form a Type I receptor or with an IL-13Ra’ subunit to form a Type II receptor. Binding IL-4 to an IL4-Ra subunit leads to multimeric receptor complex formation and the subsequent activation of the Janus Kinase/signal transducers and activator of transcription pathway. IL-4 relevance in PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19654945/ OA is also supported by genetic evidence, as highlighted by the association of the IL-4 receptor gene polymorphisms observed in different subsets of OA. In addition, our previous study showed a differential systemic modulation of soluble IL-4 receptor levels in different OA subsets compared to normal subjects. In this study, we investigated the differential protein expression of IL-4 and its receptors in OA and normal cartilage, as well as IL-4 modulating activity on IL-1b catabolic effects. In particular, we evaluated whether IL-4 was able to affect the IL-1b-induced production of chemokines, ECM degrading enzymes and their inhibitors in human OA chondrocytes. Among several potential inflammatory/catabolic mediators, chemokines were selected because of their relevance in OA pathophysiology and because, due to their small size, they can greatly contribute to the crosstalk between joint compartments . The two ADAMTS and MMP-13 were selected because they are pivotal matrix-degrading enzymes in OA disease, being responsible for the initial aggrecan and collagen 2 cleavage, respectively, the main components of cartilage extracellular matrix. Our aim was to determine the molecular reasons for the impairment of IL-4 anti-catabolic activity in osteoarthritis. We found that IL-4 is able to abrogate the IL-1b-dependent induction of RANTES and MMP-13, at both RNA and protein levels, and since we also found that IL-4 expression is reduced in OA cartilage, we hypothesize that the overall reduction of this anticatabolic/anti-inflammatory activity plays a pivotal role in the functional impairment of osteoarthritic cartilage. Materials and Methods All 
the data analyzed in the manuscript will be made freely available upon request for the purpose of academic, noncommercial research. Ethics statement The study was approved by the ethical committee of the Rizzoli Orthopaedic Institute and written informed consent was obtained from all patients. Patient names were replaced by arbitrary codes for the sake of anonymity. IL-4 and IL-4R expression on cartilage samples Patients. IL-4 and IL-4R subunit expression was investigated in full thickness cartilage specimens of samples derived from either normal cartilage or from 6 OA patients AEB-071 chemical information undergoing knee replacement. The grading of OA cartilage samples undergoing analysis was 1-2 according to published criteria. More in detail, immunohistochemistry was used to assess the zonal distribution of each of the IL-4R subunits across cartilage, and the percentage of positive cells in either the superficial or the mid-deep layers. Immunofluorescence, coupled with confocal microscopy analysis, was instead required to assess IL-4 expression at the single cell level in order to provide quantitative information and compare NC and OA cartilage. Furthermore, immunofluorescence was also used to assess the colocalization of IL-4Ra1 with either IL-2Rc chain or IL-13Ra1. The diagnosis of OA was based on clinical, laboratory and radiologic evaluations. Full thickness cartilage specimens collected as described in were snap-frozen and stored at 2 80uC until processing to obtain serial cryostat sections for immunohistochemistry or confocal microcopy perfo