Poster Presentation Lorne Infection and Immunity 2023

Age, chorioamnionitis, and the innate immune system in preterm infants (#177)

Josephine C Owen 1 2 , Steven X Cho 1 2 , Ina Rudloff 1 2 , Merrin A Pang 1 2 , Jason C Lao 1 2 , Catriona A McLean 3 4 , Alex Veldman 1 2 5 6 , Claudia A Nold-Petry 1 2 , Marcel F Nold 1 2 7
  1. Department of Paediatrics, Monash University, Melbourne, Victoria, Australia
  2. Ritchie Centre, Hudson Institute of Medical Research, Melbourne, Victoria, Australia
  3. Department of Anatomical Pathology, Alfred Health, Melbourne, Victoria, Australia
  4. Department of Medicine, Central Clinical School, Monash University, Melbourne, Victoria, Australia
  5. Department of Pediatrics, Helios HSK, Wiesbaden, Germany
  6. Department of Pediatric Cardiology, J. Liebig University, Gießen, Germany
  7. Monash Newborn, Monash Children's Hospital, Melbourne, Victoria, Australia

Background: Trained immunity, also known as innate immune memory, describes the functional reprogramming of innate immune cells in response to prior stimulation. Trained immunity may lead to heightened immune responses to secondary, heterologous stimuli, but it is currently unknown whether trained immunity can develop in vulnerable premature neonates. Our research aims to examine the effect of gestational and postnatal age on neonatal innate immune responses, and the development of innate immune memory after early-life exposures to challenges such as chorioamnionitis.

Methods: We collected blood from a population of 28 very/extremely premature neonates across five timepoints: cord blood and day 1, week 1, week 2, and at 12-16 weeks of postnatal age. Samples were then either vehicle-treated, or stimulated with 100ng/ml lipopolysaccharide, and we characterised monocyte and dendritic cell subtypes using flow cytometry, including analysis of the anti-inflammatory receptors CD85k and CD163, and of the immune activation receptor CD86. 

Results: Both gestational and postnatal age significantly affected monocyte populations. At rest, the proportion of intermediate monocytes increased almost 1.5-fold from 25+0 weeks to 28+6 weeks corrected gestational age. Upon lipopolysaccharide stimulation, however, the proportion of classical monocytes increased by 1.7-fold. Expression of CD85k on monocyte and dendritic cell subtypes also increased by over 2-fold with increasing age. Abundance of CD85k on non-classical monocytes increased by 11.5-fold with increasing gestational age, and abundance of CD85k on dendritic cells increased by over 3-fold between birth and 12-16 weeks of postnatal age. Chorioamnionitis was associated with an acute reduction in CD86 expression by monocytes of up to 58.9% in cord blood and day 1 samples. However, at the week 1 and 2 timepoints, chorioamnionitis-exposed neonates demonstrated a 30% reduction in CD85k abundance on dendritic cells, and 25% reduction in CD163 abundance on intermediate monocytes. These longitudinal findings suggest the development of an innate immune memory after chorioamnionitis, resulting in increased pro-inflammatory responses to secondary stimulation with lipopolysaccharide.

Conclusion: These findings demonstrate a role of age, both gestational and postnatal, on the developing preterm innate immune system, and illuminate the possibility for the development of trained immunity in premature neonates in response to chorioamnionitis.