R. B. Hawkins1, J. C. Rincon1, S. L. Raymond1, R. Ungaro1, J. L. Wynn1, L. L. Moldawer1, S. D. Larson1 1University Of Florida College Of Medicine,Department Of Surgery,Gainesville, FLORIDA, USA
Introduction: Sepsis is a leading cause of morbidity and mortality in the neonatal population. Neonates have attenuated immunity compared to adult counterparts, but this difference is poorly understood. Interleukin-10 (IL-10) has emerged as an important anti-inflammatory cytokine that is associated with impaired neutrophil function and increased mortality from neonatal sepsis. Aluminum hydroxide (alum) is often used as an adjuvant in pediatric vaccines, but its use as an immune stimulant alone has not been well described. We have previously demonstrated that alum pretreatment improves survival from polymicrobial sepsis in neonatal mice. We sought to better understand the mechanism of alum’s survival benefit through its effects on IL-10 and phosphorylated protein kinase B (pAKT).
Methods: Wild-type neonatal mice aged 5-7 days were used for experiments. Control mice received a sham injection while alum-pretreated mice received a subcutaneous injection of 50 µg alum 24 hours prior to induction of sepsis or sacrifice. 24 hours later, some mice were sacrificed and blood samples were obtained to evaluate for baseline cytokine changes associated with alum pretreatment. Sepsis was induced using the cecal slurry method. Mice were sacrificed at 6, 18, and 24 hours after induction of sepsis and blood and spleen samples were obtained. IL-10 cytokine analysis was performed using a customized mouse cytokine magnetic bead Milliplex® panel. pAKT levels were determined from splenic tissue at 6 and 24 hours following induction of sepsis using a Western blot assay.
Results: Neonatal mice who received alum pretreatment had a significant decrease in circulating IL-10 levels compared to non-treated counterparts at baseline. After induction of sepsis, both alum-pretreated and non-treated groups had significant elevation in IL-10 levels. There was no significant difference in circulating IL-10 levels between non-treated and alum-pretreated mice at 6, 18, and 24 hours after induction of sepsis. pAKT levels were significantly elevated at 6 and 24 hours after induction of sepsis. Alum pretreatment caused significantly less elevation of pAKT at 6 and 24 hours following induction of sepsis.
Conclusion: IL-10 is an important anti-inflammatory cytokine that may contribute to a diminished innate immune response in neonates. Alum pretreatment is associated with decreased circulating IL-10 levels at baseline, which may be partially responsible for alum’s survival benefit in the cecal slurry model. The PI3K-AKT pathway is involved in modulation of circulating IL-10 levels, and our data suggest that alum pretreatment limits production of pAKT following sepsis. These data suggest a possible therapeutic role for alum or other immunomodulators to affect the PI3K-AKT and IL-10 pathways to improve survival from neonatal sepsis.