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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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Functional Complementation Analysis FCA: A Laboratory Exercise Designed and Implemented to Supplement the Teaching of Biochemical Pathways
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Polyphosphate suppresses complement via the terminal pathway.

Jovian M Wat1, Jonathan H Foley, Michael J Krisinger

  • 1Centre for Blood Research, Life Sciences Institute.

Blood
|December 17, 2013
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Summary
This summary is machine-generated.

Polyphosphate, a polymer found in blood, suppresses the complement system, a key part of innate immunity. This discovery reveals a new role for polyphosphate in regulating immune responses and highlights the link between blood coagulation and immunity.

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Area of Science:

  • Biochemistry
  • Immunology
  • Molecular Biology

Background:

  • Polyphosphate (polyP) is a linear polymer of inorganic phosphate synthesized by all cells.
  • When released into circulation, polyP exhibits prothrombotic and proinflammatory activities by influencing the coagulation cascade.

Purpose of the Study:

  • To investigate the role of polyphosphate in regulating the complement system, an evolutionarily related proteolytic cascade.
  • To determine if polyphosphate modulates complement activity and understand the mechanism of action.

Main Methods:

  • Erythrocyte lysis assays were used to assess hemolytic activity.
  • Ion- and enzyme-independent terminal pathway complement assays were performed.
  • Physicochemical analyses including native gels, gel filtration, and differential scanning fluorimetry were employed.

Main Results:

  • Polyphosphate suppressed total hemolytic activity in a concentration- and size-dependent manner.
  • Polyphosphate lost its suppressive ability after phosphatase treatment, indicating polymer integrity is essential.
  • Polyphosphate was found to bind and destabilize the C5b,6 complex, inhibiting the formation of the membrane attack complex.

Conclusions:

  • Polyphosphate dampens the innate immune response by suppressing the complement cascade.
  • These findings establish a new function for polyphosphate in blood and underscore the intricate relationship between coagulation and innate immunity.