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Interleukin-6 suppression of neutrophil apoptosis is neutrophil concentration dependent
W L Biffl1, E E Moore, F A Moore
1Department of Surgery, Denver General Hospital, University of Colorado Health Sciences Center 80204, USA.
Abstract:
Apoptosis of polymorphonuclear leukocytes (PMNs) is a critical step in the resolution of tissue inflammation. PMN apoptosis has been studied extensively in vitro, and diverse inflammatory mediators have been shown to modulate the process. The reported effects of interleukin-6 (IL-6) on PMN apoptosis are inconsistent; however, analysis of published studies reveals at least one discriminating factor--the use of varied concentrations of PMNs in the experimental design. Consequently, we hypothesized that the in vitro effects of IL-6 on PMN apoptosis varied with the concentration of PMNs in culture. PMNs isolated from healthy human donors were cultured at concentrations from 1 to 20 x 10(6)/mL, and incubated with IL-6 doses from 1 to 100 ng/mL. PMNs cultured at 1-5 x 10(6)/mL were unaffected by IL-6; in contrast, IL-6 inhibited apoptosis in PMNs cultured at 10-20 x 10(6)/mL, compared with untreated similarly concentrated PMNs. These data suggest caution in interpreting in vitro studies of apoptosis; on the other hand, appropriately designed experiments may help elucidate the regulation of apoptosis in vivo.
Insights
Interleukin-6 (IL-6) affects polymorphonuclear leukocyte (PMN) apoptosis differently based on cell concentration. High PMN concentrations showed inhibited apoptosis with IL-6, unlike low concentrations.
Area of Science:
- Immunology
- Cell Biology
- Inflammation Research
Background:
- Polymorphonuclear leukocyte (PMN) apoptosis is crucial for resolving inflammation.
- In vitro studies on PMN apoptosis and inflammatory mediators show inconsistent results.
- Previous research suggests varying PMN concentrations may explain inconsistent interleukin-6 (IL-6) effects.
Purpose of the Study:
- To investigate the hypothesis that IL-6's in vitro effect on PMN apoptosis is concentration-dependent.
- To clarify the role of PMN concentration in modulating IL-6's impact on apoptosis.
Main Methods:
- Human PMNs were isolated from healthy donors.
- PMNs were cultured at concentrations ranging from 1 to 20 x 10^6/mL.
- Cultures were treated with IL-6 (1-100 ng/mL) and apoptosis was assessed.
Main Results:
- IL-6 did not affect PMN apoptosis at concentrations of 1-5 x 10^6/mL.
- IL-6 significantly inhibited PMN apoptosis at concentrations of 10-20 x 10^6/mL.
- Inhibition was observed when compared to untreated PMNs at the same concentrations.
Conclusions:
- The concentration of PMNs in vitro is a critical factor influencing IL-6's effect on apoptosis.
- Caution is advised when interpreting in vitro apoptosis studies with variable PMN concentrations.
- Well-designed experiments considering PMN concentration may better elucidate in vivo apoptosis regulation.