Chorioamnionitis Induces a Unique Time Course of Inflammatory Changes and Immune Reponses in the Brain and Spleen

Inflammatory oxidative microenvironments can alter heme oxygenase-1 (HO-1) homeostasis. Dysregulation of HO-1 favors proinflammatory signals, while transferrin receptor 1 (TfR1) regulates anti-inflammatory signal transduction. Previously, we have shown that chorioamnionitis (CHORIO) induces sustained elevations in HO-1/TfR1 at postnatal day (P)2 and mononuclear cell-driven inflammation at term age equivalent P7. Here, we hypothesized that an altered HO-1/TfR1 developmental time course would coincide with inflammatory/immune signal changes in the brain.

To induce CHORIO in rats, we performed a laparotomy followed by bilateral transient uterine artery occlusion and intra-amniotic injection of lipopolysaccharide (LPS) at E18. The control group received laparotomy only with equivalent duration of anesthesia. We used real-time polymerase chain reaction (RT-PCR), multiplex electrochemiluminescent immunoassay (MECI), and flow cytometry (FC) to study changes in pro- and anti-inflammatory gene expression, immune cell secretome, and immune cells at critical and clinically relevant timepoints following CHORIO.

We found an acute reduction in anti-inflammatory signals in the cortex on embryonic day (E)19. This was followed by an increased proinflammatory signature on postnatal day (P)2. There were also significant alterations in the phenotypic distribution of splenic T cells on P7, a key organ in immune function. Furthermore, we showed that the microenvironment of the cortex at P21 was skewed toward a proinflammatory state by significant increases in IL-6. The prominence of T-helper cells (Th) in brain concomitant with a proinflammatory state at P21 suggests emerging inflammation and potential for neural injury.

Defining how these and other inflammatory/immune signatures contribute to perinatal brain injury and investigating distinct immune signatures at more developmental time courses will be beneficial for targeting emerging therapies.