Olfactomedin-4 Is a Candidate Marker for a Pathogenic Neutrophil Subset in Septic Shock

Abstract

Objectives: Heterogeneity in sepsis-related pathobiology presents a significant challenge. Resolving this heterogeneity presents an opportunity to understand pathobiology and improve patient care. Olfactomedin-4 is a neutrophil subset marker and may contribute to sepsis heterogeneity. Our objective was to evaluate the expression of olfactomedin-4 and characterize neutrophil heterogeneity in children with septic shock.

Design: Single-center, prospective cohort, as well as secondary analysis of existing transcriptomic and proteomic databases.

Setting: Tertiary care PICU.

Patients: Patients from 5 days to 18 years old with septic shock were enrolled. Data collected included the expression of olfactomedin-4 messenger RNA, serum protein concentrations, and percentage of neutrophils that express olfactomedin-4.

Interventions: None.

Measurements and main results: Secondary analysis of existing transcriptomic data demonstrated that olfactomedin-4 is the most highly expressed gene in nonsurvivors of pediatric septic shock, compared with survivors. Secondary analysis of an existing proteomic database corroborated these observations. In a prospectively enrolled cohort, we quantified the percentage of olfactomedin-4+ neutrophils in patients with septic shock. Patients with a complicated course, defined as greater than or equal to two organ failures at day 7 of septic shock or 28-day mortality, had a higher percentage of olfactomedin-4+ neutrophils, compared with those without a complicated course. By logistic regression, the percentage of olfactomedin-4+ neutrophils was independently associated with increased risk of a complicated course (odds ratio, 1.09; 95% CI, 1.01-1.17; p = 0.024).

Conclusions: Olfactomedin-4 identifies a subpopulation of neutrophils in patients with septic shock, and those with a high percentage of olfactomedin-4+ neutrophils are at higher risk for greater organ failure burden and death. Olfactomedin-4 might serve as a marker of a pathogenic neutrophil subset in patients with septic shock.

Figure 1. OLFM4 transcript is higher in non survivors and complicated course

A. Graph showing OLFM4 mRNA expression is significantly higher in non-survivors (n=29) than survivors (n=151; * p=0.006) from septic shock. B. OLFM4 mRNA expression is also higher in those patients with complicated course (n=53) compared to non-complicated course (n=126; * p<0.001).

Figure 2. OLFM4 Plasma protein expression is higher in patients with complicated course

A. When comparing septic shock survivors (n=388) and non-survivors (n=62), there was no statistical difference (p=0.099). B. OLFM4 Plasma protein concentration is higher in those patients with complicated course (n=134) than without complicated course (n=316; * p=0.005).

Figure 3. Percentage OLFM4+ neutrophils is higher in those patients with complicated course

A. Left figure depicts flow cytometric analysis showing forward and side scatter of leukocytes from a patient with septic shock with cells analyzed surrounded with black line; right shows the fluorescence markers used to identify neutrophils (CD66b positive, black box) and percentage of neutrophils that express OLFM4. B. Percentage of OLFM4+ neutrophils is not different between healthy controls (n=31), PICU controls (SIRS and sepsis; n=26), or patients with septic shock (n=43). C. When comparing just patients with septic shock, those with a complicated course (n=7) had a higher percentage OLFM4+ cells when compared to non-complicated course (n=34; * p=0.025).