Leukemia inhibitory factor is an anti-inflammatory and analgesic cytokine

Abstract

The mRNA for leukemia inhibitory factor (LIF), a neuroimmune signaling molecule, is elevated during skin inflammation produced by intraplantar injection of complete Freund's adjuvant (CFA). Moreover, although LIF knock-out mice display normal sensitivity to cutaneous mechanical and thermal stimulation compared with wild-type mice, the degree of CFA-induced inflammation in mice lacking LIF is enhanced in spatial extent, amplitude, cellular infiltrate, and interleukin (IL)-1beta and nerve growth factor (NGF) expression. Conversely, local injection of low doses of recombinant LIF diminishes mechanical and thermal hypersensitivity as well as the IL-1beta and NGF expression induced by CFA. These data show that upregulation of LIF during peripheral inflammation serves a key, early anti-inflammatory role and that exogenous LIF can reduce inflammatory hyperalgesia.

Fig. 1.

Several measures of inflammation after injection of CFA are strongly enhanced in LIF knock-out mice. The LIF knock-out mice display a significantly greater elevation of both IL-1β and NGF than the WT mice (p < 0.05;n = 5). IL-1β and NGF levels measured by ELISA are expressed as the ratio of the values obtained from the ipsilateral paw over the contralateral paw. Both WT (+/+) and LIF null mutant (−/−) mice were examined 48 hr after CFA injection in the ipsilateral paw. Swelling is expressed as the change in the dorsoventral paw diameter value from preinflamed levels in WT (+/+) and LIF (−/−) null mutant mice. The percent increase in the mutant mouse was substantially greater (p < 0.01, Mann–WhitneyU test) than in the WT mice. n = 12 for naive and WT; n = 6 for all other groups.

Fig. 2.

Adjuvant-induced inflammation produces a greater immune cell infiltration in LIF mutant (−/−) than in WT (+/+) mice. Hematoxylin and eosin staining of the footpad skin, 48 hr after CFA injection, reveals a much thicker dermis (top) in the −/− compared with +/+ mice. Bottom panels reveal that this difference is attributable to more polymorphonuclear neutrophils (arrowhead) in the dermis of −/− compared with +/+ mice. Scale bar: top panels; 200 μm; bottom panels, 20 μm.

Fig. 3.

Administration of LIF to the paw reduces and/or delays the mechanical and thermal hypersensitivity caused by CFA. LIF (100 ng total) was injected into the plantar and dorsal surfaces of the hindpaw 10 min before CFA injection, and the sensitivity to mechanical and thermal stimuli was measured as described in Materials and Methods. Thermal hyperalgesia at 1 and 3 hr is significantly reduced by LIF (***p < 0.001), and the difference is maintained at 48 hr (**p < 0.01). Mechanical sensitivity, which begins to appear at 3 hr, is also attenuated at that time (***p < 0.001). n = 6 for each data point.

Fig. 4.

Intraplantar injection of LIF at 50, 100, and 500 ng into the paw of noninflamed rats failed to modify mechanical sensitivity. The highest dose (500 ng) did, however, significantly decrease thermal response latency at 3 and 6 hr after injection (*p <0.05; **p < 0.01).n = 4 for each data point.

Fig. 5.

Intraplantar injection of LIF reduces the inflammation-induced elevation in IL-1β and NGF 3 hr after CFA administration. Preadministration of 100 ng of LIF into the plantar and dorsal surfaces of the hindpaw before CFA injection reduces the elevation in IL-1β levels by 60% and NGF levels by 50%.n = 4; *p < 0.05 CFA versus naive; ^#p < 0.05 CFA + 100 ng of LIF versus CFA.