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.