Date on Master's Thesis/Doctoral Dissertation

12-2016

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Physiology and Biophysics

Degree Program

Physiology and Biophysics, PhD

Committee Chair

Polk, Jr, Hiram

Committee Co-Chair (if applicable)

Galandiuk, Susan

Committee Member

Galandiuk, Susan

Committee Member

Joshua, Irving

Committee Member

Bhatnagar, Aruni

Committee Member

Maldonado, Claudio

Committee Member

Schuschke, Dale

Author's Keywords

monocyte; sepsis; NFkappaB; inflammation; IKappaB kinase; endotoxin tolerance

Abstract

Trauma, major surgery and systemic infection can lead to a subsequent immunosuppressed state which can predispose patients to nosocomial infection and death. Approximately a sixth of patients will have impaired monocyte function, as determined by decreased HLA-DR expression or decreased TNF-α production in response to ex-vivo lipopolysaccharide (LPS) stimulation. This project aimed to develop an in-vitro model of impaired monocyte function using isolated monocytes from healthy volunteers, to study the effect of monocyte impairment on IκK signaling, and determine the role of IκK in the impaired monocyte response. These studies have provided the following results:

  1. Monocytes treated with low dose LPS (10 ng/mL) exposure exhibit an impaired inflammatory response to a subsequent 100 ng/mL LPS challenge. Levels of TNF-α and IL-10 production, as well as monocyte HLA-DR expression, were decreased in the impaired monocyte compared with its naïve counterpart.
  2. Impaired monocytes that exhibited this impaired response were found to have decreased NFκB activation. In addition, while total levels of IκK-α and IκK-β were similar between naïve and impaired conditions, decreased IκK phosphorylation was observed in the impaired monocyte.
  3. Loss of IκK function studies using IκK-16 (a specific IκK inhibitor) showed that decreases in both TNF-α and IL-10 production were attributable to decreased IκK activation, demonstrating a causal relationship between IκK function and the monocyte cytokine response. However, HLA-DR expression was not dependent on IκK function, suggesting that other signaling pathways may also be altered in monocyte impairment that may affect HLA-DR expression.
  4. The impaired monocyte phenotype also results in decreased chemokine production (such as MCP-1 and IP-10) and growth factor secretion (such as GM-CSF).

Our data highlight the importance of IκK function in the host defense response to infective stimuli, but also demonstrate the effects of negative feedback regulation following a primary stimulus. Excessive IκK stimulation, or indeed suppression of IκK activity, is likely to be detrimental to the surgical patient. Future studies of IκK function in the surgical patient, as well as translating potential therapies to modulate the IκK pathway, could ameliorate monocyte impairment and decrease the susceptibility to infection in the surgical patient.

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