Stunning of neutrophils accounts for the anti-inflammatory effects of clodronate liposomes

The authors show that the anti-inflammatory effects of clodronate liposomes do not result from the depletion of mononuclear phagocytes but from a functional stunning of polymorphonuclear neutrophils. These findings necessitate a critical revision of the current literature on the role of monocytes and macrophages in inflammation. Clodronate liposomes (Clo-Lip) have been widely used to deplete mononuclear phagocytes (MoPh) to study the function of these cells in vivo. Here, we revisited the effects of Clo-Lip together with genetic models of MoPh deficiency, revealing that Clo-Lip exert their anti-inflammatory effects independent of MoPh. Notably, not only MoPh but also polymorphonuclear neutrophils (PMN) ingested Clo-Lip in vivo, which resulted in their functional arrest. Adoptive transfer of PMN, but not of MoPh, reversed the anti-inflammatory effects of Clo-Lip treatment, indicating that stunning of PMN rather than depletion of MoPh accounts for the anti-inflammatory effects of Clo-Lip in vivo. Our data highlight the need for a critical revision of the current literature on the role of MoPh in inflammation.