AbstractIntroduction Chronic rhinosinusitis (CRS) is commonly classified based on the presence or absence of nasal polyps (NPs). Eosinophil infiltration is observed in NPs of patients in Western countries. In contrast, in East Asian countries, including Japan, CRS with NPs (CRSwNP) is subdivided based on the presence (eosinophilic CRS [ECRS]) or absence (non-eosinophilic CRS [NECRS]) of eosinophils in NPs. However, detailed analyses of other immune cells, such as lymphocytes, in NPs have not been performed. Therefore, clarification of the types of cells that infiltrate NPs is important to understand CRS pathogenesis.Objectives We analyzed the lymphocytes that infiltrate the paranasal sinus mucosa of ECRS and NECRS patients.Methods Eighteen patients with CRSwNP participated in this study, out of whom 6 were NECRS patients, and 12 were ECRS patients. The mucosa specimens, collected from patients during sinus surgeries, were subjected to collagenase treatment to prepare single cell suspensions. Then, mononuclear cells were isolated, and CD4+ T, CD8+ T, and CD20+ B-cell populations were examined using flow cytometry.Results In both NECRS and ECRS patients, CD8+ T-cells were dominant over CD4+ T-cells. Notably, CD4+ T-cell/B-cell ratio, but not CD8+ T-cell/B-cell or CD4+ T-cell/CD8+ T-cell ratios, was significantly higher in ECRS patients than in NECRS patients.Conclusion The CD4+ T-cell/B-cell ratio can be used as a potential indicator to differentiate between ECRS and NECRS.