysozyme Pathway
  • Classical Pathway, Lectinic Pathway, Lysozyme Pathway
  • Classical Pathway, Lectinic Pathway, Alternative Pathway (correct)
  • Classical Pathway, Classical Pathway, Alternative Pathway

    • The lectinic pathway is activated by microbial sugar or proteins.

    False

    Which of the following are not components of the complement system?

    <p>Calnexin</p> Signup and view all the answers

    How are complement components identified?

    <p>Complement components are identified by the letter &quot;C&quot; followed by a number, such as &quot;C1&quot;, &quot;C3&quot;, or &quot;C4&quot;.</p> Signup and view all the answers

    Complement activity is only present in the bloodstream.

    <p>False</p> Signup and view all the answers

    What is the most abundant enzyme of the complement system?

    <p>C3</p> Signup and view all the answers

    What does MAC stand for?

    <p>Membrane Attack Complex</p> Signup and view all the answers

    The alternative pathway is the most recently discovered pathway

    <p>False</p> Signup and view all the answers

    The main difference between the standard proteasome and the immunoproteasome is that the immunoproteasome specifically works on ubiquitinated proteins?

    <p>False</p> Signup and view all the answers

    What is the role of the invariant chain in MHC class II molecules?

    <p>The invariant chain fills and protects the pocket of the MHC class II complex, preventing it from binding to endogenous peptides and ensuring proper folding and stability of the molecule. It also functions in assembling HLA class II molecules (DP, DM, DO).</p> Signup and view all the answers

    The TCR binds to the MHC/peptide complex with very high specificity.

    <p>True</p> Signup and view all the answers

    Which molecule is responsible for transporting peptides from the proteasome intot the ER?

    <p>TAP1</p> Signup and view all the answers

    What is the MHC restriction?

    <p>MHC restriction means that T cells can only recognize antigens when presented by a specific MHC molecule.</p> Signup and view all the answers

    What are the four major pathways of antigen processing?

    <p>The four major pathways of antigen processing include: 1. exogenous pathway, 2. endogenous pathway, 3. autophagy, and 4. cross-presentation.</p> Signup and view all the answers

    The MHC affinity refers specifically to the strength of the interaction between a TCR and the MHC/peptide complex.

    <p>False</p> Signup and view all the answers

    How are the gamma-delta T cells different from alpha-beta T cells?

    <p>Gamma-delta T cells typically recognize lipid antigens through CD1 molecules, whereas alpha-beta T cells recognize protein antigens presented by MHC class I or II molecules. Gamma-delta T cells are also less abundant than alpha-beta T cells, but they express an invariant TCR and are more prevalent at mucosal surfaces.</p> Signup and view all the answers

    What is the major difference between the MHC class II molecules and DM/DO molecules?

    <p>DM/DO molecules do not form the groove that MHC class II molecules do, so they are not expressed on the cell surface. Their function is to help MHC class II molecules fold properly and transport them to the cell surface.</p> Signup and view all the answers

    The invariant chain is only found in association with MHC class II molecules.

    <p>True</p> Signup and view all the answers

    What class of MHC molecule presents endogenous antigens?

    <p>MHC Class I</p> Signup and view all the answers

    What is the role of autophagy in antigen processing?

    <p>Autophagy allows the presentation of endogenous proteins that are not normally processed by standard proteasomes. This process contributes to the immune response to pathogens and other internal threats.</p> Signup and view all the answers

    Cross-presentation is a process that allows dendritic cells to present exogenous antigens on MHC class II molecules.

    <p>False</p> Signup and view all the answers

    Which of the following cell types is NOT a professional APC?

    <p>Neutrophils</p> Signup and view all the answers

    The MHC polymorphism is involved in the susceptibility to certain autoimmune diseases.

    <p>True</p> Signup and view all the answers

    MHC class I alleles are more polymorphic than MHC class II alleles.

    <p>False</p> Signup and view all the answers

    The HLA genes are responsible for our immune system's specific response to various pathogens.

    <p>True</p> Signup and view all the answers

    Which molecule acts as the bridging factor between MHC class II molecules and the phagosome?

    <p>DM</p> Signup and view all the answers

    What does the term "MHC restriction" refer to?

    <p>MHC restriction refers to the requirement that T cells must recognize an antigen in association with a specific MHC molecule.</p> Signup and view all the answers

    Study Notes

    The Complement System

    • First identified in the early 1900s by Jules Bordet
    • Bordet observed animal serum could kill bacteria
    • Heating serum reduced effectiveness, but mixing old and fresh serum restored the killing ability
    • Serum contained complement proteins that aided fresh serum
    • Complement system consists of over 30 proteins (proteases) in bodily fluids
    • Activates via three pathways
      • Classical pathway: triggered by conformational change of IgM and IgG (first described)
      • Lectinic pathway: triggered by microbial sugars or viral proteins
      • Alternative pathway: triggered by spontaneous cleavage of C3

    Classical Pathway

    • C1q is the protagonist, especially
    • Requires two antibodies to bind
    • C1q binds antibodies
    • This activates C1r and C1s, which activate C4
    • C4 cleaves into C4b (binds to pathogen) and C4a (released)
    • C2 cleaves into C2a (binds to C4b) and C2b (released)
    • This complex (C4b2a) creates a C3 convertase
    • C3 convertase cleaves C3 into C3b (binds to complex) and C3a (released)
    • Forms C5 convertase (C4b2a3b). This further cleaves C5.

    Complement system activation

    • Cascade reaction: Each activated protein cleaves and activates the next inactive protease.
    • Short-lived, but limited by Complement Control Proteins
    • Activated complement components form two parts:
      • One part attaches to the cell surface (bacteria or infected cell) becoming the active protease
      • Other part released and triggers inflammation.
    • Components labelled by letter C + number (e.g., C1, C3, C4). The numerical order is not necessarily the order of activation.

    The goals of complement activation

    • Create a pore in the pathogen to induce cell lysis
    • Induce inflammation.

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    Description

    Explore the intricate details of the complement system, including its components and pathways of activation. Learn about the classical, lectinic, and alternative pathways, as well as the roles of crucial proteins like C1q and C3 convertase. Test your knowledge on how these processes contribute to the immune response.

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