Local immunoglobulin hyperproduction is observed in nasal polyps (NPs) with and without ectopic lymphoid tissues (eLTs).

Our aim was to identify the T-cell subsets involved in local immunoglobulin production independent of eLTs in NPs.

The localization, abundance, and phenotype of CD4⁺ T-cell subsets were studied by immunofluorescence, flow cytometry, and single-cell RNA sequencing. Purified nasal T-cell subsets were cultured with autologous peripheral naive B cells to explore their function. Programmed death ligand 1 and programmed death ligand 2 expression in NPs was investigated by immunofluorescence staining and flow cytometry.

Accumulation of PD-1^highCXCR5^–CD4⁺ T cells outside lymphoid aggregates was found in NPs. Nasal PD-1^highCXCR5^–CD4⁺ T cells were characterized by a unique phenotype that was related to B-cell help and tissue residency and distinct from PD-1^–/intCXCR5^– and CXCR5⁺ CD4⁺ T cells in NPs as well as PD-1^highCXCR5^highCD4⁺ follicular helper T cells in tonsils. Compared with the frequencies of PD-1^highCXCR5^–CD4⁺ T cells and their IFN-γ⁺, IL-17A⁺, and IL-21⁺ subsets in the control inferior turbinate tissues, the frequencies of these cells and their subsets were increased in both eosinophilic and noneosinophilic NPs, whereas the frequencies of the IL-4⁺ and IL-4⁺IL-21⁺ subsets were increased only in eosinophilic NPs. Nasal PD-1^highCXCR5^–CD4⁺ T cells induced immunoglobulin production from B cells in a potency comparable to that induced by tonsillar follicular helper T cells. PD-1^highCXCR5^–CD4⁺ T-cell frequencies were correlated with IgE levels in eosinophilic NPs. PD-L1 and PD-L2 suppressed the function of PD-1^highCXCR5^–CD4⁺ T cells, and their levels were reduced in NPs. PD-1^highCXCR5^–CD4⁺ T-cell abundance was associated with the postsurgical relapse of NPs.

PD-1^highCXCR5^–CD4⁺ T cells participate in local immunoglobulin production independent of eLTs in NPs.