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Calcium spikes in activated macrophages during Fcgamma receptor-mediated phagocytosis

Jesse T Myers1, Joel A Swanson

  • 1Cellular and Molecular Biology Graduate Program and Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor 48109-0620, USA.

Journal of Leukocyte Biology
|October 16, 2002
PubMed

Insights

Increased calcium spiking in activated macrophages during Fc receptor-mediated phagocytosis does not directly enhance antimicrobial activity. This finding clarifies the role of calcium signaling in macrophage immune responses.

Area of Science:

  • Immunology
  • Cell Biology
  • Calcium Signaling

Background:

  • Intracellular calcium ([Ca(2+)](i)) dynamics are linked to Fcgamma receptor (FcR)-mediated phagocytosis in macrophages.
  • Macrophage activation influences cellular responses, including calcium signaling pathways.

Purpose of the Study:

  • To investigate the relationship between FcR-mediated phagocytosis and intracellular calcium ([Ca(2+)](i)) spikes in activated macrophages.
  • To determine if increased calcium spiking in activated macrophages contributes to enhanced microbicidal activity.

Main Methods:

  • Utilized ratiometric fluorescence microscopy to measure [Ca(2+)](i) in murine bone marrow-derived macrophages during phagocytosis of IgG-opsonized erythrocytes.
  • Employed activation stimuli including lipopolysaccharides (LPS), interferon-gamma (IFN-gamma), and interleukin-6 (IL-6).
  • Assessed the impact of calcium inhibition using thapsigargin (Tg) and ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) on phagosome-lysosome fusion and reactive species generation.

Main Results:

  • Activated macrophages exhibited significantly increased calcium spiking during FcR-mediated phagocytosis compared to nonactivated cells.
  • Calcium spikes were traced to the endoplasmic reticulum, as confirmed by inhibition with thapsigargin (Tg).
  • Inhibition of calcium spikes or lowering [Ca(2+)](i) did not impede phagosome-lysosome fusion or the production of reactive oxygen and nitrogen species.

Conclusions:

  • While activated macrophages show enhanced calcium spiking during phagocytosis, this phenomenon is not directly responsible for their increased microbicidal functions.
  • The study suggests that calcium spikes during FcR-mediated phagocytosis in activated macrophages do not play a critical role in phagosome maturation or antimicrobial effector mechanisms.

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