In this study, we present data on patients with pemphigus vulgaris (PV), pemphigus foliaceus (PF), bullous pemphigoid (BP), mucous membrane pemphigoid (MMP), and ocular cicatricial pemphigoid (OCP), who had decreased levels of serum IgM, during their systemic therapy. This evidence concerns the gene CD40LG and acquired polycythemia vera.