Adjuvant pretreatment with alum protects neonatal mice in sepsis through myeloid cell activation

Summary The high mortality in neonatal sepsis has been related to both quantitative and qualitative differences in host protective immunity. Pretreatment strategies to prevent sepsis have received inadequate consideration, especially in the premature neonate, where outcomes from sepsis are so dismal. Aluminium salts‐based adjuvants (alum) are used currently in many paediatric vaccines, but their use as an innate immune stimulant alone has not been well studied. We asked whether pretreatment with alum adjuvant alone could improve outcome and host innate immunity in neonatal mice given polymicrobial sepsis. Subcutaneous alum pretreatment improves survival to polymicrobial sepsis in both wild‐type and T and B cell‐deficient neonatal mice, but not in caspase‐1/11 null mice. Moreover, alum increases peritoneal macrophage and neutrophil phagocytosis, and decreases bacterial colonization in the peritoneum. Bone marrow‐derived neutrophils from alum‐pretreated neonates produce more neutrophil extracellular traps (NETs) and exhibit increased expression of neutrophil elastase (NE) after in‐vitro stimulation with phorbol esters. In addition, alum pretreatment increases bone marrow and splenic haematopoietic stem cell expansion following sepsis. Pretreatment of neonatal mice with an alum‐based adjuvant can stimulate multiple innate immune cell functions and improve survival. These novel findings suggest a therapeutic pathway for the use of existing alum‐based adjuvants for preventing sepsis in premature infants.