Date Approved

5-2023

Document Type

Dissertation

Degree Name

PhD in Molecular Cell Biology and Neuroscience

Department

Cell Biology and Neuroscience

College

Graduate School of Biomedical Sciences, Virtua Health College of Medicine and Life Sciences of Rowan University

First Advisor

Kingsley Yin, PhD

Committee Member 1

Dimitri Pestov, PhD

Committee Member 2

Gary Goldberg, PhD

Committee Member 3

Robert Nagele, PhD

Committee Member 4

Bernd Spur, PhD

Subject(s)

Immunomodulation; Inflammation Mediators; Docosahexaenoic Acids; Inflammation; Sepsis; Fatty Acids; Pseudomonas aeruginosa; Spleen; Lung

Disciplines

Bacterial Infections and Mycoses | Biological Phenomena, Cell Phenomena, and Immunity | Cell Biology | Disease Modeling | Immunology of Infectious Disease | Laboratory and Basic Science Research | Life Sciences | Medical Cell Biology | Medical Molecular Biology | Medicine and Health Sciences | Molecular Biology | Pathogenic Microbiology

Abstract

Dysregulated hyperinflammatory host immune response to underlying bacterial infections is a characteristic of sepsis. In sepsis, bacteria often trigger abnormal hyperinflammatory responses which can cause multiple organ failure and if sustained can lead to an immunosuppressive phase where the host is susceptible to secondary infections caused by opportunistic bacteria like Pseudomonas aeruginosa (P. aeruginosa). In our studies, we used a 2-hit model of cecal ligation and puncture (CLP) followed by P. aeruginosa secondary lung infection to investigate cellular and molecular mechanisms in the beneficial action of resolvin D2 (RvD2). Resolvins of the D-series are a group of fatty acids known as Specialized Pro-resolving Mediators (SPMs), synthesized endogenously from docosahexaenoic acid (DHA) by different immune cells including neutrophils and macrophages during infection and inflammation. In CLP sepsis, we observed that production of RvD2 in spleens had returned to basal levels by 48 hours after CLP surgery. Administering RvD2 (100 ng/mouse, i.v.) in CLP mice at this time point where endogenous RvD2 synthesis is low enabled CLP mice to clear blood bacteria more efficiently at 24 hours after administration compared to saline controls. There was no significant difference in plasma cytokine production. To further understand cellular and molecular mechanisms, we used flow cytometry to identify different immune cells in spleen and found that RvD2 treatment increased splenic neutrophils (Ly6G+) and myeloid-derived suppressor cells (MDSCs: CD11b+ Ly6G+ Ly6C+) compared to vehicle treated mice. RvD2 treatment increased oxidative burst in splenic neutrophils but not in splenic MDSCs compared to vehicle treated mice. These results provide evidence that RvD2 can expand splenic neutrophil and MDSC numbers to effect greater blood bacterial clearance even when given 48 hours after primary infection. When mice were challenged with P. aeruginosa (intranasally; 24 h after RvD2 treatment) we found that RvD2 increased bacterial clearance in lungs, increased alveolar macrophage numbers and reduced lung IL-23. These results suggest that late RvD2 administration boosted host defense to reduce infection and inflammation. This study provides insight into immunomodulatory effects of RvD2 in a 2-hit infection model of sepsis (Sundarasivarao et al., 2022).

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