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Updated: Aug 12, 2026
Flow Cytometry-based Assay for the Monitoring of NK Cell Functions
Published on: October 30, 2016
Low-dose remifentanil infusion does not impair natural killer cell function in healthy volunteers
A J Cronin1, N M Aucutt-Walter, T Budinetz
1Penn State College of Medicine, Milton S Hershey Medical Center, 500 University Drive, H187, Hershey, PA 17033, USA. acronin@psu.edu
Background:
Mu opioid agonists suppress natural killer (NK) cell activity in animal models. Studies in human volunteers, however, have yielded conflicting results, with morphine suppressing and fentanyl increasing NK cell activity. This study evaluated the effect of a constant 8-h infusion of remifentanil on NK cell number and function in human volunteers.
Methods:
After IRB approval and informed consent was obtained, 10 healthy volunteers underwent an 11 pm to 7 am infusion of saline, and at least 1 week later an infusion of 0.02-0.04 microg x kg(-1) min(-1) remifentanil. Blood was collected at 7 am for measurement of NK cell cytotoxicity using a (51)Cr release assay and measurement of NK cell number using fluorescent flow cytometry.
Results:
Median and range of the total NK cell cytotoxicity (KU ml(-1)) was 745.0 (498.3-1483.6) on the control morning and 818.6 (238.5-1454.5) on the morning following the remifentanil infusion. Neither the number of NK cells ml(-1) (2.5 x 10(5) (1.4 x 10(5)-4.2 x 10(5)) vs 2.7 x 10(5) (1.1 x 10(5)-4.4 x 10(5))) nor the cytotoxicity per 1000 NK cells (KU 1000 NK cells(-1)) (3.0 (1.8-5.2) vs 2.9 (0.9-6.7)) changed between the control and remifentanil conditions.
Conclusions:
An 8-h infusion of remifentanil did not affect NK cell activity in normal volunteers. This result differs from previous findings of morphine-induced NK cell activity suppression and fentanyl-induced NK cell activity enhancement in normal volunteers.
Insights
Remifentanil infusion did not alter natural killer (NK) cell number or function in healthy volunteers. This contrasts with previous studies showing morphine and fentanyl affect NK cell activity.
Area of Science:
- Immunology
- Pharmacology
- Anesthesiology
Background:
- Mu opioid agonists are known to affect natural killer (NK) cell activity.
- Previous studies in humans have shown conflicting results regarding opioid effects on NK cells, with morphine suppressing and fentanyl enhancing activity.
Purpose of the Study:
- To evaluate the impact of a constant 8-hour infusion of remifentanil on NK cell number and function in healthy volunteers.
Main Methods:
- Ten healthy volunteers received either a saline infusion or a remifentanil infusion (0.02-0.04 microg x kg(-1) min(-1)) for 8 hours.
- Blood samples were collected to measure NK cell cytotoxicity using a (51)Cr release assay and NK cell number via fluorescent flow cytometry.
Main Results:
- No significant changes were observed in NK cell number (cells/mL) or NK cell cytotoxicity (KU/mL) after remifentanil infusion compared to the control.
- Specifically, neither the total NK cell cytotoxicity nor the cytotoxicity per 1000 NK cells differed between the control and remifentanil conditions.
Conclusions:
- An 8-hour infusion of remifentanil does not affect NK cell number or function in healthy volunteers.
- These findings differ from prior research indicating that other mu opioid agonists, like morphine and fentanyl, can alter NK cell activity.
