Accumulation of effector memory CD8+ T cells in nasal polyps

Background: T lymphocytes are prevalent in sinus mucosa and are implicated in chronic rhinosinusitis (CRS) pathogenesis. However, the major T-cell subpopulations, helper (CD4(+)) and cytotoxic (CD8(+)), have not been adequately examined in CRS. This study was designed to characterize human sinus mucosa and peripheral blood (PB) CD4(+) and CD8(+) T cells and their level of differentiation in CRS with nasal polyps (NPs), CRS without NPs, and control patients. Methods: A prospective study was performed. Percentages of CD4(+) and CD8(+) T cells and their levels of differentiation were analyzed in sinus mucosa and PB by flow cytometry. Cell populations were defined as naive, central memory, effector memory, and effector T cells using cell surface markers CD45RA, CD62L, and CD27. The influence of coexisting allergy, sinus eosinophilic mucus (EM), and culture results were examined. Results: In all patients, sinus mucosa had a lower percentage of CD4(+) and a higher percentage of CD8(+) T cells compared with PB. However, CRS with NPs (n=86) had a significantly higher percentage of mucosal CD8(+) T cells compared with CRS without NPs (n=40) in control (n=13) patients (p<0.0001). Effector memory T cells were increased in sinuses compared with PB in all patients; however, the percentage of effector memory CD8(+) T cells was greatest in CRS with NP mucosa (p=0.002). Surprisingly coexisting allergy or culture results did not influence the mucosal T-cell phenotype. CRS with NP patients with sinus EM had a significantly higher percentage of mucosal CD8(+) T cells. Conclusion: Sinus mucosa in CRS with NPs is characterized by a significant enrichment of CD8(+) T cells and a relative deficiency of CD4(+) T cells. The majority of NP CD8(+) T cells had a terminally differentiated, mature, effector memory phenotype, which raises the question, whether these cells are pathogenic or appear as a consequence of inflammation, independent of the presence of allergy or positive microbial culture.