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Activation Pathways of the Complement System definitions

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  • Complement System
    A group of proteins in blood plasma that, when activated, enhance immune responses like inflammation, opsonization, and microbe lysis.
  • Alternative Pathway
    A route of complement activation initiated by C3b binding directly to microbial surfaces, independent of antibodies.
  • Lectin Pathway
    A complement activation route triggered by mannose-binding lectins recognizing mannose on microbial surfaces.
  • Classical Pathway
    A complement activation route initiated by antibodies binding to antigens on microbes, linking innate and adaptive immunity.
  • C3 Convertase
    An enzyme complex formed in all complement pathways that cleaves C3 into C3a and C3b, amplifying immune responses.
  • C3b
    A complement protein fragment that binds to microbes, promoting opsonization and further complement activation.
  • C3a
    A small peptide generated from C3 cleavage that promotes inflammation during immune responses.
  • Opsonization
    A process where microbes are marked for enhanced phagocytosis by immune cells, often via C3b binding.
  • Cell Lysis
    Destruction of microbial cells by membrane attack complexes formed during complement activation.
  • Inflammation
    A localized immune response characterized by redness, heat, and swelling, often triggered by complement fragments like C3a.
  • Mannose-Binding Lectin
    A pattern recognition protein that binds mannose residues on microbes, initiating the lectin pathway.
  • Antibody
    A Y-shaped protein produced by adaptive immunity that binds specifically to antigens on microbes.
  • Antigen
    A foreign molecule, often on microbes, that elicits an immune response and is recognized by antibodies.
  • Adaptive Immunity
    A specific immune defense system involving antibodies that can remember and target particular pathogens.