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Complement System

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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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.
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Antibodies can bind to pathogens, preventing them from infecting host cells. This process...

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Antimicrobial proteins are important components of the immune system. They aid the body in combating pathogens by either killing them directly or hindering their replication processes. Four main types of antimicrobial substances are interferons, the complement system, iron-binding proteins, and antimicrobial proteins.
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Hypersensitivity Reactions: Immune-Complex Reactions

Hypersensitivity Reactions: Immune-Complex Reactions

Type III hypersensitivity reactions occur when antigen–antibody complexes form and activate the complement system. Normally, these complexes help the clearance of antigens by phagocytes and red blood cells. However, when large numbers of immune complexes are present, they can deposit in tissues—particularly in the walls of blood vessels—leading to inflammation and tissue injury. These deposits trigger complement activation and neutrophil recruitment, resulting in serum sickness, a systemic...

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Related Experiment Video

Updated: Jun 19, 2026

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

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

Published on: January 29, 2014

THE ROLE OF THE COMPONENTS OF COMPLEMENT IN SPECIFIC IMMUNE FIXATION.

L Pillemer¹, S Seifter, E E Ecker

¹Institute of Pathology, Western Reserve University, and the University Hospitals, Cleveland.

The Journal of Experimental Medicine

|October 30, 2009

Summary

This summary is machine-generated.

Complement fixation involves multiple components, with C'4 and C'2 binding to immune aggregates. This study clarifies the roles of complement components (C'1, C'2, C'3, C'4) in immune reactions.

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Depletion of Specific Cell Populations by Complement Depletion

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Last Updated: Jun 19, 2026

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

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Depletion of Specific Cell Populations by Complement Depletion

Depletion of Specific Cell Populations by Complement Depletion

Published on: February 5, 2010

Area of Science:

Immunology
Biochemistry

Background:

The complement system is crucial for immune responses.
Understanding complement component fixation to immune aggregates is vital for elucidating immune mechanisms.

Purpose of the Study:

To investigate the fixation patterns of individual complement components to specific immune aggregates.
To determine the factors influencing complement component binding and inactivation.

Main Methods:

Experiments involving antigen-antibody aggregates and varying concentrations of complement components.
Analysis of complement component inactivation and adsorption under different experimental conditions (temperature, pH, time).

Main Results:

C'4 is invariably inactivated/adsorbed by specific aggregates, indicating it's a combining component.
C'2 is fixed with C'4, while C'3 fixation is partial or absent.
Mid-piece (containing C'1) shows variable adsorption.
Thermolabile serum constituents are necessary for C'4 fixation.
Specific immune fixation involves C'4, C'2, and C'1, differing from non-specific adsorption.

Conclusions:

Complement fixation is a complex process involving multiple components, primarily C'4-C'2 and C'1, binding to antigen-antibody complexes.
C'4 is directly involved in specific immune fixation, with its binding influenced by thermolabile factors.
The findings challenge the notion of mid-piece (C'1) as the sole combining complement component.