C1q: A Multifunctional Ligand for a New Immunoadsorption Treatment

C1q is a highly conserved protein with multiple functions involved in innate and adaptive immunity. It plays an important role in the activation of the classical pathway of the complement system to mediate the scavenging of infectious agents, apoptotic products, and immune complexes by the mononuclear phagocyte system (MPS). Exhibiting this function, C1q is able to bind various molecules (complexed IgG, IgM, fibrinogen, fibronectin, lipopolysaccharides, DNA, C‐reactive protein [CRP], and viral proteins). Moreover, the collagen‐like region of C1q is a target of autoantibodies. Immune complexes and anti‐C1q autoantibodies are known to be involved in the pathogenesis of autoimmune diseases. Therefore, C1q is a promising candidate to extract waste material from the circulation. Following the development of the C1q immunoadsorbent, 8 patients with systemic lupus erythematosus (SLE) were treated in a first clinical trial. These preliminary results indicate that C1q immunoadsorption is a safe, compatible, and effective treatment for these patients.