IVIG efficacy in CIDP patients is not associated with terminal complement inhibition

Patients with acute and chronic inflammatory demyelinating neuropathies exhibit elevated serum and cerebrospinal fluid (CSF) levels of terminal complement activation products and therapeutic inhibition of complement activation is currently tested for its safety and efficacy in patients with Guillain-Barré syndrome (GBS). Here, we determined serum levels of the complement activation products C3a, C5a and the soluble terminal complement complex (sTCC) in 39 individuals with chronic inflammatory demyelinating polyneuropathy (CIDP) who participated in one of the largest ever conducted clinical trial in patients with CIDP (ICE trial) and received Intravenous Immunoglobulin (IVIG) or placebo (albumin) in 3 week intervals for up to 24 weeks. In placebo-treated patients with spontaneous disease remission, serum sTCC levels moderately decreased over time. Levels of complement activation products were, however, not modulated by IVIG and remained unchanged in patients with a beneficial response to IVIG therapy as compared to those with steady or worsened disease. These results suggest that the therapeutic efficacy of IVIG in CIDP is based on immunomodulatory mechanisms different from complement inhibition. Terminal complement activation merits further investigation as a surrogate marker for disease progression and therapeutic target in patients with CIDP.