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Related Concept Videos

Complement System01:27

Complement System

The complement system is a group of approximately 20 plasma proteins that strengthen the body's defenses against infections through opsonization, inflammation, and cell lysis. Opsonization involves coating pathogens with complement proteins, making them more recognizable and facilitating phagocyte engulfment. Certain complement proteins induce inflammation that attracts immune cells to the site of infection. Cell lysis involves the destruction of pathogens through the formation of a membrane...
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The Extrinsic Apoptotic Pathway

The extrinsic apoptotic pathway is initiated when extracellular death-inducing signals, such as specific cytokines, activate the death receptors expressed on the cell surface. The immune cells involved in this pathway are natural killer cells (NK cells) and cytotoxic T-lymphocytes. NK cells are critical in innate immune response, while cytotoxic T-lymphocytes are associated with adaptive immune response. These cells recognize specific receptors expressed on the altered cells and activate...
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Anticoagulant Drugs: Vitamin K Antagonists and Direct Oral Anticoagulants

Oral anticoagulants are vital tools in preventing and treating blood clotting disorders. This diverse class of medications can be categorized as vitamin K antagonists, exemplified by warfarin, and direct thrombin inhibitors (DTIs), such as dabigatran, as well as factor Xa inhibitors, including rivaroxaban.
Warfarin, a prominent vitamin K antagonist family member, exerts its effect by inhibiting the enzyme VKORC1 (vitamin K epoxide reductase complex 1). By hindering this enzyme, warfarin...
Feedback Inhibition00:46

Feedback Inhibition

Biochemical reactions are occurring constantly in cells, converting starting substances to different products, usually with the help of enzymes that speed the reactions. Without enzymes, it would take far too long for most reactions to occur to be useful to the cell!
Extrinsic and Intrinsic Pathways of Hemostasis01:20

Extrinsic and Intrinsic Pathways of Hemostasis

Blood clotting or coagulation involves extrinsic and intrinsic pathways, which ultimately merge into the common pathway, forming a fibrin clot.
The Extrinsic Pathway
The extrinsic pathway of coagulation is typically initiated by tissue damage that exposes blood to tissue factor (TF), a protein released by the damaged tissue cells outside the blood vessels—this interaction with TF triggers biochemical reactions involving specific clotting factors. The key player here is Factor VII, which forms a...
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Antibody Actions

Antibodies, or immunoglobulins, are critical players in the immune system's arsenal against invading pathogens. Produced by B cells and plasma cells, their primary role is to detect and bind to specific antigens, molecules found on the surface of pathogens like bacteria or viruses. Beyond antigen recognition, antibodies perform several vital functions that contribute to immune defense.
Neutralization
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Related Experiment Video

Updated: May 24, 2026

Targeted Antibody Blocking by a Dual-Functional Conjugate of Antigenic Peptide and Fc-III Mimetics (DCAF)
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Targeted Antibody Blocking by a Dual-Functional Conjugate of Antigenic Peptide and Fc-III Mimetics (DCAF)

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Inhibiting alternative pathway complement activation by targeting the factor D exosite.

Kenneth J Katschke1, Ping Wu, Rajkumar Ganesan

  • 1Department of Immunology, Genentech Incorporated, South San Francisco, California 94080, USA.

The Journal of Biological Chemistry
|February 25, 2012
PubMed
Summary
This summary is machine-generated.

An anti-factor D Fab fragment (AFD) effectively inhibits the alternative complement pathway by blocking macromolecular substrate access, not catalytic activity. This provides a molecular basis for targeting inflammatory diseases like age-related macular degeneration.

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Methods for Quantitative Detection of Antibody-induced Complement Activation on Red Blood Cells
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Methods for Quantitative Detection of Antibody-induced Complement Activation on Red Blood Cells
06:29

Methods for Quantitative Detection of Antibody-induced Complement Activation on Red Blood Cells

Published on: January 29, 2014

Area of Science:

  • Immunology
  • Structural Biology
  • Drug Discovery

Background:

  • The alternative complement pathway amplifies inflammatory responses and is a therapeutic target.
  • Age-related macular degeneration involves complement system dysregulation.

Purpose of the Study:

  • To develop and characterize an anti-factor D Fab fragment (AFD) as a therapeutic agent.
  • To elucidate the molecular mechanism of AFD inhibition of factor D (FD).

Main Methods:

  • Generation of an anti-factor D Fab fragment (AFD).
  • Biochemical assays to assess FD proteolytic activity.
  • X-ray crystallography to determine the structure of AFD in complex with FD.

Main Results:

  • AFD potently inhibited FD-mediated activation of C3bB, a macromolecular substrate.
  • AFD did not inhibit FD's proteolysis of small synthetic substrates.
  • Crystal structures revealed AFD binds to FD exosites, blocking macromolecular substrate access.

Conclusions:

  • AFD inhibits FD by sterically hindering macromolecular substrate binding, not by blocking the catalytic site.
  • This mechanism provides a molecular basis for AFD's therapeutic potential in complement-mediated inflammatory diseases.