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 neonatal sepsis with luciferase-expressing K1-encapsulated 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 significantly in the liver with infection and were predominantly F4/80+ and CD11b+ with subpopulations that emerged expressing additional markers. This information paired with single-cell RNA sequencing further identified the most robust populations as monocytes, monocyte-derived cells, and Kupffer cells followed by smaller populations of dendritic cells and neutrophils. The transcriptome demonstrated a diverse range of functionality amongst populations that included differential expression of genes implicated in bactericidal, metabolic, and inflammatory changes. Collectively, the transcriptome of IL-27 producers from the livers of infected animals suggests an uncoordinated mix of inflammatory and suppressive activity that may contribute to immune dysregulation characteristic of sepsis. Together, this work provides previously undescribed insight into the details of IL-27 producers during early-life infection. This further provides essential information needed to support IL-27 as a therapeutic target for neonatal bacterial sepsis.