Treatment of NZB/WF1 mice with an anti-C5 blocking monoclonal antibody was first reported to diminish lupusrelated manifestations [3]. Administration of recombinant soluble complement receptor I-related gene/protein y (Crry-Ig) or decay accelerating factor (DAF) also have been reported to be protective against renal disease in MRL/lpr mice [4,5].While immune complex-mediated complement activation is known to initiate the classical pathway in SLE, substantial complement activation through the alternative complement pathway (AP) plays a crucial role in SLE-related tissue injury. Later reports suggested that the AP pathway is activated in a drug (adriamycin)-induced glomerulopathy [6] and the genetic absence of the alternative pathway component complement factor B (fB) improved lupus cerebritis in MRL-lpr mice [7]. Furthermore, the targeted delivery of the alternative pathway inhibitor fH by a hybrid molecule (complement receptor (CR) 2-fH) to MRL/lpr lupus-prone mice decreased autoimmunity and kidney pathology more extensively than CR2-Crry which has a more general effect on complement activation [8].These studies have collectively shown that the alternative pathway is involved in the expression of kidney inflammation whereas as an intact classical pathway does not seem to oppose the effect of inhibition of the alternative pathway component.
A novel transmembrane complement receptor, complement receptor of the immunoglobulin superfamily (CRIg), has been described and found to be an intrinsic inhibitor of complement activation of the alternative pathway. CRIg is involved in the internalization of circulating C3-opsonized particles and is located primarily on the surface of tissue macrophages, binds C3 cleavage components and blocks C5 convertase [9]. Recently, a soluble form, CRIg-Fc (CRIg conjugated to Fc portion of IgG), has been shown to significantly alleviate inflammation and reduce bone destruction in mice injected with collagen or mice infused with anti-collagen antibodies by limiting the presence of local joint C3a and the production of inflammatory cytokines [10].However,thesearthritismodels did not allow the evaluation of a possible effect of CRIg on the production of autoantibodies.
We asked whether administration of CRIg-Fc can prevent the progression of autoimmunity and organ damage in MRL/ lpr mice. We report herein that administration of CRIg-Fc to MRL/lpr mice results in decreased skin and kidney inflammation, decreased proteinuria and pyuria, as well as decreased C3 consumption in the absence of an effect on the levels of serum anti-dsDNA autoantibodies.
2. Materials and methods
2.1. In vivo drug treatment
The use of animals and experiment protocols were conducted in accordance with the guidelines of the Institutional Animal Care and Use Committees (IACUC) at Beth Israel Deaconess Medical Center (Boston, MA) under an approved protocol. Five-week old female MRL/lpr lupus-prone mice were purchased from The Jackson Laboratory (Bar Harbor, ME) and housed in our sterile pathogen-free animal facility. Four to ten female MRL/lpr animals were injected intraperitoneally three times per w