Response to: ‘Serum complement factor C5a in IgG4-related disease’ by Fukui et al

We appreciate the interest shown by Dr S Fukui and colleagues1 in our recent paper, ‘How to diagnose IgG4-related disease (IgG4-RD)’.2 IgG4-RD is characterised by increased serum IgG4 concentrations and number of IgG4-positive plasma cells in affected lesions.3 However, its diagnosis can be difficult, because clinical signs vary depending on the organs affected. A Japanese team established comprehensive diagnostic criteria for IgG4-RD, 2011...