Treatment with two carbon monoxide (CO)-releasing molecules, which liberate the gaseous HO product CO, blocked HLA I Ab-dependent EC activation. I Ab-dependent up-regulation of VCAM-1. Treatment with two carbon monoxide (CO)-releasing molecules, which liberate the gaseous HO product CO, blocked HLA I Ab-dependent EC activation. Finally, in anin vitroadhesion assay publicity of ECs to HLA I Abdominal muscles led to increased monocyte binding, which was counteracted by up-regulation of HO-1. In conclusion, HLA I Ab-dependent EC activation is modulated by endothelial HO-1 and targeted induction of this enzyme may be a novel therapeutic approach intended for the treatment of AMR in solid organ transplantation. == Intro == Antibody (Ab)-mediated rejection (AMR) is a major limiting factor intended for long-term graft survival after kidney and heart transplantation [14]. The endothelium of allografts plays a key role in the pathogenesis of AMR [5, 6], because it is targeted by donor-specific Abs (DSAs), which are directed against human leukocyte antigen (HLA) and/or non-HLA molecules [7, 8]. It is well established that HLA Abdominal muscles can cause EC injury by complement fixation [7, 9], but more recently, complement-independent effects of HLA Abs Rabbit Polyclonal to IKK-gamma have also been implicated in AMR [1013]). Although the mechanisms of how these Abs mediate EC damage independent of complement fixation are not completely understood, HLA class I (HLA I) Abs have been shown to directly cause activation of ECs [5, 6]. EC activation is critically involved in the pathogenesis of acute and chronic inflammation [14]. Moreover, it is characterized by alterations of intracellular endothelial signaling, which up-regulates expression of inducible adhesion molecules and chemokines [15], and in turn modulates coordinated recruitment of leukocytes to the site of inflammation [16, 17]. Current therapeutic regimens intended for AMR such as plasmapheresis and treatment with CD20 Abdominal muscles (rituximab) are primarily intended to reduce levels of circulating pathogenic DSAs [4, 18, 19]. The clinical success rate of these therapies, however , is limited, and alternative treatment strategies are urgently needed. The antioxidant enzyme heme oxygenase (HO)-1, which is the inducible isoform of catalytic heme degradation [20], offers previously been shown to have protective effects in the endothelium [21, 22]. Moreover, overexpression of HO-1 has been shown to inhibit up-regulation of proinflammatory adhesion molecules in tumor necrosis element (TNF)–activated ECs [23] and to have anti-inflammatory therapeutic potential in various cardiovascular disorders [2427]. In transplantation settings, survival of cardiac xenografts has been linked to endothelial HO-1 in a mouse-to-rat heart transplantation model [28] and genetic transfer of HO-1 into blood vessel walls has been shown to protect against allogeneic rejection of aortic vascular transplants [29]. Moreover, HO-1 continues to be demonstrated to have beneficial effects against complement-mediated damage of HLA Abs [30]. In the current study, we hypothesized that HO-1 may specifically modulate HLA I Ab-dependent activation of ECs. It is demonstrated that HLA I Abs up-regulate inducible adhesion molecules and chemokines in human ECs and cause increased endothelial adhesion of monocytes. Both HLA I Ab-dependent effects in ECs are modulated by specific regulation of HO-1. == Materials and Methods == == Abs and chemicals == The murine monoclonal antibodies (MoAbs) W6/32 and G46-2. 6, both of which are directed against distinct monomorphic HLA I epitopes, were from either ATCC (Manassas, VA, USA)(W6/32) or BD Bioscience (San Jose, CA, USA)(G46. 2 . 6) and were prepared as previously explained [31]. The murine isotype control MoAb (MCA929EL) was from AbD Serotec (Oxford, UK), human HLA-A2 (clone BB7. 2) and microglobulin-2 2b-57 as IgG2b isotype control were from Biolegend (London, UK). Polyclonal rabbit anti-human VCAM-1 and anti-human glyceraldehyde dehydrogenase BQU57 (GAPDH) for Western blot analyses were from Santa Cruz Biotechnology (Santa Cruz, CA, USA), polyclonal rabbit anti-human HO-1 from Enzo Life Sciences (Lrrach, Germany). Secondary HRP-conjugated goat anti-rabbit IgG was from BioRad (Hercules, CA, USA), murine monoclonal VCAM-1 (51-10C9) for blocking leukocyte BQU57 binding BQU57 to VCAM-1 on ECs from BD Biosciences (Heidelberg, Germany) and isotype mouse IgG1 control Ab (MOPC-21) from Biolegend (London, UK). Phosphatidylinositol 3-kinase (PI3K)/Akt inhibitors wortmannin and LY294002, NF-B inhibitors MG132 and Bay 117082 or extracellular-regulated kinase BQU57 (ERK) inhibitors UO126 and PD98059 were from Merck Biosciences (La Jolla, CA,.