Takeda K, et al. - Researchers examined patients with chronic rhinosinusitis with nasal polyposis (CRSwNP), to determine the reactive allergens of IgE antibodies produced locally in nasal polyps (NPs) of these patients. They also focused on the differentiation pathway of IgE-producing B cells in the NPs. They characterized single cell-derived monoclonal antibodies to determine IgE reactivity and used high-throughput immunoglobulin (HTS Ig) sequencing to analyze immunoglobulins expressed in NPs. They found that, via IgG/A1-IgE class switching, nasal bacteria-reactive B cells differentiated into IgE-producing B cells. This finding suggests that the disease pathogenesis involves allergic conversion of the mucosal response against nasal bacteria.