Immunohistochemical detection of leukemia inhibitory factor after focal cerebral ischemia in rats

The cytokine leukemia inhibitory factor (LIF) modulates neuronal function d uring development and promotes neuronal survival after peripheral nerve inj ury, but little is known about LIF expression after cerebral ischemia. In t he present study, the localization of LIF protein was immunohistochemically examined in rats after 3.5, 12, 24, 48, and 96 hours of reperfusion follow ing 1.5 hours of middle cerebral artery occlusion (MCAO) induced by the int raluminal suture method. Double-staining immunohistochemistry with microtub ule-associated protein-2 (MAP2), glial fibrillary acidic protein (GFAP), le ctin histochemistry, and interleukin (IL) 6 was also performed. The sham gr oup and immunosorption test did not show any cleat LIF immunoreactivity. De finite LIF immunoreactivity was first detected after 12 hours of reperfusio n in each of the brain regions examined: ischemic core, periinfarct region, and contralateral cortex. However, expression of LIF was most prominent in the periinfarct region at each time point, peaked at 24 hours, and then gr adually declined until 96 hours of reperfusion. Some LIF-positive neurons i n the periinfarct region expressed IL-6. At 96 hours of reperfusion, GFAP-l abeled astrocytes around the infarct core also expressed LIF protein. Induc tion of LIF mRNA and protein was also confirmed by reverse transcription po lymerase chain reaction and western blot analysis, respectively. These find ings suggest that LIF expression in ischemically threatened neurons may ref lect a repair or defense mechanism against the ischemic insult.