The data with cross expression of IL-33 and ST2 by various CNS cells suggest complex autocrine and paracrine mechanisms of IL-33/ST2 signalling in the CNS compartment. It has been well documented that IL-33 is a pleiotropic cytokine [10, BT-13 33C35] in regulating immune responses in various immune mediated diseases [36C38], and systemic administration of recombinant IL-33 to EAE mice after disease onset induces type 2 immune responses and reduces CNS inflammation [18]. around axons. Furthermore, the expression levels and patterns of IL-33 and ST2 in the lesions of acute and chronic MS patient brain samples are enhanced compared with the healthy brain tissues. Finally, our data using rat myelinating co-cultures suggest that IL-33 may play an important role in MS development by inhibiting CNS myelination. Electronic supplementary material The online version of this article (doi:10.1186/s40478-016-0344-1) contains supplementary material, which is available to authorized users. are associated with increased disease susceptibility [13, 14]. Amyotrophic lateral sclerosis is also shown to be associated with reduced serum IL-33 levels compared with healthy controls [15] which may reflect a corresponding increase in availability of soluble ST2 receptor. The role of IL-33 in inflammatory CNS diseases such as multiple sclerosis (MS) is usually of particular interest as MS is usually a disease characterised by immune-mediated demyelination of axons, thus IL-33 has the potential to modulate both the immune and the CNS system and therefore to influence disease pathology. This is supported by recent findings of increased expression of IL-33 in the periphery and CNS tissues of MS patients [16, 17]. However the pathophysiological significance of these observations remains obscure, studies on experimental autoimmune encephalomyelitis (EAE) provide contradictory findings as to the role of BT-13 IL-33 in neuroinflammatory disease. Ablation of BT-13 IL-33 signalling by deleting its receptor in mice resulted in exacerbation of EAE [18, 19], whilst utilising an IL-33 blocking antibody resulted in the converse effect, inhibiting disease onset and reducing its severity [20]. The reason for this dichotomy remains unknown but may reflect an unexpected role for IL-33 within the CNS compartment, above and beyond its ability to act as an immunomodulatory cytokine. Surprisingly despite increased evidence supporting a role for IL-33 in a variety of CNS diseases, its function within the CNS under normal and pathological conditions is usually unknown. As a first step towards resolving these questions we determined cellular expression of IL-33 and ST2 by immunohistochemistry in the brain tissues of MS patients together with appropriate controls. Following that we investigated the function of IL-33/ST2 signaling pathway in CNS using rat CNS myelinating co-cultures. Materials and Methods Antibodies The following main antibodies were utilized for human brain tissues: anti-IL-33 (Enzo Lifescience), anti-ST2 (Sigma-Aldrich), anti-GFAP (DAKO), and anti-Iba1 (Wako). Antibodies against SMI-31 and CA-II were purchased from Abcam. Main antibodies for immunolabelling cells within the myelinating cultures include: anti-ST2 (Sigma-Aldrich), anti-GFAP (DAKO), anti-SMI-31 (Abcam), anti-MBP (Chemicon). The antibody O4 [21], and other anti-NeuN and anti-Olig2 antibodies were purchased from Millipore. All the main antibodies were tested and an optimal dilution of 1 1:100 of the original purchased stock was TIE1 used in staining except CA-II was diluted 1:500. Appropriate isotype control BT-13 antibodies, biotinylated antibodies and fluroscence conjugated antibodies were purchased from Sigma-Aldrich, DAKO, R&D Systems or Jackson Immunoresearch. MS individual specimens Archived formalin-fixed, paraffin-embedded brain materials from 14 MS patients and 6 controls without neurological disease or evidence of brain lesions were used in this study. Samples from MS patients have been extensively characterised in the Center for Brain Research of the Medical University or college of Vienna. The samples include: 7 acute MS patients (Marburgs type) with 2 females and an average age of 49.4 years, these cases all died within one year after disease onset and were selected because of the abundance of active MS lesions; 7 chronic MS patients with 4 females and an average age of 63.1 years, all with a clinical course of secondary progressive MS, these cases were determined on the presence of large numbers of slowly expanding and inactive chronic lesions; 6 healthy controls with 4 female and an average age of 58.7 years. Immunohistochemical staining was performed on the brain samples of all the patients and controls. Images between samples in each group were compared and verified by MS pathologists, representative images of consistent data in each group were offered. The study was approved by the ethics committee.