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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...
T Cell Activation and Clonal Selection01:22

T Cell Activation and Clonal Selection

T cells are integral to our adaptive immune system, recognizing and effectively responding to foreign antigens. T cell activation and clonal selection are pivotal in orchestrating this immune response. This article elucidates these mechanisms, detailing the roles of cluster of differentiation (CD) markers, major histocompatibility complex (MHC) molecules, costimulatory signals, and the process of clonal selection.
Naive T cells that have not yet encountered an antigen express two primary CD...
Inflammatory Response01:28

Inflammatory Response

An inflammatory response is a localized, nonspecific immune reaction that occurs when a tissue is injured. It is characterized by redness, swelling, heat, and pain, which are commonly called the cardinal signs and symptoms of inflammation. Inflammation can sometimes result in a loss of function.
Inflammation can be triggered by various stimuli, such as impact, abrasion, chemical irritation, infections, and extreme hot or cold temperatures. These can damage cells and connective tissue fibers,...
Interactions Between Signaling Pathways01:19

Interactions Between Signaling Pathways

Signaling cascades usually lack linearity. Multiple pathways interact and regulate one another, allowing cells to integrate and respond to diverse environmental stimuli.
Convergence and divergence, and cross-talk between signaling pathways
Two distinct signaling pathways can converge on a single functional unit, which may either be a single protein or a complex of proteins. The response is either functionally distinct or synergistic between the two pathways but different from the response...
B Cell Activation and Differentiation01:24

B Cell Activation and Differentiation

The adaptive immune response, a sophisticated defense mechanism, relies on the activation and differentiation of B lymphocytes, or B cells. These processes enable our bodies to mount a tailored response against specific pathogens such as bacteria, free virus particles, toxins, and parasites.
When naive B cells encounter a specific antigen that can bind to the B cell receptor (BCR) on their surface, they undergo sensitization to respond to the antigen's presence. Sensitization begins with...
Cell Signaling Feedback Loops01:07

Cell Signaling Feedback Loops

Positive and negative feedback loops are crucial for regulating biological signaling systems. These feedback loops are processes that connect output signals to their inputs.
Negative feedback loops
Most signaling systems have negative feedback loops that can perform different functions such as output limiter, and adaptation.
Output limiter
Upon receiving an input signal, the cellular response rapidly increases until a threshold is reached. Beyond this threshold, a negative feedback loop...

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Related Experiment Video

Updated: Jun 26, 2026

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

Complement activation and inhibition: a delicate balance.

A P Sjöberg1, L A Trouw, A M Blom

  • 1University of Copenhagen, Department of Cellular and Molecular Medicine, Faculty of Health Sciences, DK-2200, Copenhagen, Denmark.

Trends in Immunology
|January 16, 2009
PubMed
Summary
This summary is machine-generated.

The complement system

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Last Updated: Jun 26, 2026

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

Published on: January 29, 2014

Measuring the 50% Haemolytic Complement (CH50) Activity of Serum
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Published on: March 29, 2010

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Co-immunoprecipitation Assay for Studying Functional Interactions Between Receptors and Enzymes

Published on: September 28, 2018

Area of Science:

  • Immunology
  • Innate immunity
  • Complement system biology

Background:

  • The complement system is crucial for innate immune defense, identifying microbes and host molecules for clearance.
  • Proper regulation of complement-mediated opsonisation is essential to prevent immune system pathology.
  • Dysregulation of complement on endogenous ligands is linked to various diseases.

Purpose of the Study:

  • To investigate the differential binding of complement regulators to C1q when interacting with endogenous ligands versus immune complexes.
  • To elucidate the mechanisms underlying complement dysregulation in disease pathogenesis.

Main Methods:

  • The study focuses on the interactions between C1q, complement inhibitors (factor H, C4b-binding protein), and various ligands including endogenous molecules and immune complexes.
  • Comparative analysis of binding affinities and downstream complement activation pathways.

Main Results:

  • C1q binds to both endogenous ligands and immune complexes.
  • Complement inhibitors C4b-binding protein and factor H bind to C1q when it is engaged with endogenous ligands.
  • In contrast, inhibitors do not bind C1q when it is complexed with immune complexes, leading to full complement activation.

Conclusions:

  • The differential regulation of complement activation by inhibitors on endogenous ligands versus immune complexes is a key finding.
  • Understanding these distinct regulatory mechanisms is vital for developing therapeutic strategies targeting complement-mediated diseases.
  • Imbalances in complement regulation contribute to conditions like age-related macular degeneration and rheumatic disorders.