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Sequential potentiation and inhibition of PMN reactivity by maximally stimulated platelets

K A Aziz1, J C Cawley, A T Treweeke

  • 1Department of Haematology, The University of Liverpool, United Kingdom.

Journal of Leukocyte Biology
|March 1, 1997
PubMed

Insights

Platelets enhance immune cell function, but dense granule contents, like AMP, can inhibit this response during maximal stimulation. This finding is crucial for understanding immune cell regulation.

Area of Science:

  • Immunology
  • Hematology
  • Cellular Biology

Background:

  • Granulocyte-macrophage colony-stimulating factor (GM-CSF) and platelet alpha-granule contents, like platelet factor four (PF4), enhance polymorphonuclear leukocyte (PMN) responses.
  • Previous studies showed synergistic enhancement of PMN response by GM-CSF and partially stimulated platelet supernatants.
  • The role of maximally stimulated platelet contents, including dense granule release, on PMN reactivity requires further investigation.

Purpose of the Study:

  • To investigate the combined effect of GM-CSF and supernatants from maximally stimulated platelets on PMN reactivity.
  • To identify the factors released from platelet dense granules and their impact on PMN oxidative burst and priming.
  • To elucidate the mechanism by which platelet-derived factors modulate PMN function.

Main Methods:

  • Incubation of PMN with GM-CSF and supernatants from maximally stimulated platelets.
  • Measurement of PMN chemiluminescence (CL) as an indicator of oxidative burst.
  • Assessment of PMN priming by GM-CSF and the effect of platelet supernatant components.
  • Incubation of PMN with ATP/ADP and their conversion products to mimic platelet-dense granule release.
  • Analysis of the effects of nucleotides and their metabolites (AMP) on PMN reactivity to fMLP.

Main Results:

  • Platelet supernatants from maximally stimulated platelets initially enhanced PMN chemiluminescence but subsequently inhibited it and prevented GM-CSF-induced PMN priming.
  • A low molecular weight inhibitory factor from platelet dense granules was identified, requiring PMN presence for its generation.
  • ATP/ADP, mimicking dense granule contents, induced a biphasic effect on PMN reactivity, with inhibition linked to conversion to AMP.
  • Adenosine monophosphate (AMP) directly inhibited PMN response to fMLP and blocked GM-CSF priming.

Conclusions:

  • While partially stimulated platelets enhance PMN function, maximally stimulated platelets release factors that can inhibit immune cell responses.
  • Nucleotides released from platelet dense granules are converted to AMP, which counteracts the priming effects of PF4 and GM-CSF on PMNs.
  • This biphasic regulation by platelet granule contents highlights a complex interplay in modulating PMN activity during inflammatory processes.

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