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Continued tumor necrosis factor receptor expression by trauma patients' monocytes (Mphi) despite TNF alpha secretion
C L Miller-Graziano1, K Kodys, F Gonzalez
1Department of Surgery, University of Massachusetts Medical Center, Worcester 01655, USA.
Abstract:
In investigating various mechanisms for continued elevated tumor necrosis factor alpha (TNF alpha) production in trauma patients' monocytes (Mphi), we examined TNF receptor (TNFR) levels on the patients' Mphi as a possible altered pathway leading to continued autocrine TNF alpha stimulation. Mphi TNFR synthesis and shedding are both increased as TNF alpha protein production increases. In fatal meningococcal infections, TNFR shedding fails to pace TNF alpha production. Here, isolated normal and trauma patients' Mphi (injury severity score greater than 30), were examined by flow cytometry using phycoerythrin-labeled TNF alpha to detect increased or decreased TNFR expression concomitant to Mphi production of secreted TNF alpha (as measured in the LM bioassay). Immunoaberrant patients (mitogen proliferation depressed) had reduction in detectable TNF alpha binding by their TNFR, while Mphi from immunocompetent (normal mitogen response) trauma patients' Mphi had a TNFR expression intensity comparable to normals' Mphi. Upon in vitro stimulation of TNF alpha (IFN gamma + muramyl dipeptide) normals' and immunocompetent patients' MO TNFR expression is decreased for the entire 18 h period during which secreted TNF alpha is produced, but immunoaberrant trauma patients' Mphi increased their TNFR expression, while concomitantly producing both secreted and cell-associated TNF alpha protein. Patients' Mphi with highly elevated TNF alpha levels are still expressing high levels of TNFR and capable of auto-stimulating TNF alpha production. This elevated TNFR expression could be due to reduced shedding, overproduction of TNFR, or both.
Insights
Trauma patients with high tumor necrosis factor alpha (TNF alpha) levels show altered TNF receptor (TNFR) expression on monocytes. This suggests a mechanism for sustained inflammation and potential autocrine stimulation in severe injury.
Area of Science:
- Immunology
- Cell Biology
- Trauma Pathophysiology
Background:
- Elevated tumor necrosis factor alpha (TNF alpha) production is observed in trauma patients, contributing to sustained inflammation.
- Tumor necrosis factor receptors (TNFRs) on monocytes (Mphi) play a role in TNF alpha regulation, with synthesis and shedding influenced by TNF alpha levels.
- Dysregulation in TNFR shedding has been implicated in conditions like fatal meningococcal infections, failing to keep pace with TNF alpha production.
Purpose of the Study:
- To investigate altered TNF receptor (TNFR) expression on monocytes (Mphi) from trauma patients as a potential mechanism for elevated TNF alpha production.
- To determine if TNFR expression levels correlate with TNF alpha production and autocrine stimulation in trauma patients.
- To compare TNFR expression in trauma patients with differing immune statuses (immunoaberrant vs. immunocompetent).
Main Methods:
- Isolation and analysis of monocytes (Mphi) from normal individuals and trauma patients (Injury Severity Score > 30).
- Flow cytometry using phycoerythrin-labeled TNF alpha to assess TNFR expression.
- Measurement of secreted TNF alpha using the LM bioassay.
- In vitro stimulation of TNF alpha production using interferon gamma (IFN gamma) and muramyl dipeptide.
Main Results:
- Immunoaberrant trauma patients (depressed mitogen proliferation) showed reduced TNF alpha binding to TNFR, while immunocompetent trauma patients had comparable TNFR expression to normal individuals.
- Upon in vitro TNF alpha stimulation, TNFR expression decreased in normal and immunocompetent trauma patients during TNF alpha production.
- Conversely, immunoaberrant trauma patients exhibited increased TNFR expression concurrently with both secreted and cell-associated TNF alpha production.
Conclusions:
- Trauma patients with highly elevated TNF alpha levels maintain high TNFR expression, indicating a potential for self-stimulation of TNF alpha production.
- This sustained TNFR expression may result from reduced shedding, overproduction of TNFR, or a combination of both mechanisms.
- Altered TNFR dynamics in monocytes represent a significant pathway contributing to persistent inflammation in severe trauma patients.