Interleukin-27-Producing Cells in Gram-negative Neonatal Sepsis Display Diverse Phenotypes and Functions in the Liver

Neonates have increased vulnerability to life-threatening infections due to the distinct immune landscape. Interleukin (IL)-27 is a key component of this immune profile that we have previously shown to be elevated in both newborn humans and mice. IL-27 continues to increase in the serum and tissues consistent with poor outcomes during gram-negative neonatal bacterial sepsis. Presently, we dissected the IL-27 producer profile at a single-cell level using IL 27p28eGFP reporter mice in our previously established model of sepsis with luciferase-expressing Escherichia coli. Whole animal imaging regionally highlighted the spleen, liver, and lungs as key infection sites by bacterial luminescence. Flow cytometry showed that IL-27 producers increased in the liver with infection and were predominantly F4/80+ and CD11b+. This information paired with single-cell RNA sequencing further identified the most robust populations as monocytes and derived cells, neutrophils, and Kupffer cells. The transcriptome demonstrated that some populations increased in bactericidal, metabolic, and inflammatory activities while others became less active. Sepsis is a disease characterized by extreme immune dysregulation similar to that shown in our cells. The phenotype and transcriptome of IL-27 producers from the livers of infected animals suggests suppressive activity, which contributes to the dysregulated immune environment observed in sepsis. Together, this work provides previously undescribed insight into the details of IL-27 producers during systemic early life infection. This further provides essential information to support IL-27 as a therapeutic target for neonatal bacterial sepsis.