Biomarkers of ‘acute-onset’ chronic inflammatory demyelinating polyneuropathy

Sir, We read with great interest the article by Sung et al. (2014) reporting the usefulness of nerve excitability testing in differentiating acute-onset chronic inflammatory demyelinating polyneuropathy (A-CIDP) from acute inflammatory demyelinating polyneuropathy (AIDP). Discriminating the two conditions at an early stage is crucial as treatment options and prognoses differ (Odaka et al., 2003; Ruts et al., 2010). Although nerve excitability studies were found to be helpful, this neurophysiological technique is not easily accessible to the average clinician who manages this group of patients. Thus, biomarkers such as serological analyses may prove to be more useful and practical in the assessment of this group of patients. Recently, IgG autoantibodies to contactin 1, a key axo-glial junction molecule, were detected in three patients with chronic inflammatory demyelinating polyneuropathy (CIDP), all of whom shared similar clinical features of an aggressive form of CIDP (Querol et al., 2013). We hypothesized that this particular set of antibodies may also be associated with A-CIDP, acting as a potential biomarker. We investigated sera from 14 patients with A-CIDP (Odaka et al., 2003; Quek et al. 2014), 25 with CIDP, 25 with AIDP, 25 with acute motor axonal neuropathy and 25 normal control subjects. Human recombinant contactin 1 and 2 proteins were purchased from Sino Biological Inc. and coated onto 96-well Nunc MaxiSorp ELISA plates (ThermoFisher Scientific) (0.5 µg/ml, 50 µl/well) before being left at 37°C for 1 h. Patients’ sera were diluted at 1:500 or higher in PBS containing 0.5% casein sodium, and kept at 4°C overnight before being washed with 0.05% Tween 20 in PBS. Peroxidase-conjugated anti-human IgG, IgA or IgM antibodies (1:1 000; Dako) were added to the wells, incubated at 37°C for 1 h, and washed again with 0.05% Tween 20 in PBS. The plates were developed with o-phenylenediamine dihydrochloride solution, and 15 min later the reaction was stopped with 2 N HCl. The optical density was measured at 492 nm. All samples were tested in triplicates. Serum was considered positive when the calculated absorbance was 0.1 or higher at 1:500 dilution. This study was approved by the Ethics Committee of Dokkyo Medical University and National University of Singapore. In our study, we detected anti-contactin 1 IgG antibodies in 1 of 25 (4%) patients with CIDP and 1 of 25 patients with AIDP (Fig. 1). Both patient groups had high titre (1:20 000) of anti-contactin 1 IgG antibodies. Anti-contactin 1 antibodies were negative in the 14 patients with A-CIDP, the acute motor axonal neuropathy patients and normal control subjects. Anti-contactin 2 antibodies were negative in all patients. Representative results of anti-contactin antibodies. Rows 1 and 8 represent wells with no antigen coating. Rows 2 to 4 were coated with contactin 1 whereas rows 5–7 were coated with contactin 2. Goat anti-contactin 1 and rabbit anti-contactin 2 IgG antibodies specifically reacted with contactin 1 and 2, respectively, indicating that the ELISA technique was successful at detecting each anti-contactin antibody. Patient 1 had AIDP. Patients 2 and 3 had A-CIDP. Patient 4 had CIDP. Anti-contactin 1 IgG antibodies were positive in Patients 1 and 4, but negative in Patients 2 and 3. Anti-contactin 2 antibodies were negative in all the patients. In the current study, we were not able to find an association between anti-contactin 1 antibodies and A-CIDP. Instead, we detected anti-contactin 1 IgG antibodies in AIDP and CIDP at a similar frequency to our previous study using a cell-based assay (Devaux et al., 2012). Although the current study used ELISA, we were still able to detect the presence of IgG antibodies against contactin 1 in CIDP and AIDP patients, suggesting contactin 1 as a potential target antigen in demyelinating neuropathies. The search for pathogenic antigens in A-CIDP, however, remains elusive although it is likely that IgG rather than IgM or IgA is involved, given the half-life of IgG is 3 weeks and patients tend to relapse within weeks of plasma exchange (Odaka et al., 2003; Ruts et al., 2010). Further studies investigating other potential myelin targets are important to improve our understanding of the relationship between variants of CIDP and serological analyses which will inevitably lead to more effective therapeutic options. N.Y. was supported by Singapore National Medical Research Council (IRG 10nov086) and Singapore National Medical Research Council (CSA/047/2012).