The Soluble Isoform of CTLA-4 Correlates with Interferon-alpha Activity in Systemic Lupus Erythematosus

To the Editor: \n\nSystemic lupus erythematosus (SLE) is a multisystem autoimmune disorder characterized by fluctuating levels of immune response hyperactivity, high serum titers of nucleic antigen-specific autoantibodies, and persistent production of type-I interferon (IFN)1. One route to controlling SLE has been to exploit the properties of T cell lymphocyte costimulation inhibitor (CTLA-4), a selective costimulation inhibitor, which suppresses auto-antigen-specific T cell response intensity2. Although the full-length cell-surface receptor CTLA-4 is well characterized, other alternatively spliced isoforms exist, including a soluble form of the molecule (sCTLA-4)3. Initial analysis of sCTLA-4 in patients with SLE described raised serum levels compared with healthy donors, and sCTLA-4 levels correlated with disease activity4, but little is known of whether it plays any role in SLE. Currently, this is a relevant question because there is anecdotal evidence that CTLA4-Ig can have clinical benefits for some patients with SLE5.\n\nStudies of sCTLA-4 using current anti–CTLA-4 antibodies should be interpreted with caution because they are raised against the extracellular region, found in the receptor, cleaved receptor artifact and the soluble isoform, hence obscuring the contribution of native sCTLA-4. Here, using antibodies raised specifically against native sCTLA-46,7, we determined whether sCTLA-4 contributes to the immune response underlying SLE, particularly regarding SLE markers IFN-α and anti-dsDNA antibody levels. The study included 104 patients with SLE and 40 healthy volunteer donors and first compared serum levels of IFN-α (Figure 1). All methods were carried out in accordance with the Grampian … \n\nAddress correspondence to F.J. Ward, University of Aberdeen, Immunity, Infection and Inflammation group, Division of Applied Medicine, Institute of Medical Sciences, Foresterhill, Aberdeen, UK. E-mail: mmd475{at}abdn.ac.uk or L.N. Dahal, L.N.Dahal{at}liverpool.ac.uk