Nasal polyp cell populations and fungal-specific peripheral blood lymphocyte proliferation in allergic fungal sinusitis.

Background: Allergic fungal sinusitis (AFS) is considered a different disease from other polypoid chronic rhinosinusitis diseases (CRS) with eosinophilic mucus (EM) termed eosinophilic mucus chronic rhinosinusitis (EMCRS). To substantiate this, studies on cellular responses to fungi and sinus mucosal inflammatory cell populations in AFS and other EMCRS diseases are required. This study was designed to examine polyp inflammatory cell populations and peripheral blood fungal-specific T-cell responses in AFS, other EMCRS subgroups (defined later), and polypoid CRS without EM.

Methods: A prospective study was performed. Clinical characteristics, including CRS symptoms, sinus computed tomography (CT) scans, allergy status, intraoperative endoscopy, presence of EM, and fungal culture results were used to define patient groups. Polyps and peripheral blood were examined for populations of eosinophils, lymphocytes (CD4+, CD8+ T cells, natural killer cells, and B cells), and neutrophils using immunohistochemistry, cytospin preparations and flow cytometry. Fungal-specific peripheral blood lymphocyte proliferation was examined in AFS patients, other EMCRS patients, CRS patients, and controls.

Results: There was no significant difference in the percentage of cell populations and fungal-specific lymphocyte proliferation between AFS and other EMCRS diseases. However, AFS and other EMCRS polyps had a higher percentage of eosinophils and CD8+ T cells whereas CRS polyps had higher CD4+ T cells. Fungal-specific lymphocyte proliferation was significantly greater in AFS and other EMCRS patients regardless of fungal allergy, whereas in CRS and controls, higher proliferation was observed in fungal-allergic individuals.

Conclusion: These findings question the basis for differentiating AFS from other EMCRS diseases based on fungal allergy and fungi in EM. Fungal-specific cellular response was present in AFS and other EMCRS diseases, different from that associated with fungal allergy, suggesting a nonallergic fungal immune response. Increased CD8+ T cells in EMCRS polyps signify a different type of inflammation to CRS that may be driven by CD8+ T cells.