Interleukin‐1β injection causes loss of tail tips in neonatal mice

Early‐life immune challenges and inflammation are risk factors for a range of developmental disorders. During the course of a study examining interactions between the common antipyretic acetaminophen (APAP; paracetamol) and interleukin‐1β (IL‐1β)‐induced inflammation in neonatal mice we observed that subcutaneous (s.c.) injection of IL‐1β often leads to significantly shorter, blunt‐tipped tails. Three times during early development, on postnatal day 5 (P5), P8, and P11, C57BL/6J pups were given s.c. injection of either .2 μg/kg IL‐1β or 5 cc/kg injection of saline vehicle followed, after a 45 min delay, by a second injection, of either 103.9 mg/kg APAP or saline. IL‐1β was observed to reduce tail length—via a blunting of the tail tip—in treated vs. untreated mice, an effect that was significant as early as P11 and persisted through the end of the study (~P74). Interestingly, IL‐1β‐induced tail blunting was significantly lessened by APAP, an interaction that may have occurred as a result of the opposing actions of APAP and IL‐1β on cyclooxygenase‐2. Although this specific hypothesis and the mechanisms underlying the effects of IL‐1β on tail length require further study, they add to the literature suggesting that IL‐1β may be a critical mediator of specific adverse effects of early‐life inflammation.