Two subcutaneous booster injections with in total 50 g mBSA/Freund’s complete adjuvant were given in the neck region 1 week after the initial immunization. throughout the 7 day course of arthritis. Treatment of AIA with intravenously delivered Lip-PLP strongly suppressed joint swelling and synovial infiltration whereas colloidal platinum containing liposomes specifically targeted the macrophages within the inflamed synovial intima coating. studies showed that Lip-PLP phagocytosed by M1 macrophages resulted in a suppression of the M1 phenotype and induction of M2 markers (IL-10, TGF-, IL-1RII, CD163, CD206 and Ym1). findings, PLP-liposomes do not cause a shift of synovial lining macrophages towards M2. Intro Synovial lining macrophages play a crucial part in Soluflazine the onset and maintenance of joint swelling during arthritis , . Previous studies have shown that their selective removal with clodronate-liposomes prior to induction or during founded experimental arthritis resulted in mainly diminished synovial swelling , . Even though activation stage of macrophages is very versatile, numerous subpopulations have been defined reflecting stadia of polarization. Classically triggered macrophages are induced by combined activation with lipopolysaccharide (LPS) and interferon gamma (IFN-) and these macrophages communicate a unique set of genes providing rise to a pro-inflammatory phenotype. Characteristically, these cells produce cytokines like TNF-, IL-1, IL-6 and IL-12 in high amounts and upregulate MHC-II and CD86, which facilitate antigen demonstration , . The pro-inflammatory activation state of macrophages can be further enhanced through the high affinity receptor FcRI in response to immune-complexes . Furthermore, classically triggered macrophages create reactive oxygen varieties like nitric oxide (NO) Soluflazine via nitric oxide synthase 2 (NOS2/iNOS) and stimulate T-cells towards a Th1 or Th2 phenotype . More recently, it has been explained that Soluflazine macrophages can also be on the other hand triggered studies performed with human being and murine monocytes showed that glucocorticoids can travel monocytes towards an M2-like phenotype characterized by expression of CD163, a strong marker for M2 macrophages , . In line with that, monocytes from healthy volunteers showed upregulation of CD163 after relatively high doses of intravenous glucocorticoids . Glucocorticoids can be targeted to inflamed knee joints more effectively by systemic intravenous injection KIAA1819 within long circulating stealth liposomes during experimental arthritis , . Recently, we found that intravenous liposomal delivery of glucocorticoids greatly improved its potency and a single injection strongly inhibited knee joint swelling in experimental arthritis C. The strong effect on inhibition of joint swelling may be due to alteration of the macrophage phenotype within the lining coating. The aim of this study was Soluflazine to determine the effect of the liposomally delivered glucocorticoid prednisolone phosphate (Lip-PLP) on M1/M2 polarization of macrophages within the synovial intima coating. For this, we analyzed gene expression of various M1 and M2 markers in the inflamed synovium during immune-complex induced arthritis (ICA) and antigen-induced arthritis (AIA). In ICA, the synovium is definitely triggered by immune complexes whereas in AIA, activation is definitely driven by both immune complexes and T cells. As with the arthritis models the synovium is definitely highly infiltrated with leukocytes, we also analyzed the effect of Lip-PLP inside a model in which the synovium was triggered towards an M1 phenotype with LPS and IFN- by local injection into the knee joint, which did not result in synovial infiltration. Additionally, we analyzed the direct effect of Lip-PLP on M1 triggered bone marrow derived macrophages studies, do not skew them to a more M2 phenotype. Materials and Methods Ethics statement All studies were carried out in strict accordance with the recommendations in the Guidebook for the Care and Use of Laboratory Animals of the Dutch national legislation. The protocol was authorized by the local Committee within the Ethics of Animal Experiments of the Radboud University or college Nijmegen (Permit Quantity: RU-DEC 2006-182). All surgery was performed under 2,5% isoflurane with N2O/O2 anesthesia, and all efforts were made to minimize suffering. Liposome preparation Liposomes were prepared as explained previously , using a lipid formulation of dipalmitoyl phosphatidylcholine (DPPC, Lipoid GmbH, Ludwigshave, Germany), PEG 2000-distearoyl phosphatidylethanolamine (DSPE) and cholesterol (Sigma Chemical Co., Poole, UK) inside a molar percentage of 1 1.850.151.0. These lipids were dissolved in ethanol which was then.