¹University Medical Center Schleswig-Holstein, Department of Internal Medicine I, Division of Rheumatology, Kiel
²University Medical Center Schleswig-Holstein, Department of Internal Medicine I, Kiel
³German Institute for Aerospace Medicine (DLR), Köln

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Introduction: Nasopharyngeal swabs have become an established, simple, and non-invasive method for sampling the upper respiratory tract [1]. While they are primarily used for pathogen detection, their potential for analyzing the local immune response remains largely unexplored. This study aimed to establish a method for isolating and characterizing immune cells from nasopharyngeal swabs and directly comparing them with peripheral blood samples. Additionally, swabs from the nasal vestibule and nasal cavity were analyzed to assess immunological differences in anatomically distinct regions of the upper respiratory tract.

Methods: A healthy cohort was recruited to establish a standardized method for isolation immune cells from nasopharyngeal swabs. Peripheral blood samples were collected simultaneously from all participants.

Isolated immune cells were characterized by multicolor flow cytometry, with a specific focus on B cell subpopulations.

Results: With our method, 1*104 -1*106 CD45+ cells are detectable in nasopharyngeal swabs, 38.5% (median; range 18.1%–65.7%) of them being CD19+ B cells. The overall immune cell count (CD45+) was significantly higher in nasopharyngeal samples compared to other regions of the upper respiratory tract. Notably, plasma cells were scarcely or not detectable in the nasal vestibule (0.4 % of B cells), while they were present in substantial numbers in nasopharyngeal swabs (3.2% of B cells).

Compared to blood, we detected significantly more memory B cells in nasopharyngeal swabs (38.8% vs 49.9%; p=0.015), 50.1% of them being IgA positive (vs 16.9% in PBMC). Nasal swabs showed comparable frequencies of plasma cells, but they were characterized by a significantly higher CD138 expression (MFI 2.3 vs 24.9; p<0.0001) and less HLA-DR (MFI 52.0 vs 6.1; P<0.0001) resembling a more mature phenotype, compared to plasma cells in the blood. Several markers associated with homing and migration, such as CCR10, showed differences between B cells in the nasopharynx and those in peripheral blood.

Conclusion: This study demonstrates that nasopharyngeal swabs can be utilized not only for pathogen diagnostics but also for characterizing the local immune response. The successful establishment of a method for isolating and analyzing immune cells from the upper respiratory tract provides a foundation for future research into mucosal immunity and its relationship to systemic immune responses.

Disclosures: The authors and I declare that the research was conducted in the absence of financial or commercial relationships that could be construed as a potential conflict of interest.

References

[1] Ramirez SI, Faraji F, Hills LB, Lopez PG, Goodwin B, Stacey HD, Sutton HJ, Hastie KM, Saphire EO, Kim HJ, Mashoof S, Yan CH, DeConde AS, Levi G, Crotty S. Immunological memory diversity in the human upper airway. Nature. 2024 Aug;632(8025):630-36. DOI: 10.1038/s41586-024-07748-8