A functional SNP in the regulatory region of the decay-accelerating factor gene associates with extraocular muscle pareses in myasthenia gravis

Complement activation in myasthenia gravis (MG) may damage muscle endplate and complement regulatory proteins such as decay-accelerating factor (DAF) or CD55 may be protective. We hypothesize that the increased prevalence of severe extraocular muscle (EOM) dysfunction among African MG subjects reported earlier may result from altered DAF expression. To test this hypothesis, we screened the DAF gene sequences relevant to the classical complement pathway and found an association between myasthenics with EOM paresis and the DAF regulatory region c.-198C>G SNP (odds ratio=8.6; P=0.0003). This single nucleotide polymorphism (SNP) results in a twofold activation of a DAF 5′-flanking region luciferase reporter transfected into three different cell lines. Direct matching of the surrounding SNP sequence within the DAF regulatory region with the known transcription factor-binding sites suggests a loss of an Sp1-binding site. This was supported by the observation that the c.-198C>G SNP did not show the normal lipopolysaccharide-induced DAF transcriptional upregulation in lymphoblasts from four patients. Our findings suggest that at critical periods during autoimmune MG, this SNP may result in inadequate DAF upregulation with consequent complement-mediated EOM damage. Susceptible individuals may benefit from anti-complement therapy in addition to immunosuppression

Prevention of experimental autoimmune myasthenia gravis by rat Crry-Ig: A model agent for long-term complement inhibition in vivo

Despite its vital role in innate immunity, complement is involved in a number of inflammatory pathologies and has therefore become a therapeutic target. Most agents generated for anti-complement therapy have short half-lives in plasma, or have been of mouse or human origin, thereby limiting their use either to murine models of disease or to short-term therapy. Here we describe the generation of a long-acting rat therapeutic agent based on the rat complement inhibitor, Crry. Characterisation of various soluble forms of Crry demonstrated that the amino-terminal four short-consensus repeat domains were required for full regulatory and C3b-binding activities. Fusion of these domains to rat IgG2a Fc generated an effective complement inhibitor (rCrry-Ig) with a circulating half-life prolonged from 7 min for Crry alone to 53 h for rCrry-Ig. Systemic administration of rCrry-Ig over 5 weeks generated a weak immune response to the recombinant agent, however this was predominantly IgM in nature and did not neutralise Crry function or cause clearance of the agent from plasma. Administration of rCrry-Ig completely abrogated clinical disease in a rat model of myasthenia gravis whereas soluble Crry lacking the immunoglobulin Fc domain caused a partial response. rCrry-Ig not only ablated clinical disease, but also prevented C3 and C9 deposition at the neuromuscular junction and inhibited cellular infiltration at this site. The long half-life and low immunogenicity of this agent will be useful for therapy in chronic models of inflammatory disease in the rat