Intraperitoneal administration of aluminium-based adjuvants produces severe transient systemic adverse events in mice.

Vaccines typically come with adjuvants that trigger the innate immune system in order to prepare best possible inflammatory conditions as to allow the adaptive immune system to become activated, generally for the induction of antibodies. The oldest approved and most abundant immunological adjuvants are salts of aluminium, which are also frequently used in animal models of immunisation and allergy desensitization. In rodents, the intraperitoneal administration of aluminium adjuvants is commonly performed and considered safe. In the current investigation, we show that intraperitoneal administration of aluminium adjuvants is associated with a dose-dependent hypothermic reaction within 10 min of the injection. The body temperature of mice dropped as much as 4 °C, and the clinical symptoms included apathy, hunched posture, and piloerection. The temperature normalised and other clinical manifestations disappeared within 60-80 min of the intraperitoneal aluminium injection, which caused strong infiltration of neutrophil and eosinophil granulocytes into the peritoneal cavity, a clinical manifestations typically associated with inflammasome activation. However, the observed reactions to aluminium adjuvants were independent of NALP3, caspase-1, and interleukin-1β, but dependent on histamine. Hence, aluminium adjuvants may have potential local and systemic side effects, which warrants further investigations into the nature of these side effects, but also into the possible implications on health in man.