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Related Concept Videos

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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A complementation test is a simple cross to identify whether the two mutations are located on the same gene or different genes. It was first performed by Edward Lewis in the 1940s while working on fruit flies. He developed the test to identify the location and arrangement of different mutations on chromosomes.
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The histone proteins have a flexible N-terminal tail extending out from the nucleosome. These histone tails are often subjected to post-translational modifications such as acetylation, methylation, phosphorylation, and ubiquitination. Particular combinations of these modifications form “histone codes” that influence the chromatin folding and tissue-specific gene expression.
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Related Experiment Video

Updated: Feb 10, 2026

Evaluation of the Interplay Between the Complement Protein C1q and Hyaluronic Acid in Promoting Cell Adhesion
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Evaluation of the Interplay Between the Complement Protein C1q and Hyaluronic Acid in Promoting Cell Adhesion

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Extracellular Histones Inhibit Complement Activation through Interacting with Complement Component 4.

Yasir Qaddoori1, Simon T Abrams1, Paul Mould2

  • 1Institute of Infection and Global Health, University of Liverpool, Liverpool L69 7BE, United Kingdom.

Journal of Immunology (Baltimore, Md. : 1950)
|May 13, 2018
PubMed
Summary
This summary is machine-generated.

Histones, released from damaged cells, inhibit complement activation by binding to C4b. This natural feedback mechanism prevents excessive host cell injury, primarily affecting classical and lectin pathways.

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Area of Science:

  • Immunology
  • Molecular Biology
  • Cellular Biology

Background:

  • Complement activation forms the membrane attack complex, potentially lysing host cells.
  • Histones released from damaged cells act as damage-associated molecular patterns, but their role in complement is unclear.

Purpose of the Study:

  • To investigate the effects of histones on the human complement system.
  • To identify specific complement proteins that interact with histones.

Main Methods:

  • Histone-conjugated beads were used to pull down proteins from human serum.
  • Mass spectrometry identified C-reactive protein and C4.
  • Surface plasmon resonance analyzed histone-complement protein interactions.
  • Complement activity assays assessed the impact of histones on classical, lectin, and alternative pathways.

Main Results:

  • Histones H3 and H4 strongly bound to C4 (KD ~1 nM), without affecting C4 cleavage.
  • Histone binding to C4b significantly inhibited C3 and C5 convertase activity.
  • Both classical and mannose-binding lectin pathways were dramatically inhibited by histones.
  • The alternative pathway was largely spared, but overall complement activity was reduced.
  • Histone-mediated inhibition could not be fully restored by excess C4, suggesting additional targets.

Conclusions:

  • Histones inhibit complement activation, likely through interaction with C4b and potentially other targets.
  • This histone-mediated inhibition acts as a natural feedback mechanism to prevent excessive host cell damage.
  • The findings highlight a novel role for histones in regulating innate immunity.