Central origin of IL-1beta produced during peripheral inflammation: role of meninges.

Brain expression of Interleukin-1beta (IL-1beta) and its modulation have been extensively documented in different animal models. The majority of the studies were based on techniques such as RT-PCR, RIA and ELISA using global extracts. Meningeal tissue or choroid plexus both belong to the peripheral compartment. Thus, their presence in nervous tissue extracts may lead to erroneous interpretations. We measured IL-1beta mRNA in the cerebellum, hippocampus and cerebral cortex collected with meninges and in the same structures collected without meninges after a peripheral lipopolysaccharide (LPS) stimulation (0.5 microgram/g body weight), using RT-PCR. The presence of meninges in the extracts dramatically increased IL-1beta mRNA levels after LPS treatment while basal levels (before LPS injection) were not affected. Indeed, two-thirds of the response originated from the meningeal tissue and choroid plexus. Immunohistochemical studies showed that IL-1beta labelled cells, identified as macrophages, were exclusively localized in the ventricular and meningeal spaces, in our LPS condition treatment. These results point out the need of integrated analyses of data obtained with different techniques to demonstrate the presence in the nervous tissue of a molecule which is also widely expressed in the peripheral compartment.