Leukaemia inhibitory factor is required for normal inflammatory responses to injury in the peripheral and central nervous systems in vivo and is chemotactic for macrophages in vitro

The cytokine leukaemia inhibitory factor (LIF) is up-regulated in glial cells after injury to the peripheral and central nervous systems. In addition, LIF is required for the changes in neuropeptide expression that normally occur when the axons of sympathetic and sensory neurons are transected. We investigated whether LIF is also necessary for the initial inflammatory response that follows mechanical injury to the sciatic nerve and cerebral cortex of adult mice. We find that inflammatory cell infiltration into crushed sciatic nerve is significantly slower in LIF knock-out (KO) mice compared with wild-type (WT) mice. Similarly, the microglial and astroglial responses to surgical injury of the cortex are significantly slower in LIF KO mice compared with WT mice. Consistent with these in vivo results, LIF is chemotactic for peritoneal macrophages in a microchamber culture assay. Thus, LIF is a key regulator of neural injury in vivo, where it is produced by glia and can act directly on neurons, glia and inflammatory cells. We also find that the initial inflammatory response to cortical injury is diminished in interleukin (IL)-6 KO mice. Surprisingly, however, the inflammatory response in LIF-IL-6 double KO mice is very similar to that of the single KO mice, suggesting that these cytokines may act in series rather than in parallel in this response.