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Related Concept Videos

Antibody Structure01:10

Antibody Structure

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Overview
Antibodies, also known as immunoglobulins (Ig), are essential players of the adaptive immune system. These antigen-binding proteins are produced by B cells and make up 20 percent of the total blood plasma by weight. In mammals, antibodies fall into five different classes, which each elicits a different biological response upon antigen binding.
The Y-Shaped Structure of Antibodies Consists of Four Polypeptide Chains
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Antibody Actions01:26

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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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Antibody Structure and Classes01:25

Antibody Structure and Classes

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Antibodies, also known as immunoglobulins, are produced by B cells in response to foreign substances, such as bacteria and viruses. These proteins are critical for recognizing and neutralizing these substances, protecting the body from potential harm.
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Complement System01:27

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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...
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Immunoglobulin-like Cell Adhesion Molecules

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Immunoglobulin-like cell adhesion molecules or Ig-CAMs are a versatile group of cell surface glycoproteins belonging to the immunoglobulin protein superfamily. Ig-CAMs possess the characteristic immunoglobulin protein domains and other domains such as the fibronectin type III domain. The Ig domains are glycosylated to varying degrees in different Ig-CAMs.
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Antigens Involved in Adaptive Immunity01:26

Antigens Involved in Adaptive Immunity

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An antigen is any substance the immune system identifies as foreign and potentially harmful to the body, prompting an immune response. Antigens have two functional properties: immunogenicity and reactivity. Immunogenicity is the ability of an antigen to stimulate a specific immune response. At the same time, reactivity describes the antigen's ability to react with the cells and antibodies produced in response to it.
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Methods for Quantitative Detection of Antibody-induced Complement Activation on Red Blood Cells
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Complement activation by IgG subclasses is governed by their ability to oligomerize upon antigen binding.

Nikolaus Frischauf1, Jürgen Strasser1, Ellen G F Borg2

  • 1Medical Engineering, Nano Structuring and Bio-Analytics, University of Applied Sciences Upper Austria, Linz 4020, Austria.

Proceedings of the National Academy of Sciences of the United States of America
|October 22, 2024
PubMed
Summary

Different IgG antibody subclasses activate complement by forming distinct IgG oligomers on antigen surfaces. This oligomerization ability, not just hinge flexibility, dictates complement C1 activation, crucial for immunotherapy.

Keywords:
C1Fc–Fc interactionsIgG oligomerizationIgG subclassesclassical complement pathway

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Area of Science:

  • Immunology
  • Biophysics
  • Structural Biology

Background:

  • Complement activation by antibody-antigen complexes is vital in immunity and antibody-based therapies.
  • Previous understanding attributed IgG subclass-mediated complement activation to hinge flexibility and C1 affinity.
  • A unified mechanism explaining how IgG subclasses modulate complement activation was lacking.

Purpose of the Study:

  • To elucidate the unifying mechanism behind differential complement activation by IgG subclasses.
  • To investigate the role of IgG oligomerization on antigenic surfaces in C1 activation.
  • To develop a mechanistic model for C1 binding to IgG oligomers.

Main Methods:

  • High-speed atomic force microscopy to visualize IgG oligomer structures.
  • Quartz crystal microbalance experiments to quantify complement recruitment efficiency.
  • Tumor cell lines and vesicle-based assays to assess complement activation and lysis.

Main Results:

  • Complement activation efficacy is determined by the ability of IgG subclasses to form C1-activating oligomers on surfaces.
  • Direct visualization revealed distinct IgG oligomer structures and distributions.
  • A mechanistic model accurately described C1 binding to IgG oligomers, enabling kinetic and equilibrium dissociation constant calculations.

Conclusions:

  • IgG subclass-dependent complement activation is governed by their varying capacity to form multivalent IgG oligomers on antigenic surfaces.
  • This oligomerization-driven mechanism provides a comprehensive understanding of complement activation by IgG subclasses.
  • Findings can inform the rational design of antibody-based immunotherapies.