S. L. Raymond1, J. C. Rincon1, A. Cuenca1, D. C. Nacionales1, L. L. Moldawer1, S. D. Larson1 1University Of Florida,Department Of Surgery,Gainesville, FL, USA
Introduction: Sepsis is one of the leading causes of death among neonates with over 1 million deaths annually. Development of neonatal sepsis results in part from a failure of host innate immunity. Alum has long been used as a vaccine adjunct and is currently FDA approved for clinical use. However, the exact mechanisms by which alum enhances immunity are poorly understood. The purpose of this study is to delineate the mechanisms by which alum enhances neonatal protective immunity and improves survival in sepsis.
Methods: To determine the impact of adaptive immunity, we studied Rag1-knockout mice which do not develop functional B or T cells. 6 day old neonatal wild type C57BL/6J (WT) and Rag1-knockout mice received pretreatment with Imject alum®, 100 μg s.c. and 24 hours later underwent i.p. administration of cecal slurry (CS) (LD40-60) to induce polymicrobial intra-abdominal sepsis. Survival was assessed for 7 days. To determine the contribution of innate immunity, 5 day old neonatal WT mice were depleted of neutrophils or Gr1+ cells (neutrophils, monocytes, dendritic cells) by administration of either anti-Ly6G antibody (1 mg/kg i.p.) or anti-Gr1 antibody (60 μg i.p.), respectively. At day 6, Imject alum®, and on day 7, cecal slurry were administered. Survival was assessed for 7 days.
Results: Alum pretreatment significantly improved survival following polymicrobial sepsis in both neonatal WT and Rag1-knockout mice compared to untreated controls (p<0.05). Administration of anti-Ly6G resulted in a >95% reduction of circulating neutrophils. Alum pretreatment improved survival in anti-Ly6G neutrophil-depleted neonatal mice following sepsis (p<0.05) (Fig. 1). Conversely, following Gr1+ cell depletion, mortality was increased compared to non-depleted mice (p<0.05). Additionally, alum treatment following Gr1+ cell depletion failed to improve survival in sepsis.
Conclusion: Pretreatment of neonatal mice with the commonly used pediatric vaccine adjuvant alum improves survival in polymicrobial intra-abdominal sepsis. We demonstrate, for the first time, that alum improves survival independent of functional B or T cells and in the absence of neutrophils. Our data suggests that the protective effect of alum is likely dependent on non-granulocyte Gr1+ myeloid cells, mainly monocytes and dendritic cells. These novel findings suggest a therapeutic potential of administering FDA approved alum-based adjuvants to neonates to enhance innate immune function and prevent neonatal sepsis.
