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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...
Factors Affecting Illness01:18

Factors Affecting Illness

When a person's physical, emotional, intellectual, social development or spiritual functioning is compromised, this deviation from a healthy normal state is called illness. Illness creates stress that in turn harms individuals. Irritation, anger, denial, hopelessness, and fear are behavioral and emotional changes an individual experiences in the phases of illness. A variety of factors influence a person's health and well-being.
For instance, risk factors are connected to illness, disability,...
Antimicrobial Proteins01:23

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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.
Interferons
Interferons (IFNs) are proteins produced by lymphocytes, macrophages, and fibroblasts infected with viruses. While IFNs cannot prevent viruses from entering and...
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Anticoagulant Drugs: Low-Molecular-Weight Heparins

Hemostasis is a crucial process that prevents excessive blood loss from damaged blood vessels. It involves various mechanisms such as vasoconstriction, platelet adhesion and activation, and fibrin formation. The importance of each mechanism depends on the type of vessel injury. In contrast, thrombosis is the abnormal formation of a blood clot within the blood vessels, leading to potential complications if the clot obstructs blood flow. Thrombosis can be caused by increased coagulability of the...
Psychoneuroimmunology: Cardiovascular Disease01:27

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Psychoneuroimmunology (PNI) is a multidisciplinary field that examines how psychological factors, particularly stress, interact with the immune system and impact physical health. Research in PNI has shown that chronic or traumatic stress can disrupt both the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. These disruptions contribute to serious health conditions, including cardiovascular diseases.
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Factors Affecting the Risk of Infection01:26

Factors Affecting the Risk of Infection

The hosts' susceptibility to infection depends on several factors. The integrity of the skin and mucous membranes helps protect the body against microbial attacks. When the skin is altered, the chance of infection, limb loss, and even death increases.
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Related Experiment Video

Updated: Jun 2, 2026

Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay
13:08

Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay

Published on: September 9, 2012

Complement factor I in health and disease.

Sara C Nilsson1, Robert B Sim, Susan M Lea

  • 1Department of Laboratory Medicine, Medical Protein Chemistry, Lund University, Sweden.

Molecular Immunology
|May 3, 2011
PubMed
Summary
This summary is machine-generated.

Factor I (FI) regulates complement pathways by degrading C3b and C4b. FI deficiency causes severe infections, autoimmune diseases, or atypical hemolytic uremic syndrome.

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Last Updated: Jun 2, 2026

Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay
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Evaluation of the Interplay Between the Complement Protein C1q and Hyaluronic Acid in Promoting Cell Adhesion
06:54

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

Published on: June 15, 2019

Area of Science:

  • Immunology
  • Biochemistry

Background:

  • Factor I (FI) is a key regulator of all complement pathways.
  • It degrades activated complement proteins C3b and C4b with cofactor assistance.

Purpose of the Study:

  • To summarize the role of Factor I in complement regulation.
  • To describe the clinical consequences of Factor I deficiency.
  • To detail the structure and enzymatic activity of Factor I.

Main Methods:

  • Literature review of Factor I function and deficiency.
  • Structural analysis of the Factor I heterodimer.
  • Enzymatic activity assessment with natural and synthetic substrates.

Main Results:

  • Complete FI deficiency leads to complement consumption, causing severe infections, glomerulonephritis, and autoimmune diseases.
  • Incomplete FI deficiency is linked to atypical hemolytic uremic syndrome.
  • FI is an 88kDa heterodimer with specific structural domains and cofactor-dependent enzymatic activity.

Conclusions:

  • Factor I is essential for preventing complement-mediated pathology.
  • FI deficiency has significant clinical implications, ranging from infections to severe systemic diseases.
  • Understanding FI structure and function is crucial for managing complement-related disorders.