B. Mathias1, J. Rincon1, A. L. Cuenca1, D. Nacionales2, L. L. Moldawer2, S. D. Larson1 1University Of Florida,Division Of Pediatric Surgery/Department Of Surgery,Gainesville, FL, USA 2University Of Florida,Department Of Surgery,Gainesville, FL, USA
Introduction: Each year, severe infection and sepsis in the neonatal period is responsible for over 3 million deaths worldwide. Contributing to this high mortality is the neonate’s functionally distinct innate immune response. In previous studies, we have demonstrated that adjuvant activation via the TLR4 receptor improves outcomes in neonatal sepsis. Unfortunately, TLR agonists (e.g. LPS, resiquimod) are contraindicated in clinical use due to sepsis-like symptoms they induce. Aluminum (alum) salts are currently used as adjuvants in pediatric vaccines to improve immune responses; however, the mechanisms by which alum mediate these responses are incompletely understood. Therefore, the purpose of our study was to determine if alum enhances immune effector cell recruitment and function in the setting of polymicrobial sepsis.
Methods: 5-7 day old (neonate) C57BL/6J (B6) mice received either no pretreatment (control) or subcutaneous (SQ) injection of aluminum hydroxide (alum; 100 µg) 24 h prior to sepsis. Neonates then underwent intraperitoneal (IP) administration of cecal slurry (CS; LD25-45) to induce intra-abdominal polymicrobial sepsis. Following injection of CS, mice were observed for 7 days to determine survival. Peritoneal wash was collected at 0, 2, 6 and 24 h following sepsis. Harvested cells were analyzed by flow cytometry for cell phenotype and phagocytosis activity (E.coli bioparticles).
Results: Subcutaneous alum pretreatment did not alter peritoneal macrophage or neutrophil recruitment following IP septic challenge. Despite a decrease in total peritoneal macrophages from baseline (0 h) in both groups, alum pretreatment significantly improved peritoneal macrophage phagocytosis at 6 h compared to controls (70.4±6.2 vs. 40.2±13.2; p<0.05). Alum pretreatment 24 h prior to septic challenge also demonstrated improved macrophage phagocytosis at baseline (68.9±19.2 vs. 17.8±26.6; p<0.05). Peritoneal neutrophil phagocytosis was unchanged at baseline and 6 h following septic challenge. However, neutrophil phagocytosis was a significantly increased at 18 h (88.2±9.9CS vs. 62.2±12.1; p<0.001) and 24 h (62.6±24.2 vs. 30.3±13; p<0.01) following sepsis in alum pretreated neonates compared to controls. Alum pretreated neonates had significantly improved survival compared to control animals when challenged with cecal slurry (p=0.023).
Conclusion: We demonstrate here that the vaccine adjunct alum modulates immune effector cell function and improves survival to polymicrobial sepsis in neonates. Alum pretreatment leads to improved phagocytosis in peritoneal macrophages and neutrophils likely influencing this survival advantage. These findings suggest that alum improves the neonate’s innate immune response and offers a potential novel clinical approach to preventing neonatal sepsis.