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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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Intracellular complement activation-An alarm raising mechanism?

M P Reichhardt1, S Meri2

  • 1Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom.

Seminars in Immunology
|April 11, 2018
PubMed
Summary
This summary is machine-generated.

The complement system, an ancient defense mechanism, functions not only outside but also inside cells. Intracellular complement activation influences immune responses, cell differentiation, and metabolism, acting as a cellular danger signal.

Keywords:
Adaptive immunologyC3C3aC5C5aC5aR1C5aR2Cellular homeostasisComplementComplement signalingInflammasomeIntracellular complementIntracellular defenseMetabolism

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Area of Science:

  • Immunology
  • Cell Biology
  • Metabolism

Background:

  • The complement system is traditionally viewed as an extracellular defense mechanism.
  • Recent findings indicate complement components are synthesized and activated within various cell types, not just the liver and macrophages.

Purpose of the Study:

  • To explore the intracellular functions of the complement system.
  • To understand the role of intracellular complement activation in cellular processes and immune responses.

Main Methods:

  • Analysis of complement component production in diverse cell types (lymphocytes, adipocytes, epithelial cells).
  • Investigation of intracellular complement activation (e.g., C3, C5) and its downstream effects.
  • Examination of receptor-mediated signaling pathways involving complement activation products.

Main Results:

  • Many cell types, including lymphocytes and adipocytes, produce complement components.
  • Intracellular C3 and C5 activation in T cells impacts immunological tolerance and Th1 differentiation.
  • Adipocytes uniquely produce complement sensors (C1q) and Factor D, crucial for alternative pathway amplification.
  • Complement activation products signal through intracellular and cell membrane receptors (e.g., C3aR, C5aR1, C5aR2, MCP/CD46).

Conclusions:

  • Intracellular complement activation has diverse roles, including antimicrobial defense, cell differentiation, and metabolic influence.
  • Complement components act as intracellular alarm molecules, contributing to the cellular danger response.
  • These findings link complement activation to cellular metabolism, intracellular defense, and adaptive immunity.